ROLE OF HORN FLIES (HAEMATOBIA-IRRITANS) IN STAPHYLOCOCCUS AUREUS-INDUCED MASTITIS IN DAIRY HEIFERS

Objective-To determine whether Staphylococcus aureus can colonize in h orn flies and whether colonization is sufficiently persistent for tran smission of the organism to cows by flies. Animals-2 Jersey heifers ex posed to infected horn flies. Procedure-Staphylococcus aureus was allo wed to colonize in horn flies, and duration of colonization was determ ined. Flies with colonized S aureus were allowed to feed on teats of u ninfected heifers to determine whether intramammary infection could be transmitted from fly to heifer. Scab material from naturally infected heifers was submitted for bacteriologic culture to determine whether S aureus was present and whether scabs could serve as a possible sourc e of S aureus for flies. Results-Staphylococcus aureus colonized in ho rn flies and remained for up to 96 hours after exposure. Exposure of t eats of uninfected heifers to horn flies colonized with S aureus resul ted in intrammary infection in 3 of 4 exposed teats. Culture of scab m aterial from teats of naturally infected heifers revealed high concent ration of S aureus (> 10(7) colony-forming units/mg), and flies withou t previously colonized S aureus were allowed to feed on scabs; S aureu s colonized in them just as readily as it did in flies that had fed on experimentally infected blood. Conclusions-Horn flies are capable of transmitting S aureus-induced intramammary infection to heifers, and s cabs on teats are a potential source of S aureus. Fly control on dairy cows in herds with known S aureus problems is recommended as a method to help prevent these infections.