Environmental and socio-economic predictors of anthrax spatial distribution in Kenya

Abstract

Anthrax spatial distributions and the potential driving factors remain poorly understood worldwide and in Kenya. This study aimed at establishing environmental and social economic predictors of the spatial distribution of anthrax in Kenya through (1) determining the relationship between selected environmental and socio-economic factors on spatial distribution of anthrax through use of an ecological niche modelling framework; (2) predicting the effect of climate change on the future spatial distribution of anthrax; and (3) establishing the influence of socio-economic factors in vulnerability to anthrax. Ecological Niche Model (ENM) of boosted regression trees (BRT) algorithm was applied to predict the suitable spatial environments for anthrax under current and future climate scenarios in Kenya. The model fitted confirmed anthrax occurrences from three distinct sources of retrospective records (2011 to 2017), sporadic anthrax outbreaks (2017 to 2018) and active surveillance (2019 to 2020) against selected predictor variables to yield current and future anthrax risk maps. Finally, the underlying socio-economic vulnerability due to the risks of anthrax distribution was assessed by laying over socio-economic indicators in spatial multicriteria decision analysis to produce socio-economic vulnerability maps. The high-risk areas for anthrax outbreaks were identified predominantly in: regions around western Kenya bordering Uganda; southwestern regions bordering Tanzania and regions around central highlands of Kenya. Based on the current scenario, the number of humans affected was estimated at ~ 193,00,840 people/sq.km while that of livestock was at ~7,750,675 animals / sq.km. The important contributing predictor variables were predominantly cattle density, rain of the wettest month, monthly precipitations, soil clay, soil pH, soil carbon, longest dry season and temperature range. The anthrax highly suitable areas expanded from current to future climatic scenarios with current at 36131 km2, RCP 4.5, 40012 km2, and RCP 8.5, 39835 km2. Highly socio-economic vulnerable areas closely correlated with areas of high anthrax risk currently and into the future. At current vulnerability index > 75%, approximately 40,369,455 people were estimated to be at risk. This study results will guide risk-based surveillance and strategies for managing anthrax under One Health approach and also contributes to future research studies within Kenya and beyond.