Human Viruses Jumping to Wild Apes

Anne Casselman
for National Geographic News
February 4, 2008
Scientists who study endangered great apes in Africa may be a mixed blessing—while they may scare off poachers, people also carry with them dangerous diseases, a new study says.

The research found that recent respiratory disease outbreaks among chimpanzee and gorilla populations come from great-ape researchers and ecotourists.

But at the same time human presence deters poachers, acting as a boon to population numbers.

"This shows, in our opinion, that we have a stronger positive effect than ... a negative effect," said senior study author Fabian Leendertz, a wildlife epidemiologist at Robert Koch-Institut in Berlin, Germany.

Between 1999 and 2006 three chimpanzee study groups in Taï National Park in Côte d'Ivoire (Ivory Coast) suffered a total of five outbreaks of respiratory disease. Nearly all of the chimpanzees showed symptoms of illness, and many of them died.

Genetic analysis of the virus cultures collected from the dead chimpanzees revealed that the pathogens were human. "We were a bit shocked because this was the first time that it was ever really proven that an acute disease-causing pathogen has jumped from us to the great apes and caused damage there," Leendertz said.

Tony Goldberg, a veterinarian and disease ecologist at the University of Illinois at Urbana-Champaign, was not involved in the research.

"We've known for a long time that wild apes have suffered epidemics of respiratory disease," he said.

"And for a long time people have suspected that human respiratory viruses were the culprit—but we've never had the smoking gun evidence until now."

The study appeared in a recent issue of the journal Current Biology.

Contamination Area

Viruses found in the apes are associated with respiratory disease in human infants and children. As people grow older and develop immunity, they tend to be less and less affected, spreading them as easily as the common cold without any visible symptoms.

(Learn more about human diseases.)

"You could have a tourist or researcher who feels absolutely no symptoms at all but is carrying one of these viruses," Goldberg said.

Because there's no telling who could be infectious, study author Leendertz now considers the great-ape research camp a "contaminated area."

To stem the transmission, members of his research team have started to wear masks, which reduce the spread of virus-laden particles.

They also have disinfection baths for boots and clothes at the edges of the camp, and researchers make sure to wear different garments and footwear within the camp.

Apes can also transmit diseases to people. In recent years outbreaks of the Ebola virus—a severe, often-fatal hemorraghic fever—have arisen in Africa, most likely sparked when a person contacted an infected ape. And the origin of the HIV virus has been traced to a group of chimpanzees in Cameroon.

The Big Virus Swap

"It's a tricky issue, because ... we love them, we study them, we know all of them by name, but at the same time we bring a big danger to them," Leendertz said.

While researchers and tourists may be eager to adopt hygiene measures, the people who live in the vicinity of great apes may still be exposing the animals to viruses.

Many chimpanzees and gorillas breach the forest boundary every so often and enter human settlements.

"Contrary to what people tend to generally think, these apes are actually sharing habitats with people," Goldberg said.

Some experts advocate focusing on health care for people who live at national park borders.

"The idea [is], if you can improve their public health, you indirectly improve the health and conservation of the primates," Goldberg added.

New Form of Pollution?

This is not the first time that our germs have damaged ecosystems.

In one case gorillas died from scabies-mite infections, most probably contracted by handling human clothing, Goldberg said.

In 1994 in Serengeti National Park, 1,000 of 3,500 lions died of canine distemper, which they contracted from wild dogs. Humans were indirectly the culprit, since their domestic dogs helped spread the disease.

(Related news: "Wild Dog Urine May Be Used as "Fences" in Africa" [March 11, 2004].)

In addition Asian elephant populations of Nepal are suffering as their numbers dwindle from human tuberculosis.

"We are in the situation where space can be a bit limited and we are moving closer and closer together," Leendertz said.

"These remote habits are not so remote anymore."

Free Email News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).


© 1996-2008 National Geographic Society. All rights reserved.