Disease

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.

KEY TERMS

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.

See also Epidemic; Epidemiology; Etiology; Syndrome.

Larry Blaser