Atlas of livestock parasites
digitized collection of microscopical preparations

Atlas of Parasites Contents Information sources Glossary Administration

Nematodirus helvetianus (cattle)



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Nematode (order Strongylida) 

"thin-necked intestinal worm, thread-necked strongyle"

Distribution: worldwide. 

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

Life Cycle: The life cycle is the direct one typical of roundworms, except that infective third-stage larvae develop within the eggs; molts 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.

Diagnosis: These relatively long roundworms grow up to 25 mm in length. Eggs, which appear in feces, are larger than most strongyle eggs.

Size: 212 µm x  97 µm, 2-8 blastomeres surrounded by wide fluid-filled cavity, shell thin, colourless.

Clinical features: 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, such as Haemonchus and Trichostrongyles.

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


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