Experimental inoculation of house flies Musca domestica with Corynebacterium pseudotuberculosis biovar equi

Corynebacterium pseudotuberculosis (Actinomycetales Corynebacteriaceae) infection in horses causes three different disease syndromes: external abscesses, infection of internal organs and ulcerative lymphangitis. The exact mechanism of infection in horses remains undetermined, but transmission by insect vectors is suspected. The present study first determined the optimal culture media for inoculation of house flies (Musca domestica L.) (Diptera Muscidae), with C. pseudotuberculosis biovar equi and the time required for fly inoculation. A second experiment determined the duration of bacterial survival on flies. Exposure of house flies to 3 different preparations of blood agar supplemented with dextrose and colonized with C. pseudotuberculosis determined that a 10 minute exposure to the bacteria was enough to inoculate the flies. C. pseudotuberculosis could be recovered for up to 24 hours after house flies were exposed for 30 minutes to a blood agar plate colonized with the bacteria and moistened with 10% dextrose. These findings support the hypothesis that the house fly is a potential vector of pigeon fever and aid in establishing a protocol for a future experimental model to demonstrate the role of house flies as mechanical vectors in C. pseudotuberculosis infection.