Ecological niche modeling of geographic distribution of Bacillus anthracis and risk of Anthrax disease in Africa

Anthrax is one of the seven major neglected zoonotic diseases in Africa. The disease is responsible for enormous economic losses as well as considerable human morbidity, especially in endemic areas. Despite this, the ecology and distribution of the causative agent, Bacillus anthracis, is poorly understood. At the continent level, there is glaring paucity of knowledge on the potential environments conducive for spore survival and subsequent disease outbreaks. We modeled the ecological niche of B. anthracis and risk of Anthrax using Maximum Entropy (MaxEnt), Bioclimatic analysis and prediction system (BIOCLIM) and a genetic algorithm (GARP). Model inputs included climatic (temperature and rainfall), topographic (slope and aspect) and records of Anthrax outbreaks in Africa. The three model performances were better than random expectations, statistically significant (p < 0.05), and with ROC/ AUC scores ranging from 71.8% (BIOCLIM) to 88.1% (GARP). The predicted total land area of highly suitable environments ranged from 5.713 million(18.9%) to 20.044 million Km2 (66.3%). Qualitative assessments of historical records of Anthrax outbreaks across Africa confirm model predictions. Conducive environments for the sporulation and viability of B. anthracis corresponded to a range of temperature, precipitation and topographic regimes in the semi-arid, sub-humid and dry to moist subtropical mid-latitude conditions in eastern and southern Africa. West and Central Africa, and the extreme North Africa presented marginal, while the much of the Sahel and Congo basin were predicted to be of low suitability. Results of the three models indicated extensive spatial suitability for B. anthracis and high risk of Anthrax in Africa. Given the current status of Anthrax in Africa (neglected zoonosis), our results should be important in efforts geared at prevention or eradication of the disease. Our findings will also aid in anticipating outbreaks and differentiating endemic/natural outbreaks from other forms outbreaks.