Nematodirus helvetianus: Thin-necked intestinal worm, thread-necked strongyle.

General Description: These relatively long roundworms grow up to 25mm in length.

Life Cycle: The life cycle is the direct one typical of roundworms, except that infective third-stage larvae develop within the eggs; moults to this stage occur on pasture about 2 to 4 weeks after leaving the host. Infective larvae in eggs are very resistant to drying and freezing. The host may be infected by ingesting the free infective larvae. The prepatent period is about 4 weeks.

Location: Small intestine.

Geographical Distribution: Worldwide.

Significance: Thread-necked strongyles become a problem when animals are heavily infected. Decreased weight gains are costly. Nematodiriasis may be more severe when animals are infected at the same time by other parasites.

Effect on Host: The host is harmed chiefly by the larval stages of Nematodirus. When present in large numbers, larvae cause destruction of the intestinal wall. Development of many adults may retard the growth of animals.

Diagnostic Information: Eggs, which appear in faeces, are larger than most strongyle eggs.

Control: Pasture rotation and treating cattle with a suitable anthelmintic.

Nematodirus, adult, anterior end		Nematodirus, adult, posterior end		Nematodirus - egg