Role of horn flies (Haematobia irritans) in Staphylococcus aureus-induced mastitis in dairy heifers

Abstract

Abstract Objective To determine whether Staphylococcus aureus can colonize in horn flies and whether colonization is sufficiently persistent for transmission of the organism to cows by flies. Animals 2 Jersey heifers exposed to infected horn flies. Procedure Staphylococcus aureus was allowed to colonize in horn flies, and duration of colonization was determined. Flies with colonized S aureus were allowed to feed on teats of uninfected 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 Saureus was present and whether scabs could serve as a possible source of S aureus for flies. Results Staphylococcus aureus colonized in horn flies and remained for up to 96 hours after exposure. Exposure of teats of uninfected heifers to horn flies colonized with S aureus resulted in intrammmary infection in 3 of 4 exposed teats. Culture of scab material from teats of naturally infected heifers revealed high concentration of S aureus (> 107 colony-forming units/mg), and flies without previously colonized S aureus were allowed to feed on scabs; Saureus 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 Saureus-induced intramammary infection to heifers, and scabs on teats are a potential source of S aureus. Fly control on dairy cows in herds with known Saureus problems is recommended as a method to help prevent these infections. (Am J Vet Res 1998;59: 1122-1124)