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Endoparasites - Nematodirus

Nematodirus spathiger, Nematodirus battues, Nematodirus filicollis, Nematodirus abnormalis: Thin necked intestinal worm.

General Description: Relatively long, thin nematodes, from 10 to 30mm in length, with a thin anterior portion that enlarges at the front end of the worm, giving the head region a swelled appearance.

Life Cycle: Direct life cycle. Infective larvae develop within the eggshell on pasture. Larvae within eggshells are very resistant to drying and freezing and may thus survive winter weather to infect sheep in early spring or late winter. Nematodirus battus and N filicollis, in fact, require prolonged exposure to cold temperatures before they are able to hatch. Infection is by ingestion of third-stage larvae, free-living or in eggs. The prepatent period ranges from 15 to 28 days.

Location: Small intestine.

Geographical Distribution: Nematodirus spathiger - worldwide. Nematodirus filicollis and Nematodirus abnormalis - worldwide except Africa.

Significance: For many years Nematodirus was not considered to be pathogenic, but clinical evidence demonstrates that they are.

Effect on Host: Larval stages are the primary cause of disease. The lining of the small intestine is greatly damaged; pieces of it may become loose and be shed in faeces. Loss of appetite, diarrhoea, and weight loss may occur. Wool growth is reduced in chronic infections. The overwintering of infective Nematodirus battus larvae in Great Britain provides larvae for infection in the spring. Lambs on such pasture receive great numbers of larvae in a short period of time. Acute diarrhoea and dehydration result; 10 percent of the lambs may die.

Diagnostic Information: Characteristic large strongyle-type eggs appear in faeces.

Control: Pasture management and regular anthelmintic treatments of infected sheep should be employed to reduce parasite loads.

Nematodirus – anterior end   Nematodirus spathiger – male posterior end
Nematodirus – posterior   Nematodirus – (Big Egg)


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