There are three species of Metastrongylus or lungworms. Female lungworms live in air passages in the lungs where they produce large numbers of thick-shelled eggs, which the infected pig coughs up, swallows and passes in manure. Earthworms swallow the eggs, which hatch in the earthworm's intestine and become infective in three to four weeks. Pigs become infested by eating earthworms which harbor the infective larvae. Lungworm infestation causes coughing and shallow breathing.
Hemorrhages occur on the surface of the pig's lungs during early stages of lungworm invasion.
Constant irritation by lungworms can bring about consolidation of lung tissue around sites occupied by worms. Tips of lungs become grayish or whitish and very hard in some cases. Secondary pneumonias are common. Pigs infected with lungworms tend to go off feed, become unthrifty and fail to grow. Diagnosis is made by isolating eggs or larvae from feces or by demonstrating larvae in nasal secretions.