Parascaris equorum

Life cycle

The predilection site for adult worms is the small intestine of equines.

Preparasitic phase

The life cycle is direct. Eggs are passed in the feces of infected animals and at temperatures of 25'C to 35'C will be infective within 10 days. The infective stage is an egg containing a second stage larva  (Egg+L2).

Parasitic phase

Infection and migration to the lungsor_da_ar.gif (344 bytes)

Foals become infected by ingesting eggs containing L2s. These hatch in the gut and, L2s migrate through the wall of the small intestine (A) to the liver (B) via the hepatic portal system. Most L2s reach the liver within 24 hours after infection. The molt from L2 to L3 appears to occur between the mucosa of the small intestine and the liver

Within 7-14 days after infection, the majority of larvae have migrated on to the lungs (C) via the heart and pulmonary arteries.

Migration from lungs to the gut bl_da_ar.gif (345 bytes)

L3s break out of the alveolar capillaries into the alveoli and migrate up the bronchial tree to the trachea and pharynx. They are coughed up and swallowed. The final two parasitic molts (L3--> L4 --> immature adults) take place in the small intestine. The prepatent period ranges from 12-16 weeks.

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Parasites and Parasitic Diseases of Domestic Animals
Dr. Colin Johnstone (principal author)
Copyright 1998 University of Pennsylvania
This page was last modified on January 24, 2000