contortus

Haemonchus contortus, commonly called the barber's pole worm, is a parasitic nematode that infects the stomach (abomasum) of small ruminants such as sheep and goats, and occasionally cattle and deer. It is widely distributed in warm and temperate regions and is a major cause of production losses due to parasitism in many parts of the world.

Taxonomy and biology. H. contortus belongs to the family Haemonchidae within the order Strongylida. Adult worms are slender and reddish and feed on host blood, which can lead to anemia, edema, and weight loss. The parasite has a direct life cycle: eggs passed in feces hatch into free-living larvae (L1 and L2) and molt to the infective third-stage larvae (L3) on pasture. Cattle and small ruminants ingest L3, which then molt to adults in the abomasum. The prepatent period is roughly 18–21 days under favorable conditions. The parasite thrives in warm, moist environments and can exhibit seasonal transmission patterns.

Clinical disease and diagnosis. Heavy infections cause anemia, pale mucous membranes, bottle-jaw edema, reduced growth, and poor-conditioning. Diagnosis relies on clinical signs, fecal egg counts, and hematological or serological tests. Fecal egg counts alone can be unreliable due to intermittent shedding and inhibitions by refugia. Targeted selective treatment and FAMACHA scoring (conjunctival color) are commonly used to guide deworming.

Control and resistance. Anthelmintic resistance to multiple drug classes is a global concern. Management includes strategic deworming, refugia maintenance, pasture rotation, mixed-species grazing, and vaccination in some regions. Vaccines against H. contortus exist in some markets and are part of integrated control programs.