<i>Strongylus vulgaris</i> – An ancient threat revisited

Summary The equine bloodworm, Strongylus vulgaris, was historically considered the most pathogenic equine intestinal helminth parasite and was ubiquitous prior to the introduction of modern anthelmintic products. The frequent use of anthelmintics in recent decades is believed to have significantly reduced or eliminated the parasite from most managed equine populations, but recent data have demonstrated that it is enzootic and still causes serious abdominal disease in horses in some countries. Non‐strangulating intestinal infarctions (NSII) have been statistically associated with S. vulgaris infection, but a non‐invasive antemortem diagnosis of this condition is not possible at this time. The clinical presentation of NSII is variable but is often characterised by peritonitis and does not necessarily include colic manifestations. Current diagnostic tools can reliably detect the patent intestinal stage of infection with strongyles, whereas diagnosis of the more pathogenic prepatent stages remains a challenge. The parasite has not been reported to be resistant to any of the anthelmintic classes, but validated methodology for species‐specific anthelmintic efficacy evaluation is currently lacking. Epidemiological studies have suggested seasonal patterns in S. vulgaris transmission and infection, but only a few countries and climate types have been represented and some of these studies are over 50 years old. Quarantining and anthelmintic treatment of new arrivals has been associated with a lower risk of S. vulgaris infection, but more work is needed to develop protocols for the control of this parasite.