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Endoparasites - Ostertagia

Ostertagia (Teladorsagia) circumcincta, Ostertagia trifurcata, Ostertagia lyrata: Small brown stomach worm.

General Description: Brownish, thread-like nematodes up to 12mm in length. Males are smaller with relatively straight, slender spicules.

Life Cycle: Typical direct nematode life cycle. Hatched larvae become infective in about 6 to 7 days and may survive on pasture for up to 4 months. Infection is by ingestion of these third-stage larvae. The minimal prepatent period is about 17 days, but many larvae enter the wall of the abomasum and become dormant (hypobiosis). Development to the adult stage may resume at any time; some larvae require up 3 months for this process.

Location: Abomasum.

Geographical Distribution: Widespread in moist, temperate regions of the world, especially where climates are cooler.

Significance: This nematode causes serious losses by producing weight loss and decreased wool production.

Effect on Host: Larvae in the glands of the abomasul wall cause irritation and erosion of cells. Continual, rapid replacement of damaged cells prevents cellular maturation. Consequently, the abomasum develops a lining of immature cells that are not joined together well and that do not secrete hydrochloric acid and the enzyme pepsinogen, two important elements of digestion. As a result, fluid leaks between cells into the gut. The pH of the gut contents rises from pH2 to pH7, resulting in poor digestion and increased growth of bacteria. The gut becomes more inflamed. Fluid absorption, a major function of the intestine, is blocked, causing profuse, watery diarrhoea. Albumin is an important blood protein, of which large amounts may be lost in fluid leaked into the gut. Lost albumin must be replaced from the diet. This is difficult to achieve since improper digestion prevents adequate absorption of nutrients in the intestine. Ostertagiasis is worsened by the fact that infected animals lose their appetite and do not feed. Weight loss occurs: animals may lose up to 20 percent of their body weight in 7 to 10 days. Death may follow.

Diagnostic Information: Strongyle-type eggs appear in faeces.

Control: Pasture management can reduce damage by stomach worms. Overstocking should be avoided, and lambs should be weaned early and separated from ewes. Minimise contamination of feed and living quarters with manure. Anthelmintic treatment of infected animals with chemicals effective against larval stages at appropriate times is important. A diet with sufficient nutrients, especially iron, is essential to help sheep overcome the effects of Ostertagia infection.

Ostertagia – anterior end   Ostertagia cicumcinta – male posterior end
Hypobiotic larvae – abomasum   Osteragia circumcincta – female vulva area


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