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Endoparasites - Haemonchus

Haemonchus contortus, Haemonchus placei: Large stomach worm, twisted wire worm, barber´s pole worm.

General Description: Adults are 10 to 30 mm long. Males are shorter than females and have an even, reddish colour and a bursa with an asymmetrical dorsal lobe and barbed spicules. Females are identified as "barber´s pole worms" because their white ovaries are wound around their red blood-filled intestine.

Life Cycle: Eggs laid by adults in the abomasum are passed in the faeces and hatch on the ground. On pasture they undergo a typical series of moults, becoming infective in about 4 to 6 days. Ingestion of these larvae from pasture begins the infection. Fertile adults may appear in approximately 28 days, but disease signs may appear earlier because larvae and immature adults, as well as fertile adults, suck blood.

Location: Abomasum.

Geographical Distribution: Worldwide in warm wet areas. Uncommon in New Zealand cattle.

Significance: Stomach worm, a common parasite, is one of the most pathogenic nematode parasites of ruminants. Very heavy infections often cause death in young and well-fed animals.

Effect on Host: Adult Haemonchus and fourth-stage larvae puncture small blood vessels of the abomasal wall, feeding on the blood. Haemonchus is thought to inject an anticoagulant into the wound so that the host actually loses more blood than the worms ingest. The host must replace this blood, particularly the lost red cells, drawing on its limited iron reserves. When these are exhausted, an iron-deficiency anaemia results. Death may occur if the anaemia is severe. The disease haemonchosis is characterised by anaemia, subcutaneous oedema, and weight loss.

Diagnostic Information: Strongyle-type eggs appear in the faeces. However, in acute infections anaemia and death may occur before the worms reach reproductive maturity.

Control: Treatment with anthelmintics. Management practices such as pasture rotation and avoidance of overcrowding may be helpful.

Haemonchus adult   H. contortus anterior
Haemonchus – adult, posterior end, (note asymmetric ray)   Scanning electron microscope photo – H. contortus – anterior

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