A wide range of infectious agents may cause ewes to abort or deliver potentially viable lambs that die before, during, or soon after birth. They include Campylobacter fetus var intestinalis, Chlamydia pecorum (previously Chlamydia psittaci and Chlamydophila pecorum), Listeria ivanovii, several Salmonella species, Brucella ovis, Leptospira spp, Yersinia pseudotuberculosis, Toxoplasma gondii, Coxiella burnetti and Akabane and Border Disease virus (Plant 1990).
In early August 2010, the owner of a mob of 180 mature Merino White Suffolk ewes noticed five dead premature foetuses and two live premature lambs. The ewes, due to commence lambing two weeks later and in fat condition, were grazing a small paddock of ryegrass, cocksfoot and clover without supplementary feeding. Cats were present in sheds near the paddock.
Five dead premature lambs were presented for examination on 4 August 2010. On autopsy, the lambs were noted to be small, premature and autolysed but otherwise no abnormalities were detected.
The placenta submitted to the laboratory was autolysed with no other significant histological findings. Serological testing of heart blood was negative for Toxoplasma. The abomasal contents from two foetuses were culture negative for Listeria and Campylobacter but from one sample a moderate, pure growth of Yersinia enterocolitica was cultured.
Yersinia pseudotuberculosis causes disease in a wide range of animals including man (Karbe and Erickson 1984). It was recognised as an occasional cause of abortions in ewes (Watson and Hunter 1960) and was isolated from a stillborn lamb in Western Australia (Dennis 1966), from caseous abdominal abscesses in a ewe, epididymitis/orchitis in rams and was regularly cultured in cases of enteritis most commonly in young sheep (Glastonbury 1990). Yersinia enterocolitica also causes disease in man and other animals (Brewer and Corbel 1983). It was much less commonly isolated as a cause of enteric yersiniosis (Glastonbury 1990) but was also isolated from sheep foetuses, with 'unexpected frequency,' at least in the UK (Corbel et al. 1990).
Y. pseudotuberculosis is a normal inhabitant of the intestinal tract of sheep and cattle (Karbe and Erickson 1984, Glastonbury 1990). Y. enterocolitica has been isolated from the faeces of normal pigs and cattle (Brewer and Corbel 1983) and may be present as a normal intestinal inhabitant of some sheep. It is presumed that susceptible pregnant ewes are occasionally infected orally, from either sheep or other animals, producing placentitis and a generalised bacterial infection of the foetus.