![]() ![]() Similar findings were also reported for two other chimpanzees inoculated with SIVcpz in captivity 6. Only one naturally infected chimpanzee was subjected to virological and immunological analyses, and in this ape, SIVcpz infection was not associated with CD4 + T-cell decline, loss of T-cell function, or degenerative changes in lymph node architecture 4 – 6. ![]() Since the first description of SIVcpz in wild-caught chimpanzees, only seven naturally infected apes have been studied in captivity, five of whom died as infants of unknown causes shortly after they were placed in sanctuaries 2. Little is known about the in vivo pathogenicity of SIVcpz because, until recently, it has been impossible to identify and monitor infected apes in the wild 2. These findings challenge the prevailing view that all natural SIV infections are non-pathogenic and suggest that SIVcpz has a substantial negative impact on the health, reproduction and lifespan of chimpanzees in the wild. These results indicate that SIVcpz, like HIV-1, is associated with progressive CD4 + T-cell loss, lymphatic tissue destruction and premature death. One female, who died within 3 years of acquiring SIVcpz, had histopathological findings consistent with end-stage AIDS. Immunohistochemistry and in situ hybridization of post-mortem spleen and lymph node samples from three infected and two uninfected chimpanzees revealed significant CD4 + T-cell depletion in all infected individuals, with evidence of high viral replication and extensive follicular dendritic cell virus trapping in one of them. We also found that SIVcpz-infected females were less likely to give birth and had a higher infant mortality rate than uninfected females. By following 94 members of two habituated chimpanzee communities in Gombe National Park, Tanzania, for over 9 years, we found a 10- to 16-fold higher age-corrected death hazard for SIVcpz-infected ( n = 17) compared to uninfected ( n = 77) chimpanzees. Here we show that SIVcpz, the immediate precursor of HIV-1, is pathogenic in free-ranging chimpanzees. Unlike the human viruses, however, SIVs do not generally cause acquired immunodeficiency syndrome (AIDS) in their natural hosts 3. African primates are naturally infected with over 40 different simian immunodeficiency viruses (SIVs), two of which have crossed the species barrier and generated human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2) 1, 2. ![]()
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