SERUM AND SKIN SURFACE ANTIBODIES AND THEIR ASSOCIATIONS WITH SHEEP BITING LICE, BOVICOLA-OVIS, ON EXPERIMENTALLY INFESTED SHEEP

The sheep biting louse (Bovicola ovis) feeds superficially on the skin of sheep but appears to stimulate an immune response. In this study w e examined the association between louse infestation and serum and ski n surface antibodies. Louse numbers were monitored on experimentally i nfested Polypay and Columbia ewes for two years and on their lambs in the second year. Serum and skin wash samples were tested for antibodie s to soluble extracts of B. ovis, Stomoxys calcitrans and Musca autumn alis by enzyme linked immunosorbent assay (ELISA). In addition, the ef fects of skin wash extracts on B, avis were examined in vitro. The tit re of anti-B. ovis antibodies in the serum did not differ significantl y between infested and naive awes. However, there was an increase in s erum antibody titre which coincided with periods of high louse density in ewes with high louse counts. Infested lambs had higher serum antib ody levels than naive lambs. Substantial cross reactivity was evident among extracts of the different insects. Densities of lice on the ewes during population decline were negatively related to the titre of ski n surface antibodies. Skin washings collected from sheep during B. ovi s population decline reduced the number of louse progeny when incorpor ated into louse diet. These results indicate that B. ovis stimulates a n immune response in sheep and suggest that compounds on the skin surf ace may play a role in the regulation of louse populations.