Study Confirms Chimps as Source of AIDS Virus
Solving a long-puzzling mystery about the origins of the AIDS epidemic, Alabama researchers have shown that the most prevalent form of the AIDS virus, human immunodeficiency virus type 1, almost certainly passed to humans from a common subspecies of chimpanzee.
Studying the virus in these animals could lead to new ways of protecting humans from the disease, experts said.
Examining the DNA compositions of HIV-1 and several chimpanzee viruses, Dr. Beatrice H. Hahn and her colleagues at the University of Alabama at Birmingham concluded that the virus passed from chimps to humans three separate times in a small region of western equatorial Africa about 50 years ago before spreading to an estimated 35 million human carriers today.
The transmission most likely occurred during butchering of the animals, which were subsequently eaten.
Hahn presented the results at the Sixth Conference on Retroviruses and Opportunistic Infections in Chicago on Sunday and they will be published in Thursday’s edition of Nature.
“This is an important finding with significant potential,” said Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases. “This may allow us to . . . study infected chimpanzees in the wild to find out why these animals don’t get sick, information that may help us better protect humans from developing AIDS.”
The findings also suggest that the still widespread practice of butchering and eating chimpanzees presents a risk of introducing new strains of HIV or other viruses into the human population.
Researchers have already found nearly a dozen instances in which rarer forms of HIV have been transmitted to humans by primates. HIV type 2, which is common in some areas of Africa and Asia, for example, was transmitted from the sooty mangabey, a monkey from West Africa.
The origins of AIDS have long been a source of mystery, but most researchers have leaned toward the belief that the virus originated in primates.
Nevertheless, “There have been a lot of loose ends that made people uncomfortable drawing that conclusion,” Hahn told a news conference Sunday. The new results “nail it,” she said.
Animals carry many viruses that may not harm them but have more serious consequences when transmitted to humans. Influenza, for example, is harbored by ducks, chickens and pigs and new variants can easily spread to humans, touching off major epidemics.
The humans species is the only one that is infected by HIV. Chimpanzees are infected by a closely related virus called simian immunodeficiency virus, or SIV, which exists in many forms.
Such viruses must undergo some type of genetic mutation in order to infect humans. Hahn and her colleagues discovered three chimp viruses with DNA sequences that are very close to HIV--so close that it probably required only a minor genetic change for them to make the jump from one species to another.
The viruses, termed SIVcpz, were found only in Pan troglodytes troglodytes, a subspecies of chimp whose range covers Cameroon, Equatorial Guinea, Congo and the Central African Republic.
Among humans, there are three major types of HIV-1, which researchers call M, N and O. M is the variety that has spread around the world; N and O are seen only in western equatorial Africa. The natural habitat of the newly discovered viruses exactly overlaps the area in western equatorial Africa where these three groups were first recognized.
Hahn believes that each type arose from a separate chimp-to-human transmission of SIVcpz, probably in the late 1940s or early 1950s.
She said a French team headed by Dr. Phillippe Mauclere of the Pasteur Institute in Paris recently found three more chimps infected with SIVcpz at a game sanctuary in Cameroon. A sample from one of the animals has been genetically analyzed, and it, too, bears a strong resemblance to HIV-1.
Last year, researchers said they had found the first known case of AIDS in a Bantu man who died in 1959 in what is now Congo--further suggesting that region as the source of the virus.
SIVcpz is rare in chimpanzees in the United States, probably because they are captured while very young, presumably before they have had a chance to contract the virus during sexual intercourse. Those in this country, such as the ones used in Hahn’s study, reside predominantly in research colonies.
Hahn found the virus twice among living animals that she studied. The third sample came from frozen specimens taken from a 26-year-old chimpanzee named Marilyn. Marilyn died 14 years ago from complications of childbirth at a U. S. Air Force primate center.
