Environmental Factors Influencing Anthrax Distribution in an East African Protected Area

Abstract

Anthrax outbreaks caused by the soil-borne bacterium Bacillus anthracis have been known to occur often in Africa, impacting both wildlife and livestock and occasionally infecting humans. Modelling the current distribution and predicting suitable habitats for this bacteria species is therefore critical for supporting effective planning and control measures for anthrax outbreaks. Despite its impact, the knowledge on the ecology of this pathogen is still limited. This can be due to intricate interactions between anthropogenic and environmental factors and the variety of species it affects. Therefore, detailed, site-specific analyses are essential for contributing to the understanding of the ecology of anthrax. This study used the maximum entropy modelling algorithm (MaxEnt) method to predict suitable habitat and environmental conditions that may support anthrax distribution and spore survival in Tarangire National Park, in Tanzania. Model inputs included 14 predictors from World Climatic, Landsat satellite, and World Soil Information datasets, as well as 636 presence-only occurrence data from park records from 2013 to 2023. The predicted suitable area favouring anthrax spores encompassed most of the savannah and open grassland in the northern part of the park, as well as narrow patches in the park's central region. The mean test AUC score was 0.91, and the predicted probability was 0.98 for anthrax presence. On average, the predicted probability of suitable conditions substantially improved with increasing levels of extractable phosphorus, exchangeable potassium, mean annual temperature, and soil pH. Furthermore, the probability of suitable habitat was highest at lower levels of fire frequency, exchangeable sodium, and extractable aluminium. The extensive track record of anthrax outbreaks in the area may be explained by the presence of these favourable soil characteristics and climate, which point to the long-term occurrence of anthrax spores in the park. However, the existence of suitable habitat in the northern part of the park presents opportunities for mobilising resources to mitigate the situation through activities such as targeted disease surveillance and the use of controlled fire.