Atlas of livestock parasites
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Metastrongylus salmi



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Metastrongylus salmi

General Description:
The adult lungworm is a slender white nematode up to 6 cm long. The eggs are embryonated (each contains a larva) when laid.

Life Cycle:
The eggs are laid in the bronchi and are coughed up, swallowed, and passed in the feces. The ova hatch after being ingested by earthworms. Infective third-stage larvae develop in 10 days and accumulate in the circulatory system of the intermediate host earthworms, where they may overwinter. Pigs become infected by ingesting these worms. The lungworm larvae then penetrate the intestines and proceed via the lymph and blood vessels to the lungs. The prepatent period is about 2 weeks.

Bronchi and bronchioles.

Geographical Distribution:
Common throughout the world.

Lungworms cause retarded growth and can carry the swine flu and hog cholera viruses. Metastrongylus primarily infect feeder pigs and older stock kept on old lots and permanent pastures. Continual reinfection of swine in these environments produces losses that make the lungworm one of the several most important parasites of pigs.

Effect on Host:
The larvae invading swine lungs irritate the air passages, rupture tissues, and cause inflammation. This damage predisposes the pigs to secondary bacterial infections, causing pneumonia. The viruses of hog cholera and swine influenza can be carried by pig lungworm larvae. Pigs infected with lungworm usually have a persistent cough, with loss of condition and retarded growth.

Diagnostic Information:
Characteristic eggs or larvae in the feces or adults in the respiratory tract at necropsy are diagnostic.

Lungworm control is synonymous with earthworm control. If swine are not housed in worm-free quarters, nose rings will prevent pigs from rooting for earthworms. Pasture rotation is not very practical in the management of Metastrongylus problems, as infected earthworms have been found up to 4 years after abandonment of a hog lot.


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