Skin lesions in Aubrac cows strongly associated with fly bites ( Haematobia irritans )

Background The horn fly Haematobia irritans is known to cause problems in cattle including weight loss and decreased milk production; cutaneous lesions have not been widely reported and descriptions of the clinical manifestations are quite variable. Hypothesis/objectives This study describes the clinical and histopathological lesions of several Aubrac cows that presented with focal to confluent areas of alopecia, skin scaling and thickening, suspected to be induced by H. irritans bites. Animals Twenty seven, three‐ to six‐year‐old Aubrac cows, kept in mountain pastures in France, that presented with an apparently asymptomatic alopecic dermatosis. Methods Samples for skin cytological evaluation, skin scrapings and trichograms were examined; also, skin biopsy specimens from affected animals were used for histopathological examination. Results Clinical lesions consisted of focal to coalescing, symmetrical areas of hair loss and scaling, located on the back, flanks, and lateral and caudal aspects of the thighs. Histopathological examination revealed perivascular, oedematous, eosinophilic dermatitis with eosinophilic folliculitis and furunculosis. Species identification of several flies captured on the cows revealed H. irritans . The final clinicopathological diagnosis was eosinophilic dermatitis and folliculitis and furunculosis, suspected to be due to H. irritans fly‐bite. Conclusion and clinical importance Fly‐bite ( H. irritans ) dermatitis should be included in the differential diagnosis of alopecic dermatoses in cows.