No abstract

Pigs are considered as a major reservoir of human pathogenic Yersinia enterocolitica and a source of human yersiniosis. However, the transmission route of Y. enterocolitica from farm to pork is still unclear. The transmission of pathogenic Y. enterocolitica from pigs to carcasses and pluck sets was investigated by collecting samples from 364 individual ear-tagged pigs on the farm and at the slaughterhouse. In addition, isolated strains were analyzed, using pulsed-field gel electrophoresis. Isolation of similar genotypes of pathogenic Y. enterocolitica 4/O:3 in animals on the farm and at the slaughterhouse and in carcasses shows that carcass contamination originates from the strains a pig carries during the fattening period. Direct contamination from the carrier pig to its subsequent pluck set is also the primary contamination route for pluck sets, but cross-contamination appears to have a larger impact on pluck set contamination than on carcasses. In this study, the within-farm prevalence of pathogenic Y. enterocolitica varied from 0% to 100%, indicating specific farm factors affect the prevalence of Y. enterocolitica in pigs. The association of farm factors with the high prevalence of pathogenic Y. enterocolitica on farms was studied for the first time, using correlation and two-level logistic regression analyses. Specific farm factors, i.e. drinking from a nipple, absence of coarse feed or bedding for slaughter pigs, and no access of pest animals to pig house, were associated with a high prevalence of pathogenic Y. enterocolitica 4/O:3.

The presence of Listeria monocytogenes in the pork production chain was followed from farm to slaughterhouse by examining the farm and slaughterhouse levels in the same 364 pigs, and finally by analyzing the cut meats from the same pig lots. Both organic and conventional farms were included in the study. Altogether, 1,962 samples were collected, and the 424 L. monocytogenes isolates were analyzed by pulsed-field gel electrophoresis. The results from microbial analyses were combined with data from an on-farm observation and a questionnaire to clarify the associations between farm factors and prevalence of L. monocytogenes. The prevalence of L. monocytogenes was 11, 1, 1, 24, 5, 1, and 4% in feed and litter, rectal swabs, intestinal contents, tonsils, pluck sets (including lungs, heart, liver, and kidney), carcasses, and meat cuts, respectively. The prevalence was significantly higher in organic than in conventional pig production at the farm and slaughterhouse level, but not in meat cuts. Similar L. monocytogenes genotypes were recovered in different steps of the production chain in pigs originating from the same farm. Specific farm management factors, i.e., large group size, contact with pet and pest animals, manure treatment, use of coarse feed, access to outdoor area, hygiene practices, and drinking from the trough, influenced the presence of L. monocytogenes in pigs. L. monocytogenes was present in the production chain, and transmission of the pathogen was possible throughout the chain, from the farm to pork. Good farm-level practices can therefore be utilized to reduce the prevalence of this pathogen.

The transmission of Yersinia pseudotuberculosis in the pork production chain was followed from farm to slaughterhouse by studying the same 364 pigs from different production systems at farm and slaughterhouse levels. In all, 1,785 samples were collected, and the isolated Y. pseudotuberculosis strains were analyzed by pulsed-field gel electrophoresis. The results of microbial sampling were combined with data from an on-farm observation and questionnaire study to elucidate the associations between farm factors and the prevalence of Y. pseudotuberculosis. Following the same pigs in the production chain from farm to slaughterhouse, we were able to show similar Y. pseudotuberculosis genotypes in live animals, pluck sets (containing tongue, tonsils, esophagus, trachea, heart, lungs, diaphragm, liver, and kidneys), and carcasses and to conclude that Y. pseudotuberculosis contamination originates from the farms, is transported to slaughterhouses with pigs, and transfers to pluck sets and carcasses in the slaughter process. The study also showed that the high prevalence of Y. pseudotuberculosis in live pigs predisposes carcasses and pluck sets to contamination. When production types and capacities were compared, the prevalence of Y. pseudotuberculosis was higher in organic production than in conventional production and on conventional farms with high rather than low production capacity. We were also able to associate specific farm factors with the prevalence of Y. pseudotuberculosis by using a questionnaire and on-farm observations. On farms, contact with pest animals and the outside environment and a rise in the number of pigs on the farm appear to increase the prevalence of Y. pseudotuberculosis.

Efficiency of environmental surveillance of poliovirus circulation was studied using simulation models. First, three transmission models were defined for describing different scenarios of poliovirus infections in a large unstructured population. Second, environmental factors, such as the total volume of the sewage network and losses of viruses, were modeled for computing the virus output at the sewage sampling site. Third, the effect of sampling and laboratory procedures was accounted for in the probability of detection, given the amount of polioviruses in a specimen. The simulation model can be used for theoretical assessments of the likely efficiency of environmental surveillance, compared with acute flaccid paralysis (AFP) surveillance. Under reasonable assumptions in a vaccinated population, the AFP surveillance can be outperformed if the poliovirus outbreak is not large. However, this depends on the assumed case-to-infection ratio and on the sampling frequency of the sewage water specimens. Increasing the latter will lead to a higher detection probability, which will further enhance the method based on environmental surveillance.