The bacterial disease anthrax is a key cause of animal mortality in a West African tropical forest, according to a study reported by Hoffmann et al. on page 82. The researchers examined the cause of mammal deaths at rainforest sites across eleven African countries over three decades (C. Hoffmann et al. Nature 548, 82–86; 2017).

Credit: Michael Nichols/NGC/Getty

Anthrax can kill wildlife, livestock and humans, and is known to be a particular problem in arid African ecosystems. In 2001, lethal anthrax cases were reported in wild chimpanzee (Pan troglodytes verus) populations in the rainforest of Taï National Park in Côte d'Ivoire (F. H. Leendertz et al. Nature 430, 451–452; 2004). But the extent to which the disease affects rainforest inhabitants has been unclear.

Between 1989 and 2014, Hoffmann and colleagues searched for signs of anthrax in the carcasses of a wide range of mammals, and monitored the distribution of the anthrax-causing bacterium in animal bones and carrion flies, a source of mammalian DNA. They found that anthrax caused 38% of the wildlife mortality observed over this period, and affected a broader range of mammals than in arid ecosystems, such as chimps, monkeys, mongooses and porcupines.

The authors' modelling of chimp populations in the region (pictured: a chimp in Taï National Park) suggests that anthrax will probably reduce the size of these populations, potentially resulting in their loss from this part of Africa, over the next 150 years. This is a risk that is only set to increase if chimp mortality from hunting and human-borne diseases continues to rise.Footnote 1