July 22, 2009

Study Challenging Prevailing View of AIDS In Nonhuman Primates

Researchers at Yerkes National Primate Research Center, Emory University, contributed key comparative data for a landmark study showing African wild chimpanzees infected with simian immunodeficiency virus (SIV), an HIV-1-like virus, die prematurely and develop hallmarks of HIV-1 infection and AIDS.

This surprising discovery by scientists at the University of Alabama at Birmingham (UAB), and reported in the July 23 issue of Nature, alters the current view of AIDS virus infections in African nonhuman primates. SIVs are found exclusively in African nonhuman primate species and represent the original source of human immunodeficiency viruses (HIV-1 and HIV-2). Until now, scientists believed all African nonhuman primates naturally infected with SIVs, including chimpanzees, would not develop AIDS.

Beatrice Hahn, MD, a member of the Yerkes Scientific Advisory Board and a professor of medicine at UAB, and her researcher collaborators followed 94 free-ranging chimpanzees in Tanzania's Gombe National Park for nine years. They found SIV-infected chimps compared to uninfected chimps were 10 to 16 times more likely to die prematurely, experienced immune system failure and had lower birth rates and higher infant mortality. Laboratory tests revealed one chimp appeared to have end-stage AIDS.

The data the Yerkes Research Center contributed to the study was a comparison of the survival of SIV-infected and uninfected sooty mangabeys, medium-sized African monkeys important in AIDS research. Yerkes is uniquely suited to conduct AIDS research in nonhuman primates because it has large breeding colonies of both uninfected and naturally infected sooty mangabeys.

"As expected, there was no indication of increased mortality associated with SIV infection in sooty mangabeys," explains James Else, DVM, associate director for veterinary resources at Yerkes and a contributing author of the UAB study. "Sooty mangabeys can have a high viral load and chronic disease, but over many generations they have somehow learned to live with the infection and do not get sick.

"The value of Yerkes' research with natural nonhuman primate hosts of SIV, such as the sooty mangabey, cannot be overstated," adds Dr. Else. "You have two extremes: people who are infected with HIV and do not have access to appropriate medical care are dying at a high rate, and sooty managbeys with SIV are not dying at all.

"The mortality rate for SIV-infected chimpanzees is somewhere in between. As we better understand the mechanisms that enable the naturally infected sooty mangabeys to avoid getting sick and learn more about why the infected wild chimps are not getting as sick as people, we will apply that knowledge to Yerkes research focused on producing a vaccine that prevents people with HIV from getting sick," Dr. Else concludes.


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