Within a four-month period 130 of the 143 gorillas the researchers were following had died.
Since then the scientists have followed gorilla populations throughout 1,500 square miles (4,000 square kilometers) of the surrounding area.
Bermejo and colleagues estimate that more than 5,000 gorillas died in the area from the disease, with each Ebola outbreak resulting in greater than 90 percent mortality.
"A quarter of the gorillas in the world have died from Ebola in the last 12 years," Walsh told the Reuters news service. "It's huge."
It is not yet clear how the virus remains hidden between outbreaks or spreads, Walsh said. But there are some indications that fruit bats may be the culprits. (Related: "Fruit Bats Likely Hosts of Deadly Ebola Virus" [November 30, 2005].)
"Add commercial hunting to the mix, and we have a recipe for rapid ecological extinction," the authors write in Science. "Ape species that were abundant and widely distributed a decade ago are rapidly being reduced to tiny remnant populations."
There is a glimmer of hope, however, Walsh added—a newly developed vaccine that has been shown to be effective at protecting laboratory monkeys from the Ebola virus.
"If we can develop this vaccine for gorillas, then I think it is feasible to carry out a vaccination program," Walsh said.
He estimates that it would cost around two million U.S. dollars to develop the vaccine and around five million dollars to vaccinate a sufficient number of gorillas.
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