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Anthrax, one of the Neglected Zoonotic Diseases, still remains a major cause of high mortalities in humans and animals in developing countries. The disease is endemic in southern Africa in domestic animals and wildlife and occurs regularly in the Etosha National Park (ENP) in Namibia. This dissertation presents results of a molecular-epidemiological study using genotyping methods such as SNP-Analysis, MLVA 31 Marker and SNR-Analysis to determine the diversity of B. anthracis strains present in Namibia. Based on a total of 44 Namibian genotypes (GTs) ArcGIS was used for the cartography of isolates and the spatial, temporal and spatio-temporal cluster analysis for the GTs found in ENP. A statistical approach was used to compare results with previous studies carried out in other National Parks.
The goal of this dissertation was to show the advantages of molecular fingerprinting methods over routine bacteriology of B. anthracis as well as their use in establishing disease patterns. Sample material included historic and recent carcass swabs of wild and domestic animals originating from Namibia as well as soil samples obtained from different habitats within ENP.
SNP-analysis revealed four distinct phylogenetic groups that imply four different entries of B. anthracis strains into Namibia (Beyer et al., 2012). Analysis of 525 isolates using MLVA 31 Marker determined that 44 distinct GTs are found in Namibia, of which 24 have been shown to be exclusively present in ENP. Moreover, 268 isolates of five selected GTs for SNR analysis represent a total of 53 SNR-types.
It is further eminent that certain B. anthracis GTs predominantly did affect selected species such as zebra and springbok and specific regions within the Park. Spatial and species-specific distribution of GTs was attributed to certain migration patterns of wildlife species such as zebra and elephants in the ENP and showed correlation with specific soil types and vegetation zones. Comparisons of the cluster of diagnostic findings of B. anthracis with GTs did, contrary to expectation, show a much smaller cluster for the most dominant GT (53% of ENP isolates) than the second most dominant (22% of ENP-isolates). GT clustering failed to reveal disease pattern not already apparent from clustering of findings of conventional diagnostics. Beyer et al. (2012) postulated Anthrax outbreaks in ENP as recurrent or ongoing events lasting for different time periods.
While the predominant number of historic cases in wildlife species in ENP was reported for the rainy season, continuous surveillance during rainy and dry season in ENP did not show significant seasonal variation in disease cases.
Results previously obtained by Lindeque (1991) regarding the seasonal increase of Anthrax cases could only be confirmed partially.
Studies of the fate of B. anthracis in different habitats within ENP seem to support the “incubator” theory, except for one of the analyzed categories. Further data are necessary to confirm this trend. The herein presented data seem to be reflective of a seasonal dependent infection risk. Although a higher proportion of samples tested positive in the dry season compared to the rainy season, the B. anthracis concentration of positive cases from the latter season were higher, indicative for a higher risk for lethal infections.
The observed overlapping pattern of GT clusters coincided with the occurrence of multiple strain infections. Often different GTs were found in the same habitat and were isolated both from wildlife species and water holes, indicating these water places to be potential sources of infections.