A chimpanzee named Marilyn has helped confirm that the AIDS virus first passed into people from chimps, researchers said Sunday.
Genetic tests show the HIV virus is closely related to a virus that infects chimps but does not make them sick. It would have been first passed to humans when people butchered and ate chimps, as often happens in Africa.
Dr. Beatrice Hahn of the University of Alabama and colleagues made the discovery when analyzing blood and tissue samples from a lab chimp named Marilyn after she died at the age of 26.
"She had never been used in AIDS research and had not received human blood products after 1969," Hahn wrote in her report in the science journal Nature. "She died in 1985 after giving birth to still-born twins."
There have been many competing theories about where HIV comes from. Some groups have even suspected that homosexual men were deliberately infected, but most scientists believed it must have come from apes or monkeys.
Humans are the only creatures that can get HIV, which stands for human immunodeficiency virus.
Apes and monkeys get a simian immunodeficiency virus, known as SIV. Nonetheless, only three cases of chimpanzees infected with SIV had been documented.
When Hahn's team found the virus in Marilyn, they compared it to the other SIV viruses and to several strains of HIV.
In one case the virus was genetically not very close to HIV. But it came from a subspecies of chimp known as Pan troglodytes schweinfurthii.
The three SIV strains taken from the west African chimps, known as Pan troglodytes troglodytes and including Marilyn, very strongly resembled the three subgroups of HIV.
