AIDS TRACED TO CHIMPANZEES.

Byline: Lawrence K. Altman The New York Times

The riddle of the origin of the AIDS virus has apparently been solved, according to an international team of scientists who reported Sunday that they had traced its roots to a related virus in a subspecies of chimpanzee in Africa.

Because the chimpanzee is able to live with the virus without falling ill, the scientists expressed hope that their discovery would eventually help improve therapies and develop an effective vaccine against the AIDS virus.

The researchers, who reported their findings at the opening session of a scientific meeting here, said the simian virus was closely related to HIV-1, the type of AIDS virus that has caused the overwhelming majority of cases in the world. Since the virus jumped to humans, perhaps through exposure to blood in hunting or handling the meat of chimpanzees, it has been transmitted among humans to infect an estimated 30 million people in the world.

``The chimpanzee, which has served as the source of HIV-1, also quite possibly holds the clues to its successful control,'' the head of the team, Dr. Beatrice Hahn of the University of Alabama at Birmingham, said in an interview.

Although scientists have long suspected that HIV-1 came from the chimpanzee, they have not been able to identify the precise subspecies until now.

The subspecies is known as Pan troglodytes troglodytes, and the chimpanzee virus is known as SIVcpz, for simian immunodeficiency virus chimpanzee.

Future research needs to focus on why HIV-1 is lethal for humans while SIVcpz seems to cause no illness in the chimpanzee, even though humans and chimpanzees are 98 percent genetically similar, Hahn and other scientists said.

Although there have long been clues that HIV-1 came from chimpanzees, how to document the link had been one of the biggest mysteries in AIDS. But, as exciting as the discovery is to the scientists, their enthusiasm has been dampened by another discovery: The subspecies is being slaughtered to ``the brink of extinction'' in its natural habitat in west and central Africa, Hahn said. The researcher is now leading efforts to publicize the scientific dangers that she believes will result from the chimpanzee's extinction.

Dr. Anthony Fauci, the head of the National Institute of Allergy and Infectious Diseases, said Hahn's study was ``important and quite an interesting advance'' and opened a new avenue of research.

Fauci said in an interview that his federal institute would finance meritorious research on the simian virus. One aim will be to determine whether the different outcomes of infection in humans and chimpanzees result from tiny changes in the genetic makeup of the virus or the host. Another aim will be to understand why the chimpanzee's immune system appears to resist the damaging effects of the AIDS virus while the human's is susceptible.

Dr. Harold Jaffe and Dr. Thomas Folks, two leading AIDS researchers at the Centers for Disease Control and Prevention, said in interviews in Atlanta that determining the source of the AIDS virus might also help scientists learn how to identify novel microbes earlier and thus prevent similar diseases from becoming epidemic.

Since the recognition of AIDS in 1981, Jaffe said, scientists have asked, ``If this kind of transmission happened in the past, is it continuing to go on?''

The latest findings might lead to new tests to discover viruses in nature that could cause human disease. As people disturb more and more animal habitats around the world, scientists say, there is a growing risk that they will be exposed to previously unknown disease agents. Transplanting animal organs into humans, should it come into wider use, would also be an avenue for infection.

``That is everyone's nightmare, that there is another virus out there that either could be or has been transmitted to humans that we cannot detect with current methods,'' Jaffe said. ``No one wants to miss detecting the next HIV epidemic.''

Hahn, whose paper is due to be published in this week's issue of the journal Nature, said, ``My research interest for the last 10 years has been the origin and evolution of this entire class of viruses, not just the human viruses but also the primate cousins.'' Hahn, a virologist, works with her husband, George Shaw, who has gone to Africa twice in the last 10 years for such studies.

The two SIVcpz-infected chimpanzees that have been in captivity longest, for 26 and 15 years, did not develop AIDS, but much more needs to be learned about the infection in chimpanzees in the wild, Hahn said.

Folks said the work being reported Sunday was ``provocative and gives us lots of ideas about the evolution of the viruses, but it does not give us the final piece of the puzzle.''

Folks said ``it should be a priority to look systematically'' for the AIDS-like viruses in animals because scientists were now ``forced to draw conclusions based on very small numbers of isolates.''

The meeting under way here, the sixth annual Conference on Retroviruses and Opportunistic Infections, is an event at which scientists discuss viruses like HIV. At this meeting last year, scientists reported that analysis of a blood sample preserved since 1959 from the oldest documented case of HIV-1 infection showed that the first such infection probably occurred about 50 years ago.