These parasites are often
referred to as ascarids.
These are the largest
parasites reaching a length of up to 30cm long and about the thickness of a
pencil. Their
eggs, which contain the infective larvae, are well protected by a thick
sticky outer coat that enables them to survive for years on pasture and in
stables.
Horses and foals are
infected by swallowing the eggs picked up from the pasture or from cracks
and crevices in contaminated stabling. The larvae migrate through the
bloodstream to the liver and lungs before returning to the small Intestine
to develop Into adults again. These can be present in the foal's small
intestine from 12 weeks of age.
Adult worms can cause stop
weight gain and lead to the emaciation of the foal. Heavy burdens can block
the gut causing
digestive problems, and in rare cases a fatal blockage or rupture of the
gut. Migrating larval stages can cause 'summer colds' with fever, coughing and
loss of appetite as they migrate through the lungs.
Foals develop their own
immunity to these worms at about 18 months of age.
