Processionary caterpillar setae and equine fetal loss: 1. Histopathology of experimentally exposed pregnant mares.
Authors: Todhunter K H, Cawdell-Smith A J, Bryden W L, Perkins N R, Begg A P
Journal: Veterinary pathology
Summary
# Editorial Summary: Processionary Caterpillar Setae and Equine Fetal Loss Equine amnionitis and fetal loss (EAFL) remains a significant reproductive challenge, particularly in regions where Processionary caterpillars (*Ochrogaster lunifer*) are endemic, yet the precise mechanism linking caterpillar exposure to abortion had not been definitively established. Todhunter and colleagues administered suspended whole caterpillar material (50–100 g) orally to six pregnant Standardbred mares at various gestational stages over five consecutive days, systematically euthanising animals at intervals from day 2 to day 24 post-exposure to examine histopathological changes. Setal fragments penetrated the entire gastrointestinal tract in all treated mares, with migration into the uterus (5/6 mares), mesenteric lymph nodes (5/6) and liver (4/6), triggering acute gastroenteritis and colitis alongside endometritis and focal serositis; setal invasion of mucosal tissues produced lesions ranging from superficial erosion to deep ulceration, with inflammatory responses including microabscesses and microgranulomas in deeper tissues. These findings provide compelling evidence that caterpillar setae function as mechanical vectors for bacterial translocation across the gastrointestinal and uterine barriers, fundamentally altering our understanding of EAFL pathogenesis. Practitioners in endemic regions should consider caterpillar exposure as a significant risk factor during mid-gestation, warranting prophylactic management strategies and client education regarding pasture monitoring and exposure prevention during vulnerable periods.
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Practical Takeaways
- •Processionary caterpillar ingestion by pregnant mares poses a direct risk to fetal viability through setal fragment migration to the uterus acting as a bacterial vector
- •Monitor pregnant mares in endemic areas (Australia) for signs of gastroenteritis and endometritis, particularly during caterpillar season when EAFL risk increases
- •Understanding this toxin pathway may inform prevention strategies and early intervention protocols for mares at risk of EAFL
Key Findings
- •Caterpillar setae migrated to uteri and mesenteric lymph nodes in 5 of 6 treated mares, with setal fragments found in liver of 4 mares
- •All 6 treated mares developed acute gastroenteritis; 5 of 6 developed acute colitis and endometritis
- •Setal invasion of mucosa caused lesions ranging from superficial erosion to deep ulceration with neutrophilic, eosinophilic, and mononuclear inflammatory responses
- •Direct migration of setal fragments through gastrointestinal tract to uterus suggests mechanism for bacterial-induced abortion in EAFL