The Ebola virus may have killed more than 5,000 gorillas in West Africa, enough to send them into extinction if people continue to hunt them, researchers have said.

Ebola fever is one of the most virulent viruses ever seen, killing between 50% and 90% of victims. The virus is transmitted by direct contact with blood, organs or other bodily fluids. There is no cure or good treatment, although several groups are working on vaccines. The virus is spreading from one group of the already endangered animals to another and it appears to be spreading faster than it is among humans. Several experts have noted that chimpanzees and gorillas are also killed by the virus, and suspect that people may have caught it from infected apes, perhaps when hunting them.

In 2001 and 2002, several outbreaks of Ebola had begun killing people along the Gabon/Congo border. By October 2002, the researchers had found 32 dead gorillas, and of the 12 they tested for Ebola, nine were positive. Eventually the researchers counted 221 dead gorillas. Based on what they and other experts knew, they extrapolated what the total impact must be to come up with the estimate of 5,500 gorillas killed by Ebola in that area.

A quarter of the gorillas in the world have died from Ebola in the last 12 years. This, combined with commercial hunting will lead to rapid extinction.

Their report supports a study published in July that showed gorillas were spreading the virus within their social groups. Gorilla groups share territories, often eating fruit from the same tree, although at different times. Feces from a sick gorilla could easily infect other gorillas. Gorillas and chimpanzees also touch and handle the bodies of other apes when they find them, something known to transmit Ebola between humans.