Abortion in a thoroughbred mare associated with an infection with avirulent Rhodococcus equi.
Authors: Nakamura Y, Nishi H, Katayama Y, Niwa H, Matsumura T, Anzai T, Ohtsu Y, Tsukano K, Shimizu N, Takai S
Journal: The Veterinary record
Summary
# Editorial Summary An eight-year-old thoroughbred with no prior health concerns aborted at 196 days of gestation, prompting investigation of the abortifacient agent through immunohistological and bacteriological examination of fetal tissues and maternal samples collected four days post-abortion. Rhodococcus equi was isolated in pure culture from multiple fetal sites (lung, heart, stomach contents) and maternal specimens (intrauterine fluid and faeces), with immunohistochemical confirmation in fetal lung tissue and characterisation via PCR and mouse pathogenicity testing as avirulent strains; notably, all isolates shared identical pulsed-field gel electrophoresis profiles, indicating a common source infection. Whilst histological examination revealed minimal lesion development in fetal tissues, the amnion and umbilical cord displayed characteristic oedema and petechial haemorrhages, and the mare developed elevated anti-R. equi antibody titres post-abortion. This case demonstrates that avirulent R. equi strains—traditionally regarded as non-pathogenic—can nonetheless cause significant reproductive failure in mares, challenging assumptions about virulence determinants and highlighting the importance of considering this organism in abortion investigations even when clinical signs in the dam are absent; practitioners should recognise that faecal shedding of R. equi by apparently healthy mares may pose transplacental infection risks, particularly during mid-gestation.
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Practical Takeaways
- •Avirulent R equi can cause abortion in mares despite being considered non-pathogenic; clinicians should consider this organism in cases of unexplained fetal loss
- •Faecal shedding by mares represents a potential source of intrauterine infection; maintain hygiene and monitor mares with diarrhoea during pregnancy
- •Post-abortion serology and bacteriology of intrauterine fluids are valuable diagnostic tools when placental tissue is unavailable
Key Findings
- •Avirulent Rhodococcus equi was isolated in pure culture from fetal lung, heart, and stomach contents, as well as intrauterine fluid and dam's faeces
- •Histological examination revealed oedema and petechial haemorrhages of amnion and umbilical cord but no significant fetal lesions
- •High anti-R equi antibody titre in mare after abortion confirmed infection
- •Pulsed-field gel electrophoresis showed identical VspI profile in all isolates from fetus and dam, indicating common source