OPPORTUNISTIC ILLNESSES

Death from AIDS is generally due not to HIV infection itself, but to opportunistic infections that occur when the immune system can no longer protect the body against agents normally found in the environment. The appearance of any one of more than 25 different opportunistic infections, called AIDS-defining illnesses, along with a CD4 T-cell count of less than 200 cells per cubic millimeter of blood provides the clinical diagnosis of AIDS in HIV-infected individuals.

The most common opportunistic infection seen in AIDS is Pneumocystis carinii pneumonia (PCP), which is caused by a fungus that normally exists in the airways of all people. Bacterial pneumonia and tuberculosis are also commonly associated with AIDS. In the late symptomatic phase of AIDS, bacterial infection by Mycobacterium avium can cause fever, weight loss, anemia, and diarrhea. Additional bacterial infections of the gastrointestinal tract commonly cause diarrhea, weight loss, anorexia (loss of appetite), and fever. Also, during advanced AIDS, diseases caused by protozoal parasites, especially toxoplasmosis of the nervous system, are common.

In addition to PCP, people with AIDS often develop other fungal infections. Thrush, an infection of the mouth by the fungus Candida albicans, is common in the early symptomatic phase of AIDS. Other infectious fungi include species of the genus Cryptococcus, a major cause of meningitis in up to 13 percent of people with AIDS. Also, infection by the fungus Histoplasma capsulatum affects up to 10 percent of people with AIDS, causing general weight loss, fever, and respiratory complications or severe central nervous system complications if the infection reaches the brain.

Viral opportunistic infections, especially with members of the herpes virus family, are common in people with AIDS. One herpes family member, cytomegalovirus (CMV), infects the retina of the eye and can result in blindness. Another herpes virus, Epstein-Barr virus (EBV), may result in a cancerous transformation of blood cells. Infections with herpes simplex virus (HSV) types 1 and 2 are also common and result in progressive sores around the mouth and anus.

Many people with AIDS develop cancers, the most common types being B-cell lymphoma and Kaposi’s sarcoma (KS). Kaposi’s sarcoma—a cancer of blood vessels that results in purple lesions on the skin that can spread to internal organs and cause death—occurs mainly in homosexual and bisexual men. Although the cause of KS is unknown, a link between KS and a new type of herpes virus was discovered in 1994.