Parascaris equorum


Pathological changes in P. equorum infections in foals are similar to those seen in pigs infected with Ascaris suum and closely follow the pathway of migrating larvae. Focal hemorrhages are first seen in the liver 24 hours after an intial infection and are followed by the infiltration of eosinophils into tracks produced by  larvae during their wandering through the liver parenchyma. As larvae move on to the lungs, these hemorrhagic lesions  resolve and are replaced by fibrous tissue eosinopils and lymphocytes which appear grossly similar to "milk spot" lesions in livers of pigs infected with A. suum

Larval migrations through the lungs are associated first with the apearance of petechial hemorrhages followed by intense infiltrations of eosinophils around alveoli, bronchioles and small blood vessels. These are later replaced by lymphocytes. Beginning approximately four weeks after infection, lymphocytic nodules begin to appear under the pleura. They are raised, greyish-green in color and contain dying larvae and lymphocytes surrounded by a fibrous capsule. These nodules are more common in older foals that have experienced multiple natural reinfections and may indicate a strong immune response to migrating larvae.


A wide array of clinical signs have been attributed to P. equorum infections in foals and they include:

witeball.gif (201 bytes) coughing
witeball.gif (201 bytes) nasal discharges
witeball.gif (201 bytes) death (following impaction and intestinal rupture)
witeball.gif (201 bytes) reduced weight gains/weight loss
witeball.gif (201 bytes) reduced food intake

In foals up to 6 months old, coughing and greyish-white nasal   discharges are seen during larval migrations through the lungs. Endoscopic examinations of the trachea, at this time,  show a frothy mucus in the upper air passages.

Rapidly developing worms in the small intestine may be associated with a reduction in food intake and poor weight gains compared with worm-free animals. Infected foals have low levels of serum albumin that is attributed to a reduced appetite combined with the ingestion of amino acids(such as methionine) in the small intestine by feeding worms.

Heavy infections may result in gut impactions and death following rupture of the small intestine. Although this is not a common outcome of Parascaris infections, it's possibility emphasizes the necessity for good parasite control in growing foals. Asc20ath.jpg (20073 bytes)
P. equorum - rupture of the small intestine


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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