Massive Great Ape Die-Off in Africa—Ebola Suspected

National Geographic News
Updated February 6, 2003
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A catastrophic die-off of lowland gorillas and chimpanzees at the very heart of their range in central Africa has been reported by scientists.

Scientists working with the ECOFAC program (an EC-funded regional forest conservation program for central Africa) in northern Republic of Congo said today that they were witnessing what appears to be a massive decline in ape populations in the Lossi Gorilla Sanctuary (about 100 square miles/250 square kilometers) situated about 10 miles (15 square kilometers) to the southwest of the famous Odzala National Park (5,250 square miles/13,600 square kilometers).

The region is thought to contain the majority of central Africa's lowland gorillas because of its isolation, the presence of several protected areas, and large undisturbed areas of habitat types particularly favored by gorillas.

"Spanish primatologists Magdalena Bermejo and Germain Ilera, who have been studying gorillas at Lossi for the past nine years, report that the eight families (139 individuals) they have been monitoring since 1994, have disappeared from their study area of 40 square kilometers (15 square miles) in the sanctuary," ECOFAC said in a news release today.

The first deaths were reported on November 26, and in mid-December scientists from Gabon's Centre International de Recherches Medicales de Franceville (CIRMF) collected samples from four gorilla and two chimpanzee carcasses and confirmed the presence of Ebola virus in all six cases.

Since then Bermejo and Ilera and their teams of trackers have been combing the area for signs of great apes and have found only one gorilla group of six individuals on the eastern edge of their study area.

Two of the missing gorilla families were habituated for tourism viewing. They were the first lowland gorillas ever to be habituated in central Africa and generated much needed revenue for the local villagers, ECOFAC said.

The Lossi Gorilla Sanctuary was created at the request of the villagers when they realized that the long-term benefits from gorilla viewing far outweighed any short-term benefits from hunting. The disappearance of these families is an enormous setback for the villages, ECOFAC said.

"This most recent outbreak at Lossi suggests that the devastating effects of the Ebola virus on great ape populations appears to be moving eastwards. The forests in and around the Odzala National Park are known to contain the highest known density of lowland gorillas in Africa."

Scientists from Rennes University working with ECOFAC have documented up to 47 families of gorillas visiting a single three-hectare (7.4-acre) forest clearing in the north of Odzala.

The epidemic appears be spreading from west to east. Scientists from the World Wildlife Fund working in Minkebe National Park in northern Gabon documented the disappearance of great apes from an estimated area of 20,000 square kilometers (7,700 square miles) sometime between 1990 and 2000, and suspected that the Ebola virus might have been the cause. Three Ebola epidemics were recorded in villages in the Minkebe area between 1994 and 1996.

Between November 2001 and June 2002 at least 80 people died during an outbreak of the disease in the cross border area of northeastern Gabon and northwestern Congo (Mekambo-Ekata-Mbomo-Kelle). During this epidemic, scientists from ECOFAC, CIRMF, and WCS (Wildlife Conservation Society) also documented deaths of great apes in the same area and the Ebola virus was confirmed from one carcass. In several cases it was established that handling fresh ape carcasses that they had found in the forest had contaminated humans.

No one knows how the disease entered the first human or ape, said William Karesh, head of the Wildlife Conservation Society's Field Veterinary Program. "But we do know that the virus is subsequently spread from infected animals to other animals and from infected people to other people."

Karesh said that there was no known way to contain the epidemic among animals. "When people are infected we can educate them about the risk of touching or consuming dead or sick animals, and if they are sick, to immediately let authorities know so they can be isolated before they infect other people.

"But for animals, at this time, we have to let the disease run its course in the forest because there are no known treatments besides supportive care for infected humans."

Karesh said it was not known whether infected humans could be spreading the disease to apes.

"This has not been the case as far as we know, but sick individuals who refuse to remain in quarantine and move to other areas will take the disease with them and infect the people they come in contact with.

"There is a chance that if they were seriously ill and unable to continue traveling through the forest, in theory they could be found by chimpanzees or gorillas who could, again in theory, contract the disease from the infected human or their body fluids.

"Humans definitely are the major source of spreading the disease among humans. The typical Ebola outbreak involves one or maybe two or three people contracting the disease from some source in the forest and then infecting family members and neighbors in a chain that can grow to hundreds of people.

"Similarly, our understanding of the social nature of chimps and gorillas suggests that the same happens to them. One or a few chimps or gorillas become ill and then infect the other members of their family group. As the group is dying, some individuals infected later may be left to wander off and join another group or may be found dead by a member of another family group, allowing this cycle to continue."

Named after the Ebola River, in the Democratic Republic of Congo, the site of an outbreak of the virus in 1976, Ebola is an RNA virus of African origin that causes an often fatal hemorrhagic fever.

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