Evaluation of three newly developed enzyme-linked immunosorbent assays andtwo agglutination tests for detecting Salmonella enterica subsp enterica serovar Dublin infections in dairy cattle

In this study test characteristics of three newly developed enzyme-linked i mmunosorbent assays (ELISAs) for Salmonella enterica subsp. enterica serova r Dublin were evaluated and compared with two agglutination tests. The ELIS As involved were an indirect ELISA with serovar Dublin lipopolysaccharide ( LPS ELISA), an indirect ELISA with serovar Dublin flagellar antigen (GP ELI SA), and a double-antibody sandwich blocking ELISA that uses monoclonal ant ibodies against S. enterica subsp, enterica serovar Enteritidis flagellin ( GM-DAS ELISA). The agglutination tests involved were two routine serum aggl utination tests with either somatic (O) or flagellar (H) antigen. Diagnosti c specificity of the three ELISAs was determined using 840 serum samples fr om seven dairy herds without any history of serovar Dublin infection. Cutof f values at a titer of 100, 100, and 10, respectively, for the LPS ELISA, G P ELISA, and GM-DAS blocking ELISA resulted in a specificity of 99.3, 100, and 100%, respectively. Using these cutoff values the LPS ELISA, GP ELISA, and GM-DAS ELISA were able to detect, respectively, 30, 46, and 38% of 50 f ecal culture-positive animals from 13 herds with a recent serovar Dublin in fection. With the same cutoff values, active carriers (n = 18) were detecte d for 94.4% with the LPS ELISA and for 100% with the GP and GM-DAS ELISAs. Kappa values determined on the results of all tests from 8 of the 13 serova r Dublin-infected herds and the 7 control herds demonstrated a good correla tion between the results of all ELISAs and the H-agglutination test. The re sults of the O-agglutination test failed to correlate with those of the oth er tests. Using a set of sera from 170 aborting cows (with 25 abortions due to serovar Dublin), test results of the ELISAs and the H-agglutination tes t were comparable. The H-agglutination test may be used successfully for si ngle sample testing, especially to diagnose abortion due to serovar Dublin, It is concluded that the ELISAs are useful diagnostic tools in serovar Dub lin control programs and that they are preferred to agglutination tests for reasons of automation and costs.