CASE NOTES

Yersiniosis Causing Stillbirths in Maiden Ewes

Dr Meg Parsons BVBiol BVSc District Veterinarian, Local Land Services, Northern Tablelands

Posted Flock & Herd March 2023

Summary

While abortion and stillbirth outbreaks in sheep are seen less frequently compared to their bovine counterparts, they are of significant economic consequence - resulting in lower marking percentages and an increased number of dry ewes.

Yersinia stillbirths are rare in available literature. More common causes of sheep abortion seen in the Northern Tablelands region of New South Wales include Campylobacter and Toxoplasma, both of which were diagnosed by private and district veterinarians in the region in 2022.

History

In August 2022 the owner of a mixed farming property near Inverell in the Northern Tablelands noticed a high number of stillborn lambs over the first five days of lambing in his maiden ewes. The lambs appeared to be full term with no notable external abnormalities. The producer ran 5,000 head of sheep, including these 1,700 Dohne maiden ewes. They had been joined with Dohne rams for seven weeks, then pregnancy scanned in lamb at 100%. During pregnancy they grazed improved pastures, and then two weeks prior to the start of lambing were moved onto an oat crop with access to commercial mineral lick blocks. They started lambing to schedule on 7 August 2022. By the end of the lambing period it was estimated that 10% of lambs had been stillborn. This mob of lambs then marked at 90%, so accounting for dystocia and other losses between scanning and marking, it is estimated 130 lambs were lost due to the Yersinia outbreak alone.

While the maidens appeared to be in excellent health, earlier in the same month on this property a mob of older Dohne ewes were examined for scours, progressing to death, in a small proportion, despite internal parasite treatment and nutritional supplementation. They were diagnosed with Yersiniosis, with faecal cultures positive for both Yersinia pseudotuberculosis and Yersinia enterocolitica.

Autopsy and Laboratory Findings

Initial Examination & Findings

One stillborn lamb was presented for examination on 12 August 2022; there was no placenta available with this submission. On post-mortem examination there were no significant gross findings. Upon histological examination there was mild, multifocal, acute, suppurative pneumonia, and minimal to mild, multifocal, acute hepatitis. There was also congestion of the cerebrum and brainstem, with midbrain and brainstem vacuolation that was noted to resemble myelinic oedema but of unknown cause.

A sterile sample of foetal stomach contents cultured mixed bacteria, with Yersinia then identified. Furthermore, a pure, profuse growth of Yersinia enterocolitica was cultured from fresh liver.

Campylobacter culture was negative and there was no evidence of toxoplasmosis on histological examination (Bunker, 2022).

Additional Examination & Findings

A second stillborn lamb and placenta were examined on 25 August 2022. The placenta was grossly abnormal with approximately one quarter having changes affecting both cotyledons and the chorioallantois. The main affected tissue was centred around the cervical area, with a few variable smaller foci dispersed over the body of the membranes. The abnormal tissue was characterised by well-demarcated areas of light-yellow discolouration and thickening of the membranes; when transected these areas were full thickness with a granular appearance to the tissue (see Figure 1).

Figure 1.

Histologically there was severe, multifocal to focally extensive, chronic, active, suppurative and histiocytic placentitis with interstitial oedema, vasculitis and thrombosis (Jordan, 2022).

The lamb had no abnormalities visible externally. On post-mortem examination there was moderate, diffuse erythema of the small intestine and diffuse, mottled dark red discolouration of the lung tissue (see Figure 2).

Figure 2. Stillborn lamb on post-mortem

On histological examination there was marked inflammation of the lung with chronic, active, severe, diffuse, histiocytic and suppurative bronchointerstitial pneumonia. Mild inflammation of the cerebrum was also noted, and there was meningioencephalitis that was characterised as mild, multifocal and lymphohistiocytic with chronic gliosis.

Yersinia pseudotuberculosis was cultured from both the placenta and foetal stomach contents. Campylobacter culture was negative and there was no evidence of Toxoplasma infection on histopathology.

In conclusion for the second set of samples, there was a diagnosis of Yersinia pseudotuberculosis causing a suppurative and histiocytic placentitis and bronchointerstitial pneumonia, and a lymphohistiocytic meningoencephalitis (Jordan, 2022).

Discussion

Yersinia pseudotuberculosis and Yersinia enterocolitica are gram-negative coccobacillus that cause disease in a variety of animals and are recognised zoonoses (Fearnley et al., 2005; Fenwick & Collet, 2005; Schaale et al., 2013; Yang et al., 2016).

Enteritis is the most common presentation of Yersinia spp. infection in sheep, with greater infections detected in wet winters (Brightling, 2006; Stranger, McGregor & Larsen, 2018). This reported trend is consistent with what was found on this property, namely a diagnosis of Yersina scours during the winter of 2022 that had been unseasonably wet.

Yersina spp. have been documented to cause sporadic cases of abortion in sheep, though it is quite uncommon (Bruere & West, 1993; Fenwick & Collett, 2005; Watt, 2012). Yersinia infections causing abortion can also be replicated experimentally (Karbe & Erickson, 1984; Corbel et al., 1992). During experimental studies it appears stillbirths occur most commonly when ewes, and thus their placentas, are infected at four months gestation or more (Karbe & Erickson, 1984). Prior to four months gestation infection either causes abortions or there is resolution of infection and birth of healthy lambs (Karbe & Erickson, 1984).

Gross and histological changes are similar across all cases of Yersina abortions reported and are consistent with those found in this case. They are indicative of non-specific foetal infection and not pathognomonic for Yersinia (Jerrett & Slee, 1989).

In New South Wales the more common differential diagnoses for infectious abortions and stillbirths in sheep include Campylobacter spp., Toxoplasma gondii, Listeria spp., Salmonella spp., and Brucella ovis (Brigjtling, 2006; Peffer, 2020). Diagnosis of Yersina abortions or stillbirths can be achieved through isolating the organism from the placenta, foetal stomach contents, or foetal organs, including the lungs and liver (Karbe & Erickson, 1984; Jerrett & Sleep, 1989; Corbel et al., 1992).

Yersina spp. are commonly identified in Australian sheep flocks, without necessarily causing sub-clinical or clinical disease (Brightling, 2006; Yang et al.,2016). Both Yersinia pseudotuberculosis and Yersinia enterocolitica are environmental pathogens and ubiquitous in livestock (Watt, 2012; Schaake et al., 2013).

It is hypothesised in this case that due to the higher environmental contamination from faecal shedding in the older ewes, combined with the poor weather conditions ideal for Yersinia survival, there was a greater population of the bacteria in the environment. Due to the extreme wet conditions of the season, there was also the potential for spread of contamination through run-off between paddocks. Periods of cold, wet weather, reduced nutrition over winter, and increased nutritional requirements during pregnancy lead to higher stress levels in animals making them more susceptible to Yersina infection (Brightling, 2006). Additionally, the affected mob were younger sheep (maidens) and therefore less likely to have any prior Yersinia exposure, and thus immunity.

References

Brightling, A. (2006). Livestock Diseases in Australia. C.H. Jerram & Associates - Science Publishers
Bruere, A.N. & West, D.M. (1993). The Sheep: Health, disease and production. Foundation for Continuing Education of the N.Z. Veterinary Association
Corbel, M.J., Ellis, B., Richardson, C., & Bradley, R. (1992). Experimental Yersinia enterocolitica placentitis in sheep. British Veterinary Journal, 148(4), 339-349 doi.org
Fearnley, C., On, S.L.W., Kokotovic, B., Manning, G., Cheasty, T., & Newell, D.G. (2005). Application for fluorescent amplified fragment length polymorphism for comparison of human and animal isolates of Yersinia enterocolitica. Applied Environmental Microbiology, 71(9), 4960-5 doi.org
Fenwick, S.G., & Collett, M.G. (2005). Yersinia spp. Infections. In J.A.W. Coetzer & R.C. Tustin (Eds.), Infectious Diseases of Livestock 2^nd Ed. Oxford
Jerrett, I.V., & Slee, K.J. (1989). Bovine abortion associated with Yersinia pseudotuberculosis infection. Veterinary Pathology, 26, 181-183 doi.org
Karbe, E., & Erickson, E.D. (1984). Ovine abortion and stillbirth due to purulent placentitis caused by Yersinia pseudotuberculosis. Veterinary Pathology, 21, 601-606 doi.org
Peffer, K. (2020). Abortions in sheep - the silent killer. NSW Government Local Land Services. www.lls.nsw.gov.au
Schaake. J., Kronshage, M., Uliczka. F., Rohde, M., Knuuti, T., Strauch, E., Fruth, A., Wos-Oxley, M., & Dersch, P. (2013). Human and animal isolates of Yersinia enterocolitica show significant serotype-specific colonization and host-specific immune defence properties. Infectious Immunology, 81(11), 4013-4025 doi.org
Stanger, K.J., McGregor, H. & Larsen, J.W.A. (2018). Outbreaks of diarrhoea ('winter scours') in weaned Merino sheep in south-eastern Australia. Australian Veterinary Journal, 96(5), 176-183 doi.org
Watt, B.R. (2012). A case of Yersinia enterocolitica abortion in ewes. Flock and Herd www.flockandherd.net.au
Yang, R., Ryan, U., Gardner, G., Carmichael, I., Campbell, A.J.D., & Jacobson, C. (2016). Prevalence, faecal shedding and genetic characterisation of Yersinia spp. in sheep across four states of Australia. Australian Veterinary Journal, 94(5), 129-137 doi.org