USIA Washington File - 2 February 1999

Washington -- A team of international scientists have announced they have traced the origin of the AIDS virus to a closely related virus in a subspecies of chimpanzee in Africa.

The scientists, who reported their findings January 31 at the Conference on Retroviruses and Opportunistic Infections being held in Chicago, said that research will now focus on why the human immunodeficiency virus (HIV) that causes AIDS is lethal for humans while the related virus causes apparently no illness in the chimpanzees, even though humans and chimpanzees are 98 percent genetically similar.

Although scientific researchers have long suspected that HIV-1, the type of AIDS virus that has caused the overwhelming majority of cases in the world, came from chimpanzees, scientists have not been able to identify the precise subspecies until now. The chimpanzee virus is known as SIVcpz, or "simian immunodeficiency virus chimpanzee." "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 research team, Dr. Beatrice Hahn of the University of Alabama at Birmingham, said in an interview.

Hahn, whose paper will be published in this week's issue of the journal Nature, said despite the enthusiasm with the discovery, her team is worried about the fact that the subspecies in which SIVcpz was found is at "the brink of extinction" in its natural habitat in west and central Africa. Hahn believes the chimpanzee's extinction represents a danger to science because much more needs to be learned about the infection in chimpanzees in the wild.

Hahn's team has confirmed the origin of the AIDS virus by analyzing frozen tissue from Marilyn, a chimpanzee who died in 1984 at the age of 26. The researchers have been able to perform various kinds of genetic analysis that were unavailable at the time Marilyn died. The chimpanzee subspecies lives in the African region where AIDS is thought to have started.

HIV presently infects about 35 million people worldwide, with the first infection probably having occurred 50 years ago, scientists have reported. Hahn and her colleagues said that they have conclusive evidence that the HIV virus has spread on at least three distinct occasions. Hahn believes in the theory that humans have been infected from chimpanzees in Africa through exposure to their blood in hunting and when dressing meat. However, why the epidemic came when it did is not known precisely.

Dr. Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases, said in an interview that his federal institute would finance substantial research on the simian virus. He said one focus of the research will be on whether the different outcomes of infection in humans and chimpanzees result from small changes in the genetic makeup of the virus or the host.

The latest findings might lead to new tests to discover viruses in nature that could cause human disease. "No one wants to miss detecting the next HIV epidemic," said Dr. Harold Jaffe, a leading AIDS researcher at the Center for Disease Control and Prevention in Atlanta, Georgia.

Because the chimpanzees are able to live with HIV without developing the illness, scientists hope their discovery will be helpful in improving therapies and eventually developing a vaccine against the AIDS virus.