Salmonella enterica subsp. enterica along the pig commodity chain in Vietnam

Foodborne diseases are a particularly important concern in the current Vietnamese context, shortly after accession to the WTO, not only for public health reasons, but also because of the global evolution of consumer demand and habits, the production chain and state regulations. Salmonella enterica subsp. enterica (Salmonella) is known as one of the most frequent food-borne zoonoses in the world and has been isolated in human and pork products in Vietnam, where pork represents 77% of total meat consumption. The aim of this paper is to describe Salmonella prevalence and epidemiology results along the pig commodity chain, at farm, slaughterhouses (both in Hanoi suburb, 206 samples and in slaughter plants connected with Nam Sach farmers in Hai Duong Province, 126 samples,) and for traditional raw meat fermented Vietnamese sausages 'nem chua'. The prevalences by fattening pigs at farm (19%) and in caecal content before slaughter (52% and 40%) were comparable to other studies, whereas the carcass contamination rates were much higher (95.7% and 67%). 35.7% of 213 'nem chua' samples were positive. Serotyping of these isolates suggested that Salmonella contamination is mainly originated from the pig meat itself, with a smaller contribution from the sausages' processing steps. The results confirm that slaughterhouses in Vietnam are the key point to be focused on for improving food safety in the pork commodity chain. The potential public health threat of Salmonella in pork products has been proven by the high prevalence found on 'nem chua' sausages. Further serotyping and genotyping of Hanoi slaughterhouses' isolates aimed to understand the ways of contamination of Salmonella at this important key step. The direct contamination of carcasses through faecal material from the same pig was not clear, but a direct faecal contamination was observed for the tank and the well water. Thus, our results suggested that the main source of carcass contamination was indirect, through the slaughtering environment. Moreover, the results may indicate that live pigs could be infected during lairage through contaminated water and environment, leading to a persistence of certain clones over longer periods. Since the majority (about 90%) of the pig production in Vietnam goes through small slaughter plants, we propose priority economical hygienic control measures adapted to small plants, that could largely decrease the carcass contamination rate. (Résumé d'auteur)