Atlas of livestock parasites
digitized collection of microscopical preparations

Atlas of Parasites Contents Information sources Glossary Administration

Large strongyles



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Large Strongyles (Strongylus

vulgaris, Strongylus edentatus, and Strongylus

equinus) are reportedly the most damaging

parasites in horses throughout the world, of

which, Strongylus vulgaris is the most

notorious of these parasites. Their life cycle is

direct where the adults live in the large

intestine (colon) and cecum and reproduce by

laying eggs that pass back into the

environment of the animals via the feces. As

adults, these parasites are all plug feeders on

the intestinal wall and are bloodsuckers. The

prepatent period, which is the time it takes for an infective larva once ingested by a horse

to reach an egg-laying adult parasite, can take as much as six and one-half months.

The reason it takes so long for these parasites to mature is because the immature stages

undergo a period of migration through the body of the horse. These immature parasites

cause considerable damage during the migration through the body on their way to the

large intestine. Part of their migration is through the mesentery artery where excessive

numbers can cause obstruction, fever, and shock-like symptoms. The larvae can remain

in the artery for three to four months causing severe problems including restricted blood

flow resulting in diarrhea, aneurysm and colic, which may result in the death of the horse.


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