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HIV-related viruses still cross species line

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4:53pm, February 8, 2001
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Scientists generally agree that simian viruses resembling the human immunodeficiency virus (HIV), which causes AIDS, originally spread from chimpanzees and sooty mangabeys to people in central Africa (SN: 2/6/99, p. 84). Researchers now have hard evidence that other variations of simian immunodeficiency virus (SIV) occur in wild nonhuman primates and continue to cross into people in Africa.

Although captive primates have shown SIV infections, scientists wanted to investigate the virus' prevalence in the wild. They collected blood samples from 384 wild-born baboons and monkeys in Cameroon-17 species altogether.

Only chimpanzees in west-central Africa harbor a viral strain that is "truly closely related" to the most lethal AIDS strain, but other primates bear watching as viral reservoirs, says Beatrice H. Hahn of the University of Alabama in Birmingham. The blood samples revealed that 18 percent of the animals harbored SIV antibodies that bind strongly to HIV proteins. That finding indicates that some SIV strains in animals today, while not lethal to people, have clear similarities to HIV, says Hahn's colleague Eric Delaporte of the Institute for Research and Development in Montpellier, France.

Another 14 percent of the animals had antibodies that bind less strongly to HIV proteins in this cross-species test, says Delaporte. Several of the SIV subtypes identified were previously unknown, he said at the Eighth Annual Retrovirus Conference in Chicago this week.

Such field research is valuable because "there may be more subtypes of SIV out there" that are still unidentified and could pose risks to people, says Yongjun Guan of the McGill University AIDS Center in Montreal.

Indeed, many people hunt these animals for "bushmeat" or keep them as pets, creating continual human exposure to SIV strains, says Hahn.

She and others have now documented nine instances in which chimps, sooty mangabeys, and apparently a mandrill have passed along an SIV virus to a person in Africa in recent years. Researchers found antibodies to these viral strains in people's blood, indicating cross-species infection. Hahn wants to amass data on wild SIV strains to create tests for detecting them in people.

"We don't know what triggers a virus to catch on in humans," she says. "You start by cataloguing what's in the wild."

Having field teams obtain blood samples from wild primates is one approach. A new technique analyzes animals' urine and fecal samples gathered in the bush. In a separate study presented at the meeting, Hahn and her colleagues reported identifying SIV antibodies in droppings and urine from wild chimpanzees in Uganda. The finding demonstrates that this noninvasive screening technique can detect viral strains in these animals, she says.

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