New Strain of AIDS Virus Discovered in Africa

New Strain of AIDS Virus Discovered in Africa

By Rick Weiss
Washington Post Staff Writer
Tuesday, September 1, 1998

French researchers have discovered a new strain of the AIDS virus in Africa that is so different from other known strains that it easily escapes detection by standard blood screening tests.

The new variant does not currently threaten the safety of the blood supply or otherwise pose a significant public health threat since the virus, a form of HIV-1, is extremely rare. It was discovered in a 40-year-old Cameroonian woman who died of AIDS complications in 1995 and has since been implicated in only three other cases of AIDS, all in that west-central African country.

Nonetheless, experts said, the emergence of the new strain is a reminder that HIV remains a microbial moving target. Novel strains are evolving constantly within infected people, who serve as incubators for new mutants, and inside chimpanzees and other wild animals that harbor simian versions of the virus.

Indeed, according to the French team's genetic analysis, the new virus is about equally related to the strain of HIV most commonly found in people and to a kind of virus isolated from wild chimpanzees -- yet it's considerably different from both of those groups. They conclude that the new variant probably developed independently in chimpanzees and made the leap to people fairly recently.

"The isolation and characterization of this highly divergent strain indicate that the emergence of [AIDS-related viruses] in humans is ongoing," the scientists report in the September issue of the journal Nature Medicine, released yesterday. Francois Simon and Francoise Brun-Vezinet of the Bichat Hospital in Paris led the research with colleagues in Cameroon and its southern neighbor Gabon.

The Cameroonian woman from whom the new viruses were retrieved was first hospitalized with AIDS symptoms in May 1995. Standard antibody tests, like those used in the United States to screen out HIV-positive blood donors, were negative. HIV-1 was diagnosed only with a highly sensitive "Western blot" test, which is commonly used in research but otherwise reserved in this country to confirm a positive or uncertain result from a screening test.

Blood from the woman, taken in May and December just before she died, was frozen and sent to Paris for analysis. Tests indicated that the AIDS viruses in the woman belonged to neither of the two known subtypes of HIV-1: group M (which accounts for the vast majority of AIDS cases worldwide and is the strain that screening tests look for) or the rarely encountered group O. The virus had many of the genetic hallmarks of a simian form of HIV, called SIV, found in chimpanzees.

To see how prevalent the new strain might be, the team tested 700 frozen samples of blood collected from Cameroonian AIDS patients between 1988 and 1997. Of these, 16 were neither group M nor group O but showed resemblances to SIV. Three of them -- collected in 1992, 1995 and 1997 -- appeared to match the strain found in the woman.

Simon Wain-Hobson, an AIDS researcher at the Pasteur Institute in France, called the viruses "rare birds" and said he would be surprised if they became major factors in the global AIDS epidemic.

"Will it spread? Well, of course, that's a virus's job. If you don't spread, you're dead," Wain-Hobson said. "The question is, 'How far?' " The most likely answer, he predicted, is "not very far," given the massive head start by group M viruses and the apparent lack of any special features that make the new strain more aggressive than others.

Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, said the discovery supports scientists' suspicions that there is a steady, albeit low-level, incidence of "viral jumps" from animals into people. Many believe that AIDS arose as a result of people coming in contact with the blood of SIV-infected sooty mangabeys, chimpanzees or other nonhuman primates.

Fauci called the new strain "an interesting curiosity" unlikely to become a threat to public health.

"The worst possible scenario is it spreads into people who, when screened for blood donation, will not be picked up as being infected," Fauci said. But multiple protections are built into the blood donation system to keep that from happening, he said, including questionnaires to help identify high-risk donors before they give blood.

"If you go through those multiple layers, it's extremely unlikely to wake up one day and say, 'Whoa! The blood supply is contaminated with a strain of the virus that we have missed,' " Fauci said.

Robert C. Gallo, head of the Institute of Human Virology in Baltimore and co-discoverer of HIV, agreed with that assessment, saying that screening tests would be developed if needed. But he said the discovery is a reminder of the virus's unflagging potential to learn new tricks.

"We've got to keep our eyes on the ball," he said.