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 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.
Tonsils of 829 fattening pigs originating from Belgium (n ¼ 201), Italy (n ¼ 428), and Spain (n ¼ 200) were collected between 2005 and 2007 to study the prevalence of enteropathogenic Yersinia in slaughter pigs. Isolation of Yersinia enterocolitica and Yersinia pseudotuberculosis was done by selective enrichment and by cold enrichment for 7 and 14 days. Pathogenic Y. enterocolitica and Y. pseudotuberculosis isolates were identified by polymerase chain reaction targeting the chromosomal genes ail and inv, respectively, as well as the plasmid-encoded virF of both species. A significantly higher ( p < 0.001) prevalence of ail-positive Y. enterocolitica in Spain (93%) than in Belgium (44%) or Italy (32%) was observed. virF-positive Y. enterocolitica was present in 77% of ail-positive samples. Bioserotype 4=O:3 was the most common type in all three countries. Bioserotypes 2=O:5 and 3=O:9 were found in Italy (1%) and Belgium (9%), respectively. The prevalence of inv-and virF-positive Y. pseudotuberculosis was 2% and 1% in Belgium and Italy, respectively. Y. pseudotuberculosis was not detected in pigs from Spain. Bioserotypes 1=O:1 (20%), 1=O:2 (20%), and 2=O:3 (60%) were found in Belgium, and 1=O:1 (60%) and 2=O:3 (20%) in Italy. The most efficient method for isolation of Y. enterocolitica was combined cold enrichment for 7 and 14 days; however, the isolation method for Y. pseudotuberculosis was cold enrichment for 14 days. Fattening pigs seem to be an important reservoir of pathogenic Y. enterocolitica in Belgium, Italy, and Spain. Bioserotype 4=O:3 of Y. enterocolitica and bioserotypes 2=O:3 and 1=O:1 of Y. pseudotuberculosis have been shown to predominate.
Tonsils of 457 fattening pigs from Estonia (n = 151), Latvia (n = 109), and the Leningrad Region of Russia (n = 197) were collected between 2004 and 2007 to study the prevalence of enteropathogenic Yersinia in slaughter pigs. Yersinia enterocolitica and Yersinia pseudotuberculosis were isolated by selective and cold enrichment. Pathogenic Y. enterocolitica and Y. pseudotuberculosis were identified by PCR targeting the chromosomal genes ail and inv, respectively. The presence of the virulence plasmid was confirmed by PCR targeting the virF gene of Y. enterocolitica and Y. pseudotuberculosis. The prevalence of ail-positive Y. enterocolitica was 89% in Estonia, 64% in Latvia, and 34% in Russia, with 81% of ail-positive samples being virF-positive. A statistically significant (p < 0.05) difference between Estonian and Latvian pigs and between pigs from Latvia and the Leningrad Region of Russia was observed when assuming randomized sampling. Y. enterocolitica bioserotype 4/O:3 was the only pathogenic type found. The prevalence of inv and virF-positive Y. pseudotuberculosis was higher in Russia (7%) than in Latvia (5%) and Estonia (1%), with a statistically significant difference between pigs from Estonia and the Leningrad Region of Russia when assuming both randomized sampling and clustering at farms. All Y. pseudotuberculosis isolates were bioserotype 2/O:3. A total of eight pigs (2%), one pig from Latvia and seven pigs from the Leningrad Region of Russia, carried both pathogenic Y. enterocolitica and Y. pseudotuberculosis in the tonsils. Cold enrichment was found to be a more efficient method compared to selective enrichment to isolate both species. Pigs seem to be an important reservoir of human enteropathogenic Y. enterocolitica 4/O:3 and Y. pseudotuberculosis 2/O:3 in these countries.
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