HIV Progression to AIDS

The great majority of human patients infected with Human Immunodeficiency Virus (HIV) eventually succumb to a collapse of their adaptive immune system (AIDS, primarily caused by a loss of CD4+ T cells). In the days before combination antiretroviral drugs, this demise happened within a few years of infection. The pandemic HIV-1 virus currently infecting humans appears to directly descended from a chimpanzee virus infecting up to 10% of wild chimpanzees in equatorial Africa. Another less common virus causing AIDS is HIV-2, a virus derived from West African monkeys (sooty mangabeys). Both species of non-human primate hosts show limited deterimental effects due to infection with these respective viruses (although some wild chimps with SIV have been recently reported to have increased mortality with infection).  Chimpanzees have been experimentally infected with human HIV isolates, and with rare exceptions have not shown the typical progression to AIDS. Some chimpanzee populations in the wild do manifest an AIDS-like syndrome related to natural SIVcpz infections, but the disease still appears to be milder.  There is no clear explanation for the different outcome of HIV infection in these species (the rare humans who are resistant to HIV infection or are “long-term non-progressors" seem to use other unique mechanisms). Notably, unlike in the case with other primates, infection of humans with HIV appears to result in more T-cell death.