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Endoparasites - Oesophagostomum

Oesophagostomum columbianum (only reported in NZ in sheep imported from Australia), Oesophagostomum venulosum: Nodule worm

General Description: Adult nematodes up to 20mm long with a narrowed front end.

Life Cycle: Direct nematode life cycle. Infective larvae appear in 6 to 7 days after eggs pass in faeces. Ingestion of third-stage larvae produces infection. Larvae burrow into the wall of the gut anywhere from the stomach to the rectum. Here they moult to the fourth stage before leaving the gut wall and migrating to the large intestine, where they undergo their final moult and grow to the adult stages. The prepatent period is about 41 days.

Location: Large intestine.

Geographical Distribution: Worldwide with few exceptions.

Significance: Persistent infections cause wasting of animals; wool and meat production are seriously impaired. Intestines are condemned for casing use because of nodule formation.

Effect on Host: Oesophagostomum columbianum larvae in the gut wall cause nodule formation which impairs the ability of the intestine to absorb fluid; diarrhoea results. Nodules may rupture and cause abdominal cavity infection leading to sheep deaths. Adult nodular worms cause a thickening of the large intestine wall, also limiting its ability to absorb fluid. Irritation results in production of mucus which appears in faeces. Since nodular formation is rare with Oesophagostomum venulosum, it is considered to be less pathogenic. Appetite of infected animals is greatly reduced. They do not consume enough feed for growth and maintenance. Moreover, the food they do eat is not properly digested and absorbed. Sheep lose much weight as a result, and wool growth is minimal.

Diagnostic Information: Strongyle-type eggs may be found in faeces of animals with chronic infections. Acute cases may only have fourth-stage larvae in faeces.

Control: Pasture management and anthelmintic treatment of infected sheep should be used to keep parasite loads minimised. Strategic drenching is needed and checks that the anthelmintic is effective against this parasite.


   
Oesophagostomum – anterior end   Oesophagostomum – male posterior end   Nodules in intestine

           

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