They believe the simian immunodeficiency virus,S.I.V., probably crossed from chimpanzees to humans in the last one hundred years.

VOA: special.2009.09.08

Scientists have believed that S.I.V.did not cause a similar immune system problem for primates.

VOA: special.2009.09.08

Doctor Hahn says she suspects chimps first got infected with S.I.V.

VOA: special.2009.09.08

Now,researchers say they have evidence that chimpanzees with S.I.V.

VOA: special.2009.09.08

Seventeen chimps were found to be infected with S.I.V.

VOA: special.2009.09.08