Prevalence and Dynamics of Pathogenic 4/O:3 Among Finnish Piglets, Fattening Pigs, and Sows.

Pigs are considered the main reservoir of , and hence, understanding the ecology of this foodborne pathogen at the farm level is crucial. We calculated Bayesian estimates for the ability of a commercial enzyme-linked immunosorbent assay (ELISA) diagnostic test kit to detect antibodies against pathogenic in pigs. The sensitivity and specificity of the test were 75.4% and 98.1%, respectively. We also studied the dynamics of infection in 3 farrow-to-finish pig farms by following the same 30 pens of pigs through their lifetime from farrowing unit to slaughterhouse. Each farm was sampled 4 times, and 864 fecal and 730 serum samples were collected altogether. Pathogenic 4/O:3 was isolated from 31.6% of the fecal samples by culturing, and antibodies were detected in 38.2% of the serum samples with the commercial ELISA test. The pathogen was not isolated from farrowing units or all-in/all-out weaning units. However, in the weaning and fattening units using continuous management systems, the pathogen was isolated from every pen at some point of the study. After the pigs were transported into slaughterhouse, 150 tonsils were collected and 96.7% were positive by culturing. Among the strains isolated from feces and tonsils, 56 different genotypes of pathogenic 4/O:3 were found by multilocus variable-number tandem-repeat analysis (MLVA). Finally, we collected tonsils of 266 sows from 115 farrowing farms, and 4/O:3 was detected in 6.0% of the samples by the culture method, whereas 77.1% of the tonsils were serologically positive; the estimate for true seroprevalence was 95.8%. In conclusion, sows may not be the main source of for piglets, although sows may still play a role in maintaining in pig farms. Instead, pigs appear to get this foodborne pathogen mainly during the fattening period, especially if continuous management is applied.