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Thread worm (Strongyloides ransomi)

(506) These worms are very thin and hair like, 3-4mm long, and are one of the few species that can also multiply outside the host. S. ransomi is more important in warm climates where it is a major parasite of the sucking pig.

The life cycle

Unlike the other round worms of the intestine the threadworm larvae enter the pig by penetrating the skin or mucous membranes of the mouth and are transported by the blood to the lungs, coughed up and swallowed. They then develop to maturity in the small intestine. The infective larvae can also cross the placenta or be excreted by the colostrum and therefore infect piglets within 24 hours of birth. The prepatent period is from 3-7 days. Infection is uncommon in good dry farrowing houses.

Clinical signs

Larvae may be found in body tissues of young pigs particularly if infection has taken place via colostrum. Migration causes considerable damage and results in coughing, stiffness, pain, vomiting and bloody diarrhoea particularly from 10-14 days of age. Mortality can be high.


This is carried out by recognising the eggs in fresh faeces or the presence of the worm at post-mortem examination.


  • See Fig.11-9. below
Management control and prevention
  • The eggs already contain infective larvae and infection may occur as soon as they leave the sow.
  • Control is by good farrowing house hygiene and all-in all-out procedures to remove the free living forms.
  • Treat the sow with broad acting anthelmintics seven days prior to farrowing before entry into the farrowing house.
  • See introduction.

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