It seems that a previously benign cousin of deadly anthrax may have stolen some of its fatal tricks, and could be threatening the survival of West African chimpanzees in the process. Researchers have discovered that the bacteria, which usually lives in the soil, may now be a major pathogen to rainforest mammals and play a significant role in their ecology.

When we think of anthrax, we tend to imagine its use as a deadly biological weapon. But the bacteria is found naturally occurring in many parts of the world, and will often seasonally flare up in grassland environments, mainly killing the grazing ungulates. This is why the emergence of an anthrax–like pathogen in the rainforests of the Côte d'Ivoire – as opposed to the savanna – caught the attention of scientists.

At the chimpanzee research station in the Taï Forest, scientists have been able to collect samples of 204 chimpanzee carcasses, as well as the bones from 75 mammals that also lived in the forest. They found that an astonishingly high 40 percent of all mammals sampled that died in the rainforest were infected with the bacteria Bacillus cereus.

This microorganism is the cousin of Bacillus anthracis, the bacteria more commonly associated with anthrax, but until now it was thought to be a fairly anonymous organism that could occasionally cause food poisoning in people. It now seems, however, that B. cereus has pilfered some of the sections of DNA (known as plasmids) from B. anthracis that causes anthrax.

When the bacteria switched from being benign to deadly is not known, but the genetic diversity seen within B. cereus suggests that it may have happened a while ago. What is known, however, is that it may play a major role in rainforest ecology, and could be a serious threat to the region's mammals. The researchers found that the bacteria was not only limited to ungulates but a whole host of species, from chimps and monkeys to porcupines and duikers.

In fact, so virulent is this new strain of anthrax that, in their new paper in Nature, the scientists predict it could even lead to the entire population of Taï Forest chimpanzees being wiped out within 150 years.

The next challenge is to find out how the bacteria is being spread. One theory is that carrion flies may be transporting the microorganism from animal to animal. The researchers found traces of B. cereus DNA on 17 flies, which would explain how species of monkey that spend their lives in the canopy have been infected, but cannot conclusively blame the insects.

The other burning question is how does it affect people? No one quite seems to know, yet.