Serodiagnosis of sarcoptic mange in pigs

A serodiagnostic test (ELISA) for detecting antibodies to Sarcoptes scabiei in the sera of pigs was evaluated. The ELISA results from 221 specific pathogen-free pigs of three different age categories were used to establish a cut-off value for the assay. Background optical density values differed significantly between the three groups, the sows having the highest values. The mean + 3 sd of their values was chosen as the cut-off. Four farrow-to-finish herds of pigs with sarcoptic mange were investigated. Skin scrapings were taken from each animal for the demonstration of S scabiei and their sera were assayed for the presence of antibodies to the mite. All the herds had active infections with S scabiei and antibodies to S scabiei were found in a significant number of the animals sampled. The sensitivity and specificity of the ELISA were 87.8 and 99.5 per cent, respectively, employing clinical diagnosis as the gold standard. A higher sensitivity (100 per cent), but a lower specificity (32.8 per cent) was obtained when the results of skin scrapings were used as the gold standard.