Disease. As in all human societies, disease has played a profound but ever‐changing role throughout American history.

The Columbian Encounter and the Early Colonial Era.

When Europeans first reached the New World, they encountered a hitherto unknown indigenous population as well as a novel natural and biological environment. Amerindians probably had migrated from Asia to Alaska across a land bridge produced by a lowering of the oceans during the last Ice Age. Many pathogens responsible for infectious diseases that took a heavy toll in Asia, Europe, and Africa probably did not survive the migration through the harsh climate of Siberia and Alaska. New World peoples were thus isolated from many of the epidemic and endemic diseases that had profoundly shaped population structures elsewhere. The absence of contact with diverse populations also gave them a far more homogeneous genetic inheritance.

These and other factors gave precolumbian America a unique disease environment. Many Old World diseases—malaria, smallpox, bubonic plague, and some of the infectious diseases associated with childhood—were unknown. The greatest risks to the Amerindian population involved accidents, wildlife diseases associated with hunting and food‐gathering, warfare, and sporadic famines and food shortages. The relative absence of domesticated livestock minimized zoonotic (animal‐transmitted) diseases, and low population density and the absence of commercial contacts among tribes reduced the potential dangers of epidemic infectious disease. Nevertheless, life expectancy at birth for Native Americans—as well as Europeans—was generally in the low thirties on the eve of colonization, even though the causes of morbidity and mortality among both varied sharply.

The migration of Europeans to the Americas beginning at the end of the fifteenth century had a catastrophic impact on the indigenous population. The introduction of new diseases into a population often lacking immunological defenses led to extraordinarily high mortality rates. Infants lacked antibodies from their mothers, who had never been exposed to these new diseases. Children and adults often did not receive the kind of care that might have mitigated the impact of disease; neither custom, tradition, nor religion provided any guide. Genetic homogeneity may have also enhanced vulnerability. Whatever the reasons, the Amerindian population suffered a precipitous decline in the period following the first contacts with Europeans. Diseases such as smallpox, measles, whooping cough, chicken pox, and malaria—to cite only a few—exacted a heavy toll. On the eve of colonization the population of the future contiguous United States was between two and twelve million. When the nadir was reached in the early twentieth century, the number of Native Americans had fallen to about 250,000. Disease and the ensuing social demoralization, not military conquest, played the major role in this demographic disaster.

The colonists, meanwhile, faced their own novel health problems. The Atlantic crossing, which could last three or four months, posed its own risks. Within the new environment the settlers faced rigorous conditions. The construction of adequate housing, securing an uncontaminated water supply, and the development of an adequate and varied food supply took time. During the period of adjustment (often aptly described as a process of “seasoning”), many new settlements experienced extraordinarily high mortality and morbidity rates that, if unchecked, threatened their very existences.

The period of seasoning varied from place to place. In New England the process of adjustment was brief; within a short time, mortality rates dropped and inhabitants enjoyed unprecedented levels of health. In seventeenth‐century Andover, Massachusetts, the average age of death among the first generation was nearly seventy‐one, and infant and child mortality was correspondingly low. Nor was Andover unique. Consequently, New England's population grew rapidly in the seventeenth century.

The southern colonies, by contrast, remained dangerous places. The importation of such tropical diseases as malaria and yellow fever into a region with a warm and moist climate proved devastating; mortality rates in the South exceeded those of New England, the Middle Atlantic colonies, and even Great Britain. On average, seventeenth‐century white male New Englanders who survived to the age of twenty outlived their Maryland counterparts by more than two decades. The greater resistance of African Americans to the ravages of imported tropical diseases undoubtedly contributed to the growth of slavery in the South. This pattern of regional variation in mortality and morbidity would persist until well into the twentieth century.

The Era of Infectious Diseases and Epidemics.

The eighteenth century brought changes to the disease ecology of the American colonies. Natural population growth, high rates of immigration, and the geographic mobility that accompanied the growth in trade and commerce enhanced the movement of infectious pathogens. Smallpox and yellow fever epidemics appeared in growing port cities. Since many infectious diseases had not gained a foothold in the American colonies, the population included a disproportionately high number of susceptible persons. The result was the partial replication of the harsh disease environment characteristic of England and Europe. Although the colonial population continued to grow, its curve resembled a saw‐tooth shape on an upward gradient because of the impact of epidemic disease. However hard hit by infectious diseases, colonial America nonetheless had lower mortality rates than those of England and Europe.

Mortality rates among the young from such diseases as measles, mumps, whooping cough, and a variety of respiratory and intestinal disorders rose dramatically during the eighteenth century, particularly in more densely populated towns. Although the spectacular epidemics of yellow fever and smallpox were the most feared, the worst killers were intestinal disorders, including typhoid fever and various forms of dysentery.

Seasonal patterns as well as population density shaped morbidity and mortality patterns. Intestinal diseases were most frequent in warmer months because of stagnant water, contaminated food, and large insect populations that could transmit malaria and yellow fever. Respiratory and pulmonary diseases peaked in cold weather. Because infectious diseases that killed the young were by far the dominant cause of morbidity and mortality, the proportion of aged persons in the population remained low; chronic and degenerative diseases were relatively rare.

The morbidity and mortality patterns in place by the late eighteenth century persisted in one form or another for much of the nineteenth century. Nevertheless, a changing social and physical environment as well as population movements both to and within the United States contributed to a significant modification of the earlier disease environment, especially in urban areas. The immigration of destitute groups such as the Irish into densely populated neighborhoods where squalor and unhygienic conditions prevailed dramatically increased health risks. Infants and young children were particularly susceptible to infectious diseases. Intestinal disorders continued to take the highest toll, but other diseases associated with population density and unsanitary conditions—typhus, typhoid, smallpox, and respiratory disorders—also loomed large. Population growth exceeded the ability of municipal governments to provide a safe water supply or a sanitation system to remove organic waste and to ensure clean streets (which were usually covered with heaps of animal wastes). Housing codes were all but absent; inadequate ventilation and crowding quickly transmitted infectious diseases. Tuberculosis emerged as the leading cause of death. Occupations that posed a threat to health went largely unregulated. Urban areas also continued to experience periodic epidemics related to the quickened pace of trade and commerce. Cholera became an international disease during the nineteenth century as rapid ocean transportation magnified the ability to move pathogens. Southern cities experienced both cholera and yellow fever epidemics. Recent scholarship indicates a decline in the life expectancy of Americans in the nineteenth century. Indeed, only in‐migration from abroad and from rural areas assured urban growth.

Rural areas and small towns, by contrast, often escaped the infectious diseases that plagued urban areas even though health indicators declined during the first half of the nineteenth century. In 1830, for example, urban death rates were between two and three times higher than rural areas; small‐town rates tended to fall midway between. Under certain circumstances, however, the advantage conferred upon rural inhabitants became a liability. During the Civil War, young men recruited from rural areas, lacking the immunity of their urban counterparts who had survived the infectious diseases of infancy and childhood, died in large numbers when they encountered unhygienic conditions and dangerous pathogens in the military camps. Indeed, the overwhelming number of Civil War deaths occurred not from battlefield wounds, but from respiratory and enteric disorders as well as smallpox, measles, malaria, and other diseases.

Although infectious diseases remained the major causes of mortality, their distribution varied by region and class. Malaria, yellow fever, and hookworm, for example, were largely confined to the South. (Malaria had been present in the Northeast and upper Mississippi Valley, but an inhospitable environment contributed to its eventual disappearance.) Social class and race were important factors as well. Lower‐class and minority ethnic and racial groups tended to have higher mortality rates. Nutritional levels and sanitary conditions undoubtedly exacerbated the impact of infectious diseases on these groups. But more prosperous groups did not escape the threat of infectious disease; infant mortality remained high at all levels of the population. Hidden from public view, severe mental illness and other chronic diseases often resulted in dependency.

The Era of Chronic and Infectious Diseases.

Beginning in the second half of the nineteenth century, the United States, as well as England and many European nations, experienced what has become known as the second “epidemiological transition.” The first, which occurred perhaps ten thousand or more years ago, involved the development of agriculture, which created a more stable food supply. The result was a more sedentary population that increased in both size and density. Population growth in turn heightened the potential for epidemic and infectious diseases. During the second epidemiological transition, infectious diseases began a period of sustained decline as a cause of mortality, to be replaced by chronic and degenerative diseases. This unparalleled transformation had a profound impact on virtually all human beings.

Slowly but surely, infectious diseases declined as major elements in mortality in the late nineteenth century. By 1940 most of the infectious diseases associated with childhood—viral diseases such as measles, mumps, whooping cough, and chicken pox, and bacterial diseases that included scarlet and rheumatic fever—were insignificant in mortality rates, while heart disease and cancer loomed much larger. What caused this massive shift in morbidity and mortality? Most scholars agree that medical interventions played virtually no role. Before World War II, the function of medicine was primarily the diagnosis of disease. With the exception of a few surgical procedures and antitoxins, such as the diphtheria antitoxin, physicians had few effective therapies. Antibiotic therapy against bacterial diseases did not become common until after 1945, and the development of vaccines for most viral infectious diseases still lay in the future. Yet in 1945 infectious diseases had ceased to be a major element in shaping mortality patterns.

It is easier to describe the decline of mortality from infectious diseases than to explain it. Many scholars have attributed it to economic growth and a rising standard of living. The difficulty with such global explanations is that they are not based on empirical data that shed light on the precise mechanisms responsible for the mortality decline for specific diseases. Some have pinpointed dietary improvements as the most important factor. Yet the relationship between diet—excluding severe malnutrition, which rarely existed in the United States—and most infectious diseases is tenuous at best. Moreover, economic growth involves more than living standards; it includes rising levels of literacy and education and a variety of other complex social changes. Some of these changes and their interactions—including housing arrangements, population density, water and food purity, personal hygiene, individual behavioral patterns, and public‐health activities—may have had a more direct influence on mortality levels. Although the importance of economic development in the reduction in mortality is generally recognized, no consensus exists on the precise role of specific factors.

In some cases the reduction in mortality followed specific public‐health interventions. Typhoid fever, for example, was generally disseminated by contaminated water. The building of central sewer systems did not seem to have a major impact, but reduced mortality did follow the introduction of water filtration. The reduction in mortality from tuberculosis, on the other hand, presents far greater complexities. Mortality began to fall well before overt efforts were made to contain the disease. Improved diet and a reduction in exposure thanks to better housing and the building of sanitoriums may account for growing resistance to the disease, but the evidence for these explanations remains inconclusive. The fall in infant and child mortality from diarrheal diseases probably followed changes in baby‐feeding practices, improvement in the milk supply, and public‐health authorities' efforts to sensitize parents to more effective means of care and prevention. Whatever the precise reasons, the mortality decline was clearly a function of reduced exposure and greater resistance among the population.

The mortality decline that began in the late nineteenth century also reflected a dramatic increase in survival rates among infants and children. Longevity among the elderly increased as well, but not as spectacularly. As infant and child mortality fell, more Americans survived to adulthood and old age, and the median age and the proportion of elderly in the population increased commensurately.

The change in the age distribution of the population mirrored a shift in the causes of mortality. In the nineteenth century, infectious diseases were the major causes of mortality; death stalked infants and children. In the twentieth century, by contrast, the major causes of death were chronic and degenerative diseases, and death in old age became the norm. Indeed, the longer individuals survived, the more likely they were to die from cancer or cardiovascular, cerebrovascular, or pulmonary diseases. In 1993, heart disease, cancer, strokes, and pulmonary disease accounted for 67 percent of all deaths. Although the etiology of these diseases remains unclear, the presumption is that they involve a complex blend of genetic, environmental, and behavioral factors. To be sure, mortality within each category has not remained constant. Deaths from heart disease peaked in the first half of the twentieth century and declined in the second half. Similarly, the mix of types of cancers has changed even while the overall mortality rate has remained relatively stable. Moreover, mortality within all these categories differs by class, race, ethnicity, and gender. But given the aging of the population and the fact that human beings may have a determinant life span, chronic and degenerative diseases seem likely to remain major elements in mortality.

The decline in mortality from infectious disease and the development of effective antibiotic therapy after 1945 encouraged a belief that such diseases no longer posed a threat. Yet neither past nor present experience justified such optimism. The rapidity of modern transportation and the opening of hitherto uninhabited regions raised the possibility of new viral and bacterial diseases immune to available therapies. The indiscriminate use of antibiotics also led to the emergence of resistant mutant strains that posed major threats to life. Influenza—an old viral disease—periodically reemerged, often in virulent form. The influenza pandemic of 1918–1919 killed more than half a million Americans, and subsequent experience demonstrated that its recurrence remained a distinct possibility. Other viral, bacterial, and rickettsial diseases (such as Rocky Mountain Spotted Fever) have also created a niche for themselves in response to behavioral and environmental changes. The emergence of acquired immunodeficiency syndrome (AIDS), a new disease that became the major cause of mortality among the 25–44‐year‐old age group in the 1990s, demonstrated the importance of changing behavioral patterns, while Lyme disease, a tick‐borne infection first observed in the 1970s, mirrored a novel kind of ecology. Whatever the future brings, disease and death—whatever forms they take—remain inevitable concomitants of life itself.
See also Alzheimer's Disease; Columbian Exchange; Death and Dying; Food and Diet; Hospitals; Indian History and Culture: Migration and Pre‐Columbian Era; Industrial Diseases and Hazards; Life Stages; Poliomyelitis; Poverty; Public Health; Race and Ethnicity; Sickle‐Cell Anemia; Surgery; Urbanization; Venereal Disease.

Bibliography

John Duffy , Epidemics in Colonial America, 1953.
Alfred W. Crosby Jr. , The Columbian Exchange: Biological and Cultural Consequences of 1492, 1972.
John B. and and Sonja M. McKinlay , The Questionable Contribution of Medical Measures to the Decline of Mortality in the United States in the Twentieth Century, Milbank Memorial Fund Quarterly 55 (1977): 405–428.
Abdel R. Omran , Epidemiologic Transition in the U.S.: The Health Factor in Population Change, Population Bulletin 32 (1977): 3–42.
Henry F. Dobyns , Their Numbers Become Thinned: Native American Population Dynamics in Eastern North America, 1983.
Gretchen A. Condran,, Henry Williams,, and and Rose A. Cheney , The Decline in Mortality in Philadelphia from 1870 to 1930: The Role of Municipal Services, Pennsylvania Magazine of History and Biography 108 (1984): 153–77.
Stephen J. Kunitz , Mortality Change in America, 1620–1920, Human Biology 56 (1984): 559–82.
Samuel H. Preston , Fatal Years: Child Mortality in Late Nineteenth‐Century America, 1991.
Charles Merbs , A New World of Infectious Disease, Yearbook of Physical Anthropology 35 (1992): 3–42.

Gerald N. Grob

disease can be broadly defined as any illness or sickness that impairs or disrupts the normal functioning of the human body. Definitions of disease, however, have varied over time and place, and diagnostic categories vary. We will be concerned here with concepts of disease in the Western medical tradition. Medicine itself can be defined as ‘the science and art concerned with the cure, alleviation, and prevention of disease, and with the restoration and preservation of health’. Thus the definition, treatment, and prevention, of disease is intimately associated with the development of medicine itself, and several specialist areas of medicine are specifically concerned with broad aspects of disease. For example nosology, the classification of diseases, was for many centuries the cornerstone of medicine; therapeutics is the treatment of disease; diagnosis is the art the physician uses to determine from the patients' signs and symptoms what the underlying causative mechanism may be; epidemiology is the study of disease in populations.

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 categories

One 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 diseases

Hereditary 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 diseases

infectious 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

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 intolerances

Deficiency (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 pollution

Concern 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 diseases

Mental 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 diseases

Ironically, 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.

Cancer

Cancer 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 diseases

These 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

Bibliography

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.

Disease

NATURALISM AND NOMINILISM

DISEASE, ILLNESS, SICKNESS, AND HEALTH

CONTROVERSIES IN DEFINING CONDITIONS AS DISEASE

SOCIAL DYNAMICS OF DISEASE AND HEALTH INEQUALITIES

BIBLIOGRAPHY

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.

NATURALISM AND NOMINILISM

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.

DISEASE, ILLNESS, SICKNESS, AND HEALTH

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.

CONTROVERSIES IN DEFINING CONDITIONS AS DISEASE

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.

SOCIAL DYNAMICS OF DISEASE AND HEALTH INEQUALITIES

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

BIBLIOGRAPHY

American Psychiatric Association. 1994. Diagnostic and Statistical Manual of Mental Disorders. 4th ed. Washington, DC: Author.

Boorse, Christopher. 1977. Health as a Theoretical Concept. Philosophy of Science 44: 542–573.

Bray, George A. 2004. Obesity Is a Chronic, Relapsing Neurochemical Disease. International Journal of Obesity and Related Metabolic Disorders 28 (1): 34–38.

Bray, George A. 2006. Obesity: The Disease. Journal of Medicinal Chemistry 49 (14): 4001–4007.

Centers for Disease Control and Prevention. 2006. National Diabetes Surveillance System. http://www.cdc.gov/diabetes/statistics/.

Eubank, Stephen, Hansan Guclu, V. S. Anil Kumar, et al. 2004. Modeling Disease Outbreaks in Realistic Urban Social Networks. Nature 429 (6988): 180–184.

Heshka, Stanley, and David B Allison. 2001. Is Obesity a Disease? International Journal of Obesity and Related Metabolic Disorders 25 (10): 1401–1404.

Hofmann, Bjorn. 2001. Complexity of the Concept of Disease as Shown through Rival Theoretical Frameworks. Theoretical Medicine and Bioethics 22 (3): 211–236.

Hofmann, Bjorn. 2002. On the Triad: Disease, Illness, and Sickness. Journal of Medicine and Philosophy 27 (6): 651–673.

Hofmann, Bjorn. 2005. Simplified Models of the Relationship between Health and Disease. Theoretical Medicine and Bioethics 26 (5): 355–377.

Hofmann, Bjorn M., and Harald M. Eriksen. 2001. The Concept of Disease: Ethical Challenges and Relevance to Dentistry and Dental Education. European Journal of Dental Education 5 (1): 2–11.

Humphreys, Margaret, Philip Costanzo, Kerry L. Haynie, et al. Racial Disparities in Diabetes a Century Ago: Evidence from the Pension Files of the U.S. Civil War Veterans. Social Science and Medicine 64 (8): 1766–1775.

King, Lester S. 1954. What Is Disease? Philosophy of Science 21: 193–203.

Kottow, Michael H. 2002. The Rationale of Value-Laden Medicine. Journal of Evaluation in Clinical Practice 8 (1): 77–84.

Kovacs, Jozsef. 1998. The Concept of Health and Disease. Medical Health Care and Philosophy 1 (1): 31–39.

Kunst, Anton E., Feikje Groenhof, Otto Andersen, et al. 1999. Occupational Class and Ischemic Heart Disease Mortality in the United States and 11 European Countries. American Journal of Public Health 89 (1): 47–53.

Rose, Geoffrey, and Michael Marmot. 1981. Social Class and Coronary Heart Disease. British Heart Journal 45 (1): 13–19.

Szasz, Thomas. 1974. The Myth of Mental Illness: Foundations of a Theory of Personal Conduct. New York: Harper and Row.

Szasz, Thomas. 1998. Parity for Mental Illness, Disparity for the Mental Patient. Lancet 352 (9135): 1213–1215.

Szasz, Thomas. 1998. What Counts as Disease? Rationales and Rationalizations for Treatment. Forsch Komplementarmed 5 (S1): 40–46.

Twaddle, Andrew. 1994. Disease, Illness, and Sickness Revisited. In Disease, Illness, and Sickness: Three Central Concepts in the Theory of Health, eds. Andrew Twaddle and L. Nordenfelt, vol. 18, pp. 1–18. Linkoping, Sweden: Studies on Health and Society.

Vagero, Denny, and Mall Leinsalu. 2005. Health Inequalities and Social Dynamics in Europe. British Medical Journal 331 (7510): 186–187.

World Health Organization. 1992. Basic Documents. Geneva: World Health Organization.

Bernard F. Fuemmeler

Disease

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.

Infectious diseases

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.

Noninfectious diseases

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.

Epidemiology

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 impairment of the normal state or functioning of the body as a whole or of any of its parts. Some diseases are acute, producing severe symptoms that terminate after a short time, e.g., pneumonia; others are chronic disorders, e.g., arthritis, that last a long time; and still others return periodically and are termed recurrent, e.g., malaria. One of the most common bases for classifying disease is according to cause. External factors that produce disease are infectious agents, including both microscopic organisms ( bacteria , viruses , and protozoans ) and macroscopic ones ( fungi and various parasitic worms ). Only infectious diseases can be transmitted—by humans, certain animals and insects, and infected objects and substances (see communicable diseases ). Other external agents that can cause disease are chemical and physical agents (drugs, poisons, radiation), which can be encountered in specific work situations, deficiency of nutrients in the environment, and physical injury. Diseases that arise from internal (endogenous) causes include hereditary abnormalities (disorders inherited from one or both parents), congenital diseases (disturbances in the development of a normal embryo), allergies (hypersensitive reactions to substances in the environment), endocrine disorders (generally either overfunctioning or underfunctioning of an endocrine gland), circulatory disorders (diseases of the heart and blood vessels), and neoplasms, or tumors (masses of abnormally proliferating cells). Degenerative diseases occur as a result of the natural aging of the body tissues. Finally, a wide range of diseases are attributed to, or at least influenced by, emotional disturbances. Psychoses and neuroses result in disturbed behavior; the so-called psychosomatic diseases (certain kinds of colitis, many forms of headaches) are thought to be brought about by emotional stress. Most diseases occur as a result of a combination of both internal and external conditions, i.e., an interaction between the body and the environment. Thus a person may be hereditarily predisposed to tuberculosis, although the tubercule bacillus (the infectious agent) must be present for the disease to occur. In ancient times disease was ascribed to supernatural, spiritual, and humoral factors. The discovery by Louis Pasteur and others of the role played by microorganisms in infection and the study of cellular pathology by Rudolf Virchow in the 19th cent. were of the utmost importance in establishing the true nature of disease.

188. Disease

1. AIDS mysterious new disease, incurable and usually fatal. [U.S. Hist.: WB, A:153]
2. Black Death killed at least one third of Europe’s population (1348–1349). [Eur. Hist.: Bishop, 379–382]
3. bubonic plague ravages Oran, Algeria, where Dr. Rieux perseveres in his humanitarian endeavors. [Fr. Lit.: The Plague ]
4. Cancer Ward, The novel set in cancer ward of a Russian hospital. [Russ. Lit.: The Cancer Ward in Weiss, 64]
5. Decameron, The tales told by young people taking refuge from the black death ravaging Florence. [Ital. Lit.: Magill II, 231]
6. Fiacre, St. intercession sought by sick. [Christian Hagiog.: Attwater, 130]
7. influenza epidemic caused 500,000 deaths in U.S. alone (1918–1919). [Am. Hist.: Van Doren, 403]
8. Joram suffered for abandoning God’s way. [O.T.: II Chronicles 21:15, 19]
9. Journal of the Plague Year Defoe’s famous account of bubonic plague in England in 1665. [Br. Lit.: Benét, 529]
10. Lazarus leper brought back to life by Christ. [N.T.: John 11:1–44]
11. Legionnaires’ disease 28 American Legion conventioneers die of flu-like disease in Philadelphia (1976). [Am. Hist.: Facts (1976), 573, 656]
12. Molokai Hawaiian island; site of government leper colony. [Am. Hist.: NCE, 1807]
13. Naaman leprous Syrian commander healed by Elisha. [O.T.: II Kings 5]
14. red death, the pestilence, embodied in a masque, fatally penetrates Prince Prospero’s abbey. [Am. Lit.: Poe The Masque of the Red Death ]
15. Rock, St. legendary healer of plague victims. [Christian Hagiog.: Attwater, 299]
16. 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]
17. seven plagues, the visited upon the earth to signify God’s wrath. [N.T.: Revelation]
18. St. Anthony’s Fire horrific 11th-century plague. [Eur. Hist.: Brewer Note-Book, 34]
19. Syphilis Fracastoro’s epic concerning Syphilis, mythical first victim. [Ital. Lit.: RHD, 1443; Plumb, 342]
20. ten plagues, the inflicted upon Egypt when Pharaoh refuses to let the Israelites emigrate. [O.T.: Exodus 7-12]
21. Typhoid Mary (Mary Mallon, 1870–1938) unwitting carrier of typhus; suffered 23-year quarantine. [Am. Hist.: Van Doren, 354]

Disease

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

Bibliography

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.

disease Many kinds of disease are mentioned in the Bible but it is difficult to identify them by their modern names. The incidence of disease and the means of cure were highly important in biblical times, and its causes were sometimes ascribed to God as punishment for sin—as when a plague hit the whole nation because of David's presumption in counting the population (2 Sam. 24). But such a view of God was modified by the later Chronicler (1 Chron. 21: 1; cf. 2 Sam. 24: 1) who attributes the whole episode indirectly to Satan. In the NT Satan and his creatures are said to be responsible (Mark 1: 25; Luke 13: 16, 32) for illness. The connection between sin and disease is questioned by Job (Job 2: 10) and by Jesus (John 9: 1–3).

The vast number of disfiguring and painful complaints, the cases of paralysis and mental illness, malformations of limbs and organs, and the inadequacies of medical care (Mark 5: 26) and diagnosis (1 Sam. 16: 15) all bear witness to the precariousness of existence as an essential part of the context of the biblical narratives.

disease Any departure from health, with impaired functioning of the body. Disease may be acute, severe symptoms for a short time; chronic, lasting a long time; or recurrent, returning periodically. There are many types and causes of disease: infectious, caused by harmful bacteria or viruses; hereditary and metabolic; growth and development; immune system diseases; neoplastic (tumour-producing); nutritional; deficiency; endocrine system diseases; or diseases due to environmental agents, such as lead poisoning. Treatment depends on the cause and course of the disease. It may be symptomatic (relieving symptoms, but not necessarily combating a cause) or specific (attempting to cure an underlying cause). Disease prevention includes eradication of harmful organisms, vaccines, public health measures and routine medical checks.

dis·ease / diˈzēz/ • n. a disorder of structure or function in a human, animal, or plant, esp. one that produces specific signs or symptoms or that affects a specific location and is not simply a direct result of physical injury: bacterial meningitis is a rare disease | a possible cause of heart disease. ∎ fig. a particular quality, habit, or disposition regarded as adversely affecting a person or group of people: departmental administration has often led to the dread disease of departmentalitis.

disease A condition in which the normal function of some part of the body (cells, tissues, or organs) is disturbed. A variety of microorganisms and environmental agents are capable of causing disease. The functional disturbances are often accompanied by structural changes in tissue.

disease (di-zeez) n. a disorder with a specific cause and recognizable signs and symptoms; any bodily abnormality or failure to function properly, except that resulting directly from physical injury (the latter, however, may open the way for disease).

disease †uneasiness, discomfort; morbid physical condition. XIV. — AN. des-, disease, OF. desaise, f. des- DIS- 2, 6 + aise EASE.

disease See HEALTH AND ILLNESS, SOCIOLOGY OF; MEDICINE, SOCIOLOGY OF.