disease

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.

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

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.