Acquired Immunodeficiency Syndrome
Acquired immunodeficiency syndrome (AIDS) is marked by progressive and gradual destruction of CD4+ T cells by the human immunodeficiency virus (HIV). The resulting immunodeficiency predisposes the patient to opportunistic infections, unusual cancers, and other distinctive abnormalities.
HIV may infect virtually any cell that has the CD4+ molecule on its surface. Such cells include monocytes, macrophages, bone marrow progenitors, and glial, gut, and epithelial cells. Infection of these cells can cause dementia, wasting syndrome, and hematologic abnormalities.
AIDS was first described by the Centers for Disease Control and Prevention (CDC) in 1981. Since then, the CDC has issued a case surveillance definition for AIDS and has modified it several times, most recently in 1993. (See AIDS-indicator conditions.)
Transmission of HIV occurs by contact with blood or body fluids and is associated with identifiable high-risk behaviors. HIV infection is disproportionately represented in homosexual and bisexual males, I.V. drug users, neonates of HIV-infected females, recipients of contaminated blood or blood products (although the risk of receiving contaminated blood has been drastically reduced since 1985), and heterosexual partners of those in high-risk groups. Because of similar routes of transmission, AIDS shares epidemiologic patterns with other sexually transmitted diseases and hepatitis B.
The natural history of AIDS infection begins with infection by the HIV retrovirus, which is detectable only by laboratory tests, and ends with the severely immunocompromised, terminal stages of this disease. The time from acute HIV infection to the appearance of symptoms (mild to severe) to the diagnosis of AIDS to, eventually, death, varies greatly and depends on individual variations and the presence of cofactors that influence progression. Combination antiretroviral therapy (for example, with ritonavir, zidovudine, and others) and prophylaxis and treatment for common opportunistic infections can delay but not stop the progression of disease.
Causes
AIDS results from a human retrovirus that is classified as either HIV-1 or HIV-2. The most common cause of AIDS throughout the world is HIV-1. Less common, HIV-2 has been predominantly identified in western Africa and is thought to be less pathogenic than HIV-1. Both HIV-1 and HIV-2 destroy CD4+ T cells, the essential regulators and effectors of the normal immune response. HIV is transmitted by contact with infected blood or body fluids. Transmission results from such high-risk behaviors as sharing a contaminated needle or having unprotected sexual contact, especially anal intercourse, which results in mucosal trauma. Transmission may also occur through transfusion of contaminated blood or blood products. Furthermore, the virus can pass from an infected mother to the fetus through cervical or blood contact at delivery or to an infant through breast milk. HIV isn’t transmitted by everyday household or social contact.
Complications
Repeated opportunistic infections eventually overwhelm the body’s compromised immune defenses. These infections invade every body system, including the lungs, bone marrow, and brain. Neuropathy (HIV encephalopathy) occurs in 40% to 60% of infected patients.
AIDS-indicator conditions
The Centers for Disease Control and Prevention recognizes the following conditions as indicators of acquired immunodeficiency syndrome (AIDS).
Candidiasis of the bronchi, trachea, or lungs
Candidiasis of the esophagus
Cervical cancer, invasive
CMV retinitis with vision loss
Coccidioidomycosis, disseminated or extrapulmonary
Cryptococcosis, extrapulmonary
Cryptosporidiosis, chronic intestinal (persisting longer than 1 month)
Cytomegalovirus (CMV) disease affecting organs other than the liver, spleen, or lymph nodes
Encephalopathy related to human immunodeficiency virus (HIV)
Herpes simplex, involving chronic ulcers (persisting longer than 1 month) or herpetic bronchitis, pneumonitis, or esophagitis
Histoplasmosis, disseminated or extrapulmonary
Isosporiasis, chronic intestinal (persisting longer than 1 month)
Kaposi’s sarcoma
Lymphoma, Burkitt’s (or its equivalent)
Lymphoma, immunoblastic (or its equivalent)
Lymphoma of the brain, primary
M. tuberculosis at any site (pulmonary or extrapulmonary)
Mycobacterium, any other species, disseminated or extrapulmonary
Mycobacterium avium-intracellulare complex or M. kansasii, disseminated or extrapulmonary
Pneumocystis carinii pneumonia
Pneumonia, recurrent
Progressive multifocal leukoencephalopathy
Salmonella septicemia, recurrent
Toxoplasmosis of the brain
Wasting syndrome caused by HIV
