Ecological suitability modeling for anthrax in the Kruger National Park, South Africa.

Pieter Johan Steenkamp,Henriette Van Heerden,Ockert Louis Van Schalkwyk,Raymond Schuch

doi:10.1371/journal.pone.0191704

Pieter Johan Steenkamp, Henriette Van Heerden + Show 2 more

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https://doi.org/10.1371/journal.pone.0191704

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Abstract

The spores of the soil-borne bacterium, Bacillus anthracis, which causes anthrax are highly resistant to adverse environmental conditions. Under ideal conditions, anthrax spores can survive for many years in the soil. Anthrax is known to be endemic in the northern part of Kruger National Park (KNP) in South Africa (SA), with occasional epidemics spreading southward. The aim of this study was to identify and map areas that are ecologically suitable for the harboring of B. anthracis spores within the KNP. Anthrax surveillance data and selected environmental variables were used as inputs to the maximum entropy (Maxent) species distribution modeling method. Anthrax positive carcasses from 1988–2011 in KNP (n = 597) and a total of 40 environmental variables were used to predict and evaluate their relative contribution to suitability for anthrax occurrence in KNP. The environmental variables that contributed the most to the occurrence of anthrax were soil type, normalized difference vegetation index (NDVI) and precipitation. Apart from the endemic Pafuri region, several other areas within KNP were classified as ecologically suitable. The outputs of this study could guide future surveillance efforts to focus on predicted suitable areas for anthrax, since the KNP currently uses passive surveillance to detect anthrax outbreaks.

Highlights

Anthrax is a rapidly fatal disease caused by the spore-forming bacterium B. anthracis
This study presents the first estimate of ecologically suitable areas for anthrax spore survival in the Kruger National Park (KNP) in South Africa
These ecologically suitable areas for the harboring of B. anthracis spores within the soil was identified using anthrax occurrence data, a range of environmental predictors and maximum entropy modeling

Summary

Introduction

Anthrax is a rapidly fatal disease caused by the spore-forming bacterium B. anthracis. Multiple host and environmental factors are thought to play a role in the transmission of anthrax. Little is known about the spatial ecology and epidemiology of anthrax [1]. The general thought is that B. anthracis is an obligate in vivo pathogen and that little propagation occurs in soil. Septicaemic infection with anthrax causes impaired clotting function [2]. When an animal succumbs to anthrax, the host’s impaired clotting ability results in blood draining into the soil from any orifice. If the environmental conditions are suitable, the bacterium will rapidly form spores once outside the host. Depending on the environmental conditions, these spores can survive for decades in the soil until infection of a suitable host takes place.

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