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Lungworms (Metastrongylus apri)

(499) This slender worm, up to 50mm in length, is found in the small bronchi (air passages) of the lungs.

The life cycle

This is indirect. The eggs are laid by the adult worm in the bronchi, they are coughed up, swallowed and passed out via the faeces. They are eaten by earth worms in which they develop through three larval stages over ten days to become infective. The cycle is completed by the pig eating the earth worm. Infection therefore only occurs where pigs have access to earth worms, for example in outdoor production. The larvae from the earth worm penetrate the intestine and migrate via the lymph nodes and blood vessels to the lungs undergoing two more larval stages in the process. The prepatent period is 3-4 weeks.

Clinical signs

These are primarily due to irritation as the larvae migrate through the lungs and the presence of the worms and their eggs in the bronchi. This produces a persistent cough and mild pneumonia. The lung damage can precipitate or enhance other respiratory diseases. Growth rates may be impaired.

Diagnosis

This is determined by the recognition of the characteristic eggs in the faeces but these are not easy to find. The worm and its eggs can be identified at post-mortem examination by cutting the posterior margins of the diaphragmatic lung lobes and extruding them by squeezing. Lungworm infection is unlikely to occur if pigs are reared on concrete.

Treatment

  • See Fig.11-9. below
Management control and prevention
  • This is effected quite simply by preventing access to infected earth worms.
  • If pigs are at grass then it is necessary to treat the herd and move onto clean pasture that has not had pigs on before. The larvae can survive inside the earth worm for a number of years.
  • See introduction.


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