Acquired immunodeficiency syndrome (AIDS).
Enveloped virus with two copies (diploid) of a single-stranded, positive-polarity RNA genome. RNA-dependent DNA polymerase (reverse transcriptase) makes a DNA copy of the genome, which integrates into host cell DNA. Precursor polypeptides must be cleaved by virus-encoded protease to produce functional viral proteins. The tat gene encodes a protein that activates viral transcription. Antigenicity of the gp120 protein changes rapidly; therefore, there are many serotypes.
Transfer of body fluids, e.g., blood and semen. Also transplacental and perinatal transmission.
Two receptors are required for HIV to enter cells. One receptor is CD4 protein found primarily on helper T cells. HIV infects and kills helper T cells, which predisposes to opportunistic infections. Other cells bearing CD4 proteins on the surface, e.g., astrocytes, are infected also. The other receptor for HIV is a chemokine receptor such as CCR5. The NEF protein is an important virulence factor. It reduces class I MHC protein synthesis, thereby reducing the ability of cytotoxic T cells to kill HIV-infected cells. Cytotoxic T cells are the main host defense against HIV.
HIV can be isolated from blood or semen, but this procedure is not routinely available. Diagnosis is usually made by detecting antibody with ELISA as screening test and Western blot as confirmatory test. Determine the "viral load," i.e., the amount of HIV RNA in the plasma, using PCR-based assays. A high viral load predicts a more rapid progression to AIDS than a low viral load. PCR-based assays can also detect viral RNA in infected cells, which is useful to detect early infections before antibody is detectable.
Nucleoside analogues, such as zidovudine (AZT), lamivudine (3TC), stavudine (d4T), didanosine (ddI), and zalcitabine (ddC), inhibit HIV replication by inhibiting reverse transcriptase. Nonnucleoside inhibitors of reverse transcriptase, such as nevirapine and efavirenz, are used also. Protease inhibitors, e.g., indinavir, ritonavir, and saquinavir, prevent cleavage of precursor polypeptides. Highly active antiretroviral therapy (HAART) consists of two nucleoside inhibitors and one protease inhibitor. Clinical improvement occurs, but the virus persists. Enfuvirtide, a "fusion inhibitor," which blocks entry of HIV, and maraviroc, which inhibits binding of the gp120 envelope protein of HIV to the cell co-receptor CCR-5, are also useful. Treatment of the opportunistic infection depends on the organism.
Screening of blood prior to transfusion for the presence of antibody. "Safe sex," including the use of condoms. AZT with or without a protease inhibitor should be given to HIV-infected mothers and their newborns. Zidovudine (AZT), lamivudine (3TC), and a protease inhibitor should be given after a needle-stick injury. There is no vaccine.