New York Times Examines How Studying HIV-Like Viruses Among Animals May Explain Jump to Humans
Large populations of wild cats, African monkeys and some chimpanzees that are infected with viruses similar to HIV but that rarely get sick may give scientists clues as to how HIV first infected and will progress among humans, the New York Times reports in an article investigating the origins of HIV/AIDS. After discovering a virus genetically similar to HIV in three captive chimpanzees of the sub-species Pan troglodytes troglodytes from west-central Africa, Drs. Beatrice Hahn and George Shaw of the University of Alabama-Birmingham theorized that HIV made the "jump" from chimps to humans "decades ago" in western Africa when humans killed and consumed infected chimp meat. However, "to the investigators' surprise" another study -- in which the team tested the feces and urine of 58 wild chimps in Africa -- found only one wild chimp infected with a different virus that was similar to a "genetically distinct AIDS-like virus" Hahn and Shaw had found in a fourth monkey in their earlier study. The team, along with primatologists, was searching for a "reservoir" of chimps infected with HIV-like viruses that they thought must exist if the virus had been passed to humans. The study results, which appeared in the Jan. 18 issue of Science, left researchers with three hypotheses: large groups of chimps may be infected with the HIV-like virus, but those groups are so isolated that the virus has not spread to the general chimp population; chimp groups that were once infected have gone extinct; or there may not be much infection among chimpanzees. Hahn and Shaw's team is now conducting tests with chimps that are "completely wild" -- those that do not live on reservations under the observation of primatologists -- to test their new hypotheses.
Most of the infected chimps Hahn and Shaw had studied did not become ill from the HIV-like viruses they carried. Wild cats and African monkeys also carry HIV-like viruses, but do not get sick from the infections. However, the virus found in wild cats does cause illness in domestic cats. More than a decade ago an HIV-like virus that caused symptoms similar to AIDS was found in domestic house cats in the United States. Dr. Stephen O'Brien, a cat expert and head of the Laboratory of Genomic Diversity at the National Cancer Institute, began looking for the virus in serum samples obtained from wild cats such as lions and cheetahs and determined that the "vast majority" of wild cats carried the virus. However, none of the wild cats were sick. The cats had "somehow learned to live with the virus." An HIV-like virus also has been found in more than 20 species of African primates who do not develop symptoms. In contrast, Asian monkeys do get sick when exposed to the same virus that does not cause illness in African monkeys. "African primates all carry their own little viruses," Dr. Jonathan Allan of the Southwestern Foundation for Biomedical Research in San Antonio said, adding, "in some species, the viruses have been there for thousands of years. And the natural host never gets sick."
Dr. Mark Feinberg, a professor of microbiology and immunology at Emory University, examined the immune response of sooty mangabeys, a West African monkey species, to a virus "identical" to HIV-2, which is widespread in the species. HIV-2 is a human AIDS virus that is endemic to West Africa but is not found in large numbers outside that area. Feinberg, who had theorized that the monkeys would naturally have to keep the virus at bay, actually determined that the monkeys had high levels of virus in their systems and that the immune system was simply producing new cells to stay ahead of the virus. The same phenomena -- an aggressive immune system response to high viral levels -- was observed in wild cats. O'Brien said it is a "predictable adaptation" and may give researchers clues as to how HIV will progress in the human population. "When a virus gets into a population, like HIV jumped into humans, it can kill off the species or not. If it does not, either the virus becomes weakened or the species changes," he explained. Feinberg added that the same phenomena is "going to happen" in humans. "The severity of the epidemic in some parts of the world is so profound that it will clearly impact human evolution. In the past, we've been left to infer what the impact of infection was on human evolution. [Now], we will have the opportunity to observe it," he said (Kolata, New York Times, 1/29).