Stedman’s Online Medical Dictionary defines disease as an interruption, cessation, or disorder of body function, system, or organ; or a morbid entity characterized usually by at least two of these criteria: recognized etiologic agent(s), identifiable group of signs and symptoms, or consistent anatomic alterations. The International Classification of Disease, 9th Revision, Clinical Modification (ICD-9-CM) is one of the main texts used in the United States to identify, categorize, and diagnose disease. The Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV), is used to define and diagnosis mental disorders. While these sources are used in common medical practice, it is not completely clear in the philosophy of science what truly defines the diseases and disorders that these texts classify. Some have argued that there is not a simple definition of disease. Within the philosophy of medicine and bioethics, there is not only disagreement about what a disease is but whether or not disease can be defined or whether it is necessary to have a fixed definition in order to provide care.
A simplistic yet prevailing conception of what disease is can be viewed from the lens of “naturalism” or “nominilism.” Viewed from a naturalistic point of view, disease is a real thing that can be quantified, observed, or described using the language of natural science. To the naturalist, a disease can be discovered in nature, is not invented by social convention, and is not dependent on contextual circumstance. The true naturalist views disease as value free and objective. Disease from a naturalist point of view, according to the philosopher Christopher Boorse, causes interruptions in the ability to “perform typical physiological functioning with at least typical efficiency” (Kovacs 1998, p. 31). This point of view, however, has been critiqued because “typical physiology” and “typical efficiency” cannot be objectively described, nor are they value-free terms (i.e., what is meant by “typical”?).
The nominalist point, on the other hand, views disease not as something essential in nature but rather as a description of socially constructed conditions. As stated by Lester King in 1954, the point of view that “disease is the aggregate of those conditions, which, judged by the prevailing culture, are deemed painful, or disabling, and which, at the same time, deviate from either the statistical norm or from some idealized status” would fit within this nominalist point of view (King 1954, p. 197). Historically a purely naturalistic view of disease as a germ or lesion has given way to a view of disease that appeals more to a nominilist point of view. Ailments that fall within modern medical health care, such as depression or hypertension, challenge a naturalistic point of view because these conditions appeal to socially defined criteria by which one would be in need of professional care or qualify for some sort of intervention.
In discussing the concept of disease, attention has been brought to how terms such as disease, illness, or sickness relate. Oftentimes these concepts have been used interchangeably. However, philosophers argue that separating the concepts may be useful. Disease is distinguished from illness in that disease is the subject matter of the medical practitioner and scientific medicine. Illness, on the other hand, explains what the person is experiencing. Sickness is what is attributed by society to individuals who conceive of themselves as ill and whom medical professions identify as having a disease. Each of these concepts justifies action. Medical professionals are charged with identifying disease, discovering diseases, and treating persons with such conditions. Persons who are ill are charged with describing the subjective experience of their condition to others who may be able to help. Society is responsible for determining the rights and duties of a person who is ill and/or diseased. Thus conceptualizing disease as separate from illness and sickness can be useful in bringing into perspective the varying roles of the medical practitioner, the individual, and society when negative bodily conditions or states occur.
The concept of disease is also often discussed as it relates to health. That is, to understand what disease is, one must know what health is. The common language conception of health is simply the absence of disease or the negation of being at ease (i.e., dis-ease). A person who is healthy does not have a disease, and a person with a disease is not healthy. However, this simplistic model may not be applicable in all circumstances. For example, a person diagnosed with hypochondriasis certainly is suffering, but the individual does not have any general medical condition that can account for his or her feeling of illness. There are also instances when one feels healthy but may have a serious condition that places the individual at risk for a disease (e.g., a person with hypercholesterolemia or obesity may develop coronary artery disease).
The holistic approach extends the more simple approach to defining health not just as the absence of disease but as a state of complete physical, mental, and social well-being. The holistic model has been adopted and promoted by the World Health Organization. The holistic model would imply that one could meet the condition of not having a specific disease but still may not be healthy. Within the holistic model, eliminating disease from the body is not primary, but rather, health is primary. However, some have argued that a holistic program of health care with the goal of insuring complete physical, mental, and social well-being is not feasible; especially in developing countries, where there are limited resources available for the provision of care.
The model most familiar to Western medicine is the medical model of disease. The medical model suggests that disease is not just absence of health (as defined by the simplified model), but disease can be identified by some set of standard methods, such as a medical examination, laboratory tests, or correspondence with a set of symptoms. Thus within the medical model a person could potentially not have an identified pathophysiological disease but could still be labeled as having a disease as a result of having a set of symptoms and being deemed not healthy through the process of a medical examination.
Within modern medicine there are many controversies over what conditions can be properly defined as diseases. One such debate in the general medicine and public health has to do with whether or not obesity can be labeled a disease. George A. Bray, an internationally recognized researcher in the area of obesity and diabetes, has argued that obesity meets the criteria to be labeled a disease. However, other researchers have argued that caution should be taken when labeling obesity as a disease as it may not be appropriate to put it on par with other more serious life-threatening conditions. Those that argue obesity should not be considered a disease suggest that there are no real signs or symptoms of obesity apart from excess adiposity. However, this is circular because excess adiposity is the definition of obesity. Also, while obesity does cause impairment in functioning for some people, there are many people who are obese who have no diminished impairment in functioning. Those who argue that obesity is a disease equate it with other diseases, such as depression. Bray states that obesity involves “deranged neural circuitry responding inappropriately to a toxic environment” (Bray 2004, p. 34).
Another long-standing debate in the medical discipline of psychiatry is whether or not certain psychological conditions can be labeled a disease. A mainstream view of modern practice in psychiatry is that certain psychological conditions rise to the level of an illness when there is a clinically relevant disruption in functioning and distress. The DMS-IV distinguishes a mental pathological condition from a milder form by establishing clinically significant criterion. As stated in the DSM-IV, the condition must cause “clinically significant distress or impairment in social, occupational, or other important areas of functioning” (DSM-IV 1994, p. 7). The determination of significance is a clinical judgment made through the process of a clinical interview with the patient and sometimes with third parties, such as a patient’s family. Further, a mental disorder is often distinguished from a condition that arises as a direct physiological consequence of a general medical condition. For example, disorientation or hallucinations due to a brain tumor or stroke would not be considered a psychiatric condition.
Notably the explanation of aberrant behaviors or mental conditions has changed over the centuries. In past centuries aberrant behaviors and mental disorders were explained as the result of “spirits” or “sins.” With the birth of psychoanalysis, mental conditions were explained as primarily resulting from poor child rearing or the inability of an individual to meet developmental milestones marking social and moral development. However, early twenty-first-century psychiatric practice tends to explain many psychiatric conditions as the result of disruptions in neural circuitry in the brain resulting from a combination of genetic and environmental determinates.
This change in perception of psychiatric conditions is argued to be due to an increasing scientific knowledge about potential causes and treatments. However, the psychiatrist Thomas Szasz has been a prominent critic of this traditional point of view. Szasz argues that mental disorders, as mainstream psychiatry has conceptualized, are not diseases of the brain and that it is inappropriate to call abnormal behaviors and psychological states “diseases.” A crux of difference between these two points of view has to do with the way disease is defined—that is, as a “lesion” of the body or as a social construction or metaphor.
Regardless of how disease is defined, it is widely recognized that the spread of disease and the preponderance of health are linked to social factors. For instance, density and frequency of contact among individuals can influence disease outbreak. Dense social contact in urban environments may lead to a rapid spread of certain infectious diseases. Understanding the social networks and dynamics of these environments is a key strategy for developing targeted vaccinations and treatments.
Disease and health are also influenced by social and economic conditions in society. For example, in the early twenty-first century in the United States, Type 2 diabetes mellitus is more common among African American men than their Caucasian counterparts. However, a 2007 study by Margaret Humphreys and colleagues found rates of diabetes among African American men living circa 1900 to be much lower than Caucasian men at that time. Studies looking at coronary heart disease patterns have also reported prevalence shifts whereby the risk of the disease was historically more prevalent in higher socioeconomic classes and now is more prevalent in lower socioeconomic classes (Kunst et al., 1999; Marmot, Adelstein, Robinson, and Rose, 1978; Rose and Marmot, 1981). These studies highlight the fact that disease patterns as well as the social distribution of risk factors for disease can vary by type of disease, time period, and geographic region.
As disease and health are viewed as socially determined, the search for social conditions that gives rise to diseases has become a growing part of medical and public health science. Medical practice in the past centuries was focused primarily on identifying pathophysiological and biological roots for disease and had largely ignored the social contributions to disease. Correspondingly treatments and interventions for disease management have been one-to-one efforts. However, a growing awareness that societal-level phenomena play a large role in health and disease has prompted the medical community to explore some of the broader social and economic forces that influence disease and risk. As such the approach to disease management is also shifting from primarily individual-level one-to-one efforts to include environmental and policy-level interventions designed to address health.
Finding a clear definition of disease and health is not purely a philosophical matter. Conditions that carry the label of disease have practical and political implications. Society responds by directing resources, and individuals with a certain disease are relinquished from certain social responsibilities. However, what counts as disease is often difficult to determine. In some cases it might appear that a certain condition has pathophysiological roots and causes (e.g., germ or lesion) that can be discovered and treated. However, it may be discovered that there are broader social and economic conditions that allow for certain pathophysiological conditions to arise. What then is the disease? Is it the germ or the social condition? The answer that society provides becomes one of the defining features by which health care resources are allocated.
SEE ALSO Alzheimer’s Disease; Dementia; Depression, Psychological; Ethno-epidemiological Methodology; Functionings; Human Rights; Hypertension; Madness; Malnutrition; Medicine; Mental Illness; Obesity; Poverty; Psychoanalytic Theory; Public Health; World Health Organization
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Bernard F. Fuemmeler
Disease is a term for any condition that impairs the normal functioning of an organism or body. Although plants and animals also contract diseases, by far the most significant disease-related areas of interest are those conditions that afflict human beings. They can be divided into three categories: intrinsic, or coming from within the body; extrinsic, or emerging from outside it; and of unknown origin. Until the twentieth century brought changes in the living standards and health care of industrialized societies, extrinsic diseases were the greater threat; today, however, diseases of intrinsic origin are much more familiar. Among them are stress-related diseases, autoimmune disorders, cancers, hereditary diseases, glandular conditions, and conditions resulting from malnutrition. There are also illnesses, such as Alzheimer's disease, whose causes remain essentially unknown.
HOW IT WORKS
Any condition that impairs the normal functioning of an organism can be called a disease. In the human organism, as in all others, there are certain basic requirements, which in the human body include the need for a certain proper amount of oxygen, acidity, salinity (salt content), nutrients, and so on. These conditions must all be maintained within a very narrow range, and any deviation can bring about disease.
Diseases can be classified into three general groups. There are conditions that are infectious, or extrinsic, meaning that they are caused by an infection through which a virus, bacterium, or other parasite enters the body. Infectious diseases, infections, and the immune system that usually protects us against them are discussed elsewhere in this book. Our attention in the present context will be devoted to the other two broad categories—noninfectious, or intrinsic, diseases and diseases of unknown origin.
CLASSIFYING INTRINSIC DISEASES.
There are several basic varieties of intrinsic disease, or conditions that are neither contagious nor communicable. These varieties are listed in the next few paragraphs. The essay Noninfectious Diseases includes a discussion of other systems for classifying diseases of either the intrinsic or the extrinsic variety.
Hereditary diseases: diseases that are genetic, meaning that they are passed down from generation to generation. An example, discussed in Noninfectious Diseases, is hemophilia. Heredity is not a "cause," and some of the diseases of unknown origin may be transmitted from parent to offspring. Some forms of cancer are hereditary as well, as are other conditions discussed elsewhere in this book. (See Nonifectious Diseases, Mutation, and Heredity.)
Glandular diseases: Conditions involving a gland—that is, a cell or group of cells that filters material from the blood, processes that material, and secretes it either for use again in the body or to be eliminated as waste. Examples include diabetes mellitus, examined in Noninfectious Diseases, as well as various kidney and liver diseases, among them, hepatitis and jaundice. Goiter, a swelling in the neck area caused by a diet poor in iodine, is both a glandular and a dietary condition, a fact that illustrates the overlap between disease types.
Dietary diseases: These are all illnesses that relate to nutrient deficiencies—either an overall lack of adequate nutrition (i.e., malnutrition) or the absence of a key nutrient. Examples include pellagra, scurvy, and rickets, all of which are vitamin deficiencies, as well as kwashiorkor, which brings about a swollen belly and is caused by a lack of protein. Vitamin deficiencies are discussed in Vitamins, and kwashiorkor and other varieties of malnutrition are examined in Nutrients and Nutrition.
Cancers: Cancer is not just one disease but some 100 conditions. Its two main characteristics are uncontrolled growth of diseased cells in the human body and migration of the disease from the original site to distant sites within the body. If the spread is not controlled, cancer can result in death. (See Noninfectious Diseases for more.)
Stress-related diseases: Some heart conditions are hereditary or glandular, but quite a few diseases of the heart and circulatory system are exacerbated by stress. Examples include heart murmurs, hardening of the arteries, and varicose veins. We will examine heart disease and the general effects of stress shortly.
Autoimmune diseases: This is a particularly terrifying category of disease, because it involves a rejection of the body itself by the body's own immune system. Autoimmune diseases, examples of which include lupus and rheumatoid arthritis, are discussed in The Immune System.
DISEASES OF UNKNOWN ORIGIN.
Finally, there are diseases for which there is no known cause. In some cases, it is possible that heredity, diet, or some other aspect of human existence has a role, but it is not certain. And even if, say, heredity plays a part, the exact hereditary factors are not established. In any case, many of the categories of disease we have listed do not amount to "causes," but rather are types of disease. Moreover, some diseases classifiable in one of the listed categories also belong in the ranks of the diseases with unknown causes. For instance, many autoimmune diseases are mysterious to scientists. Likewise, chronic fatigue syndrome, considered a disease of unknown origin, is obviously a stress-related disorder, while fibromyalgia, characterized by sore muscles and tissues, may be stress-related as well. Two brain diseases of unknown origin, Creutzfeldt-Jakob and Alzheimer's disease, are discussed near the conclusion of this essay.
A Changing Threat
At one time the diseases that posed the greatest threat to human survival were infectious ones, such as the Black Death (actually a combination of bubonic and pneumonic plague), which killed about a third of Europe's population during the period from 1347 to 1351. Plagues or epidemics, in fact, are among the persistent themes in history, punctuating the fall of empires and the rise of others.
A plague that struck the eastern Roman (Byzantine) Empire in the sixth century, for instance, brought an end to a plan by the great Justinian I to reconquer the Italian peninsula and restore Roman rule in western Europe. It also spelled the beginning of the end of Byzantine glory (though the empire hung on until 1453) and opened the way for the rise of Islam and Muslim influence over the Mediterranean. Thus, the course of history up to the present day, including the events of the European Middle Ages, the Crusades, and even the modern-day conflict between the West and Islamic terrorists, can be traced in part back to a plague in about a.d. 540.
Wherever people have gathered in large numbers, infectious diseases have arisen. Smallpox and chicken pox, cholera and malaria, diphtheria and scarlet fever, influenza and polio—these and many other diseases have threatened the very survival of whole populations, bringing about a collective death toll that dwarfs that of twentieth-century wars and genocide. Yet it was in the twentieth century—ironically, the era when humans discovered the capacity to kill themselves in truly frightening numbers through world wars, nuclear weaponry, and totalitarian social experiments—that the threat of infectious diseases began to recede.
Thanks to successful vaccination programs, many infectious diseases are largely a thing of the past. This is true even of smallpox, a scourge that effectively ended in 1978 thanks to a United Nations inoculation program, but which reemerged as a potential threat of biological terrorism in the hands of political terrorists, such as the Islamic terrorist Osama bin Laden. It would be difficult for bin Laden's al-Qaeda organization to acquire samples of the virus, however; they are stored in only four or five laboratories worldwide (kept there for the purpose of making more vaccine if needed) and remain under heavy guard.
THE RISE OF INTRINSIC DISEASES.
Rather than infectious diseases, the much greater threat today is in the form of intrinsic diseases, or ones that are neither communicable nor contagious. The leading causes of death in the United States are as follows:
- Heart disease
- Chronic obstructive lung diseases (e.g., emphysema)
- Accidents (motor vehicle or other)
- Pneumonia and influenza
- Diabetes mellitus
- Kidney disease
- Chronic liver disease and cirrhosis
Note that the one item on the list that is not an intrinsic disease and is not disease-related at all: accidents. After that is the first extrinsic disease entry on the list, number 6, pneumonia and the closely related condition influenza. Number 8, of course, is not related to disease—at least not physical disease. The high incidence of suicide, with 11.1 such deaths per 100,000 population, probably reflects the fact that the United States is an industrialized, wealthy nation. Ironically, people who are eking out a living, struggling for survival, are far less likely to end it all voluntarily.
Also reflective of America's high level of development is the overwhelming preponderance of intrinsic, noninfectious diseases on the list. Unquestionably, the greatest threat to human health today takes the form of noninfectious diseases, such as heart disease, cancer, and diseases of the circulatory system. This is true only in the industrialized world, however: whereas only about 25% of all patients who visit doctors in the United States do so because of infectious diseases, more than two-thirds of all deaths worldwide are caused by infectious diseases, such as malaria.
Stress and Heart Disease
Stress, simply put, is a condition of mental or physical tension brought about by internal or external pressures. Many events can cause stress: something as simple as taking a test or driving through rush-hour traffic or as traumatic as the death of a loved one or contracting a serious illness. Stress may be short-lived, as when facing a particular deadline, or it may be the ongoing, crippling stress related to a job that is slowly killing the victim.
People who experience severe traumas, such as soldiers in combat, may experience a condition called post-traumatic stress disorder (PTSD). This condition first came to public attention after World War I, a war that completely dwarfed all preceding conflicts in its intensity and brutality. Formerly bright-eyed, optimistic youths came home behaving like madmen or nervous wrecks, and soon the condition gained the nickname shell shock. (Actually, shell shock dated back more than 50 years, to what might be regarded as the first modern war in the West—the first "total war" involving relatively sophisticated weaponry and a fully engaged citizenry: America's Civil War, from which combatants returned home with a condition known as "soldier's heart.")
EFFECTS OF STRESS.
Whereas PTSD has a distinct psychological dimension, in many stress-related diseases there is not as obvious a link between mental states and bodily disorders. Nonetheless, it is clear that stress kills. Some of the physical signs of stress are a dry mouth and throat, headaches, indigestion, tremors, muscle tics, insomnia, and a tightness of the muscles in the shoulders, neck, and back. Emotional signs of stress include tension, anxiety, and depression. During stress, heart rate quickens, blood pressure increases, and the body releases the hormone adrenaline, which speeds up the body's metabolism. Stress may disrupt homeostasis, an internal bodily system of checks and balances, leading to a weakening of immunity.
Diseases and conditions associated with stress include adult-onset diabetes (see Noninfectious Diseases), ulcers, high blood pressure, asthma, migraine headaches, cancer, and even the common cold. The last, of course, is an infectious illness, but because stress impairs the immune system, it can leave a person highly susceptible to infection. Furthermore, medical researchers have determined that long-term stress causes the accumulation of fat, starch, calcium, and other substances in the linings of the blood vessels. This condition ultimately results in heart disease.
The human heart weighs just 10.5 oz. (300 g), but it contracts more than 100,000 times a day to drive blood through about 60,000 mi. (96,000 km) of vessels. An average heart will pump about 1,800 gal. (6,800 l) of blood each day. With exercise, that amount may increase as much as six times. In an average lifetime the heart will pump about 100 million gal. (380 million l) of blood. The heart is divided into four chambers: the two upper atria and the two lower ventricles. The wall that divides the right and left sides of the heart is the septum. Movement of blood between chambers and in and out of the heart is controlled by valves that allow transit in only one direction.
Given its importance to human life, it follows that heart disease is an extremely serious condition. Among the many illnesses that fall under the general heading of heart disease is congenital heart disease, a term for any defect in the heart that is present at birth. About one of every 100 infants is born with some sort of heart abnormality, the most common form being the atrial septal defect, in which an opening in the septum allows blood from the right and left atria to mix.
Coronary heart disease, also known as coronary artery disease, is the most common form of heart disease. A condition termed arteriosclerosis, in which there is a thickening of the artery walls, or a variety of arteriosclerosis known as atherosclerosis results when fatty material, such as cholesterol, accumulates on an artery wall. This forms plaque, which obstructs blood flow. When the obstruction occurs in one of the main arteries leading to the heart, the heart does not receive enough blood and oxygen, and its muscle cells begin to die.
A particularly frightening category of unexplained diseases includes those that attack and destroy the brain. Among them are two conditions named after German scientists: the psychiatrists Alfons Maria Jakob (1884-1931) and Hans Gerhard Creutzfeldt (1885-1964) and the neurologist Alois Alzheimer (1864-1915). Creutzfeldt-Jakob disease, fortunately, is a rare condition. The disease, first described by the two doctors in the 1920s, initially shows itself with the loss of memory, and within a few weeks it progresses to visual problems, loss of coordination, and seizure-like muscular jerking. Death usually follows within a year.
It appears that Creutzfeldt-Jakob disease ensues when a certain protein in the brain, known as prion protein, changes into an abnormal form. As to what causes that change, scientists remain in the dark. The disease attacks about one of a million people worldwide, and victims are typically about 50-75 years of age. During the 1990s something strange happened: the disease began affecting relatively large numbers of young people in the United Kingdom. A 1996 report of British medical experts, however, linked the surge in Creutzfeldt-Jakob cases to what might be considered a dietary condition: bovine spongiform encephalopathy, or mad cow disease, contracted from eating cattle with a form of prion disease. The only way to contract such a condition, however, is by eating the brain or spinal cord of an affected cow, something that could only happen in the case of hamburger or sausage, in which one does not always know what one is getting. The cows themselves got the disease from eating feed tainted with by-products of other cows, and as a result of the outbreak, Great Britain issued wide-ranging controls prohibiting the production of feed containing any materials from cows. (These particular feed-production practices were never common in the United States.)
Whereas Creutzfeldt-Jakob disease is a little-known condition, Alzheimer's disease is all too familiar to the families of the more than four million sufferers in America today. Note the reference to the families rather than the victims themselves: one of the most devastating aspects of Alzheimer's disease is the patient's progressive loss of contact with reality, such that a patient in an advanced stage does not even know that he or she has the disease. A progressive brain disease that brings about mental deterioration, Alzheimer's disease is signaled by symptoms that include increasingly poor memory, personality changes, and a loss of concentration and judgment. Although most victims are older 65 years, Alzheimer's is not a normal result of aging. Up until the 1970s people assumed that physical and mental decline were normal and unavoidable features of old age and dismissed such cases of deterioration as "senility." Yet as early as 1906, Alzheimer himself discovered evidence that pointed in a different direction.
In that year Alzheimer was studying a 51-year-old woman whose personality and mental abilities were obviously deteriorating. She forgot things, became paranoid, acted strangely, and just over four years after he began working with her, she died. Following an autopsy, Alzheimer examined sections of her brain under a microscope and noted deposits of an unusual substance in her cerebral cortex—the outer, wrinkled layer of the brain, where many of the higher brain functions, such as memory, speech, and thought, originate. The substance Alzheimer saw under the microscope is now known to be a protein called beta-amyloid. About 75 years later scientists and physicians began to recognize a strong link between "senility" and the condition Alzheimer had identified. Since then, the public has become more aware of the disease, especially since Alzheimer's disease has stricken such well-known figures as the former president Ronald Reagan (1911-) and the actress Rita Hayworth (1918-1987).
THE IMPACT OF ALZHEIMER'S DISEASE.
A slight decline in short-term memory (as opposed to long-term memories of childhood and the like) is typical even in healthy elderly adults, but the memory loss seen in Alzheimer's disease is much more severe. As years pass, memory loss becomes greater, and personality and behavioral changes occur. Later symptoms include disorientation, confusion, speech impairment, restlessness, irritability, and the inability to care for oneself. Although victims may remain physically healthy for years, the progressive decline of their mental faculties is ultimately fatal: eventually, the brain loses the ability to control basic physical functions, such as swallowing. Persons with Alzheimer's disease typically live between five and ten years after diagnosis, although improvements in health care in recent years have enabled some victims to survive for 15 years or even longer.
Improvements in health care also may help explain the fact that the numbers of Alzheimer victims are growing. Medical discoveries of the twentieth century served to prolong life greatly, such that there are far more people alive today who are 65 years of age or older than there were in 1900. More accurate reporting no doubt plays a part as well. Whereas about 2.5 million cases were reported throughout the 1970s, by the end of the twentieth century there were some four million living Alzheimer victims, and by the mid-twenty-first century that number is expected to climb to the range of 13 million if physicians do not find a cure. Meanwhile, Alzheimer's causes the deaths of more than 100,000 American adults each year and costs $80-90 billion annually in health-care expenses.
It is not a simple procedure to diagnose Alzheimer's disease, and despite all the medical progress since the time of Alois Alzheimer, the "best" method for determining whether someone has the condition is hardly a good one. The only possible physical procedure for definitively diagnosing Alzheimer's disease is to open the skull and remove a sample of brain tissue for microscopic examination. This is rarely done, of course, because brain surgery is far too drastic a procedure for simply obtaining a sample of tissue.
The immediate cause of Alzheimer's is the death of brain cells and a decrease in the connections between those cells that survive. But what causes that? Many scientists today believe that the presence of beta-amyloid protein is a cause in itself, while others maintain that the appearance of the protein is simply a response to some other, still unknown phenomenon. Researchers have found that a small percentage of Alzheimer cases apparently are induced by genetic mutations, but most cases result from unknown factors. Various risk factors have been identified, but they are not the same as causes; rather, a risk factor simply means that if a person has x, he or she is more likely to have y. Risk factors for Alzheimer's include exposure to toxins, head trauma (former president Reagan suffered a serious head injury before the onset of Alzheimer's disease), Down syndrome (a genetic disorder that causes mental retardation), age, and even gender (women are more likely than men to suffer from Alzheimer's disease).
Familial Alzheimer's disease, an inherited form, accounts for about 10% of cases. Approximately 100 families in the world are known to have rare genetic mutations that are linked with early onset of symptoms, and some of these families have an aggressive form of the disease in which symptoms appear before age 40. The remaining 90% of cases may be caused by various combinations of genetic and as yet undefined environmental factors.
WHERE TO LEARN MORE
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"Plant and Animal Bacteria Diseases." University of Texas Institute for Cellular and Molecular Biology (Web site). <http://biotech.icmb.utexas.edu/pages/science/bacteria.html#disease>.
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A general term for any condition that impairs the normal functioning of an organism.
A term for a disease that is communicable or contagious and comes from outside the body. Compare with intrinsic.
A cell or group of cells that filters material from the blood, processes that material, and secretes it either for use again in the body or to be eliminated as waste.
A term for a disease that is not communicable or contagious and comes from inside the body. Compare with extrinsic.
During the Civil War more soldiers died as a result of disease than perished at the hands of the enemy. Disease caused roughly 65 percent of all deaths and left hundreds of thousands of additional soldiers permanently disabled. Such estimates do not account for the number of deaths that can be attributed to disease on the home front. Sick soldiers returning home or seeking care in general hospitals carried illness back to their communities, further adding to the devastation. Disease was truly an equal opportunity killer, striking rich and poor, black and white, and men and women indiscriminately. President Abraham Lincoln's (1809-1865) eleven-year-old son, William Wallace Lincoln, for example, died from typhoid fever in February 1862. Disease contributed to the war's unprecedented mortality rates while also exacting a heavy psychological burden on the sick, their caregivers and dependents, and the community at large. Likewise, disease crippled armies, reducing available manpower, and sometimes altered a commander's campaign strategy. Despite the war's heavy disease-related death toll the Civil War marked a period of steady improvement in mortality rates among soldiers. Fewer soldiers per capita died from disease during the Civil War than any other previous American war. Improvements in medical knowledge, medicine, facilities, and a general awareness of the need for proper sanitation contributed to this distinction, but despite those advances disease remained the war's principal killer.
Throughout history disease has been a constant companion of warfare. Wars typically involve armies filled with soldiers who are in constant close proximity to one another, human waste, animal waste, and who are subject to bouts of malnutrition, fatigue, depression, and unsanitary conditions. Most Civil War soldiers came from rural agrarian backgrounds. Farmers and laborers living in a rural setting are by the nature of their occu-
pation relatively isolated from contact with large numbers of individuals. Their separation greatly reduced their exposure to various childhood and epidemic diseases. When those men enlisted in the military and were suddenly thrust into a highly concentrated setting, their immune systems were unprepared to guard against an onslaught of new bacteria and viruses.
Inadequate and often nonexistent physical examinations for recruits facilitated the spread of diseases among Civil War soldiers. Most men joined the military without an inspection, while those who were examined only received a cursory physical exam. A New Jersey volunteer described the scene of one examination:
The company was drawn up in line on one side of the room and when a man's name was called he would step up to the doctor, who to him the following questions. Were you ever sick in your life, have you got the rheumatism, have you got varicose veins, and other questions of like matters, instead of finding out for himself by actual examination whether you had or not. If the questions were answered in the affirmative and he had no reason to doubt it, he would give us a thump on the chest, and if we were not floored nor showed any other sign of inconvenience, we were pronounced in good condition. (Robertson 1988, p. 147)
Without the benefit of proper physical examinations, both armies enlisted thousands of soldiers and sailors who were unfit for duty and were highly susceptible to disease.
The vast majority of soldiers contracted some form of disease during their first weeks of military service. Those first weeks of duty were a period of enormous physical and psychological adjustment. Physically, soldiers grew accustomed to a new diet and sleep routine. Psychologically, most soldiers combated homesickness that sometimes turned into prolonged bouts of depression. The average soldier was sick at least three times annually between 1861 and 1865. Approximately 5 percent of all soldiers diagnosed with a disease died as a result of that ailment or from mounting complications stemming from their original malady. For unknown reasons, soldiers serving in the western theatre suffered a higher disease mortality rate than their eastern counterparts. Additionally, African American soldiers reported a higher rate of disease and disease mortality than did white soldiers. Lackluster conditions, inadequate supplies, preexisting conditions, and overt racism possibly account for those higher numbers.
The types of diseases contracted by soldiers can be divided into three main categories: childhood diseases, camp diseases, and epidemic diseases. Soldiers raised in rural areas usually had little exposure to childhood diseases such as chicken pox, measles, mumps, and whooping cough. The worst of these was measles. In the summer of 1861 measles struck several regiments in surgeon Legrand Wilson's brigade. More than two hundred men died from measles in his brigade that summer. With hundreds more inflicted the Confederates converted a neighboring tobacco warehouse into a measles hospital. "About one hundred sick men," wrote Wilson, as reprinted in Robertson's book, "crowded in a room sixty by one hundred feet in all stages of measles. The poor boys lying on the hard floor, with only one or two blankets under them, not even straw, and anything they could find for a pillow. Many sick and vomiting, many already showing the unmistakable signs of blood poisoning" (p. 149). Measles were so prevalent in the army that twentieth-century writers such as Margaret Mitchell (1900-1949) incorporated the disease into their fictionalized accounts of the war. In Mitchell's 1936 book Gone With the Wind heroine Scarlett O'Hara's first husband, Charles Hamilton, died from measles while in camp and prior to seeing battle. Mitchell's choice of disease was more than an act of literary convenience but instead a reflection of dozens of memoirs and diaries read by the Georgian author in preparation for writing the book. Childhood diseases frequently reduced a regiment's fighting strength by half before the unit ever fired a single volley toward the enemy.
Childhood diseases reappeared throughout the war. During the summer and fall of 1862 a second wave of childhood diseases spread throughout both armies, claiming the lives of hundreds and debilitating thousands. As late as winter 1865 diseases such as measles and chicken pox continued to plague both armies, even among veteran regiments.
Soldiers who survived bouts with childhood diseases also faced a number of camp diseases. Camp diseases were caused by a variety of factors, including poor sanitary conditions, vitamin deficient diets, inadequate shelter, contaminated drinking water, and insect infestations.
Union soldiers benefited from the work of organizations such as the United States Sanitary Commission, the Christian Commission, the Western Sanitary Commission, and the Young Men's Christian Association, whose combined efforts worked toward improving sanitary conditions. Their volunteers instructed soldiers and their commanders on the importance of maintaining both a hygienic body and campsite. The Confederacy never developed a similar network of sanitary crusaders. Their armies depended on staff surgeons and commanders to improve camp conditions. James M. McPherson reproduces the words of Robert E. Lee, commander of the Army of Northern Virginia, in his 2001 book Ordeal by Fire: "Our poor sick, I know suffer much, but they bring it on themselves by not doing what they are told. They are worse than children, for the latter can be forced" (p. 385).
Maintaining a sanitary camp was beyond the capabilities of most soldiers and commanders. Sites placed on low-lying land or flood plains were subject to sitting water. Soldiers often slept on the damp ground. In such a state of affairs soldiers caught a variety of respiratory ailments, including bronchitis and pneumonia. Charles Smedley relayed an example of such problems in his 1865 memoir Life in Southern Prisons from the Diary of Corporal Charles Smedley. "Last night was the coldest we have had for some time. My attack of bronchitis has extended far into the chest, and is going to bring on that terrible "army scourge" again" (p. 33). Bronchitis was accompanied by a persistent cough and chest pain. Once diagnosed, soldiers could spend as much as a month in the hospital before their lungs regained normal function. Under regular circumstances bronchitis was rarely fatal, but diseases of the respiratory system proved to be cyclical for Civil War soldiers. Within days after being released from the hospital soldiers again began experiencing inflammation of the bronchial tubes accompanied by an abrasive cough, muscle pain, and a bloody mucus discharge. For many, such discomforts were routine parts of the daily life of a Civil War soldier.
Large armies produced substantial amounts of human waste. Disposing of human excrement in a sanitary fashion required special planning, especially when armies were on the move. Soldiers frequently scraped out temporary latrines, also known as sinks, during short encampments. Such facilities provided no privacy and were usually located within close proximity to where soldiers ate, drank, and slept. Physicians did not understand the need to locate latrines a significant distance downstream from a camp's source of drinking water. Consequently, soldiers often drank water gathered within a few yards of their latrines. Feces contain high levels of bacteria. One poorly placed latrine could spread bacterial infections such as pneumonia and diarrhea throughout an entire company of soldiers with devastating effect. Soldiers held in prison camps experienced frightening conditions. About Andersonville, John Worrell Northrop recorded the following account in his 1904 book Chronicles from the Diary of a War Prisoner in Andersonville and Other Military Prisons in the South in 1864: "Men unable to go to the swampy sinks, have dug holes close by where they lay. The rains wash these away or overflow them, and the filthy contents are carried into our resting places" (p. 71). Northrop's description, though written while in prison, portrays similar conditions in thousands of military camps, where many soldiers paid scant attention to the devastating effects of improper sanitation.
Dietary deficiencies weakened soldiers' immune system and increased their susceptibility to certain types of disease. Soldiers' letters regularly complained about their substandard diet. They ate sparingly during a campaign and when they did manage to eat a sufficient number of calories, it usually consisted of meals rich in corn protein and saturated fat. Poor diet made soldiers prone to ailments such as diarrhea and dysentery. More soldiers suffered from chronic bouts of diarrhea during the war than of any other disease. Editor David P. Jackson published the words of ancestor Oscar Lawrence Jackson in the 1922 edition of The Colonel's Diary: "A great many of our men," Oscar Lawrence Jackson wrote, "suffered with diarrhea and some with fevers and our regiment gradually ran down in strength" (p. 57). Diarrhea confounded physicians, who struggled to find an effective treatment and remained uncertain about its principal causes. Cases of diarrhea and dysentery steadily increased throughout the war, whereas diagnoses of more fatal diseases such as typhoid fever slowly decreased. Private Peter W. Homer, 1st New Jersey Cavalry Regiment, Army of the Potomac, was admitted to the hospital in January 1863 after enduring a prolonged bout of typhoid aggravated by an "exhausting diarrhea, from ten to twelve thin watery evacuations daily," recounted George C. Rable in his 2002 book Fredericksburg! Fredericksburg! (p. 105). Homer, age twenty-six, died several weeks later after recovering from typhoid but eventually succumbing to successive bouts of diarrhea. Dietary deficiencies also caused such prominent and deadly diseases as scurvy and dyspepsia, but diarrhea was the most common.
A Deadly Treatment
Surgeons in the Civil War operated under difficult conditions. Despite their heroic efforts, they often could not save their patients, who suffered from wounds and complications for which the surgeons lacked the proper medicines or technologies. Surgeons also routinely used practices that were more dangerous than helpful. For example, they often treated gunshot wounds by "hermetically sealing" the opening, a practice in which a wound was closed without removing the bullet. The practice was later all but condemned because of its nearly 100 percent mortality rate. George Alexander Otis's 1865 report on surgical procedure during the Civil War recorded only one soldier who made a full recovery after having his wound hermetically sealed. The passage below describes that soldier's treatment for a bullet wound:
Corporal Peter Welker, Co., A., 1st U.S. Sharpshooters, was admitted July 30th, 1863, into Mount Pleasant Hospital, at Washington, having received, at Manassas Gap, July 23, 1863, a gunshot wound of the chest. The missile entered near the nipple, between the fourth and fifth ribs, traversed the lung, and emerged at the inferior border of the scapula, fracturing the sixth rib. Treatment: Opiates and stimulants, the wound being hermetically sealed. When admitted, the patient had much pain in his chest dyspacea. The latter increased almost to suffocation, and was accompanied by fever. On July 31st the posterior wound gave way, and a profuse discharge of clotted blood and purulent matter escaped. The next day the anterior wound was opened, and a pint of matter of similar character escaped, after which the patient became much better. He continued to improve until furloughed. On December 13th, 1863, when readmitted, he had entirely recovered. (Otis 1865, p. 22)
carly s. kaloustian
SOURCE: Otis, George Alexander. Reports on the Extent and Nature of the Materials Available for the Preparation of a Medical and Surgical History of the Rebellion. Philadelphia: J. B. Lippincott, 1865. Available online from http://galenet.galegroup.com/servlet/.
Soldiers weakened by the rigors of military service and protracted exposure to childhood and camp diseases were especially at risk to contract any one of a number of epidemic diseases. An epidemic disease differed from most camp diseases because of the rate of its expansion and the geographic size of its growth. Common Civil War epidemics included malaria, cholera, and small pox, but at times camp diseases such as diarrhea occurred in such widespread numbers that it too could be considered a disease of epidemic proportion. A vaccination existed for small pox but its supply was irregular and the results of the inoculation varied. Civilians constantly worried that approaching armies might introduce an epidemic into their community. Residents of Bartow County, Georgia, located in northwest Georgia, grew so concerned about the rate of small pox in the Army of Tennessee that several dozen families sought refuge at locations far removed from the army months prior to beginning phases of the Atlanta campaign. Army commanders also worried that civilians might transmit epidemic diseases to their forces. While in winter quarters at Dalton, General Joseph E. Johnston (1807–1891) issued firm orders restricting civilian access to his post, citing the risk of the spread of disease as a major factor. Meanwhile in Christiansburg, Virginia, located in southwest Virginia, conditions at Montgomery White Sulphur Springs Hospital reached near chaos as a small pox epidemic ravaged their soldier patients, staff, and the surrounding community. As conditions worsened the psychological and physical hardships imposed on the staff as a result of the disease created internal strife as commanders and their subordinates uncharacteristically sniped at one another, each blaming the other for their post's situation.
Malaria, like small pox, played a prominent role in the war's military history. Commanders serving in mosquito-infested areas had to account for malaria when planning their military campaigns. During the Peninsula campaign Union troop numbers were reduced dramatically by outbreaks of malaria. Gerald F. Linderman recounted the words of one Union soldier in his 1987 book Embattled Courage: The Experience of Combat in the American Civil War, that "at times one might sit in the door of his tent and see as many as six or seven funeral parties bearing comrades to their humble resting places…. Our army seemed on the point of annihilation from disease" (p. 116). As the Army of the Potomac approached the Confederate capital Richmond many of its regiments were missing as many as 75 percent of their men due to numerous outbreaks. Malaria rarely killed soldiers but did weaken their bodies, allowing accompanying illnesses such as diarrhea to become increasingly deadly. About 5 percent of soldiers who had malaria died, while more than half returned to active duty following a hospital stay or recuperation period that typically lasted for two or more weeks.
Small pox, malaria, influenza, yellow fever, cholera, and other forms of epidemic disease spread virtually uncontested throughout the war. Even when such diseases were not present, the mere threat of their arrival and dispersion was enough to have a tremendous psychological impact upon a soldier's psyche. Union soldiers such as Alfred Lewis Castleman saw the South as a land of epidemic diseases and some worried that this fact might provide the Confederates with a distinct advantage. Castleman wrote in his 1863 book The Army of the Potomac, Behind the Scenes, "They [Confederates] will then, I think, fall back on the Cotton States, luring us on to an enemy more formidable than their guns—rice swamps, hot weather, and yellow fever" (p. 110). Some Confederate civilians saw this as an advantage. In her 1911 book The Journal of Julia LeGrand, New Orleans 1862-1863 Julia Ellen LeGrand Waitz reproduced this journal entry: "I feel that these insolent invaders with their bragging, should be conquered—come what will. Better to die than to be under their rule. The Yankees have established strict quarantine. The people of the town are frightening them terribly with tales about the yellow fever. We are compelled to laugh at the frequent amusing accounts" (p. 46).
Venereal and Behavioral Diseases
Venereal disease too struck numerous soldiers, embarrassing the infected and further reducing their side's effective fighting force. Such disease typically involved a plethora of symptoms including, but not limited to, painful urination, genital swelling, persistent rash, and genital bleeding. The surviving medical records of the Army of Tennessee indicate that no soldier died as a result of a venereal disease, but fewer than half of those infected returned to active duty. Camp followers, like prostitutes, transmitted venereal diseases such as gonorrhea, syphilis, and herpes to soldiers. This became such a problem for the Army of Tennessee that surgeons opened a venereal disease hospital in Kingston, Georgia. During winter 1863-1864, Army of Tennessee general Joseph E. Johnston received reports that many of his men at winter quarters in Dalton, Georgia, had been slipping south along the railroad to a house located on the northern bank of the Etowah River. There, the men were reportedly soliciting the services of a known prostitute, Mary Edwards. Eager to stop this behavior, Johnston ordered a detachment of cavalry to destroy Edwards' brothel. The horse soldiers attached chains to the building and pulled it off of its rock foundation, toppling it into the Etowah River. Enraged, Edwards wrote an angry letter to Georgia governor Joseph E. Brown protesting Johnston's actions. Brown, unaware of the details of the situation, forwarded her letter along with a few harsh words of his own to Johnston. Johnston curtly replied, defending his actions and claimed that women such as Edwards had "disabled more men than the enemy" through their illicit behavior.
A number of behavioral diseases also impacted the daily lives of Civil War soldiers, such as alcoholism and other forms of drug addiction. Most soldiers drank, but many developed severe alcohol problems. Alcohol provided soldiers with a release from the stressful toll of daily life. During periods of inactivity, such as winter quarters, alcohol relieved boredom and tempered feelings of homesickness. Jenkins Lloyd Jones, in his 1914 book An Artilleryman's Diary, notes from December 1864 when serving in Savannah, "Our camp is right by a liquor saloon, which is sold indiscriminately. Nearly all of a neighboring regiment are beastly drunk, and with their unearthly yells and maniac demonstrations are making the air hideous. Our own Battery also presents a sad sight. Last night—was helplessly drunk….Oh, why will not out officers put a stop to this demoralization" (p. 280).
Soldiers recovering from battle wounds, particularly Union soldiers, frequently received pain relievers such as morphine and laudanum either during surgery or throughout their recuperation. Supplies of these painkillers were limited in the Confederacy due to the blockade and poor domestic production. Morphine and laudanum were highly addictive painkillers necessary, though not always available, to ease a soldier's pain during intensive surgical procedures such as amputations. Surgeons, however, also used these drugs as sleep aids. Wounded soldiers recovering in hospitals regularly received various assorted doses of morphine to induce sleep. Such usage over even a short period of several days was enough to produce a life-long addiction for many soldiers. Post bellum physicians further aggravated the problem through their continued over-reliance on those and other painkillers. Civil War veteran surgeon and post bellum physician Robert T. Ellett of Christiansburg, Virginia, for example, routinely prescribed morphine to patients experiencing difficulty sleeping or hypertension. For those affected, postwar drug addiction was a wartime legacy many soldiers carried with them for the rest of their lives.
The Civil War was a medical catastrophe. More soldiers died from disease than battle. Most physicians and surgeons had little understanding about the relationship between soldiers' physical environment and their state of health. Medical personnel treated the disease and not the patient, frequently conquering one only to lose to another enemy whose presence attracted less attention. If they must die, soldiers wanted to do so with their face to the enemy in a manner somehow befitting all the glories of war. Disease brought a slow painful death void of heroism, yet all too familiar for most soldiers.
Castleman, Alfred Lewis. The Army of the Potomac, Behind the Scenes: A Diary of Unwritten History: from the Organization of the Army… to the Close of the Campaign in Virginia, about the First Day of January, 1863. Milwaukee, WI: Strickland and Co., 1863.
Courtwright, David T. "The Hidden Epidemic: Opiate Addiction and Cocaine Use in the South, 1860-1920," Journal of Southern History 49, no. 1(February 1983): 57-72.
Gone With the Wind. Directed by Victor Fleming. MGM Pictures, 1939.
Jackson, David P., ed. The Colonel's Diary: Journals Kept before and during the Civil War by the Late Colonel Oscar L. Jackson of Newcastle, Pennsylvania, Sometime Commander of the 63rd Regiment O. V. I. New Castle, PA: David P. Jackson, .
Jones, Jenkins Lloyd. An Artilleryman's Diary. Madison: Wisconsin History Commission, 1914.
McPherson, James M. Ordeal by Fire: The Civil War and Reconstruction. 3rd ed. New York: McGraw-Hill, 2001.
Northrop, John Worrell. Chronicles from the Diary of a War Prisoner in Andersonville and Other Military Prisons of the South in 1864 . Wichita, KS: J. W. Northrop, 1904.
Rable, George C. Fredericksburg! Fredericksburg! Chapel Hill: University of North Carolina Press, 2002.
Robertson, James I., Jr. Soldiers Blue & Gray. Columbia: University of South Carolina Press, 1988.
Shyrock, Richard H. "A Medical Perspective on the Civil War," American Quarterly 14, no. 2 (Summer 1962): 161-173.
Smedley, Charles. Life in Southern Prisons from the Diary of Corporal Charles Smedley, of Company G, 90th Regiment Penn's Volunteers, Commencing a Few Days before the Battle of the Wilderness. [Lancaster, PA:] Ladies' and Gentleman's Fulton Aid Society, 1865.
Waitz, Julia Ellen LeGrand. The Journal of Julia LeGrand, New Orleans 1862-1863. Richmond, VA: Everett Waddey Co., 1911.
Keith S. Hébert
DISEASEdisease and disaster: epidemics and society in the nineteenth century
disease, dislocation, and social order
An epidemic is a sudden disastrous event in the same way as a hurricane, an earthquake, or a flood. Such events reveal many facets of the societies in which they occur. The stress they cause tests social stability and cohesion. Epidemics, however, have their own characteristics, one of which is that while they cause social upheaval they are also caused by it. The massive dislocation brought about by the transformation of agrarian into industrial societies from the end of the eighteenth century in Western states produced its own patterns of epidemic invasions.
In Britain, for example, up to the late seventeenth century the population grew gradually. The early modern period witnessed new surges in population growth in a society with an exponentially expanding economic base. In the nineteenth century epidemic diseases caused massive levels of mortality in the first industrial society, and yet population growth soared. Toward the end of the nineteenth century Britain began to see a dramatic decline in premature mortality and an increased length of average life. In other Western industrializing societies similar patterns recurred. Changing patterns of economic development were a major factor in bringing about demographic change from the early modern to the modern period, allowing earlier marriage and rising standards of living, which led to increased fertility and less hunger. But can the modern rise of population be accounted for purely by the reduction in famine and malnutrition and improved overall levels of nutritional status? Or has intervention in the spread of infectious disease played an equally important role?
Studying the epidemic streets of nineteenth-century industrializing societies provides one insight into these questions. The sprawling urban world of high-density masses took the lives of innocents more than anything else. Infant death was responsible for a huge proportion of preventable mortality in the nineteenth-century industrial city. Among the most economically deprived who had least access to the facilities that would provide a hygienic environment for infant life, millions of infants died. They succumbed to measles, whooping cough, smallpox, and, above all, diarrhea. Children and young adults died of diphtheria and tuberculosis. Everyone from all age groups caught fever—typhoid and typhus—and the great grim reaper, cholera, brought periodic devastation. Urban proletariats, however, were largely well fed enough throughout the nineteenth century to remain above the level of malnutrition that would effect immunity to these diseases, so what accounts for declining mortality from them as the century wore on? How can this be explained if improved nutrition does not provide the whole answer?
Taking the British case as an example a bit further, the prevention of infantile diarrhea depended upon a clean water supply for washing utensils and maintaining sufficient levels of domestic hygiene. This gradually became available in Britain starting in the late nineteenth century and coincided with the period of mortality decline. Diphtheria, by contrast, needed the temporary isolation of the disease from the school population in order to prevent the disease from spreading. Starting in the 1870s, local health officers in Britain had the power to close schools and isolate victims and their siblings. At this time a number of factors began to converge that increasingly provided a protective environment for all against infectious disease. Newer levels of social stability created the opportunity for masses of the population to settle and control their immediate environments as the pace of industrial growth and urbanization slowed and its infrastructural developments became fixed and functional. Direct interventions to halt the routes of infection had also been operating for a continuous period by this time, namely, the environ-mental and preventive medical reforms of the sanitary and state medical movements. In Britain the preventive idea had been proselytized by new bearers of a professionalized hygienic ideology, medical officers of health, and by the turn of the century this began to have an effect on domestic consciousness, reducing the apathy toward infectious disease and encouraging new practices within the home. Above all a society that had experienced a century of massive economic, social, and technological transition was beginning to solidify and learn to cope with the penalties of expansion. Displaced populations were beginning to settle, social dislocation was reduced, public health intervention had begun to take effect, and infectious disease began to decline.
Two epidemic diseases of the nineteenth century illustrate this process more than any other and have come to characterize the costs of the level of urbanization that accompanied industrialization. Typhus is a disease that flourishes among populations who live under the circumstances of refugees without access to stable, hygienic shelter, clean water, and enough food. It became a persistent feature of poverty among inner-city populations, especially among the migrant and itinerant poor. Typhus is transmitted to humans through the vector of body lice. It attacks people who live in dirty conditions without access to clean surroundings and clothes. It was traditionally associated with jail inmates, armies, and famine victims, all of whom lived under such conditions. In the nineteenth century it was the migrant urban populations who suffered from typhus most. Migration became a defining demographic characteristic of early industrial societies. Agricultural laborers migrated to become industrial workers and members of the industrial proletariat, and Lumpenproletariat often moved more than once during a lifetime to follow the geography of the business cycle. But the populations that migrated to look for work became the poorest and most deprived in the urban environment. They were last in line and had least access to the facilities the city could offer—a stable roof over their heads, clean water, regular employment, and a sufficient income to provide them with an adequate subsistence. They were dirty, hungry, and, in the winter, cold. They became louse-ridden. They were attacked by typhus in droves.
Typhus became a disease that the migrant poor always had with them, but among epidemic disasters of the nineteenth century cholera was king. Asiatic cholera swept through Europe from India like an avenging angel. Caused by waterborne fecal germs, cholera revealed its own story about the social, political, and economic relations of industrial societies. It demonstrated the dysfunction of mass aggregation in the urban environment and the tenuous stability of class relations. Over the course of the century, it stimulated governments into creating policies to improve the environmental conditions that had facilitated its massive pandemic spread. Cholera killed with shocking speed and vicious regularity. At its peak it could wipe out communities in a week. The social-psychological effect of cholera on the nineteenth-century mentality was devastating. It became the symbol of the human costs of exponential industrial and economic growth.
Understanding epidemic disease in industrial society and how to control it required nineteenth-century state and civic authorities to rethink their approaches. Following traditional patterns of quarantine and isolation employed in the control of plague proved inadequate. For one thing, cholera seemed to defy the contagionist theory of disease. It bypassed quarantine procedures and isolation measures, cutting across all traditional barriers erected to protect the community. Miasmatic etiology seemed to offer a more plausible explanation. It could explain cholera's transmission across cordon sanitaires and suggested the answer might be to clean up the environment rather than issue quarantines, which stopped the economic lifeblood of free-market trading societies. As cholera raged among urban communities until late in the nineteenth century, politicians, doctors, and disease theorists fought over how it was caused and how it could be eliminated.
Epidemic disease took the question of population health to a high point on the political agenda of the nineteenth century. Disease became the definitive symbol of the dislocations experienced by industrializing societies.
Numerous scholars who have looked at disease in history, such as William H. McNeill and Alfred W. Crosby, have discovered how it has frequently precipitated widespread social disruption and upheaval and has been a factor in bringing about revolutionary changes. Disease has subsequently been examined as a test of social cohesion at different periods. Much of the scholarly work on nineteenth-century cholera, for example, has set out to demonstrate the link between pandemic waves and revolutionary uprisings. Other scholars have suggested that cholera was the spur to the development of public health administration throughout Europe. More recent studies, however, have challenged this view and have demonstrated how a much broader set of events combined with epidemic episodes to stimulate the growth of public health administrations.
Did disease precipitate social disruption or was it precipitated by it? Certainly cholera pandemics coincided with times of severe disorder and unrest in nineteenth-century Europe. The first European epidemic of 1831 to 1832 followed the tail end of the revolutions on the European continent in 1830 and took place during the most violent period of civil disorder resulting from political agitation for parliamentary reform in Britain in 1832. The second pandemic of 1848 to 1849 began in the year of revolutions in Germany and France, and the 1854 epidemic followed the outbreak of the Crimean War (1853–1856). The 1866 epidemic occurred as the German federation was demolished after Otto von Bismarck's war with Austria, and the Second Empire fell in France as cholera spread during 1871. At the time of the last wave of cholera in 1892, there were major disturbances in Russia and Poland.
Cholera created violence and rioting, especially during the epidemic of 1831 to 1832. In Russia the peasant masses rioted against their feudal lords in the belief that there was a deliberate campaign to poison the water as part of a Malthusian conspiracy to kill off the poor and relieve the state of the financial burden of poverty. Riots occurred in Paris against medical officials for similar reasons. In England the cholera riots of 1832 were directed at doctors, this time in the belief that the medical profession was encouraging the spread of cholera to obtain bodies for anatomical dissection.
It is easy to understand why cholera should have created such unrest if one considers how European authorities generally responded to it. Most authorities when faced with the prospect of the epidemic in 1831 simply employed the old quarantine procedures used in feudal times against the plague. That is, they set cordon sanitaires with military enforcement, closed down public meeting places, and sealed off cities and towns. But these measures, which were passively accepted by the masses living under absolute states in the seventeenth and eighteenth centuries, were not so easily imposed upon a generation that had witnessed the rise of radical democratic popular movements, following the lead of the American and French Revolutions. The coincidence of inexplicable mass mortality and the sudden appearance of government officials, medical officers, and military troops aroused popular suspicion and unrest. The bourgeois authorities became the object of conspiracy theories among the poor and were attacked as the agents of a class war. The homes of noblemen and the offices of health authorities were ransacked throughout Prussia, and officials were murdered in Paris. In Britain doctors were attacked in Bristol, not for being agents of the state, but as the result of the popular conceptions about their sinister, macabre trade in dead flesh.
Cholera, however, spread though Europe largely as an effect of social disorder rather than being the cause of it. It did follow dearth and famine, but there is only limited evidence that malnutrition lowers the stomach acid level and weakens resistance. Much more significantly it followed the movements of troops and the disruption of war. Cholera was first transmitted from its original home in India by the military campaign fought by the Marquis of Hastings against the Marathas in 1817. In 1831 the Russian war against Poland spread the disease from Asia to Europe. British troops spread it to Portugal, and in 1866 cholera was spread by the war between Austria and Italy. In 1854 French troops transferred the disease again eastward when they landed in Gallipoli during the Crimean War. It is easy to understand why troop movements spread the disease. War produces mass movements of refugee populations who abandon their homes only to end up living in appalling, unsanitary encampments. Troops themselves are cramped and confined in grossly unsanitary camps that rapidly spread disease to the nearest civilian settlement. Demobilized soldiers carry disease back to their civilian homes. Above all, overcrowded prisoner-of-war camps became fever hubs.
Apart from war, the increasing mobility of populations through the expansion of trade during the nineteenth century was the most important vehicle for the spread of cholera. The waterborne disease followed canal routes and rivers and was carried by sailors, traders, and shipping workers. Service occupations involving water, such as cleaning and washing and innkeeping, were always the first groups to succumb.
Cholera was also spread by social dislocation and subsequently exacerbated it. This pattern of social dislocation and epidemic spread is equally demonstrated for another acute infection characteristic of the times, typhus. Typhus has a long history of being associated with war and famine, frequently flourishing in military encampments and jails. Typhus, however, became almost endemic among some urban populations during the nineteenth century. Again, this reflected the social dislocation occurring in the everyday life of towns and cities that were undergoing rapid, large-scale economic and social change based on incessant population migration. The precise relationship of cause and effect between typhus and industrialization is, nevertheless, complex and difficult to untangle.
Taking the example of one city, the patterns of typhus epidemics in Victorian London are not immediately easy to explain. A steady decline of the disease occurred without any apparent correlation to hygiene or nutrition. There is no nutritional basis to immunity to typhus, although hunger is connected with it indirectly, and it followed periods of dearth and famine in the eighteenth century. Urban typhus, however, did not follow the slumps of the business cycle in Victorian Britain, and therefore different circumstances must account for its unpredictable pattern. Typhus epidemics in Victorian London were precipitated by the much more complex phenomenon of urban crisis rather than nutritional crisis. Urban crisis describes the combination of a number of features of deprivation, including hardship from political and economic conflicts, such as strikes and lockouts, and home-lessness and overcrowding resulting from slum clearance and demolition for the construction of railways. Such forces can produce urban stress that a disease such as typhus can exploit.
Continuing outbreaks of typhus in London occurred between 1861 and 1869. Throughout the late 1850s the workers in the building trades in London had been locked out by their masters for refusing to not join a union. The industrial unrest caused widespread hardship and malnutrition. It coincided with a massive program of housing clearance for the construction of the railways. Certain areas of London were, by the 1860s, filled with families living in grossly overcrowded conditions—up to twelve people in one room—hungry and without a clean or regular water supply.
Typhus is a rickettsia disease that is spread by the human body louse. The rickettsias multiply in the body of the louse and are ejected in its feces. Humans contract it from scratching and breaking the surface of the skin. The disease can remain active in the feces dust of the louse for a long period and therefore can be breathed in from house dust in a dwelling that has not been disinfected. Hungry people feel the cold more and in the middle of winter are less likely to change their linen or wash their clothes. In these conditions they are much more likely to harbor lice and increase the opportunity for infection (leading to the flourishing of typhus in the winter months).
It was in the areas of great overcrowding where typhus became epidemic in the 1860s and then suddenly and dramatically declined after 1870. What accounted for the decline? First, the demolition program of the railways ceased, and municipal building programs began distributing the slum populations to new housing. The fever-nest slums were subsequently demolished. Second, a clean and constant water supply became available beginning at the end of the 1860s, which enhanced the chances of improved personal and domestic hygiene. Third, London's economy stabilized, and the laboring poor experienced a comparative period of minimum prosperity. Typhus clearly followed the social dislocation that resulted from urban crisis in Victorian London. The pattern of infection among Irish immigrants demonstrates this relationship most clearly. Contemporary moralists and medical investigators presumed that typhus was indigenous to the Irish and referred to it as Irish fever. But the epidemics occurred in London before they occurred in Dublin. The fact that many Irish immigrants lived in infected localities reflects the way that this group more than any other suffered the deprivations of urban crisis and were the most vulnerable to its ravages.
Nineteenth-century typhus and cholera epidemics reveal how disease framed and is framed by history. Its biological existence was directly determined by social, economic, and political conditions, and it in turn brought about historical changes in those relationships. Epidemic diseases characterized the downside to economic and urban growth. They also revealed some of the intricate social changes taking place in industrial society.
Epidemic infections declined toward the end of the nineteenth century, creating the conditions for the demographic transformation of the increasingly aging and chronically sick populations that characterized advanced industrial societies by the middle of the twentieth century. The interventions of the state into the means by which epidemic infections were transmitted among mass urban populations and impoverished rural populations played a crucial role in their decline. Furthermore, the role of the state in providing for the public health altered the profile of disease.
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The Hippocratic tradition maintained that diseases were physiological, arising from an imbalance between the four humours, the correct balance of which maintained health. Each individual had a unique humoral balance which could be easily disrupted by conditions such as cold, biting winds, poor air, or injudicious eating. It was Paracelsus (c.1492–1541) who provided an alternative to such classical ideas by suggesting that disease was the product of active agents independent of the human patient. The English Hippocrates, Thomas Sydenham (1624–89), also believed that diseases were specific entities, which might be manifest in variable ways in individual patients, but which could be recognized by observant clinicians. Sydenham also advocated that specific remedies could be applied to each such disease, his favourite example being the prescription of Peruvian bark for intermittent fever or ague. It was during the eighteenth century that the classification of diseases became a dominant part of medicine, such taxonomies often being based on the presenting symptoms. Increasing attention to pathology and cellular mechanisms during the nineteenth century provided additional criteria whereby diseases could be described, recognized, and treated.
An increasing array of diagnostic techniques have become available during the twentieth century, and these have made it possible for even more diseases, syndromes, and conditions to be classified, and the International Classification of Disease goes some way to providing international standardization in the categorization of modern disease.
Disease categoriesOne broad classification divides diseases into two principle categories, defining disease as primarily congenital (present at birth) or acquired subsequently. The acquired category can be further subdivided to include infectious, neoplastic, traumatic, and degenerative diseases, which are not necessarily mutually exclusive. Modern concepts and definitions have obscured many of these classificatory boundaries, and occupational, nutritional and deficiency, autoimmune and allergic, and psychiatric diseases can now be included in contemporary nosologies. As the molecular mechanisms of diseases and their causations are increasingly understood, so classifications are increasingly becoming blurred and overlapping, and many diseases are now recognized as being multi-causal. The following sections will give brief overviews of some broad classes of disease.
Genetics and diseasesHereditary diseases may be passed down from generation to generation, but are not necessarily genetic disorders unless determined by one or more genes. The experiments on peas by Gregor Mendel (1822–84), on the transfer of characteristics from generation to generation, established the basic principles of heredity. Mendel and his successors determined a number of factors to define genetic inheritance, including its occurrence in known proportions amongst relatives, but not in unrelated individuals, such as in-laws. Applied to human conditions, some diseases were now identified as hereditary, including haemophilia and sickle-cell anaemia — although it had been recognized for centuries that some diseases ‘ran in the family’.
congenital abnormalities are present at birth, though some do not immediately become apparent. They are not necessarily inherited, many in fact being environmentally determined during intrauterine life. It is now known that many common diseases, including heart disease, insulin dependent diabetes, some forms of psychiatric illnesses, and autoimmune diseases, have a genetic component. But these susceptibilities are often triggered by some environmental influence, and represent a complex interaction between nature (genetic makeup) and nurture (external influences). Some forms of cancer are increasingly recognized as having a major genetic component. The genetics of some diseases, such as cystic fibrosis, beta-thalassaemia, and Duchenne's muscular dystrophy, are now well known, and it is possible to screen parents, and unborn fetuses, to detect genetic abnormalities, and to offer termination of an affected fetus. The development of in utero gene therapy offers the hope of treatment, whilst modern medicine can do a great deal to maintain individuals who, in earlier periods, would have died because of their genetic constitution.
Infectious diseasesinfectious diseases caused by microorganisms or parasites have been powerful forces in shaping human history. As early humans formed hunter–gatherer societies in about 3000 bc and began to contain and domesticate wild animals, so they became susceptible to the infections carried by the animals with which they now shared their living space. Smallpox, distemper, and measles are amongst the diseases known to have entered human populations at this time. The devastating effects of these diseases gradually became ameliorated as immunity built up in communities — major epidemics (and pandemics) were often caused by the movement of communities where such diseases were endemic into non-immune populations. Urbanization provided fresh opportunities for infectious diseases to flourish and to decimate populations — close living conditions encouraged the transfer of infections; migration into the cities from rural communities, and the dependency of urban populations on the countryside for food, provided fresh avenues for infection. Until almost the end of the nineteenth century, sustaining cities was a constant problem, and the large metropolitan areas of Western civilization were known to be centres of disease, malnutrition and starvation, and ultimately death. Diseases such as smallpox, syphilis, typhoid fever, and whooping cough were all endemic and accounted for a high infant mortality — estimates have suggested for example that the mortality rate for children under 5 was as high as 50% for much of the nineteenth century in the English city of Manchester. By the latter half of that century, the experiments of Robert Koch (1843–1910) in Germany and Louis Pasteur (1822–95) in France, amongst others, increasingly provided evidence that microganisms were the cause of several infectious diseases. Efforts were made to utilize this knowledge in the manufacture of vaccines, preparations of modified or killed bacteria that could be administered to produce a mild form of the disease and to confer immunity. Although the precise mechanisms of how such immunity was created were unknown, a number of therapeutic substances were developed, the biggest breakthrough coming at the end of the nineteenth century with the appearance of serum anti-toxins. Since then, increasing understanding of the underlying cellular mechanisms of immunity and of the biology of microorganisms; the growth and development of the pharmaceutical industry, especially the discovery of antibiotics; and the development of public health measures to prevent and treat infectious diseases, have led to a notable decline in mortality and morbidity from such diseases in the Western world. The same cannot be said for the developing world, and concerns grew at the end of the twentieth century about resistance to antibiotics, the appearance of new infectious killers such as HIV (which causes AIDS), and the re-emergence of drug-resistant forms of diseases such as TB.autoimmune diseases occur when elements of the immune system, normally responsible for recognizing and attacking ‘non-self’ cells — such as the microorganisms that cause infectious diseases — fail to distinguish between ‘self’ and ‘non-self’. Such cellular attacks on healthy constituent parts of the body can contribute to a variety of disorders, including myasthenia gravis, some thyroid disorders, and rheumatoid arthritis. There is growing evidence that conditions such as diabetes and multiple sclerosis also have an autoimmune component.
Diseases associated with food: deficiencies, excesses, and intolerancesDeficiency (nutritional) diseases arise from lack of one or more essential nutritional component, such as a vitamin or mineral, in the diet, or because of the body's inability to digest, absorb, or utilize particular nutrients. A nutritional deficiency can also occur if the body's metabolism is abnormal or if essential elements are excessively excreted. Historically, deficiency diseases have arisen in populations forced, by war or famine, to abandon their traditional diets, or by the adoption, perhaps for religious reasons, of a restrictive diet. Expeditions into new territories have always been vulnerable to dietary diseases because of the difficulty of carrying adequate supplies. The most notable example was that of scurvy, and the development of its treatment by eating citrus fruits, which occurred long before the rationale was understood — namely that this corrected a vitamin C deficiency due to lack of fresh fruit and vegetables. Subtle changes to farming or cooking methods can also lead to unexpected deficiencies. One of the best known examples is the use of white (huskless) rice instead of brown (husked) rice. This can lead to beri-beri, particularly prevalent in the Far East, which is characterized by ascending weakness in the legs and accompanying muscle tenderness, and can lead to widespread nerve irritability and congestive heart failure. This is due to a lack of thiamine, a vitamin that is essential for the mechanisms by which energy is released from foodstuffs.
Excess consumption of certain kinds of foods has been shown to be associated with the onset of conditions such as heart disease or diabetes — often exacerbating a genetic predisposition, and thus once more blurring the distinctions between different disease categories. Over consumption of alcohol, cigarette smoking, and taking other damaging drugs can all lead to disease conditions that can be classified as ‘self-inflicted’ (a category that can also include sexually transmitted diseases contracted during unprotected sex).
Food intolerances have been increasingly recognized in the latter part of the twentieth century, as some individuals show anaphylactic responses to particular allergens, such as nuts or dairy products.
Occupational diseases and the effects of pollutionConcern about the workplace as a source of disease has grown, particularly since World War II, as have the specialities of public and occupational health. Safety procedures, including the use of protective clothing, have been proposed to limit workers' exposure to dangerous chemicals or to hazardous practices. Working conditions, such as those for office workers using video display equipment, have received attention, and exposure to noise, bad ventilation, and poorly designed furniture have increasingly been recognized as playing a role in stress. Stress in turn is recognized as contributing to high blood pressure, heart disease, and stroke.
These concerns are not, however, entirely new. Lead poisoning amongst miners was recognized by Hippocrates (c.450 bce), but it was really the impact of the Industrial Revolution that focused the attention of reformers and some physicians on the impact of working conditions on health. A Leeds physician, Charles Thackrah, wrote The effects of arts, trades and professions on health and longevity (1832), which described the occupational hazards attached to numerous trades, including flock dressers, maltsters, coffee grinders, and corn-sillers. The effects of adverse and dangerous conditions on the ordinary working man became an issue for the growing number of trade or labour unions, and reform movements throughout the twentieth century campaigned for safer working conditions and adequate health care and compensation for those injured in the workplace.
Increasingly, however, environmental dangers have been recognized as having wider impact than just at the workplace. There can be pollution from accidental contamination and from large-scale industrial accidents. Disease and disasters can arise from cynical exploitation by manufacturers who ignore concerns for the welfare not only of their own workforce, but also of those living in the vicinity of their production facilities, such as the workers in the asbestos industry or the victims of the Bhopal explosion in India that killed 2000 people. Dispersal of pollutants, by air as after the Chernobyl disaster in Ukraine, or by river systems, can cause disease at vast distances from the original site of contamination.
Psychiatric diseasesMental illness can refer to disorders in perception, understanding, emotion, and behaviour, and can range from the milder psychological disorders and psychosomatic illness to the severe psychosis. Psychiatric disorders have not always been seen to be the province of the medical profession: theories about demonic possession, for example, have led to religious remedies or persecution. For many centuries doctors had little to do with those classed as ‘insane’. The insane were incarcerated and contained, rather than treated. In the twentieth century increasing acknowledgement of the interplay of social, psychological, and physical factors in the causation of many psychiatric disorders, and the development of specific pharmacological therapies, led to improved care. Here again, the categories of disease classifications have become blurred, as faulty chemical processes in the brain and genetic defects have been shown to account for some manifestations of mental disease.
Degenerative diseasesIronically, as infectious diseases were increasingly conquered during the twentieth century, degenerative diseases emerged in the West-ern world, primarily affecting the elderly. Degenerative processes can strike in particular organs or tissues, resulting in damaged joints, such as hips and knees; in weakened bones, as a result of osteoporosis; or as degeneration of the brain, causing severe mental deficits, such as dementia. It has been argued, most notably by the epidemiologist, Thomas McKeown (1912–88), that the main risks to life and good health have occurred in 3 distinct historical phases: accidents and injuries; infections; and finally degenerative diseases of longevity, which can include diseases such as Alzheimer's disease, Parkinson's diseases and some cancers.
One of the best known degenerative diseases is Alzheimer's, first described in 1906 by Alois Alzheimer, but then recognized as only a very rare brain disorder associated with cognitive dysfunction. This type of dementia is now the most common acquired progressive brain syndrome, although its cause remains unknown. Recent figures from the US have shown that Alzheimer's affects more than 4% of the over-60s population, whilst prevalence grows to 20% of the over-80s age group. The impact of chronic degenerative disease is felt not only by individuals and families, but also by social welfare and health care systems.
CancerCancer is caused by a breakdown in the normal processes of cell division and multiplication, resulting in uncontrolled cell growth producing a tumour. In the industrialized world, at the beginning of the twenty-first century, it is estimated that one-third of the population will develop cancer, with the probability currently increasing. This is partly because it is predominantly a disease of middle and old age, and as life expectancy has increased, so too has the incidence of cancer. Several cancers are known to have a genetic basis, and also the environmental impact of some pollutants, known as carcinogens, is becoming increasingly well understood.
Iatrogenic diseasesThese diseases arise from medical treatment for another condition. Sometimes the problem may be due to recognized undesirable side-effects of therapeutic drugs, or to an unusual, idiosyncratic reaction to a medicament. A scheme of reporting adverse drug reactions, the so-called ‘yellow card scheme’ was introduced in Britain in the early 1970s, in an attempt to identify such reactions. Surgical procedures, when mishaps or infections result, can also inadvertently cause further disease.
E. M. Tansey
Kiple, K. F. (ed.) (1993). The Cambridge world history of human disease. Cambridge University Press.
McKeown, T. (1979). The role of medicine: dream, mirage or nemesis. Oxford University Press.
McKeown, T. (1988). The origins of human disease. Oxford University Press.
See also allergy; drug abuse; environmental toxicology; genetics, human; Islamic medicine; medicine; mind–body interaction; work and the body.
Disease can be defined as any change in body processes that impairs its normal ability to function. The human body has certain basic requirements that must be met if it is to function normally. These requirements include the proper amount of oxygen, acidity, salinity, and other conditions. These conditions must all be maintained within a very narrow range. A deviation from that range can cause disease to develop.
Most diseases can be classified into one of three major categories: infectious diseases; noninfectious diseases; and diseases for which no cause has yet been identified. At one time, a number of conditions were also classified as genetic diseases. This category includes conditions such as sickle-cell anemia, phenylketonuria, Tay-Sachs disease, cystic fibrosis, and galactosemia. These conditions are now more appropriately known as genetic disorders.
At one time, humans were totally mystified as to the causes of common diseases such as typhoid, typhus, pneumonia, mumps, yellow fever, pneumonia, smallpox, rabies, syphilis, gonorrhea, tuberculosis, and rheumatic fever. Explanations ranged from punishment by God for evil deeds to acts of magicians or witches to an unbalance in the composition of the blood.
During the eighteenth century, the true nature of such diseases was finally discovered. Largely due to the work of the French chemist Louis Pasteur (1822–1895) and the German bacteriologist Robert Koch (1843–1910), scientists learned that infectious diseases were caused by organisms that entered the human body and upset its normal healthy state. In most cases, these organisms were too small to be seen with the unaided eye: bacteria, viruses, and fungi, for example. In other cases, they were caused by various types of worms. Diseases of the latter type are usually called parasitic diseases because the worms live off the human body as parasites.
The human body includes a number of devices to protect itself from infectious diseases. The first in line of these devices is skin. Skin can be thought of as a protective envelope surrounding the body. That envelope generally is able to prevent disease-causing organisms (germs) from entering the body.
One way in which disease can develop is for a break to occur in the skin, as in a cut or scrape. Germs that would normally be prevented from
entering the body are able to invade the bloodstream through such openings. At that point, the body puts into action a second line of defense: the immune system. The immune system is a complicated collection of chemical reactions that release compounds that attack and destroy invading organisms. Without an immune system, the human body would become ill nearly every time there was a cut in the skin.
In some instances, the immune system is unable to react adequately to an invasion of germs. In such cases, disease develops.
The spread of infectious disease. One characteristic of infectious diseases is that they are easily transmitted from one person to another. For example, a person who has contracted typhus can easily pass that disease to a second person simply by coming into contact with that person. Germs travel from the carrier of the disease to the uninfected person.
Disease can be spread by many methods other than direct contact, such as through water, food, air, and blood. Waterborne transmission occurs through contaminated water, a common means by which cholera, waterborne shigellosis, and leptospirosis are spread. Foodborne poisoning in the form of bacterial contamination may occur when food is improperly cooked, left unrefrigerated, or prepared by an infected food handler.
Diseases such as measles and tuberculosis can be transmitted through the air. Any time an infected person coughs or sneezes, infectious organisms can travel more than 3 feet (0.9 meter) to an uninfected person. Fungal infections such as histoplasmosis, coccidioidomycosis, and blastomycosis can also be spread by airborne transmission as their spores are transported on dust particles.
Vectors are animals that carry germs from one person to another. The most common vectors are insects. These vectors may spread a disease either by mechanical or biological transmission. An example of mechanical transmission occurs when flies transfer the germs for typhoid fever from the feces (stool) of infected people to food eaten by healthy people. Biological transmission occurs when an insect bites a person and takes in infected blood. Once inside the insect, the disease-causing organisms may reproduce in the gut, increasing the number of parasites that can be transmitted to the next person. The disease malaria is spread by the Anopheles mosquito vector.
Epidemics. Diseases sometimes spread widely and rapidly through a population. Such events are known as epidemics. One of the best-known epidemics in human history was the Black Death that struck Europe in the mid-fourteenth century. Caused by the microorganism Pasteurella pestis, the Black Death is also known as the bubonic plague, or simply, plague. Plague is transmitted when fleas carried by squirrels and rats bite humans and transfer the P. pestis from one person to another.
Once it reached Europe from Asia in about 1350, the plague was virtually unstoppable. In some areas, whole towns were destroyed as people either died or moved away trying to avoid the disease. Over an eight-year period, an estimated 25 million people died of the disease.
Other examples of epidemics include the worldwide spread of cholera during the mid-nineteenth century, the influenza epidemic in the United States in the early twentieth century, and the HIV (human immunodeficiency virus) epidemic in the United States beginning in the early 1980s.
Protection against infectious diseases. When scientists learned the cause of infectious diseases, they also developed the ability to prevent and cure such diseases. For example, people can now be vaccinated as a protection against many types of infectious disease. A vaccine is a material that can be injected into a person to ward off attacks by certain disease-causing organisms. The material may consist of very weak concentrations of the organism itself or of dead organisms. The presence of these organisms in the bloodstream stimulates the body's immune system to start producing chemicals that will fight off the disease if and when it actually enters the body.
In addition, scientists have discovered and invented a host of substances that will fight the germs that cause infectious diseases. The class of drugs known as antibiotics, for example, can be used to aid the body's natural immune system in combatting disease-causing organisms that have entered the body.
Childhood diseases. Chicken pox, measles, and mumps are all common childhood diseases. The term childhood disease is a bit misleading, however, since any one of these diseases can be contracted by a person at any age. The term developed simply because the diseases are much more common among young children than they are among adults.
The diseases named above are all infectious, caused by a virus. They are generally spread by direct contact between an infected and a noninfected person, and since young children are often in direct contact with each other—on the playground, riding a school bus, or in a classroom—they are especially susceptible to such diseases.
All three viral diseases have a somewhat similar pattern. There is a period of incubation, during which the virus reproduces within a person's body. Obvious symptoms then begin to appear: a rash in the case of chicken pox and measles and inflamed and swollen glands in the case of mumps. All three diseases normally disappear after a period of time, generally without leaving any long-term effects.
Most children can now be protected against childhood diseases by means of a regular program of immunization (vaccinations). There are, as yet, however, few if any treatments for the diseases themselves.
Vaccinations and drugs have been so successful in treating infectious diseases that they are no longer the massive threat to human health that they once were. Today, the greatest threat to human health are noninfectious diseases such as heart disease, cancer, and diseases of the circulatory system. In some cases, the nature of these diseases is well understood, and medical science is making good progress in combatting
them. For example, it is known that a stroke occurs when arteries in the brain become constricted or clogged and are unable to permit the normal flow of blood. The brain is deprived of blood, and cells begin to die, causing loss of muscular control, paralysis, and, eventually, death.
Your town is in a state of panic. Dozens of people have become ill in the past month with a disease that no one can recognize. You and your neighbors are worried that you too will become ill with the disease. To whom can you turn for help?
This puzzle calls for the work of an epidemiologist. An epidemiologist is a scientist who studies the cause and spread of disease. The epidemiologist uses a number of sophisticated techniques in his or her work. One of these techniques is sometimes called source and spread. Interviews are held with people who are ill to find out those with whom they have recently come into contact. The goal is to find out from whom the person got the disease and to whom it might have been passed on. This pattern of disease spread is sometimes called a web of causation.
Epidemiologists also try to track down the agent that caused the disease: a bacterium, virus, fungus, or other organism. They then try to determine how that organism has been transmitted from one person to another. By identifying the specific factors involved in an epidemic, it is sometimes possible to determine preventive actions that can be taken to reduce the occurrence of a disease. For example, it may be that everyone who has come down with the disease in your town has been swimming in the local lake. The disease can be prevented from spreading, then, by warning people not to swim in that lake.
The techniques of epidemiology have also been used to deal with noninfectious diseases. For example, some epidemiologists have argued that gun-related accidents have many of the characteristics of an infectious diseases. They say that people who are injured by guns can be studied in much the same way as people who become ill because of a disease-causing organism. This idea is still relatively new, however, and has yet to prove its worth in dealing with such problems.
Another noninfectious disease is cancer. The term cancer refers to any condition in which cells in a person's body begin to grow in a rapid and uncontrolled way. The causes of such growth are probably many and varied. For example, certain types of chemicals (known as carcinogens) can cause cancer. Certain kinds of tars, dyes, and organic compounds are known to be responsible for various forms of cancers. The largest single fatal form of cancer, lung cancer, is caused by chemicals found in tobacco smoke. Exposure to various forms of radiation are also known to cause cancer. People who are exposed to long periods of sunshine are at high risk for the development of various forms of skin cancer, the most dangerous of which is malignant melanoma. Some scientists also believe that some forms of cancer may be caused by viruses (which would make them an infectious disease).
[See also Ebola virus; Genetic disorders; Legionnaires' disease; Plague ]
Disease can be defined as a change in the body processes that impairs its normal ability to function. Every day the physiology of the human body demands that oxygenation, acidity, salinity, and other functions be maintained within a very narrow spectrum. A deviation from the norm can be brought about by organ failure, toxins, heredity, radiation, or invading bacteria and viruses.
Normally the body has the ability to fight off or to neutralize many pathogenic organisms that may gain entrance through an opening in the skin or by other means. The immune system mobilizes quickly to rid the body of the offending alien and restore or preserve the necessary internal environment. Sometimes, however, the invasion is one that is beyond the body’s resistance, and the immune system is unable to overcome the invader. A disease may then develop. When the internal functions of the body are affected to the point that the individual can no longer maintain the required normal parameters, symptoms of disease will appear.
The infection brought about by a bacterium or virus usually generates specific symptoms; that is, a series of changes in the body that are characteristic of that invading organism. Such changes may include development of a fever (an internal body temperature higher than the norm), nausea, headache, copious sweating, and other readily discernable signs.
Much more important to the physician, though, are the internal, unseen changes that may be wrought by such an invasion. These abnormalities may appear only as changes from the norm in certain chemical elements of the blood or urine. That is the reason patients are asked to contribute specimens for analysis when they are ill, especially when their symptoms are not specific to a given disease. The function of organs such as the liver, kidneys, thyroid gland, pancreas, and others can be determined by the levels of various elements in the blood chemistry.
For a disease that is considered the result of a pathogenic invasion, the physician carries out a bacterial culture. Certain secretions such as saliva or mucus are collected and placed on a thin plate of culture material. The bacteria that grow there over the next day or so are then analyzed to determine which species are present and thus, which antibiotic would be most effective in eradicating them.
Viruses present special challenges, since they cannot be seen under a microscope and are difficult to grow in cultures. Also, viruses readily adapt to changes in their environment and become resistant to efforts to treat the disease they cause. Some viral diseases are caused by any number of forms of the same virus. The common cold, for example, can be caused by any one of some 200 viruses. For that reason it is not expected that any vaccine in the near future will be developed against the cold virus. A vaccine effective against one or two of the viruses will be completely useless against the other 198 or 199 forms.
The agents that cause a disease, the virus or bacterium, are called the etiologic agents of the disease. The etiologic agent for strep throat, for example, is a bacterium within the Streptococcus genus. Similarly, the tubercle bacillus is the etiologic agent of tuberculosis.
Modern medicine has the means to prevent many diseases that plagued civilization in the recent past. Polio, a crippling disease brought about by the polio-myelitis virus, was neither preventable nor curable until the middle 1950s. Early in that decade an outbreak of polio affected an abnormally large number of young people. Research into the cause and prevention of polio immediately gained high priority, and, by the middle of the decade, Dr. Jonas Salk had developed a vaccine to prevent polio. Currently all young children in developed countries can be vaccinated against the disease.
Similar vaccines have been developed over the years to combat other diseases that previously were lethal. Whooping cough, tetanus, diphtheria, and other diseases that at one time meant certain death to victims, can be prevented. The plague, once a dreaded killer of thousands, no longer exists among the human population. An effective vaccine has eradicated it as a dread disease.
The resistance to disease is called immunity. A few people are naturally immune to some diseases, but most have need of vaccines. This type of immunity, attained by means of a vaccine, is called artificial immunity. Vaccines are made from dead bacteria and are injected into the body. The vaccine causes the formation of antibodies, which alert the immune system in the event a live bacterium invades.
The body’s immune system, responsible for guarding against invading pathogens, may itself be the cause of disease. Conditions such as rheumatoid arthritis and Lupus are considered to be the result of the immune system mistaking its own body for foreign tissue and organizing a reaction to it. This kind of disease is called an autoimmune disease—auto, meaning one’s own, and immune referring to the immune system. Scientists have found that little can be done to combat this form of disease. The symptoms can be treated to ease the patient’s discomfort or preserve his life, but the autoimmune reaction seldom can be shut down.
Disease prevention has now become a very challenging medical specialty. The physicians or preventive medicine specialists are trained in epidemiology, biostatistics, environmental and occupational health services, administration, as well as clinical prevention. They are, therefore, uniquely qualified to work with both individuals and the community to prevent disease. They initiate several programs in infectious disease prevention and control, sexually transmitted diseases, and in the prevention of chronic diseases. These health care professionals seek to identify health hazards in the work place and the community. They are active in patient care and like to say their patients are their community.
There are several components to the disease prevention program. In order to prevent disease, the prevention technologies have to be first delivered to the patient; the community at large. In the clinical prevention model, the traditional model for disease prevention, the health care provider and the patient have to interact. Early detection and treatment rely on that interaction. Screening for diseases, along with vaccination and early diagnosis all occur within this setup.
The second component of this prevention program is behavioral prevention strategies. The preventive medicine specialists use a broad array of strategies to encourage lifestyle changes such as exercise, no smoking, and healthful diets. To accomplish these behavioral changes, the patient’s knowledge and attitudes may require changing.
Environmental prevention strategies form the third component of the prevention program. Providing safe drinking water, fluoridation of drinking water, lead abatement, regulations on public smoking, seat-belt laws, and safer highways all come under this banner.
Culture— A means of growing bacteria and viruses in a flask or on a plate. The culture medium usually is agar, a form of gelatin, that may be enriched with broth or blood.
Pathogen— A shortened form of pathogenetic, meaning an agent that causes a disease.
Physiology— The functioning of the organs of the body. Pathophysiology is their functioning in a diseased state.
In order to incorporate these changes into the community, societal commitment is required. However, once these changes are made, they require very little effort from the individual and can have far-reaching effect.
Primary disease prevention is aimed at reducing risk factors or controlling the causative factors for a health problem. These include risk factors such as smoking (to prevent lung cancer), environmental exposure to lead (to prevent mental retardation in children), and sex education (to reduce sexually transmitted diseases). Health services such as vaccinations, routine physical examinations and providing preventive therapy tools such as fluoridated water also fall under this category. Secondary disease prevention involves early detection and treatment such as mammography for detecting breast cancer or contact tracing for detecting and treating persons with acquired immune deficiency syndrome (AIDS) and other sexually transmitted diseases.
Disease can be defined as a change in the body processes that impairs its normal ability to function. Every day the physiology of the human body demands that oxygenation, acidity, salinity, and other functions be maintained within a very narrow spectrum. A deviation from the norm can be brought about by organ failure, toxins, heredity, radiation , or invading bacteria and viruses.
Normally the body has the ability to fight off or to neutralize many pathogenic organisms that may gain entrance through an opening in the skin or by other means. The immune system mobilizes quickly to rid the body of the offending alien and restore or preserve the necessary internal environment. Sometimes, however, the invasion is one that is beyond body's resistance, and the immune system is unable to overcome the invader. A disease may then develop. When the internal functions of the body are affected to the point that the individual can no longer maintain the required normal parameters, symptoms of disease will appear.
The infection brought about by a bacterium or virus usually generates specific symptoms, that is, a series of changes in the body that are characteristic of that invading organism . Such changes may include development of a fever (an internal body temperature higher than the norm), nausea, headache, copious sweating, and other readily discernable signs.
Much more important to the physician, though, are the internal, unseen changes that may be wrought by such an invasion. These abnormalities may appear only as changes from the norm in certain chemical elements of the blood or urine. That is the reason patients are asked to contribute specimens for analysis when they are ill, especially when their symptoms are not specific to a given disease. The function of organs such as the liver, kidneys, thyroid gland, pancreas, and others can be determined by the levels of various elements in the blood chemistry .
For a disease that is considered the result of a pathogenic invasion, the physician carries out a bacterial culture. Certain secretions such as saliva or mucus are collected and placed on a thin plate of culture material. The bacteria that grow there over the next day or so are then analyzed to determine which species are present and thus, which antibiotic would be most effective in eradicating them.
Viruses present special challenges, since they cannot be seen under a microscope and are difficult to grow in cultures. Also, viruses readily adapt to changes in their environment and become resistant to efforts to treat the disease they cause. Some viral diseases are caused by any number of forms of the same virus. The common cold, for example, can be caused by any one of some 200 viruses. For that reason it is not expected that any vaccine will be developed against the cold virus. A vaccine effective against one or two of the viruses will be completely useless against the other 198 or 199 forms.
The agents that cause a disease, the virus or bacterium, are called the etiologic agents of the disease. The etiologic agent for strep throat, for example, is a bacterium within the Streptococcus genus. Similarly, the tubercle bacillus is the etiologic agent of tuberculosis .
Modern medicine has the means to prevent many diseases that plagued civilization in the recent past. Polio, a crippling disease brought about by the poliomyelitis virus, was neither preventable nor curable until the middle 1950s. Early in that decade an outbreak of polio affected an abnormally large number of young people. Research into the cause and prevention of polio immediately gained high priority, and by the middle of the decade Dr. Jonas Salk had developed a vaccine to prevent polio. Currently all young children in developed countries can be vaccinated against the disease.
Similar vaccines have been developed over the years to combat other diseases that previously were lethal. Whooping cough , tetanus , diphtheria , and other diseases that at one time meant certain death to victims, can be prevented. The plague, once a dreaded killer of thousands, no longer exists among the human population. An effective vaccine has eradicated it as a dread disease.
The resistance to disease is called immunity. A few people are naturally immune to some diseases, but most have need of vaccines. This type of immunity, attained by means of a vaccine, is called artificial immunity. Vaccines are made from dead bacteria and are injected into the body. The vaccine causes the formation of antibodies, which alert the immune system in the event a live bacterium invades.
The body's immune system, responsible for guarding against invading pathogens , may itself be the cause of disease. Conditions such as rheumatoid arthritis and Lupus are considered to be the result of the immune system mistaking its own body for foreign tissue and organizing a reaction to it. This kind of disease is called an autoimmune disease—auto, meaning one's own, and immune referring to the immune system. Scientists have found that little can be done to combat this form of disease. The symptoms can be treated to ease the patient's discomfort or preserve his life, but the autoimmune reaction seldom can be shut down.
KEY TERMS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
—A means of growing bacteria and viruses in a flask or on a plate. The culture medium usually is agar, a form of gelatin, that may be enriched with broth or blood.
—A shortened form of pathogenetic, meaning an agent that causes a disease.
—The functioning of the organs of the body. Pathophysiology is their functioning in a diseased state.
- AIDS mysterious new disease, incurable and usually fatal. [U.S. Hist.: WB, A:153]
- Black Death killed at least one third of Europe’s population (1348–1349). [Eur. Hist.: Bishop, 379–382]
- bubonic plague ravages Oran, Algeria, where Dr. Rieux perseveres in his humanitarian endeavors. [Fr. Lit.: The Plague ]
- Cancer Ward, The novel set in cancer ward of a Russian hospital. [Russ. Lit.: The Cancer Ward in Weiss, 64]
- Decameron, The tales told by young people taking refuge from the black death ravaging Florence. [Ital. Lit.: Magill II, 231]
- Fiacre, St. intercession sought by sick. [Christian Hagiog.: Attwater, 130]
- influenza epidemic caused 500,000 deaths in U.S. alone (1918–1919). [Am. Hist.: Van Doren, 403]
- Joram suffered for abandoning God’s way. [O.T.: II Chronicles 21:15, 19]
- Journal of the Plague Year Defoe’s famous account of bubonic plague in England in 1665. [Br. Lit.: Benét, 529]
- Lazarus leper brought back to life by Christ. [N.T.: John 11:1–44]
- Legionnaires’ disease 28 American Legion conventioneers die of flu-like disease in Philadelphia (1976). [Am. Hist.: Facts (1976), 573, 656]
- Molokai Hawaiian island; site of government leper colony. [Am. Hist.: NCE, 1807]
- Naaman leprous Syrian commander healed by Elisha. [O.T.: II Kings 5]
- red death, the pestilence, embodied in a masque, fatally penetrates Prince Prospero’s abbey. [Am. Lit.: Poe The Masque of the Red Death ]
- Rock, St. legendary healer of plague victims. [Christian Hagiog.: Attwater, 299]
- Sennacherib, army of besieging Jerusalem, Assyrian force must withdraw after an outbreak of plague. [O. T.: II Kings 19:35; Br. Lit.: Byron The Destruction of Sennacherib in Benét, 266]
- seven plagues, the visited upon the earth to signify God’s wrath. [N.T.: Revelation]
- St. Anthony’s Fire horrific 11th-century plague. [Eur. Hist.: Brewer Note-Book, 34]
- Syphilis Fracastoro’s epic concerning Syphilis, mythical first victim. [Ital. Lit.: RHD, 1443; Plumb, 342]
- ten plagues, the inflicted upon Egypt when Pharaoh refuses to let the Israelites emigrate. [O.T.: Exodus 7-12]
- Typhoid Mary (Mary Mallon, 1870–1938) unwitting carrier of typhus; suffered 23-year quarantine. [Am. Hist.: Van Doren, 354]
Disease (or "lack of ease") is any damage or injury that impairs an organism's function. Diseases (sometimes called deviations from the norm) can be classified in numerous ways. Generally, an acute disease comes on quickly and lasts for only a relatively short time. A chronic disease usually begins slowly and lasts for a longer time.
Diseases can also be classified according to type. Common disease types or categories include: infectious, genetic (hereditary), psychiatric, deficiency, degenerative, congenital (whether genetic or not), neurological, cardiovascular, metabolic, chemical, and occupational.
Infectious or microbial diseases (the pathogenic diseases) are often classified by their causative agents: bacteria, fungi, protozoans, viruses, or prions. Progressive diseases, particularly those caused by microbes, have several clinical stages: infection, incubation, acute, decline, and convalescent. "Prodromal" refers to the initial stages when perhaps only one or two early characteristics of the disease can be observed. Communicable diseases are transmitted either directly or indirectly (via carriers or vectors ) from one organism to another. Contagious diseases are rapidly transmitted infectious diseases. Malignant diseases usually progress quite rapidly and are potentially life threatening.
In contrast to disease (the deviation itself), "illness" is feeling of being sick, or suffering some effect of the disease. Many people have hypertension (the disease), for example, without feeling any illness until it is so far advanced that is causes a stroke or kidney failure. This is why hypertension is sometimes called "the silent killer."
see also Autoimmune Disease; Bacterial Diseases; Cardiovascular Diseases; Genetic Diseases; History of Medicine; Homeostasis; Neurologic Diseases; Parasitic Diseases; Psychiatric Disorders, Biology of; Sexually Transmitted Diseases; Viral Diseases
Roberta M. Meehan
Madigan, Michael T., John M. Martinko, and Jack Parker. Brock Biology of Microorganisms, 9th ed. Upper Saddle River, NJ: Prentice Hall, 2000.
Thomas, Clayton L., ed. Taber's Cyclopedic Medical Dictionary, 18th ed., Philadelphia, PA: F. A. Davis Company, 1997.