Acquired immune deficiency syndrome
Following infection with HIV, an individual may show no symptoms at all or may develop an acute but transient mononucleosislike illness. The period between initial infection and the development of AIDS is currently observed to vary from about six months to ten years. Various estimates indicate that somewhere between 26 and 46 percent of the infected individuals will go on to develop full-blown AIDS within a little more than seven years following infection. In the past, once AIDS set in, the patient went into a rapid decline; most people with AIDS died within three years. However, new drugs have turned AIDS into a manageable, rather than rapidly fatal, disease for some people.
Opportunistic Infections and Cancers
Because the T4 cell is involved in almost all immune responses, its depletion renders the body highly susceptible to opportunistic infections and tumorous growths. The most predominant and threatening complication is Pneumocystis carinii pneumonia, which is frequently the first infection to occur and is the most common cause of death. Other infections include the parasites Toxoplasma gondii (see toxoplasmosis) and Cryptosporidiosis; fungi such as Candida (see candidiasis) and Cryptococcus (see fungus diseases); mycobacteria such as Mycobacterium avium, intracellulare, and tuberculosis; and viruses such as cytomegalovirus and herpes simplex and zoster. Increased susceptibility to bacterial infection is noted particularly among children with AIDS.
Many AIDS patients develop cancers, including Kaposi sarcoma (KS), non-Hodgkin lymphoma, and Hodgkin disease. KS occurs in patients who manifest hardly any evidence of immunological impairment, indicating that other factors may also be at work. Among the non-Hodgkin lymphomas are immunoblastic and Burkitt-type as well as primary brain lymphomas. These tumors tend to be unusually aggressive and poorly responsive to chemotherapy, particularly in AIDS patients who have already experienced opportunistic infections.
Other HIV-Related Disorders and Cofactors
Neuropsychiatric manifestations occur in about 60 percent of HIV-infected persons. It is now well established that HIV can exist and proliferate within the brain, spinal cord, and peripheral nerves. This results in a broad range of symptoms, including meningoencephalitis (see encephalitis) and dementia. Evidence thus far indicates that circulating HIV-infected blood cells of the kind called monocytes may be responsible for the initiation of infection in the brain. There is little evidence to support direct infection of neuron tissue by HIV.
Blood-cell abnormalities of HIV patients include anemia, reduced white-blood-cell counts, and platelet deficiencies. Researchers have also been able to show direct infection of bone-marrow cellsÑthe precursors of circulating blood cellsÑand the proliferation of the virus within these cells. Thus bone marrow may represent an important reservoir of HIV in an infected person and provide a potential mechanism for spreading the virus through the body. Other HIV-related syndromes include nephritis (see kidney disease), arthritis, and lung inflammation (pneumonitis).
Certain cofactors appear to play an important role in HIV infection and AIDS by increasing susceptibility to infection and by enhancing viral-disease activity. Other sexually transmitted diseases appear to be of particular significance. Damage to genital skin and mucous membranes may facilitate transmission of the virus. In addition, laboratory studies show that certain other microbes frequently found in AIDS patients, such as mycoplasmas, also probably act as cofactors.