Strongylus vulgaris

Life Cycle

The life cycles of all three large strongyles have similar preparasitic phases. Adults are found in the cecum and colon of infected horses and donkeys. Strongyle-type eggs are laid by mature females and pass to the outside in host feces. Hatching and larval development to infective L3s will occur within a temperature range of 8-38 C.   Development from egg to the L3  will take about one week in mid summer in temperate climates.   Infection is by ingestion of the ensheathed L3s.

Click on the image of the gastrointestinal track (A)  to get a close up diagram of   larval migrations inside host.

(or_da_ar.gif (344 bytes)) After ingestion, S. vulgaris L3s exsheath in the small intestine, penetrate the intestinal mucosa and moult to L4s by 7 days after infection(B).  These L4s penetrate submucosal arteries and migrate along the endothelium to the cecal and colic arteries (by 14 days post infection) and then to the root of the cranial mesenteric artery and its main branches (C) which they reach by day 21 after infection.   After a period of development of 3-4 months, the larvae have molted to immature adults (L5s) but retain the fourth-stage cuticle as an external sheath. They return to the intestinal wall via the lumen of arteries.  Nodules are formed around the L5s mainly in the wall of the cecum and colon (D) Subsequent rupture of these nodules releases the young adult parasites into the lumen of the intestine where they mature in another 6 to 8 weeks.

(bl_da_ar.gif (345 bytes)) Adult male and females copulate and females lay eggs which reach the external environment in host feces.

The prepatent period is 6 to 7 months.

Click anywhere on the image to return to the S. vulgaris life cycle.


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Parasites and Parasitic Diseases of Domestic Animals
Dr. Colin Johnstone (principal author)
Copyright 1998 University of Pennsylvania
This page was last modified on January 24, 2000