Influence Of Site And Soil Type On The Distribution Of Anthrax Infectious Sites And The Contribution Of Anthrax To Elephant Mortality In Etosha National Park, Namibia

ABSTRACT

Bacillus anthracis, a soil-borne pathogen, causes the deadly zoonotic disease anthrax. Anthrax outbreaks occur frequently in Etosha National Park (ENP). ENP has nine major soil types and a distinct rainfall gradient decreasing from east to west. The sporulation success of B. anthracis is believed to be influenced by soil type, but the influence of soil type and site along a rainfall gradient on the persistence of B. anthracis in the soil is unknown. The present study investigated the influence of site along the rainfall gradient and soil type on the persistence of B. anthracis in three soil types, ferralic arenosols, calcaric regosols, and haplic arenosols. To determine the effect of soil type and site on the persistence of B. anthracis, a reciprocal transplant experiment was conducted at three experimental sites across ENP following the rainfall gradient in which soil cores were spiked with a virulent B. anthracis strain. Sampling was done over 12 months to determine the persistence of the bacilli over time. Soil from elephant (Loxodonta africana) carcass sites were also collected and tested for the presence of B. anthracis. A selective media called polymyxin-lysozyme-EDTA-thallous acetate (PLET) agar was used to isolate B. anthracis from the soil. This study revealed that site did not have a significant effect on B. anthracis cell counts. However, soil type had a significant effect on B. anthracis cell counts. The sandy ferralic and haplic arenosols of the east and west that had the lowest soil moisture content were found to have a significantly greater influence on the persistence of the bacterium compared to the calcaric regosols of central ENP. The sandy soils may, therefore, serve as endemic areas of anthrax infection in ENP. This study further revealed that anthrax did not contribute significantly to elephant mortality in ENP.