News of the Week

Ebola, Hunting Push Ape Populations to the Brink

Science  11 Apr 2003:
Vol. 300, Issue 5617, pp. 232a
DOI: 10.1126/science.300.5617.232a

Researchers are warning that a relentless epidemic of Ebola hemorrhagic fever in central Africa, combined with hunting, could push Africa's apes close to extinction within the next decade. A new analysis published online in Nature this week by ecologist Peter Walsh of Princeton University in New Jersey and others estimates the toll in Gabon, one of the last ape strongholds: More than half of the lowland gorillas and chimpanzees have disappeared since 1983. The concurrent human outbreak of Ebola in the neighboring Democratic Republic of Congo, where more than 100 people have died this year, has raised questions about the role of apes in the disease's spread.

Conservationists sounded the alarm about the role of Ebola in February, after a different group of researchers found that up to two-thirds of the gorillas—600 to 800 animals—in the Lossi sanctuary in Congo had likely fallen to Ebola since late 2002, based on positive tests for the virus on several carcasses. “It is a disaster,” says primatologist Magdalena Bermejo of the University of Barcelona, Spain, who is also a co-author on the Walsh paper. Only seven of the 143 gorillas she has been studying since 1994 have survived, says Bermejo. She fears a worse outcome if the virus jumps 20 kilometers to Odzala National Park, which holds the highest known density of apes in the world.

Until recently, Walsh says, some experts believed that ape populations in Gabon and Congo, home to 80% of the world's gorillas and most common chimps, were stable because these countries retain much of their original forest cover. But Walsh and 22 U.S., European, and Gabonese co-authors suspected that hunting and Ebola were having a heavy impact. To quantify the losses in Gabon, they compared a survey of ape nest sites in the early 1980s with survey results from 1998 to 2002.

Remains of the day.

Veterinary scientist Annelisa Kilbourn (who died last November in a plane crash) holds a femur from a lowland gorilla that died in an Ebola outbreak.


The team found that the number of nest sites fell drastically, especially close to towns, where demand for bushmeat is high. But apes were also sparser close to sites of human Ebola outbreaks, suggesting that the ape population was infected and was spreading the disease to humans. (People are thought to contract the virus from eating infected animals.) Across Gabon, ape populations have declined by 56% since 1983, says Walsh, who predicts they could fall another 80% within 1 to 3 decades.

Heavy Ebola outbreaks in Congo and civil unrest in the Democratic Republic of Congo suggest major losses of apes there as well (Science, 31 March 2000, p. 2386). In Congo and Gabon, international wildlife disease experts have suspected that Ebola caused some die-offs since 1994, although firm data have been lacking, says William Karesh of the Wildlife Conservation Society in New York City. “It looks more serious than people had been thinking,” says anthropologist Alexander Harcourt of the University of California, Davis.

The Walsh-led team urges that the status of lowland gorillas and chimps be upgraded from endangered to critically endangered. The Nature authors argue that the only near-term means of stemming bushmeat hunting is “massive investment” in law enforcement in parks. Battling the Ebola epidemic is less straightforward, partly because experts disagree about what's driving it. Some believe that logging is sparking outbreaks by disturbing the apes' habitat and putting them in closer contact with the as-yet-unknown Ebola reservoir—which could be bats, mice, or birds. If so, there might be little scientists can do except monitor.

Others, including Walsh, suspect that the sporadic human outbreaks in the 1990s resulted from a single, spreading epidemic transmitted ape to ape, as well as via other species. If so, Walsh thinks an experimental Ebola vaccine that has been shown to work on monkeys could help stem the epidemic in apes. But Ebola vaccine researcher Gary Nabel of the National Institutes of Health in Bethesda, Maryland, cautions that the vaccine could not be used on wild apes without more evidence that it would work, which could take 1 to 2 years.

Conservation groups, scientists, and African officials met in Brazzaville, Congo, in March to discuss options and appeal to donors; they plan to meet again in May in Washington, D.C. Any action plan will first have to gain villagers' trust, Karesh says. Partly because of Ebola and the resulting social breakdown, unrest is high in Congo; vehicles are frequently attacked, and doctors investigating an Ebola outbreak were turned away from one village last year. Says Karesh: “It's just this downward spiral.”

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