Ascaris suum

Pathogenesis


Migrating larvae in the liver cause an inflammatory reaction,  intralobular tissue destruction and hemorrhage. This is followed by an intense infiltration of   eosiniphils and collagen production. These lesions are visible at necropsy on liver surfaces as whitish areas and are commonly called "milk spots" since they resemble splashes of milk. In the absence of reinfection these lesions will begin to regress  after larvae migrate beyond the liver  and will be healed completely after 4 to 6 weeks: therefore their presence  at necropsy is an indication of   recent infections. In pigs that experience multiple reinfections during their lifetimes, livers become markedly fibrotic .

 

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Pig liver - normal

Pig liver - "milk spot" lesions

Pig liver - fibrosis

 

Asc9ath.jpg (26141 bytes) Migration of larvae in the lungs also produces hemorrhagic lesions and intense infiltrations of eosinophils around alveoli into which larvae are migrating on their way up the bronchial tree. Repeated infections will produce more widespread hemorrhages, edema and emphysema. The image to the left shows significant hemorrhagic lesions in the apical and cardiac lobes of Ascaris- infected lungs. Damage to lungs by migrating A. suum larvae may also exacerbate enzootic pneumonia and enhance latent infections with swine influenza virus.

 

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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