SERODIAGNOSIS OF SALMONELLA-DUBLIN INFECTION IN DANISH DAIRY HERDS USING O-ANTIGEN BASED ENZYME-LINKED-IMMUNOSORBENT-ASSAY

Usefulness of two enzyme-linked immunosorbent assays (ELISA) for scree ning of dairy herds for antibodies to lipopolysaccharide (LPS) of Salm onella dublin (O:1,9,12) was investigated. Sera (3097) were collected from 40 dairy herds located in three areas of Denmark with different p revalence of salmonellosis: ten salmonellosis-free herds from the isla nd of Samso where there is no history of salmonellosis, ten salmonello sis-free herds from the island of Sealand where outbreaks are infreque nt, and 20 salmonella infected herds from Jutland where salmonellosis is enzootic. The samples were analyzed for antibodies to S. dublin LPS using an indirect (O:9,12) and a blocking (O:9) ELISA. Using herd his tory of salmonellosis, herd location and clinical state of the herds a s reference, the herd sensitivity and herd specificity of the tests we re 100% and 100% in the indirect ELISA and 95% and 100% in the blockin g ELISA, respectively. A significant correlation was found between the two tests (r(s) = 0.46, p < 0.001). However, the indirect ELISA detec ted more seropositive animals than the blocking ELISA (17% vs. 7%, res pectively). In calves from Sealand, level of background reaction was s ignificantly lower (p < 0.001) compared to the heifers and the cows. T he percentages of seropositive calves in both tests were higher (p < 0 .01) in comparison to cows (19 vs. 8 in indirect ELISA, and 14 vs. 6 i n blocking ELISA, respectively). Results of the study indicated that i t is possible to apply LPS ELISA in serological screening for salmonel losis.