After being swallowed by a pig, the young larvae burrow into the wall of the large intestine. Within a few days, the young worms emerge, attach to the lining of the large intestine and grow to maturity. A life cycle lasts 70-90 days. Whipworms cause considerable inflammation and irritation of the intestine. Whipworm infestation is characterized by loose stools which in many cases progresses rapidly to a severe, bloody diarrhea.
Diagnosis is made by finding worm eggs in the feces or by recovering worms at necropsy.
If sexually immature worms are causing the damage, eggs may not be found in the feces. 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.