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Endoparasites - Parascaris

Parascaris equorum: Horse roundworm, Large roundworm, Ascarids

General Description: Parascaris is a rigid, heavy-bodied worm up to 50 cm. long.

Life Cycle: Parascaris has a typical direct nematode life cycle as described in the overview. Within the egg, the second-stage larvae develop to infectivity on pasture in 10 days to 6 weeks. When swallowed, larvae hatch and penetrate the wall of the intestine and are carried by the circulatory system to the liver and lungs depending on the temperature, where they break through the blood vessels and migrate up the trachea. They are then coughed up and swallowed again and mature in the small intestine.

Location: Small intestine of foals and young horses

Geographical Distribution: Very common throughout the world.

Significance: Highly significant, mostly in foals of 6 months or less, in which untreated parascariasis causes severe debilitation, poor growth, and even death.

Effect on Host: Adult worms in heavy infections can cause bile duct and intestinal obstructions, as well as occasional gut perforation. Damage is more widespread in foals, which have low resistance and may quickly accumulate massive worm burdens. Large numbers of larvae breaking into the lungs cause haemorrhages. Acute parascariasis is also accompanied by severe enteritis. Enteritis results in alternating constipation and foul-smelling diarrhoea. Infected foals become debilitated and lethargic and lose weight. Lung damage in foals causes "summer colds," with coughing, fever, and anorexia. Mature horses except the very aged rarely show clinical signs, as previous infections confer good resistance. Aged horses may lose some immunity and become readily infected.

Diagnostic Information: By identification of round, pitted thick-walled eggs in the faeces.

Control: Control programs aim at preventing or limiting infections in young animals. Pregnant animals are treated with anthelmintics and moved to clean pastures for foaling. Frequent manure removal with proper disposal will also help to keep the worm burden of foals low. The heat generated by stacked manure as it ferments will kill eggs containing larvae.

Parascaris– adult   Parascaris– egg   Parascaris blocking intestine of horse



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