ACQUIRED IMMUNODEFICIENCY SYNDROME (AIDS)
AIDS can be diagnosed when a person is HIV- positive and has CD4 count <200 cells/mL, or when a person is HIV-positive and has an AIDS-defining disease. Males are affected more frequently than females.
The human immunodeficiency virus (HIV) is an enveloped RNA retrovirus that contains reverse transcriptase. HIV infects CD4-positive cells, including CD4+ T lymphocytes, all macrophages, lymph node follicular dendritic cells, and Langer-hans cells. The mechanism of infection is by binding of CD4 by the viral gp120, followed by entry into cell by fusion, which requires gp41 and coreceptors CCR5 (β-chemokine receptor 5) and CXCR4 (α-chemokine receptor).
Transmission of HIV can occur by many mechanisms, including sexual contact(most common mode, including both homosexual transmission and an increasing rate of heterosexual transmission, with important cofactors including herpes and syphilis infection); parenteral transmission; IV drug use; blood transfusions (includ-ing those done in hemophiliacs); accidental needle sticks in hospital workers; and vertical transmission.
Diagnosis.The CDC recommends initial testing with an antigen/antibody com-bination immunoassay, followed by a confirmatory HIV-1/HIV-2 antibody differ-entiation immunoassay. If the confirmatory test is negative, testing with an HIV-1 nucleic acid test is done. Treatment varies, and can include combination antiretro-viral treatment, reverse transcriptase inhibitors, protease inhibitors, and prophylaxis for opportunistic infections based on CD4 count.
The clinical manifestations of HIV infection vary over time.
· The acute phase is characterized by viremia with a reduction in CD4 count, mononucleosis-like viral symptoms and lymphadenopathy, and seroconver-sion.
· The latent phase is characterized by asymptomatic or persistent generalized lymphadenopathy with continued viral replication in the lymph nodes and spleen, low level of virus in the blood, and minor opportunistic infections including oral thrush (candidiasis) and herpes zoster. The average duration of latent phase is 10 years.
· Progression to AIDS (third phase) occurs with reduction of CD4 count to<200 cells/mL, which is accompanied by reemergence of viremia and develop-ment of AIDS-defining diseases, possibly to eventual death.
Hairy leukoplakia is an Epstein-Barr virus (EBV)–associated condition due to infec-tion of squamous cells. White plaques are present on the tongue.
Kaposi sarcoma is the most common neoplasm in AIDS patients.
Non-Hodgkin lymphomas tend to be high-grade B-cell lymphomas; extranodal CNS lymphomas are common.
Other AIDS-defining diseases include cervical cancer, HIV-wasting syndrome, AIDS nephropathy, and AIDS dementia complex.