COMPARISON BETWEEN PERSISTING ANTILIPOPOLYSACCHARIDE ANTIBODIES AND CULTURE AT POSTMORTEM IN SALMONELLA-INFECTED CATTLE HERDS

Herds with recent clinical outbreaks of Salmonella dublin (7 herds) an d S. typhimurium (4 herds) infections were followed serologically in O -antigen ELISAs over about one year, divided in four equal sampling ph ases. Animals found to be persistent high-reactors or seronegative at the end of the study were slaughtered and subsequently cultured for sa lmonella in a selected number of organ samples. Approximately 3% of al l animals had high seroreactions up to 17 months after the outbreaks, and less than half of the seropositive animals in the S. dublin-infect ed herds were salmonella culture positive at slaughter (14/31). Howeve r, one persistently seronegative animal was also culture positive. Fur thermore, as much as 70% of the male calves investigated at postmortem in the S. dublin-infected herds were high-reactors, among which appro x. 56% were culture positive. Surprisingly, 2 of the 14 animals found culture positive turned out to be culture positive for S. typhimurium only. In the S. typhimurium study, none of the 17 animals investigated at postmortem were salmonella culture positive. All sera from these a nimals were negative in the O:9 blocking ELISA, and no serum sample wa s positive in the S. dublin ELISA, alone. In conclusion, although sero logy based on the O-antigens appears to be useful to identify salmonel la-infected herds, it seems to be insufficient for identification of p ersistently infected animals.