Dust Bathing Behaviours Of Elephants, Zebras And Wildebeest And The Potential Risk Of Inhalational Anthrax In Etosha National Park

ABSTRACT

Bacillus anthracis is a soil-borne bacterium and the causative agent of the disease anthrax which commonly infects herbivorous animals. The disease is transmitted via three routes of infection: ingestion, cutaneous or inhalation of spores. This study investigated the seasonality of dust bathing as a possible contributor to inhalational anthrax in zebra, blue wildebeest and African elephants, in relation to the seasonality of anthrax mortalities in Etosha National Park. Most anthrax cases are observed during the wet season, although elephant anthrax mortalities occur primarily during the dry season. The study was conducted from May 2013 to July 2014 focusing on the three herbivorous host species that dust bathe (African elephants, Loxodonda africana; plains zebra, Equus quagga; and blue wildebeest, Connochaetes taurinus). The objective was to determine the dust bathing behavioural patterns (seasonality and age and sex of individuals) and to correlate that with anthrax cases in the park to assess whether the three study species may be at risk of inhalational anthrax through dust bathing. Motion triggered cameras were positioned at dust bathing sites of zebras and wildebeest, while elephants dust bathing behaviour was studied through observations at four selected waterholes. Given that mud bathing is also a potential means of soil contact by elephants their mud bathing behaviours were included in the study. Polymysin-lysozyme-EDTA-thallous acetae (PLET) agar was used to grow and quantify B. anthracis spores concentration from surface soil at dust bathing sites. The findings showed that zebra dust bathed significantly more in the dry seasons than in the wet season. There was no significant difference among the seasons in dust iii bathing by wildebeest. Elephant dust bathing behaviours showed no relationship with maximum daily temperature. Mud bathing on the other hand increased with temperature, However the intensity of both mud and dust bathing by African elephants did not increase as temperature increased. To investigate whether dust bathing contributes to inhalational anthrax, 83 dust bathing soils were screened for B. anthracis only 2 were found positive with low concentrations of 20 and 10 spores/g. Firstly as a result of poor relationship between the seasonality of dust bathing and the timing of anthrax mortalities, secondly the low to no spore counts of B. anthracis in dust bath sites and, thirdly the finding that carcass sites are unlikely to become future dust bathing locations, it is unlikely for dust bathing behaviours to serve as an important risk for inhalational anthrax for herbivores in Etosha National Park.