A retrospective study of the prevalence in equine postmortems of cranial mesenteric arteritis caused by Strongylus vulgaris in Alberta (2010 to 2022).

Background: Strongylus vulgaris is one of the most pathogenic nematodes affecting equids. Larval migration through the cranial mesenteric artery (CMA) with attendant arteritis and thromboembolism can result in fatal non-strangulating intestinal infarction. Once considered a historical disease, recent studies have described the reemergence of this pathogen in several European countries; however, little is known of the current prevalence of S. vulgaris in the Canadian horse population.

Objective: To determine the prevalence of active S. vulgaris cranial mesenteric arteritis in horses submitted for postmortem examination to the Diagnostic Services Unit (DSU) at the University of Calgary Faculty of Veterinary Medicine.

Animals and procedure: We conducted a retrospective review of all equine postmortem cases submitted to the DSU between July 1, 2010 and June 30, 2022. Over 12 y, 510 horses > 2 mo of age from Alberta were submitted to the DSU for necropsy. Active cases were defined as those with endarteritis and thrombosis in the CMA or its branches. Those cases with only intimal scarring of the CMA were classified as historical.

Results: The prevalence of all CMA lesions (both historical and active) over the study period was 17.3% (88/510). Active S. vulgaris cranial mesenteric arteritis was documented in 6.1% (31/510) of equine postmortems and the sequelae of verminous arteritis were the cause of euthanasia or death in 1.5% (8/510) of the cases submitted.

Conclusion and clinical relevance: Even after historically intense efforts to eradicate this parasite, the continued effects of S. vulgaris are demonstrated by the results of this study. Strongylus vulgaris should not be regarded as a parasite of the past and verminous arteritis remains an important differential diagnosis for horses in western Canada presenting with mild colic or dull demeanor and anorexia of duration > 24 h. Furthermore, S. vulgaris should be taken into careful consideration when implementing antiparasitic control strategies. Practitioners should remain current on prevention, diagnosis, and treatment of this potentially reemerging and fatal equine disease.