Vaccination Could Protect Wild Apes Against Ebola Virus

LEIPZIG, Germany, April 16, 2007 (ENS) - Outbreaks of Ebola virus over the past 12 years have killed roughly 25 percent of the world gorilla population, and now the scientists who documented these deaths say vaccination of wild gorillas could help protect those that remain.

A study published in the May issue of the journal "The American Naturalist" provides hope that newly developed vaccines can control the devastating impact of Ebola on wild apes.

The hopeful clues come from the discovery that outbreaks may be amplified by Ebola transmission between ape social groups.

"It means that vaccinating one gorilla does not protect only that gorilla, it also protects gorillas further down the transmission chain," said Peter Walsh of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, the lead author on the study.

"Thus, protecting remaining ape populations may not require vaccinating a high proportion of individuals, as many people naively assume," Walsh said.

Scientist Peter Walsh measures gorilla dung in his research to estimate the abundance of gorillas and chimpanzees and monitor the effects of the Ebola virus. (Photo courtesy Peter Walsh via Princeton Alumni Weekly)
Direct encounters between gorilla or chimpanzee social groups are rare. So, when reports of large ape die-offs first surfaced in the late 1990s, outbreak amplification was assumed to be through spillover from some unknown reservoir host. But more recent research by Walsh and his colleagues suggests that Ebola transmission between ape groups might occur through routes other than direct social encounter.

Initial spillover from a reservoir host appears to have triggered an epidemic that spread from gorilla social group to gorilla social group.

The new study was conducted at three sites in northern Republic of Congo by Walsh and other researchers from the Max Planck Institute, David Morgan of England's Cambridge University, and Diane Doran of New York's Stony Brook University.

They found that as many as four different gorilla groups fed in the same fruit tree on a single day. In this way, infective body fluids deposited by one group might easily be encountered by a subsequent group, the researchers say.

Chimpanzees and gorillas also fed simultaneously in the same fruit tree at least once every seven days.

The study also provided the first evidence that gorillas from one social group closely inspect the carcasses of gorillas from other groups. The researchers point out that contact with corpses at funerals is a major mechanism of Ebola transmission in humans.

Together with other recent observations on patterns of gorilla mortality, these results make a strong case that transmission between ape social groups plays a central role in Ebola outbreak amplification.

A Western lowland gorilla in the Congo Basin. (Photo by Richard Parnell courtesy WCS)
Particularly troubling has been the concentration of Ebola impact on large, remote protected areas that were designed to be central to ape conservation efforts.

Ebola has not made apes totally extinct from these areas but it has pushed once huge populations down to smaller sizes at which they are dramatically less resilient to illegal hunting and other looming threats.

The current lack of a vaccination program is not due to a lack of vaccine options, as several different vaccines have now protected laboratory monkeys from Ebola and major vaccine labs are anxious to help.

"Uncertainty about whether a large Ebola control effort was necessary or even possible has paralyzed large donors and major conservation organizations," said Walsh in December, announcing the results of a separate study that first showed that 93 percent (221 of 238) individually known gorillas at the Lossi Sanctuary in northwest Congo were killed by Ebola during outbreaks in 2002 and 2003.

The scientists then used transect surveys to show that 95 percent gorilla mortality rates extended over a much larger area of several thousand square kilometers. Chimpanzees were also heavily affected, with a mortality rate of 77 percent.

"We are hoping that the starkness of our results will push some public or private donor to finally commit the two or three million dollars necessary to develop a safe and effective way of delivering Ebola vaccine to wild apes," said Walsh.

Walsh contends that Ebola vaccination is a cost effective method of ape conservation.

"People in the conservation community are intimidated by the up-front costs of vaccination and would prefer to instead spend the money on anti-poaching. What they are not factoring in is the fact that one year of Ebola vaccination could save as many apes as decades of anti-poaching," Walsh said. "We need to do both."

Walsh also points out that Ebola has the potential to quickly destroy years of ecotourism investment. For example, a gorilla habituation program at Lossi was set up in the mid-1990s in collaboration with the European Union’s Ecosystem Forestiere d’Afrique Centrale project to bring ecotourism revenue to local people.

Ebola not only wiped out the habituated gorillas at Lossi, it neutralized years of ecotourism investment in neighboring Odzala National Park by devastating gorilla populations there.

"We are in a period where relatively modest investments in both Ebola control and anti-poaching would go a very long way towards insuring the future of our closest relatives," said Walsh. "Let’s not blow it."

Walsh and his colleagues now are searching for funding to implement a vaccination program using one of the several vaccines that have successfully protected laboratory monkeys from Ebola.