Ebola Threatens to Kill Off Gorillas in Africa

The Ebola virus has killed from 3,500 to 5,500 gorillas in one region of the Congo Republic since 2002, and its continued spread, along with hunting, could wipe out the species, researchers are reporting today.

Ebola Threatens to Kill Off Gorillas in Africa

The Ebola virus has killed from 3,500 to 5,500 gorillas in one region of the Congo Republic since 2002, and its continued spread, along with hunting, could wipe out the species, researchers are reporting today.

“A lot of animals are dying,” said Dr. Peter D. Walsh, an ecologist at the Max Planck Institute for evolutionary primatology in Leipzig, and an author of a report being published today in the journal Science. “There’s a massive decline.”

Several vaccines have been developed that work in animals in the lab, including monkeys, and Dr. Walsh is eager to test them on gorillas in the wild by injecting the animals with darts or putting an oral vaccine in food. By tracking the spread of the virus and vaccinating animals in its path, it might be possible to stop outbreaks, he said.

Other researchers say that although vaccination might be feasible, it is not known whether the vaccine could made into a heat-stable version or an oral form. In addition, there would be miles of red tape to cut through, involving various conservation groups, donors and governments.

Dr. Stuart Nichol, chief of molecular biology in the Special Pathogens Branch of the Centers for Disease Control and Prevention, said: “It’s really going to be a nightmare to try to press forward with some kind of vaccine approach. On the other hand, it doesn’t feel good to sit back and do nothing. But in reality it’s going to be exceedingly difficult to do anything.”

The authors of the report have been studying western gorillas — a distinct species from eastern gorillas — since 1995 in the Lossi Sanctuary in the northwestern Congo Republic, near Gabon. In 2002, following human disease outbreaks caused by the Zaire strain of the Ebola virus, the researchers began finding dead gorillas. Over a number of months they found 33, tested 12 for Ebola and found that 9 were infected. And from October 2002 to January 2003, 130 of the 143 gorillas they had been studying — 91 percent — simply disappeared. The losses continued: 91 of 95 gorillas the researchers were watching died from October 2003 to January 2004.

In the past, other researchers have questioned whether Ebola was really killing so many gorillas, since relatively few carcasses had been tested. Dr. Nichol said he would like to see more testing, but at the same time said he believed the group’s findings and acknowledged that obtaining samples is difficult and dangerous work.

The region is a dense jungle, male gorillas attack humans who venture too close, and diseased carcasses are teeming with the virus and highly infectious. To collect samples, even in the steamy heat, scientists have to wear germ-proof “space suits” that cover them from head to toe and filter the air they breathe.

Although gorillas are hunted for meat, even in preserves where it is illegal, the authors say there is nowhere near enough hunting in the region they studied to account for so many missing animals. They estimate that 2002 to 2005, Ebola has killed 3,500 to 5,500 gorillas in a region of about 2,000 square miles; they say that estimate is a conservative one.

Apes are humans’ closest relatives, and like people they suffer a brutal illness from Ebola and die from hemorrhage and shock. Precisely how gorillas contract the disease is a mystery. Scientists assume they must catch it somehow from another animal that acts as a natural reservoir host and carries the virus without being harmed by it. Fruit-eating bats are suspected, but none has been confirmed as the reservoir, Dr. Nichol said.

Whatever the host, it could infect western gorillas by defecating on their food, which is mostly fruit. The gorillas could then infect one another, both inside their own social groups and between groups. The virus is spread by bodily fluids and by touching sick or dead animals. Dr. Walsh said that gorillas commonly eat one another’s dung, which could also transmit the virus.

Scientists have debated about whether gorillas’ infecting each other plays much of a role in spreading the disease, or whether the reservoir host is really the main culprit. The new report says the gorillas themselves do play an important part: it shows that the spread of the disease and the timing of outbreaks match the pattern that would occur if the animals were infecting one another, both within and between groups.

If the gorillas are indeed infecting each other, the path of the disease will be fairly predictable, and vaccination might be able to stop it, Dr. Walsh said. (A vaccine would be less likely to succeed if most of the cases were coming from reservoir hosts, because the pattern would be more random and unpredictable.)

The Ebola virus alone is not likely to drive gorillas to extinction, Dr. Walsh said.

“All the major parks have serious hunting and poaching problems,” he said. “It’s a slippery slope. Ebola is pushing the gorillas onto it, and other factors are pushing them down it.”

His goal is to keep the gorilla populations large enough to withstand all the other assaults on them, and stopping Ebola would be a big step in the right direction, he said.