Ascaris suum


Female worms may produce as many as 2 million eggs daily during her lifetime in the definitive host which can be a year or more. These thick-shelled eggs are resistant to freezing and drying and can therefore survive for as long as five years under most farm environments. However, exposure to sunlight and prologed exposure to drying will destroy them. Overall, these factors ensure that the normal swine environment will be well contaminated with Ascaris eggs, ensuring that all young pigs, especially  those raised on soil, will become infected. Asc17ath.jpg (20589 bytes)
Ascaris suum egg


Embryonation and development to the infective second stage larva takes between 13 and 18 days at temperatures between 30 and 33  'C provided the humidity is high and oxygenation is adequate. In temperate climates, with clearly defined seasonal changes, development will be minimal in winter and only one generation of Ascaris will occur each year. In heated confinement operations and in warm temperate climates found in the Southeast United States, development will be year round and several generations of A. suum may occur each year. Asc17bth.jpg (20234 bytes)

Ascaris suum egg containing an infective L2.

A. suum eggs will hatch in a number of animal species including ruminants, rodents and humans. However,  larvae usually do not migrate beyond the lungs. In ruminants, "milk spot" lesions and an asthma-like syndrome have been recorded in sheep and cattle grazing on pasture previously occupied by swine. In humans, clinical signs of asthma accompanied by an eosinophilia will develop 10 to 14 days after exposure to infective eggs.


In young pigs significant respiratory disease may occur during the prepatent period in response to migrating larvae. In these cases, clincial signs  may be present without finding the characteristic eggs in feces of infected pigs. In older animals infections are usually patent, in which cases a clear diagnosis can be made on finding the characteristic eggs ( small, ovoid, and thick-shelled with a mammillated outer coat) by fecal flotation.

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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