PARASITES AND PARASITIC DISEASES OF DOMESTIC ANIMALS


The Nematodes


Trichostrongyles  - life cycles

Nematodes belonging to the family Trichostrongylidae have life cycles that are closely similar. Predilection sites include the abomasum, stomach or small intestine of ruminants, horses or swine depending on the species. Some examples are given in the following table.

Nematode Host Predilection site
Ostertagia ostertagi Cattle Abomasum
Trichostrongylus axei Ruminants, horses, pigs Abomasum, or stomach
Cooperia curticei Sheep, goats Small intestine


Pre-parasitic phase

The pre-parasitic phase of larval development is entirely free living. Eggs are passed in the feces of infected hosts.  Contained embryos will develop into first stage larvae if temperature and humidity are optimal (22-26'C and 100% humidity). First (L1) and second (L2) larval stages feed on fecal and soil bacteria but the third stage(L3) cannot feed because it is enclosed by a protective, impermeable sheath (the retained L2 cuticle). These ensheathed L3's survive by utilizing nutrients stored by the actively feeding L1 and L2 stages.

Parasitic phase

The trichostongylid infective stage is an L3 enclosed in its protective sheath and hosts are infected, by ingesting L3's, as they graze on pasture.

Exsheathment is the next event in the parasitic phase of these life cycles. Exsheathment sites are species-specific and are always proximal to the predilection site of each particular trichostrongylid species. As examples, Ostertagia ostertagi, an abomasal nematode, exsheaths in the rumen, while Cooperia curticei, with its predilection site in the small intestine, exsheaths in the abomasum. Exsheathment is immediately followed by movement of parasitic L3's to the predilection site where growth and development to adults occurs (L3--> L4-->Adults).

Following sexual reproduction, mature females lay eggs approximately 2-3 weeks after infection. The time from infection to egg-laying by adult females is specific for each nematode species and is called the prepatent period.

The following table gives some prepatent periods for several members of this family.

Nematode Prepatent period
Ostertagia species 17-21 days
Haemonchus species 2-3 weeks
Cooperia species 15-18 days

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Parasites & parasitic diseases of domestic animals
Dr. Colin Johnstone (principal author)
Copyright 1998 - University of Pennsylvania
This page was last modified on February 11, 2000