Caregiver at Congo's Virunga National Park wearing a facemask to limit danger of orphan ape being exposed to human diseases.
Originally it was suspected that primates such as gorillas might be the natural reservoir of the ebola virus. It is now thought that this is unlikely and that the reservoir is probably bats. One reason we think that apes are an unlikely reservoir is that they suffer fairly severe outbreaks that can kill a high proportion of the animals, (making it difficult for the virus for persist in this population). (eg Ebola Outbreak Killed 5000 Gorillas in the journal Science in 2006). In other words the virus is spilling over into the ape populations in the same way it occasionally spills over into human populations. Over the last two decades the Zaire strain of Ebola has killed roughly one third of the world's gorilla population and only a slightly smaller proportion of the world's chimpanzees
Just last December a paper in PLoS ONE: Consequences of Non-Intervention for Infectious Disease in African Great Apes highlighted the potentially dire consequences of diseases such as Ebola and SIV's for African Great Apes.