Development and decline of serum antibody activity to Psoroptes ovis antigens in infested cattle in an endemic and nonendemic scabies area of Texas.

The serum antibody activity to Psoroptes ovis antigens, as determined by enzyme-linked immunosorbent assay (ELISA), was monitored during the development and decline phase of scabies in cattle herds under feedlot conditions in an endemic (Bushland) and a nonendemic (Kerrville) scabies area of Texas. The infestations were initiated by exposing six calves in each of the herds to P. ovis and allowing the infestations to spread to other members of the herd. The cattle in the endemic area developed more lesions and a higher incidence of the disease than did the cattle in the nonendemic area; also, there were more cattle with specific serum antibody activity in the Bushland herd than in the Kerrville herd at the peak of the infestations (late January--early February). As infestations declined because of summer latency, the number of calves with specific serum antibody activity declined in both herds. Specific serum antibody activity disappeared in the Kerrville cattle when P. ovis was no longer detected. However, specific serum antibody activity was still detected in some of the Bushland cattle in late summer (August) and fall (October) examinations, when low numbers of P. ovis were detected. These results indicate that the ELISA would be very useful in detection of specific serum antibody activity in lightly infested calves, especially during the developmental and decline phases of the disease.