Ecological dynamics of Bacillus Anthracis in water and soils at selected sites in Etosha National Park, Namibia

Loading...
Thumbnail Image
Date
2021
Journal Title
Journal ISSN
Volume Title
Publisher
University of Namibia
Abstract
Bacillus anthracis, is an endospore-forming, soil borne bacterium, also found in water and vegetation, which causes the disease anthrax. The species most affected by anthrax in Etosha National Park are the plains zebra (Equus quagga), blue wildebeest (Connochaetes taurinus), springbok (Antidorcas marsupialis) and African elephant (Loxodonta africana) Anthrax occurs seasonally with a peak incidence during the late wet season in the plains zebra (Equus quagga), blue wildebeest (Connochaetes taurinus), springbok (Antidorcas marsupialis), and during the late dry and early wet seasons in the African elephant (Loxodonta africana). Anthrax is generally assumed to be transmitted through grazing. An experimental study was conducted in the laboratory at the Etosha Ecological Institute to investigate the behaviour of an avirulent B. anthracis strain. Jars filled with water and soil were inoculated with blood containing avirulent anthrax spores and subjected to repeated settling and disturbance. One jar with no soil but only water served as a control. The aim of the experiment was to determine whether most of the anthrax spores remained in the water or attached to the soil particles. The study further investigated how B. anthracis behaves in the soil through an outdoor enclosure experiment in which thimbles were filled with three soil types, namely, ferralic arenosol, calcaric regosol and lithic leptosol. Soils were inoculated with blood containing virulent anthrax spores and water. The aim of the experiment was to determine deep transport of B. anthracis in the three soils. Sampling was done over four weeks, with the thimbles being tested for the presence of B. anthracis every centimeter (1-12cm). In both experiments, a selective media polymyxin-lysozyme-EDTA-thallous acetate (PLET) agar was used to isolate B. anthracis from the water and soil samples in this study. This study revealed that there was a significant difference in the colony counts of B. anthracis sampled from the different layers in the water jar (χ2= 54.244, df =4, p <0.05). Most of the anthrax spores were attached to the finer sediments of the soil and not in the suspension of the disturbed samples as hypothesized. Fewer B. anthracis spores were found at the surface of the water, which suggests that animals are unlikely to ingest a lethal dose of B. anthracis to cause an infection which may in turn lead to death. Furthermore, the outdoor experiment revealed that significantly higher numbers of B. anthracis spores were transported further down in the sandy ferralic arenosol throughout the study period compared to the other two soils. It is concluded that the likelihood of animals contracting anthrax from sandy soil is low.
Description
A thesis submitted in fulfillment of the requirements for the Degree of Master of Science
Keywords
Bacillus anthracis, Anthrax, Etosha National Park, Spore transport, Soil type
Citation