Anthrax is responsible for the death of a wide range of mammalian species in a tropical rainforest according to a study published in Nature this week. Demographic models suggest that anthrax may accelerate the decline of chimpanzee populations in Tai National Park, Ivory Coast, and could result in their extinction from the park.
Anthrax is most commonly associated with arid ecosystems, such as African savannahs. However, in 2001, lethal anthrax-like cases in wild chimpanzees were reported in a rainforest habitat: Tai National Park. The causative agent was identified as Bacillus cereus biovar anthracis (Bcbva). However, the epidemiology of the anthrax-like disease caused by Bcbva, and to what extent it matches that of classical anthrax, has been unclear.
Fabien Leendertz and colleagues collected samples of Bcbva from the bones and carcasses of mammals, and from flies over the course of 26 years in Tai National Park. From this, the authors were able to generate 178 whole-genome sequences of Bcbva spanning 1996-2014. The levels of genetic diversity observed, when compared with isolates from other countries, suggests that the pathogen may have been circulating in sub-Saharan Africa for a longer period than that determined for Tai National Park in this study. The authors found that 38% of observed local wildlife mortalities were associated with Bcbva, comparable to the highest levels of mortality reported for classical anthrax outbreaks in savannah ecosystems. Unlike savannah ecosystems, where ungulates constitute the vast majority of anthrax cases, the authors observed Bcbva fatalities in a broader range of species in the park, including chimpanzees, six monkey species, duikers, mongooses and porcupines.