PARASITES AND PARASITIC DISEASES OF DOMESTIC ANIMALS
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.
() 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.
() 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.