Singleton reactors in the diagnosis of swine vesicular disease: the role of coxsackievirus B5

Swine vesicular disease virus (SVDV) and Coxsackie B5 virus (CVB5) are closely related viruses that can infect swine and man and give rise to cross-reacting serum antibodies. It is, therefore, possible that SVD antibodies found in serologic screenings of pigs are induced by CVB5. Single positive animals found in screening programmes are generally referred to as singleton reactors (SR). To determine whether SR in SVDV screenings are induced by CVB5 infection, virus neutralisation tests (VNTs) and radioimmunoprecipitation assays (RIPA) were carried out on sera of SR, sera of pigs experimentally infected with SVDV, and sera from pigs vaccinated with CVB5 isolates.The SR sera reacted repeatedly positive in the SVDV UKG/27/72 VNT, but reacted differently in three other VNTs (SVDV NET/1/92, CVB5A, and CVB5B). The VNT titres obtained with the SR sera revealed a correlation between both SVDV strains, and also between both CVB5 stains, but no correlation was found between SVD and CVB5 VNT titres. Sera of experimentally infected (SVDV) or vaccinated (CVB5) pigs showed titres in all four neutralisation tests.In the RIPA, the reaction patterns of the SR sera varied considerably with all four antigens used, in contrast to sera from pigs experimentally infected with SVDV that reacted with all antigens used, and sera from pigs vaccinated with CVB5 that reacted only with CVB5 antigens. The results presented in this paper show that neither CVB5 nor SVDV infections are the only cause of the SR phenomenon. Testing for CVB5 specific antibodies can reduce the number of SR sera in the serodiagnosis of SVDV.