Modeling the spatial distribution of anthrax in southern Kenya

Abstract

Background Anthrax is an important zoonotic disease in Kenya associated with high animal and public health burden and widespread socio-economic impacts. The disease occurs in sporadic outbreaks that involve livestock, wildlife, and humans, but knowledge on factors that affect the geographic distribution of these outbreaks is limited, challenging public health intervention planning. Methods Anthrax surveillance data reported in southern Kenya from 2011 to 2017 were modeled using a boosted regression trees (BRT) framework. An ensemble of 100 BRT experiments was developed using a variable set of 18 environmental covariates and 69 unique anthrax locations. Model performance was evaluated using AUC (area under the curve) ROC (receiver operating characteristics) curves. Results Cattle density, rainfall of wettest month, soil clay content, soil pH, soil organic carbon, length of longest dry season, vegetation index, temperature seasonality, in order, were identified as key variables for predicting environmental suitability for anthrax in the region. BRTs performed well with a mean AUC of 0.8. Areas highly suitable for anthrax were predicted predominantly in the southwestern region around the shared Kenya-Tanzania border and a belt through the regions and highlands in central Kenya. These suitable regions extend westwards to cover large areas in western highlands and the western regions around Lake Victoria and bordering Uganda. The entire eastern and lower-eastern regions towards the coastal region were predicted to have lower suitability for anthrax. Conclusion These modeling efforts identified areas of anthrax suitability across southern Kenya, including high and medium agricultural potential regions and wildlife parks, important for tourism and foreign exchange. These predictions are useful for policy makers in designing targeted surveillance and/or control interventions in Kenya. We thank the staff of Directorate of Veterinary Services under the Ministry of Agriculture, Livestock and Fisheries, for collecting and providing the anthrax historical occurrence data.

Modelling the ecological niche of naturally occurring anthrax at global and circumpolar extents using an ensemble modelling framework

“…The potential disease transmission risk to livestock (cattle, goats, sheep) globally is presented in Figure 6 content, geological features and temperature (Dragon & Rennie, 1995;Kracalik et al, 2017;Otieno et al, 2021;Walsh et al, 2018;WHO, 2008).…”

Participatory mapping identifies risk areas and environmental predictors of endemic anthrax in rural Africa

“…While CEC, pH and slope were not clearly associated with the probability of points falling in high-risk areas, based on previous studies, these factors are likely to contribute to anthrax risk in certain environments by facilitating spore persistence. Higher soil calcium levels and alkaline pH have been previously associated with high-risk areas in larger geographical locations in Tanzania 20 , 48 and elsewhere 43 , 44 , 49 . Steenkamp et al .…”

“…Previous studies have found soils with high organic content to be associated with anthrax spore persistence 19 , 43 , 44 . SOC is usually determined by a combination of organic matter from plant and animal tissue residues and microbial biomass 45 .…”

Modeling the Potential Future Distribution of Anthrax Outbreaks under Multiple Climate Change Scenarios for Kenya

“…Areas of endemic anthrax can be broadly characterized by seasonal rainfall and dry periods [8,9], with pathogen persistence associated with higher pH and more organic soil conditions and topography [1,2,10,11]. A recent ecological niche modelling study estimated areas with environmental conditions suitable for anthrax outbreaks cover 22% of Kenya's landmass [12]. Livestock and wildlife outbreaks are frequent with varying intensity and host composition throughout Southern Kenya [13,14].…”

“…Specifically, BRT modeling has also been previously applied in predicting infectious diseases' distributions under climate change scenarios [46,47]. A study [12], utilized BRT to predict the current day distribution of anthrax on southern Kenya's landscape showing higher probabilities of occurrence between the western highlands and the shared Kenya-Tanzania border. Expanding their study to consider future climates is imperative to identify potential expansions or contractions of the geographic distribution of anthrax outbreaks in Kenya.…”