WASHINGTON -- The Ebola virus has killed large numbers of chimpanzees, gorillas and antelope in west central Africa and researchers say sick animals harvested as meat may be the source of five recent human outbreaks of the deadly disease.
Dr. William B. Karesh of the Wildlife Conservation Society said a study of outbreaks of Ebola disease in west central Africa shows that the virus is introduced into the human population most often by hunters who handle meat from infected animals.
After studying outbreaks that occurred from October 2001 to May 2003, Karesh said he and his team concluded that human outbreaks almost always are preceded by Ebola-related deaths of many forest animals.
Ebola is a hemorrhagic fever that kills most of its victims within a few days. In the final stages of the disease, patients start leaking blood from every orifice and eventually bleed to death. The death rate in humans is about 80 percent.
Karesh said the virus has been found in the bodies of chimpanzees, lowland gorillas and the duiker, a small short-horned antelope. Before some outbreaks, he said that there were reports of large numbers of dead animals in the forest.
The natural source of Ebola remains unknown, he said, but most of the outbreaks occur during a dry season in the "Ebola pocket," an African area that includes parts of Gabon and the Republic of Congo. A report on the study appears this week in the journal Science.
Karesh said Ebola has devastated what were once large populations of gorilla, chimp and duiker in the area.
"There is a whole region in Gabon where there's very few signs of gorillas and then there's a place in the Congo where all the gorillas died," said Karesh, a doctor of veterinary medicine. "It looks like more than half of the lowland gorillas in west central Africa have been lost through a combination of hunting and Ebola."
He said some have estimated that more than 10,000 apes have been killed in recent years by Ebola.
Dr. Gary Nabel, an expert on Ebola at the National Institutes of Allergy and Infectious Diseases, said the study by Karesh and his colleagues is an important contribution to the continuing effort to understand and control Ebola.
"We suspected that the apes were involved in spreading Ebola to humans, but not the antelope," said Nabel. "The fact that the antelope could be an intermediate host is something that we hadn't appreciated previously."
Karesh said hunting and the sale of game, a trade called "bush meat," is common in the Ebola area of Africa, and experts are worried that selling the meat of infected animals could lead to widespread disease among humans. The major factor preventing this, Karesh said, is the isolation of the Ebola pocket.
"There is a tremendous potential of (diseased meat) getting into the market, but so far most people with the infected meat get sick before they can distribute it," he said.
Human cases of Ebola have been confined to small villages and remote areas, said Karesh, but that could change if infected bush meat ever reaches crowded markets in more distant towns.
"You could have thousands of people dying before it was known what was going on," he said. "That could be a horrible tragedy."
The disease spreads from human to human through contact with bodily fluids.
For this reason, Karesh said, most secondary cases of the disease are among family members. He said a hunter may catch the virus when he kills an infected animal or handles the animal corpse discovered in the forest. When the hunter becomes ill, his family cares for him, coming in contact with vomit, sweat or blood, all of which can contain the virus. Eventually, several members of one family can be infected.
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