PRURITIS AND DERMAL RESPONSE TO INSECT ANTIGENS IN SHEEP INFESTED WITH BOVICOLA-OVIS

This study examined the relationships among louse density, pruritis an d dermal response to insect antigens in sheep infested with Bovicola o vis. Polypay and Columbia ewes were allocated to two groups, infested and naive, and louse densities and pruritis were monitored for 15 mont hs. Ten months after the initial infestation, all sheep were tested fo r hypersensitivity on the midside and ears by intradermal injection of soluble extracts of B. ovis, Stomoxys calcitrans and Musca autumnalis . The areas of skin reactions were measured at 20 min, 1, 3 and 24 h a fter injection and skin thickness was measured at 24 h. Louse densitie s on Polypays were approximately 10 times greater than on Columbias, a nd pruritis was correlated with louse numbers at mast inspections. Mos t pruritic behaviour was directed to the sides of infested sheep. Whea l and flare reactions developed rapidly to all extracts in both infest ed and naive ewes. Reactions to louse extract were larger in infested than naive sheep at all four times after injection. In the infested Po lypays, reactions to louse extract were greater than to the fly extrac ts, but in naive sheep there was little difference among extracts. Rea ctions in naive Columbias were larger than in naive Polypays at 20 min , 1 and 3 h, but had almost completely abated in both groups at 24 h. Reactions in infested Columbias were greater than in infested Polypays at 20 min. but at 24 h reactions in the Polypays were larger. Louse n umbers and pruritis were correlated with wheal areas and skin thicknes s at 24 h, but there was little relationship with the size of reaction s at earlier times. These findings are consistent with the development of a hypersensitive response to B. ovis and suggest that dermal react ions to lice may influence sheep susceptibility. (C) 1998 Australian S ociety for Parasitology. Published by Elsevier Science Ltd.