Attempts to induce nocardioform placentitis (Crossiela equi) experimentally in mares.
Authors: Canisso I F, Ball B A, Erol E, Claes A, Scoggin K E, McDowell K J, Williams N M, Dorton A R, Wolfsdorf K E, Squires E L, Troedsson M H T
Journal: Equine veterinary journal
Summary
# Editorial Summary: Nocardioform Placentitis in Mares Despite being recognised as a cause of late-gestation pregnancy loss in horses, nocardioform placentitis remains poorly characterised, prompting researchers to develop an experimental model that might illuminate its pathogenesis and aetiology. Canisso and colleagues conducted three linked studies: intrauterine inoculation of *Crossiela equi* in periovulatory mares (n=20), systemic or mucosal inoculation of the organism in mid-gestational mares (n=13, with 60 controls), and endometrial sampling of 200 Thoroughbred mares before and after mating to detect nocardioform organisms. The investigators failed to reproduce nocardioform placentitis through any inoculation route—only 3 of 20 mares in Study I showed PCR evidence of *C. equi* following intrauterine challenge, and the majority of treated mares carried pregnancies to term with grossly normal placentae, whilst no nocardioform organisms were detected in any endometrial swabs from naturally mated mares. These findings suggest that simple bacterial presence is insufficient for disease development, indicating that route of infection, exposure duration, microbial dose, or additional host predispositions (such as immunocompromise, stress, or concurrent infections) likely underpin nocardioform placentitis in clinical cases. Practitioners should recognise that whilst nocardioform organisms may occasionally be cultured from reproductive tracts, their presence alone does not predict placental disease, and future investigative work must explore these cofactors to understand which mares develop clinically significant infection.
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Practical Takeaways
- •Nocardioform placentitis cannot be reliably induced by simple bacterial inoculation, suggesting it is a multifactorial disease requiring investigation of additional risk factors in affected mares
- •Presence of C. equi or related actinomycetes in the mare's reproductive tract alone does not guarantee placental disease development, so detection requires careful clinical correlation
- •Current understanding of nocardioform placentitis pathogenesis remains incomplete; practitioners should not assume single bacterial exposure explains cases and should consider concurrent immunological, nutritional, or environmental stressors
Key Findings
- •Intrauterine inoculation of C. equi during periovulatory period identified organism in only 3/20 mares by PCR but did not induce placentitis; 16/20 delivered normal foals
- •Systemic inoculation (intranasopharyngeal, oral, or i.v.) of C. equi at midgestation in pregnant mares did not produce nocardioform placentitis; 13/13 treated mares delivered normal foals/placentas
- •Endometrial swabs from 200 Thoroughbred mares collected before and after mating showed no evidence of nocardioform microorganisms by PCR
- •Findings suggest nocardioform placentitis requires additional factors beyond bacterial presence, including route of infection, duration of exposure, dose, and unknown predisposing conditions