A study of the ecology of anthrax in the Kruger National Park, South Africa

Abstract

The ecology of anthrax in the Kruger National Park (KNP) in South Africa is described. Endemic anthrax occurs in the northern-most region of the KNP with sporadic cases seen almost annually. In addition, regular periodic epidemic outbreaks occur in the northern half of the KNP with inter-epidemic periods of between 10 and 30 years. These outbreaks were studied over a period of roughly 40 years, providing ideal opportunities to evaluate anthrax in an essentially natural setting with minimal interference by man. Several complex and interrelated patterns of disease occurrence and determinants were identified and described. Anthrax appears to be unique in the sense that it is the only disease within the KNP, or possibly world-wide, that needs to kill its host in order to propagate. It has however adapted to the KNP ecosystem in being density dependent and self-limiting, leaving in its wake viable young populations of animals. Anthrax should therefore be viewed in terms of its effect on the population and ecosystem rather than on the individual, where the death of individuals may actually be of benefit to the populations and ecosystem. It was therefore seen as an ideal natural population regulatory mechanism in a natural setting such as the KNP, having also a predilection towards older animals, leaving behind a younger population. However, in a totally fenced-in setting like the KNP, it may be subjected to ‘unnatural’ outside effects such as fences, fires and unnatural pressure on water, which may place certain marginal and highly vulnerable species such as roan antelope at risk. This has led to a situation of minimal control procedures of anthrax in the KNP. It is argued that this very complex and interrelated epidemiological web of causation and the evidence of a possible mutually beneficial relationship between the agent, host populations and KNP ecosystem, could only have developed as a result of co-evolution, which indicates that anthrax is indigenous to Africa and endemic to the KNP and southern Africa. Therefore the word ‘ecology’ is used in preference to ‘epidemiology’ to describe the effects of Bacilius antracis on a near-natural system such as the KNP