Prevalence of human pathogenic Yersinia enterocolitica in Swedish pig farms

Therese Råsbäck,Michael Stampe,Katarina Järnevi,Elina Tast Lahti,Thomas Rosendal,Anna Aspán,Axel Sannö

doi:10.1186/s13028-018-0393-5

Abstract

BackgroundPigs are the most important reservoir for human pathogenic Yersinia enterocolitica. We investigated the herd prevalence of human pathogenic Y. enterocolitica in Swedish pig farms by analysing pen faecal samples using a cold enrichment of 1 week and thereafter subsequent plating onto chromogenic selective media (CAY agar).ResultsPathogenic Y. enterocolitica was found in 32 (30.5%) of the 105 sampled farms with finisher pigs. Bioserotype 4/O:3 was identified at all but one farm, where 2/O:9 was identified. Pen-prevalence within the positive herds varied from 1/4 to 4/4 pens. The calculated intra-class correlation coefficient ICC (0.89) from a model with a random effect for grouping within herd indicated a very high degree of clustering by herd. None of the explored risk factors, including herd size, herd type, pig flow, feed type, access to outdoors, evidence of birds and rodents in the herd, usage of straw, number of pigs in sampled pen and age of pigs in pen were significantly associated with Y. enterocolitica status of the pen. The use of high pressure washing with cold water was significantly associated with Y. enterocolitica in the pen (OR = 84.77, 4.05–1772). Two culture methods were assessed for detection of Y. enterocolitica, one of which included the use of a chromogenic agar (CAY agar) intended for detection of human pathogenic Y. enterocolitica. The chromogenic media was found equal or superior to traditional methods and was used in this study. The isolates obtained were characterised by biotyping, serotyping, mass spectrometry (MALDI-TOF) and PCR. Characterisation by MALDI-TOF gave identical results to that of conventional bioserotyping. All porcine isolates were positive for the ail and inv genes by PCR, indicating that the isolates were most likely pathogenic to humans.ConclusionsHuman pathogenic Y. enterocolitica was found in nearly one-third of the Swedish pig farms with finisher pigs. The use of high pressure washing with cold water was associated with the presence of Y. enterocolitica in the pen. A modified culturing method using a chromogenic agar was efficient for detection of pathogenic Y. enterocolitica in pig faeces. The use of masspectrometry for identification and subtyping was in agreement with conventional biotyping and serotyping methods.

Highlights

Pigs are the most important reservoir for human pathogenic Yersinia enterocolitica
On CHROMagarTM Y. enterocolitica (CAY) agar, colonies of the clinical Y. enterocolitica isolates were either smooth or with a tendency of swarming seen as a thin haze (Fig. 1) except for one strain poorly growing on CAY agar (Table 1)
Risk factor analysis None of the explored risk factors, including herd size, herd type, pig flow, feed type, access to outdoors, evidence of birds and rodents in the herd, usage of straw, number of pigs in sampled pen and age of pigs in pen were significantly associated with Y. enterocolitica status of the pen

Summary

Introduction

Pigs are the most important reservoir for human pathogenic Yersinia enterocolitica. We investigated the herd prevalence of human pathogenic Y. enterocolitica in Swedish pig farms by analysing pen faecal samples using a cold enrichment of 1 week and thereafter subsequent plating onto chromogenic selective media (CAY agar). Yersiniosis caused by Yersinia enterocolitica is one of the most reported zoonoses in the EU [1] with pigs being the most important reservoir [2,3,4]. Y. enterocolitica causes gastroenteritis whereas the infection in pigs is asymptomatic [3, 5, 6]. In Sweden, pathogenic Y. enterocolitica has previously been detected in fattening pigs [11], in pigs at slaughter [12], and in wild boars [13], but the prevalence in pig farms has not been investigated

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