Diagnosis of psoroptic sheep scab with an improved enzyme-linked immunosorbent assay

An enzyme-linked immunosorbent assay (ELISA) was developed for the detectio n of specific antibodies against crude Psoroptes antigen. The diagnostic se nsitivity was 93.7% in 191 sheep with clinical signs associated with mange. These animals originated from 29 flocks in which psoroptic mites were dete cted. All of 59 sheep infested with Psoroptes ovis were seropositive. Addit ionally, in 49% of 70 clinically unaffected sheep originating from P ovis-i nfested hocks, specific antibodies could be detected, suggesting that asymp tomatic infestations can be diagnosed by serology. The specificity of the E LISA was 96.5% as determined with 254 sheep originating from 44 flocks with out clinical mange. Cross-reactivity in a low range was detected with selec ted sera of sheep with clinical chorioptic or forage mite infestations. Fou r sheep seroconverted 2 weeks after experimental P. ovis infestation, i.e. 2 weeks before clinical signs became obvious. After successful doramectin t reatment of 14 sheep with naturally acquired P. ovis infestation, the ELISA values declined slowly but remained positive in seven cases beyond 17 week s. (C) 2001 Elsevier Science B.V. All rights reserved.