Why have large outbreaks of Ebola virus killed tens of thousands of gorillas and chimpanzees over the last decade? Observations published in the May issue of The American Naturalist provide new clues, suggesting that outbreaks may be amplified by Ebola transmission between ape social groups.
The study provides hope that newly developed vaccines could control the devastating impact of Ebola on wild apes.
Direct encounters between gorilla or chimpanzee social groups are rare. Therefore, when reports of large ape die-offs first surfaced in the late 1990s, outbreak amplification was assumed to be through "massive spillover" from some unknown reservoir host. The new study, conducted by researchers from the Max Planck Institute for Evolutionary Anthropology, Cambridge University, and Stony Brook University at three sites in northern Republic of Congo, suggests that Ebola transmission between ape groups might occur through routes other than direct social encounter. For instance, as many as four different gorilla groups fed in the same fruit tree on a single day. Thus, infective body fluids deposited by one group might easily be encountered by a subsequent group. Chimpanzees and gorillas also fed simultaneously in the same fruit tree at least once every seven days.