The deadly Ebola virus, which emerged mysteriously from African forests, probably attacks people who butcher and eat infected animals, researchers said on Thursday.
The virus, which most recently killed 29 people in the Congo Republic, seems to break out when people slaughter chimpanzees, gorillas and small antelopes called duikers, the scientists said.
“Humans and duikers scavenging for meat probably became infected by contact with dead apes,” they wrote in their report, published in Friday’s issue of the journal Science.
“Almost all human Ebola outbreaks in Gabon and the Republic of Congo have been linked to the handling of dead animals by villagers or hunters, and increased animal mortality always preceded the first human cases,” added the international team of researchers, led by Eric Leroy of the Development Research Institute in Gabon.
They said health workers may be able to get a warning of Ebola outbreaks when large numbers of dead animals start appearing in forests.
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Ebola first appeared in 1976 and causes a particularly frightening and deadly form of hemorrhagic fever. Patients die of shock but may bleed internally and externally.
Depending on the strain of virus, it kills between 50 and 90 percent of patients.
Leroy and colleagues studied several outbreaks in central Africa and said villagers, and they themselves, found many dead animals just around the time of an outbreak.
They also found that great apes such as chimps and gorillas could be infected, although the original source of the virus remains unknown.
“The human outbreaks consisted of multiple simultaneous epidemics caused by different viral strains, and each epidemic resulted from the handling of a distinct gorilla, chimpanzee or duiker carcass,” they wrote.
“These animal populations declined markedly during human Ebola outbreaks, apparently as a result of Ebola infection. Recovered carcasses were infected by a variety of Ebola strains, suggesting that Ebola outbreaks in great apes result from multiple virus introductions from the natural host.”
This natural host, or reservoir, is likely to be an animal that is not made ill by the virus, scientists say.
Another blow to endangered gorillas
Gorillas in particular have been hard-hit by Ebola, the researchers noted. Along with poaching and habitat loss, this could lead to their extinction in western Central Africa, they said.
Many people in Africa depend on apes and monkeys -- known as bush meat -- for food. But some governments are trying to discourage the practice because many apes are endangered.
And other viruses, including the HIV virus that causes AIDS, are believed to have come from chimps and other close relatives of humans.
“Now we know that the virus doesn’t ’spread’ as much as it spills over from many sources in the forest,” said Dr. William Karesh of the New York-based Wildlife Conservation Society, who worked on the study.
Karesh, Leroy and colleagues found that one outbreak between October 2001 and May 2003 was caused by eight viral strains originating from different areas.