Haemonchus contortus

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Also known as: Barber's pole worm — Haemonchus placei

Kingdom Animalia
Phylum Nematoda
Class Sercernentea
Sub-class Rhabditia
Order Strongylida
Family Trichostrongyloidea
Genus Haemonchus
Species H. Contortus/ H. placei, H. Longistipes, H. similis


Haemonchus contortus is a nematode parasite from the family Trichostrongyloidea. It is found worldwide, and is an extremely important parasite of sheep and goats, particularly in tropical/ subtropical regions.

Within the UK, it is found most commonly in the South, where the climate tends to be a little warmer and drier. Some have shown complete resistance to current anthelmintics which is posing a real problem, making sheep and goat farming extremely difficult in some areas of the country.

Predilection site: Abomasum


The eggs are yellow, and approximately 70–85 μm long by 44 μm wide. The adult female is 18–30 mm and is easily recognized by its distinct “barber pole” coloration. The female has a red and while appearance, the red is due to the fact it is a blood feeder, and the white represents the ovaries coiled around the blood filled intestines.

The male adult worm is considerably smaller than the female, and is around 10–20 mm. It holds a characteristic copulatory bursa, which is an important diagnostic aid.


H. contortus is a direct parasite, therefore, it only occupies definitive hosts, namely; Sheep, cattle, goats, deer, camels, and llama.

Life Cycle

This life cycle is direct, and very much typical of a trichostrongyloid.

The females are known to be extremely productive eggs layers. The first larval stage, also known as L1 hatch on pasture and may develop into L3 within 5 days under favourable conditions. However, under cool conditions this stage of development may take several months.

L3 then moults into L4 within 48hrs. The L4 then penetrate the lining of the abomasum using their anterior spicules. L4 are able to draw blood from the host through the buccal capsule, causing severe anaemia in some cases. As adults they are able to move freely along the mucosal surface. Eggs are subsequently shed onto pasture by the host within 3 weeks of infection, and the life cycle continues.

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