BioEd Online

Anthrax has killed at least six wild chimpanzees in the tropical rainforest of the Ivory Coast - the first time the disease has been seen in these animals and in this type of habitat. As well as threatening great ape populations, the discovery raises fears that the disease could spread to humans through the illegal trade in bushmeat.

Researchers studying chimps (Pan troglodytes verus) in the Taï National Park saw 8 animals disappear or die suddenly between October 2001 and June 2002. Healthy animals became weak, vomited and died within a few hours of symptoms appearing.

Post mortems revealed that the animals suffered massive internal bleeding, suggesting bacterial infection as a possible cause. Genetic analysis of 6 animals showed Bacillus anthracis, the bacterium that causes anthrax, to be the culprit. The results are reported in this week's Nature¹.

"Finding anthrax was a big surprise," says Georg Pauli from the Robert Koch Institute in Berlin, Germany, who studied the primates. There have been no previous reports of anthrax in wild chimps, and the bacterium, which also infects humans and hooved animals, has not been found in Africa's tropical rainforests before.

Spread of infection

"It's a serious problem for chimps," says conservationist Peter Walsh from Princeton University, New Jersey. Africa's 100,000 to 200,000 remaining wild chimps are already under threat from commercial hunting, habitat destruction and the Ebola virus. It is not clear whether the anthrax outbreak is a one-off, or if there are likely to be further incidents.

The disease could also spread to humans. The bacterium forms hardy spores that can be breathed in, consumed in contaminated food and water, or can infect the skin through human-to-animal contact.

Although illegal, the bushmeat trade continues to thrive, so hunters could catch anthrax when handling infected corpses.

Passing livestock

It is unclear how the chimps became infected, making it hard for officials to instigate prevention and containment strategies.

One possibility is that the disease was imported from neighbouring countries, where anthrax is endemic. Deforestation means that cattle transport routes from Mali and Burkina Faso now pass close to the Taï National Park border, so the chimps may have caught the disease from passing livestock. "This is a reasonable suspicion," says Walsh.

Other suggestions are less likely, but still possible. The chimps may have ingested spores from contaminated water. But drinking sources are shared by many species, and no other animals have so far been diagnosed with the infection.

Or the chimps may have dined on contaminated antelope. But anthrax has never been confirmed in Ivory Coast antelope, and chimps have never been seen eating the animals.

Our lack of knowledge highlights the need for improved health surveillance of wild chimps, says Pauli. In response to the anthrax finding, he is helping to establish a survey to assess the disease status of the world's great apes.