Evaluation of different methods for the diagnosis of scabies in swine

Scabies in pigs is still very common in many countries and can be detrimental to the productivity of pigs. However, correct diagnosis of the disease can preclude meaningful comparisons of results. Therefore, the objective of the present study was to determine, on 11 pig farms, the prevalence of scabies by determination of the presence of mites in ear scrapings, the dermatitis score, the SI and the detection of specific serum antibodies. For the latter an indirect ELISA technique was performed using a free-living mite as a source of antigen. A second objective was to compare the value of these different diagnostic tests. Four farms were positive for the presence of mites. Our study indicated that the SI of piglets is not reliable as a diagnostic tool for scabies (all values were below the threshold value of 0.4, even on farms that were positive for mites) but on the two farms with the highest prevalence of mites the SI was above the threshold for the finishers. However, the fact that sows from eight of the 11 farms investigated had a SI>0.4 would indicate that for sows either the SI is not very specific, or that a cut-off level of 0.4 is not relevant for this age group. On three of the four infected farms the ADS was higher than the cut-off value of 0.5, and on the fourth farm, where the ADS was only 0.43, individual carcasses with generalised dermatitis (score 2) were present. However, an ADS>0.5 did not always coincide with the presence of mites. On six farms, ODR values were indicative for the presence of Sarcoptes, and on three of these farms this was confirmed with positive ear scrapings. In conclusion, as determined by the detection of mites in pig ears, especially the results from the dermatitis scores seem to be useful in the diagnosis of scabies. The specificity of the other parameters is not sufficient, and therefore, the detection of mites should still be used to confirm scabies on a farm, in combination with other tools.