The pathogenesis and control of strongyle infection in the horse.

This research offers an in-depth understanding of the life cycle of the equine parasite, Strongylus vulgaris, its infection pathway, and its clinical and haematological effects on horses. Additionally, the study shows how younger horses can get infected from overwintering larvae and untreated dams in the field.

Migration Cycle of the Strongylus Vulgaris

• The life cycle of the Strongylus vulgaris begins with the larvae penetrating the small and large intestines of the horse. This is followed by their migration into the lumen of submucosal arteries.
• The larvae then ascend the arterial tree, reaching a critical area known as the cranial mesenteric site within three weeks. Here, they mature to the fourth stage of their development.
• After a period of 3-4 months, these mature larvae exsheath, and the young adult worms begin a descent along the arteries back towards the intestines. They travel to the point where the arteries narrow down significantly.
• On reaching this constricted portion of the arteries, they rupture out of the nodules into the lumen of the intestine. This entire migration process, also known as the prepatent period, lasts about six months.

Clinical and Haematological Impact on Horses

• The infection of the Strongylus vulgaris results in a clinical syndrome in horses. While the observed symptoms align closely with recorded literature, they were found to be less severe in this study.
• Some significant haematological changes were noted with a sharp increase in White Blood Cells (WBC), a spike in the ratio of neutrophils to lymphocytes, and the occurrence of eosinophilia—an increased level of eosinophils in the blood.
• There was also a marked and steady increase in total serum proteins due to the surge in betaglobulins.
• The research noted higher rates of albumin catabolism in infected horses and decreased red cell survival.

Field Infection Sources

• Field studies revealed two primary infection sources for foals turned out to grass in the spring: overwintering larvae and untreated dams.
• However, the dams—foal’s mothers—were found to be the more significant source of infection. This suggests the importance of thorough treatment programs for adult horses to prevent infection of vulnerable young horses.