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, too, researchers said on Thursday, according to Reuters. The virus is spreading from one group of the already endangered animals to another, the international team of experts report in this week's issue of the journal Science. And it appears to be spreading faster than it is among humans. "The Zaire strain of Ebola virus killed about 5,000 gorillas in our study area alone," primatologist Magdalena Bermejo of the University of Barcelona in Spain and at the Programme for Conservation and Rational Utilization of Forest Ecosystems in Central Africa and colleagues wrote. Ebola hemorrhagic fever is one of the most virulent viruses ever seen, killing between 50 percent and 90 percent of victims. The World Health Organization says that it killed 1,200 people infected between its discovery in 1976 and 2004. 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. 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. But it was not clear whether the gorillas were infecting one another, or being repeatedly infected and re-infected by another species of animal, perhaps a bat. Bermejo's team had been studying a group of western gorillas in the Lossi Sanctuary in northwest Republic of Congo. "By 2002 we had identified 10 social groups with 143 individuals," they wrote.