Prevalence, faecal shedding and genetic characterisation ofYersiniaspp. in sheep across four states of Australia

Outbreaks of diarrhoea ('winter scours') in weaned Merino sheep in south-eastern Australia

OBJECTIVE

Identify the cause of outbreaks of diarrhoea during winter that are not attributable to gastrointestinal nematodes in weaned Merino sheep in the high rainfall regions of south-eastern Australia and determine the efficacy of antimicrobials used to treat this syndrome.

METHODS

We investigated 45 outbreaks on 24 farms. Faecal samples from affected animals were cultured for Yersinia, Campylobacter and Salmonella spp. Risk factors, including rainfall, temperature and worm egg count (WEC), were assessed. Yersinia spp. were identified with molecular tests and susceptibility to four antimicrobials was determined.

RESULTS

Yersinia pseudotuberculosis serotype III and virulent Y. enterocolitica were most frequently isolated. The frequency and severity of disease varied between region, farm and year. Yersinia pseudotuberculosis was detected only during winter, but Y. enterocolitica was present in all seasons. Pathogenic Yersinia species were more often isolated when WECs exceeded 500 eggs/g. A high proportion of Y. enterocolitica and Y. pseudotuberculosis were resistant to sulfafurazole (64% and 86.9%, respectively).

CONCLUSIONS

A bacterial enteritis caused by pathogenic Yersinia was the cause of the winter scours syndrome in the 24 flocks investigated. The use of molecular testing increased the sensitivity of detection and identification of Yersinia spp. No clear association between weather, WEC and disease was established, suggesting complex interactions between risk factors are more important than any single factor. Sulfonamides should not be routinely used to treat this syndrome. Rather, during an outbreak the targeted use of an effective antimicrobial, such as oxytetracycline, should be integrated with grazing management strategies, including moving affected mobs onto lower risk pastures and decreasing the stocking rate.

Faecal shedding of pathogenic Yersinia enterocolitica determined by qPCR for yst virulence gene is associated with reduced live weight but not diarrhoea in prime lambs

Associations between faecal shedding of pathogenic Yersinia enterocolitica (based on the yst virulence gene) with growth, carcass weight and diarrhoea were investigated using an observational longitudinal study of 1200 crossbred prime (meat) lambs on eight Australian farms. Live weight, breech faecal soiling score (scale 1-5) and faecal consistency score (FCS; scale 1-5) were recorded, and faecal samples collected from each lamb on three sampling occasions; weaning (≈12 weeks of age), post-weaning (≈19 weeks) and pre-slaughter (≈29 weeks). Hot standard carcass weight was measured at slaughter. Faecal samples were screened for presence and concentration of pathogenic Y. enterocolitica using quantitative PCR. Associations of pathogenic Y. enterocolitica detection and shedding intensity with lamb health and production were assessed using general linear models (carcass weight), linear mixed effects models (live weight, FCS and breech soiling score) and non-parametric tests (FCS and breech soiling score). Prevalence for non-pelleted faeces (FCS ≥ 3.0) and diarrhoea (FCS ≥ 4.0) were compared with the two-tailed z-test, odds ratios and relative risk. Lambs shedding pathogenic Y. enterocolitica were 3.78 kg lighter post-weaning (P < 0.001) and 2.61 kg lighter pre-slaughter (P = 0.035) compared to lambs in which pathogenic Y. enterocolitica was not detected. Higher faecal concentration of pathogenic Y. enterocolitica was associated with lower live weight (P < 0.001). There was no association between pathogenic Y. enterocolitica detection and carcass weight. Overall, there was no evidence of association between pathogenic Y. enterocolitica detection and diarrhoea (higher FCS, higher risk for non-pelleted faeces or diarrhoea, or higher breech soiling score). Only one flock had increased relative risk for non-pelleted faeces associated with pathogenic Y. enterocolitica detection, and one other flock had increased relative risk for diarrhoea associated with pathogenic Y. enterocolitica detection. This is the first report of an association between reduced sheep live weight and pathogenic Y. enterocolitica based on the presence of the yst gene for heat stable enterotoxin determined by qPCR in sheep. Notably, impacts on live weight were observed in the absence of diarrhoea.

Sheep carrying pathogenic Yersinia enterocolitica bioserotypes 2/O:9 and 5/O:3 in the feces at slaughter

Yersinia enterocolitica is a heterogeneous species including non-pathogenic strains belonging to biotype 1A and pathogenic strains belonging to biotypes 1B and 2-5. Pathogenic strains of biotypes 2-4 carrying the ail virulence gene have frequently been isolated from domestic pigs at slaughter. In sheep, mostly non-pathogenic biotype 1A strains have been reported. In our study, the prevalence of ail-positive Y. enterocolitica was studied by PCR and culturing in 406 young sheep (<1year of age) and 139 older sheep at slaughter in Finland. When using PCR, the detection rate was 11% (45/406) in young sheep originating from 11 (18%) farms. Surprisingly, Y. enterocolitica belonging to bioserotypes 2/O:9 and 5/O:3, carrying both chromosomal and plasmid-borne virulence genes, were isolated from the fecal samples of 10 (2%) and 23 (4%) sheep, respectively. All isolates of bioserotypes 2/O:9 (19 isolates) and 5/O:3 (53 isolates) carried the chromosomal virulence genes ail, inv, ystA, and myfA, and almost all isolates (71/72) also carried the virulence genes virF and yadA located on the virulence plasmid. The isolates showed high susceptibility to tested antimicrobials and low genetic diversity by PFGE. Y. enterocolitica bioserotype 5/O:3 is a very rare bioserotype, and has earlier only sporadically been reported in European wildlife and in sheep in Australia and New Zealand. Bioserotype 2/O:9 is a common bioserotype found in humans with yersiniosis, and has sporadically been isolated in wild and domestic animals.