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Scientists Say Ebola Has Pushed Western Gorillas to the Brink

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Science  14 Sep 2007:
Vol. 317, Issue 5844, pp. 1484
DOI: 10.1126/science.317.5844.1484

The combined threat of the Ebola virus and poaching have pushed western gorillas into the “critically endangered” category in the latest international ranking of species threatened with extinction. Although estimates suggest that tens of thousands of the animals still live in west-central Africa, the new Red List from the World Conservation Union (IUCN) moves the species into its highest alert category, in large part because of fears that continuing Ebola outbreaks could swiftly wipe out still-significant gorilla populations.

The list, released on 12 September, highlights the western gorilla as well as dozens of other species for which new data indicate an increased risk of extinction. The “critically endangered” category is usually applied when just a few hundred individuals survive in the wild. But researchers say that western gorillas, despite their relatively large numbers, are in serious trouble. An ongoing series of Ebola outbreaks has killed up to 90% of the animals in some regions (Science, 8 December 2006, p. 1522), and the use of vaccines to stem the disease faces daunting challenges. Adding to the pressure, the rapid development of logging roads has opened up vast new regions to poaching and the bush-meat trade.

Although the other species in the Gorilla genus, the eastern gorilla, is far less numerous than the western gorilla, IUCN ranks the former one level lower at “endangered” because it is outside the current area of Ebola outbreaks. As for western gorillas, there may be as many as 30,000 left in their current range, which stretches across Gabon, Equatorial Guinea, and parts of Cameroon, the Central African Republic, and the Republic of the Congo. There are two subspecies, the more common western lowland gorilla and the extremely rare Cross River gorilla, of which fewer than 200 probably remain.

It is unusual for disease to be cited as a reason for reclassification, says wildlife disease specialist Richard Kock of the Zoological Society of London, who co-chairs the IUCN Veterinary Specialist Group. But even if the new status has come sooner than expected, the change is warranted, says Kenneth Cameron, a field veterinarian with the Wildlife Conservation Society in Brazzaville, Republic of the Congo. “Is this jumping the gun a bit? Some would argue that it is,” he says. “But it is inevitable that this species is going to end up on a critically endangered list. It's simply a matter of when.”

At risk.

The threat from the deadly Ebola virus and poaching have prompted scientists to call western gorillas critically endangered.


IUCN experts found that the western gorilla population has declined by 60% in the past 20 to 25 years and estimated that in the past 15 years Ebola has killed one-third of the animals living in protected areas such as national parks. Those numbers are only the roughest of estimates, Kock says. The current gorilla range “is a huge place. … It's bloody impossible to know what's going on” in the remote forest regions, he says.

Conservationists say they hope the new status will help pressure governments and international donors to increase efforts to protect gorillas and their habitat. They also say they hope it will lead to more funding for the search for an Ebola vaccine.

What is certain is that western gorilla habitat will be under severe pressure in the next 5 years, Cameron says. Plans are under way in the Republic of the Congo to improve the road and rail connections between Brazzaville and Ouesso, the largest town in the north. Both projects will cut through prime gorilla habitat, making it easier for hunters to reach and for bush meat to be shipped back to city markets.

While public awareness campaigns and increased antipoaching efforts might help mitigate pressure from hunters, scientists are struggling to blunt the impact of Ebola. The virus can pass from ape to ape, so regions with higher population densities are especially at risk. “It appears to act like a brushfire,” Cameron says. “You get a lightning strike somewhere, and it starts to burn.”

Although admitting it's a long shot, some researchers hope a vaccine campaign could at least save enough animals to preserve the species. At least half a dozen vaccine candidates have protected mice or monkeys in the lab from the Ebola virus. But finding a way to deliver a vaccine safely to wild animals is no small challenge.

Few believe that vaccine-laden darts could reach enough gorillas to stem the spread of the disease. Peter Walsh of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, is working with a vaccine company to develop possible baits that could carry an oral vaccine. The bait must keep the vaccine viable in the hot, humid conditions of the forest, attract great apes, and be safe for other animals who might find it first. Walsh says that before the end of the year, he and his colleagues plan to begin testing darting and oral bait strategies, without incorporating a vaccine, in the Republic of the Congo.

“This is not just about Ebola,” Walsh says. “All apes are under increased disease threat, especially from human-introduced diseases. Vaccines are going to be an increasing part of conservation. … This is not going to be wasted time or money.”

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