Properties and Antibiotic Susceptibility of Bacillus anthracis Isolates from Humans, Cattle and Tabanids, and Evaluation of Tabanid as Mechanical Vector of Anthrax in the Republic of Chad

Anthrax is a zoonose caused by the organism Bacillus anthracis. Anthrax affects mainly animals, particularly cattle, but also humans. The economic loss caused by Anthrax in the Republic of Chad are very important. In this study, the potential role of tabanids in anthrax transmission has been evaluated. Tabanids were collected in infested areas of the Chari-Baguirmi Province in Chad and examined using standard bacteriological and biochemical methods. Hundreds of anthrax bacilli were isolated: in this, about 89% of the 1499 tabanids examined were contaminated by anthrax organisms. B anthracis spores were recovered from wings (31.9%) and legs (22.1%). Vegetative cells were recovered from mouthparts (18.8%) and midguts (16.3%). Anthrax Bacilli were also isolated from cattle and humans, including nine cutaneous cases associated with tabanids bites. All B. anthracis isolates displayed similar biological properties whatever their origin. They were non motile, sensitive to penicillin, non hemolytic and fully virulent as they can elicit the disease in experimental animals. All but one biochemical character were identical out of the 49 tested. Isolates were sensitive to meticillin, tetracycline, nitrofurantoin, piperacillin, oxytetracycline, sulphathiazol, benzathien-penicillin and chloramphenicol. Resistance was found against polymixin, fusidic acid, clindomycin and sisomycin. Given together, the results suggested that tabanids could be an important vector of Anthrax in Chad