Experimental inoculation of house flies, Musca domestica L., with Corynebacterium pseudotuberculosis serovar equi.

Corynebacterium pseudotuberculosis (Actinomycetales: Corynebacteriaceae) infection in horses causes three different disease syndromes: external abscesses, infection of internal organs and ulcerative lymphangitis. The route of infection in horses remains undetermined, but transmission by insect vectors is suspected. The purpose of the present study was to investigate the role of the house fly (Musca domestica L.) (Diptera: Muscidae)  as a vector of this disease, by optimizing the inoculation of the house fly with an isolate of C. pseudotuberculosis biovar equi and determining the post-exposure survival time of the bacteria in the fly. Evaluation of the exposure time necessary to inoculate the flies and its efficacy, was determined by exposing flies for 10 different time intervals (10 min to 48h) to 3 different preparations of blood agar supplemented with dextrose and colonized with C. pseudotuberculosis. The post-exposure survival time of viable C. pseudotuberculosis in flies was investigated following 30 min of exposure of the flies to a blood agar plate moistened with 10% dextrose and colonized with the bacteria. The shortest feeding time required for flies to become contaminated was 10 min. C. pseudotuberculosis was isolated from homogenates of house flies sampled up to 24h after exposure for 30 min. We have established a protocol for contaminating flies which can be used in a future experimental model to demonstrate the role of house flies as mechanical vectors in C. pseudotuberculosis infection in horses.