HIV strain came from gorillas, study finds

Western lowland gorillas in southern Cameroon appear to be the source for the second-most-lethal category of the immunodeficiency virus that crossed into humans, a new study suggests.

The category, called HIV-1 group O, has not been nearly as dangerous to humans as group M, which has infected more than 40 million people worldwide. But its origin and history had been a mystery.

Using nearly 3,000 fecal samples from gorillas in several western and central African countries, researchers reported Monday that they pinpointed the source population for group O, which infected 100,000 in west-central Africa, and for the exceedingly rare group P, which infected only two people.

The simian viruses identified by researchers leaped from chimpanzees to the gorillas, which spread it at least twice to humans, according to the study, published online in the journal Proceedings of the National Academy of Sciences.

“The gorilla virus is basically a chimp virus in gorillas,” said study co-author Dr. Beatrice Hahn of the University of Pennsylvania, who has been studying chimpanzee versions of the simian immunodeficiency virus, SIV, for two decades.

Researchers had already traced the main HIV-1 lineage, dubbed group M, to SIV in chimpanzees, which transmitted it several times to humans. The origin of the very rare group N, which infected about a dozen people, likewise has been found.

Why group O did not spread more readily between chimpanzees and western lowland gorillas, which share habitat, is of great interest to researchers looking for clues to combat the pathogen.

“Gorillas and chimps live in the same forest; they probably see each other more often than humans see them,” Hahn said. “And yet, there is only evidence for a single transmission.”