Vaccination against Strongylus vulgaris in Ponies: Comparison of the Humoral and Cytokine Responses of Vaccinates and Nonvaccinates

This chapter discusses vaccination against Strongylus vulgaris in ponies. Strongylus vulgaris is considered the most pathogenic nematode parasite of equidae because of the severe arterial lesions it causes in the mesenteric arteries during larval migration. Infective third-state larvae (L 3) ingested from contaminated pasture penetrate the mucosa of the large intestine, molt to fourth-stage larvae (L 4) in the submucosa, and then proceed along arterioles and arteries that supply the intestine to the root of the cranial mesenteric artery. Once there the larvae molt to immature adults (L 5) causing severe arteritis before returning, again via the vasculature, to the large intestine to complete their life cycle. Arterial lesions include tortuous subintimal tracts, thrombi, and, in severe cases, verminous aneurysms that can compromise perfusion of intestinal vascular beds. This syndrome known as verminous arteritis or thromboembolic disease is characterized by ischemic infarctions of the bowel, which result in toxemia, abdominal pain, and death in severe cases.