Disease

Disease, disturbance of normal body function in an organism. Disease is usually brought to a person's attention by symptoms of an abnormality of, or change in, body function: pain, headache, fever, cough, shortness of breath, dyspepsia, constipation, diarrhea, loss of blood, lumps, paralysis, or numbness, or loss of consciousness. Diagnosis is made on the basis of symptoms and from signs on discovered physical examination and from laboratory and X-ray investigations.

Trauma (injury) may cause skin lacerations and bone fractures as well as disorders specific to the organ involved. Congenital diseases include hereditary conditions and diseases beginning in the fetus, such as those due to drugs or maternal infection during pregnancy. Infectious diseases caused by viruses, bacteria, and parasites are usually communicable; insects, animals, and human carriers may be important in their spread, and epidemics may occur. Inflammation is often the result of infection, but inflammatory disease can also result from disordered immunity and other causes. In vascular diseases, organs become diseased as a result of disease in their blood supply; examples are atherosclerosis, aneurysms, thrombosis, and embolism. In tumors, including benign growths, cancer, and lymphoma, abnormal growth of a structure occurs and leads to a lump, causing pressure or spreading to other organs. In degenerative disease, death or premature aging of parts of an organ or a system lead to a gradual impairment of function. Deficiency diseases result from inadequate intake of nutrients; resulting disorders, including hormonal disorders, can lead to metabolic disease. An increasingly recognized side- effect of industrialization is occupational disease caused by chemicals, dust, or molds encountered at work. An iatrogenic disease is one produced by medical intervention in an attempt to treat or prevent another disease. Finally, psychiatric disease, including psychoses (schizophrenia and severe depression) and neuroses, are functional disturbances of the brain; they may represent disturbances of brain metabolism.

The characteristics of acute disease may be exemplified by acute infections. The onset of the condition is frequently sudden, and there may be almost total prostration, but there is the prospect of a limited period in this state. Most acute diseases, because of their finite duration, pose a minimal threat to the subject. The onset of chronic disease, on the other hand, is usually slow; there may be a progression of symptoms, or more permanent problems may develop as the sequel to a number of acute episodes.