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Endoparasites - Haemonchus

Haemonchus contortus: Barber's pole worm, Stomach worm, wireworm.

General Description: Nematodes, 10 to 30mm long. Females are larger than males and have white ovaries wound spirally around the intestine which is red with the host's blood, giving a barber's pole appearance. Males have an even red appearance, a large bursa, and barbed spicules.

Life Cycle: Typical direct nematode life cycle. Eggs on pasture may reach infective stage in 4 to 6 days and may live on pasture up to 6 months. Few survive winter temperatures. Infection is by ingestion of eggs, and the prepatent period is approximately 19 to 21 days.

Location: Abomasum.

Geographical Distribution: Worldwide, especially in warm, humid climates.

Significance: Haemonchus contortus is a common parasite that may rapidly kill young sheep. Less severe cases produce weakness in animals, making sheep raising uneconomical.

Effect on Host: Anaemia is the basic feature of infection. When large numbers of larvae infect sheep, deaths can occur suddenly while the sheep still appear to be in good health. This is termed "acute prepatent disease" when eggs are not seen with faecal examination. Chronic infections involving smaller numbers of worms may produce oedema (bottle jaw), iron-deficiency anaemia, progressive weakness, wool breaks, and death. Both fourth-stage larvae and adult worms puncture blood vessels in the stomach wall and feed on the blood that is released. Nutrients are used by the host to replace lost blood elements rather than for growth and wool production. Sheep infected with Haemonchus contortus may exhibit self-cure, greatly reducing adult parasite loads. Damage by parasites in such cases is minimal after immunity develops.

Diagnostic Information: Strongyle-type eggs appear in faeces. However, in prepatent disease, clinical signs develop before adult stages are reached.

Control: Pasture management can reduce damage by Barber's pole worms. Overstocking should be avoided, and lambs should be weaned early and separated from ewes. Minimise contamination of feed and living quarters with manure. Anthelmintic treatment of infected animals with chemicals at appropriate times is important. A diet with sufficient nutrients, especially iron, with help to reduce the damage caused by Haemonchus.

Haemonchus – male   Haemonchus - female vulva area   SEM - Haemonchus
Mass of Haemonchus adults in the contents of the abomasum   Clump of Haemonchus   Bottle jaw


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