Recent outbreaks of ebola among people in Africa also killed thousands of gorillas, animals already threatened by hunting, a new study reports.

Outbreaks in Congo and Gabon in 2002 and 2003 killed as many as 5,500 gorillas and an uncounted number of chimpanzees, a research team led by Magdalena Bermejo of the University of Barcelona in Spain reports in Friday's issue of the journal Science.

While conservationists had raised concern about gorilla mortality previously, Bermejo's study provides an estimate of how many died in the epidemic.

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"Add commercial hunting to the mix, and we have a recipe for rapid ecological extinction," the researchers wrote. "Ape species that were abundant and widely distributed a decade ago are rapidly being reduced to a tiny remnant population."

Ebola hemorrhagic fever is marked by fever, headache, joint and muscle aches, sore throat and weakness, followed by diarrhea, vomiting, stomach pain — and many suffer internal and external bleeding.

The researchers began studying gorillas in the region in 1995 and by 2001 were focusing on 143 animals who had become accustomed to having people around.

In 2002, ebola flared in among people in the region, killing dozens, and 130 of the gorillas in the study also perished. The researchers turned their attention to another group of 95 gorillas, but a 2003 ebola outbreak killed 91 of those animals.

That prompted the team to analyze the regional pattern of gorilla deaths and they concluded the disease spread primarily from gorilla to gorilla starting in the north and moving southward through the region. They concluded that at least 3,500 gorillas died in the outbreaks, possibly as many as 5,500.

They also found evidence of a large number of chimpanzee deaths, but said they didn't have enough evidence to make an estimate of the total.

The research was funded by Energy Africa Oil Company, the European Union and the University of Barcelona.