Purpose: Salmonella enterica is one of the principal causes of foodborne zoonotic enteritis. Among the different serovars, Dublin (S. Dublin) is of particular importance due to its propensity to progress to an invasive infection in humans and due to the high proportion of multi-drug resistant strains in Canada. Cattle are considered as the main reservoir of S. Dublin. This serotype has emerged since 2011 in the province of Quebec, Canada, in both cattle and human populations. First animal cases have been reported in calf production. White veal are valued for the quality of their meat, offal and liver. The liver is usually consumed mildly cooked and is considered as a probable source of foodborne exposure to S. Dublin in humans. The objective of this study was to estimate the prevalence of S. Dublin positive liver after slaughtering and the seroprevalence against S. Dublin at the calf level.
Methods & Materials: Samples were collected from 75 batches in two slaughterhouses from August 2016 to October 2017. For each batch, a liver sample was collected from 8 calves after evisceration and additionally, a blood sample from 15 calves. Liver samples were screened by PCR and then cultured, and serums were tested using an indirect ELISA (PrioCHECK® Salmonella Ab bovine Dublin).
Results: Salmonella was detected by PCR in 20 of the 547 veal livers. Typical isolates were obtained from 14 livers; all were serotyped and identified as S. Dublin, for a prevalence estimate of 3.1% (IC95%: 0.0%-7.45%). At least one seropositive calf was detected in 128 (24%) of the 75 batches. At the calf level, seroprevalence was estimated at 6.97% (IC95%: 2.83%-11.11%). S. Dublin was detected in liver of 14.0% of seropositive calves compared to 1.2% of seronegative ones (p < 0.001).
Conclusion: Our results show that veal liver can be a source of foodborne exposure to S. Dublin in humans, especially when veal liver is consumed mildly cooked. Surveillance and prevention measures associated with calf production and veal meat, including cooking recommendations could help reduce the burden associated with S. Dublin in humans. Serology could be potentially used in surveillance effort as an indicator to assess the risk of contamination.