HIV
Summary
Human immunodeficiency virus is an enveloped retrovirus with two copies of positive-sense single-stranded RNA and reverse transcriptase, which progressively destroys CD4-positive T cells. Untreated infection advances to AIDS, defined by a CD4 count below 200 cells/mm3 or an AIDS-defining illness.
Detail
HIV is a lentivirus of the family Retroviridae. Its genome encodes env (cleaved into gp120 for CD4 binding and gp41 for fusion), gag (p24 capsid, the antigen detected in fourth-generation assays), and pol (reverse transcriptase, integrase, protease). Reverse transcriptase lacks proofreading, giving the high mutation rate responsible for drug resistance and the failure of vaccine development. Infection proceeds through an acute retroviral syndrome resembling mononucleosis with high viraemia, a prolonged clinical latency during which CD4 counts fall, and then AIDS. Diagnosis uses a fourth-generation antigen/antibody immunoassay followed by an HIV-1/HIV-2 differentiation assay, with nucleic acid testing for acute infection and for neonates, whose maternal antibodies persist. Treatment is lifelong combination antiretroviral therapy, usually two nucleoside reverse transcriptase inhibitors plus an integrase strand transfer inhibitor, begun at diagnosis regardless of CD4 count; suppression to undetectable viral load prevents sexual transmission. Homozygous CCR5-delta32 deletion confers near-complete resistance to R5-tropic HIV.
Sources
- Levinson Medical Microbiology and Immunology
- Harrison's Principles of Internal Medicine
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