Infection by Strongylus edentatus and Strongylus vulgaris in a warmblood crossbred foal in Ontario.

A 6-month-old warmblood-cross filly was presented to the Ontario Veterinary College Large Animal Hospital (Guelph, Ontario) because of acute profuse diarrhea unresponsive to treatment and severe wasting. The filly progressed to obtundation over 4 d and was euthanized. Postmortem examination revealed multifocal hemorrhage within the extraperitoneal fascia and diaphragm with intralesional, 4-centimeter-long, white nematodes. In addition, verminous arteritis of the cranial mesenteric artery, right colic artery thrombosis with segmental colonic infarction, ulcerative colitis, and segmental fibrinonecrotizing enteritis were present. Morphological and molecular evaluation of nematodes from the extraperitoneal fascia and diaphragm confirmed Strongylus edentatus infection. Histopathology identified intralesional nematodes within the thrombosed cranial mesenteric artery, consistent with Strongylus vulgaris, and numerous encysted nematode larvae consistent with cyathostomins in the colon. Bacterial culture of the colon isolated Salmonella spp., later confirmed via PCR as Salmonella enterica serovar Enteritidis, and PCR of the small intestine identified Lawsonia intracellularis. Although S. edentatus is rarely diagnosed in non-feral horses in North America, this case highlights that continued vigilance for its reemergence and that of other large strongyles, including S. vulgaris, is warranted. Key clinical message: The identification of lesions associated with both S. edentatus and S. vulgaris in this foal underscores the continued relevance of large strongyle infections in contemporary equine practice. This case emphasizes the importance of considering migratory strongyles during diagnostic evaluations and implementation of parasite control strategies in all horses that, in part, target large strongyles.