Tanzania: Wild Chimpanzees Get AIDS-Like Illness

US researchers have shown for the first time that chimpanzees can fall ill and die from infection by the HIV-like simian immunodeficiency virus (SIV), overturning a decade-old consensus that chimps were immune to it. The discovery suggests that scientists will not find the solution to HIV immunity in the chimp genome. However, it sets the stage for comparative research, allowing scientists to see how humans and non-human primates respond differently to HIV and SIV infection.

"From an evolutionary and epidemiological point of view, these data can be regarded as a ‘missing link' in the history of the HIV pandemic," said Daniel Douek of the National Institute of Allergy and Infectious Disease.

Beatrice Hahn of the University of Alabama-Birmingham and colleagues studied wild chimpanzee groups for nine years at Gombe National Park in Tanzania, collecting urine and fecal samples to analyze for SIV infection. The chimp groups had a 9-18 percent infection rate. Chimps that were infected were 10-16 times more likely to die than uninfected animals, and all infected infants died. Compared to uninfected chimps that died, those infected had unusually low CD4 T cells, the same cell type that HIV targets in humans.

In the wild, other primates such as monkeys have co-existed with SIV for a long time, seemingly by evolving an ability to control the virus. Rhesus macaques are not natural SIV hosts but can become ill from an infection. Comparative research on SIV and HIV in the different hosts could help in developing HIV treatments and vaccines, said Don Sodora, a viral immunologist with the Seattle Biomedical Research Institute at the University of Washington.

However, Hahn does not believe studies should extend to reversing the movement to stop invasive research on chimpanzees. "They think and have societies," she said. "Rather than shooting them up with SIV, one should be more creative and find ways and means of answering the question without doing harm to chimpanzees."

The full report, "Increased Mortality and AIDS-Like Immunopathology in Wild Chimpanzees Infected with SIVcpz," was published in Nature (2009;460:515-519).

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