Investigation Of Biting And Non-Biting Flies As Vectors For Bacillus Anthracis In Etosha National Park, Namibia

ABSTRACT

The role of flies in the spread of anthrax, an animal disease caused by the spore-forming pathogen Bacillus anthracis, have been reported as far back as the early 1900s. Studies have implicated flies from families of Tabanidae, Muscidae, Calliphoridae and other dipteran species. This study was undertaken in the Okaukuejo area of ENP to establish the role of biting and non-biting flies that may act as vectors for B. anthracis; and at what concentrations of Bacillus anthracis do they carry and also to determine whether isolated strains of bacteria contained bacteriophages. For this purpose non-biting flies were collected from anthrax positive carcasses using a makeshift trap and analysed on TSPBA after being disinfected and squashed in 0.85% saline. Isolated strains were analysed for the presence of phages and vegetation containing fly excretions was collected. Nzi fly traps were used to collect biting flies. These results show that non-biting flies found belonged to Calliphoridae and Muscidae families the most abundant biting flies were from Tabanidae family. Of the 110 non-biting flies analysed from positive carcasses 25.4% were positive for Bacillus anthracis. The maximum concentration found in an individual was 4.0 x103 CFU/fly. There was no correlation between fly species and concentration of spores within flies. Non-biting flies mean spores were statistically equal to parenteral LD50s of Impala [100; 250] but were too low with respect to oral doses LD50s of horses and of impala. No bacteriophages were isolated from B. anthracis strains. Flies of families Calliphoridae and Muscidae can act as mechanical vectors in ENP more likely through parenteral means including myiasis infection; oral transmission via regurgitation and defecation on leaves could not be established. Biting flies as vectors of anthrax needs further investigation. Measures that control fly populations during anthrax outbreaks may be considered