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Scientists have discovered that two of the four strains of the HIV virus come from gorillas in southwest Cameroon. Their study is big news for researchers as they now know the origins of all types of HIV that can occur in people. Nikki Tagg is a researcher at the Zoological Society in Antwerp and one of the study's co-authors. (Photo: Kumbuka, a western lowland gorilla. Credit: Oli Scarff/Getty Images)