Published reports suggest that some species of earthworms may serve as paratenic hosts or even intermediate hosts for the pig parasite, Ascaris suum. This study was conducted to determine whether infective As. suum eggs could hatch and the larvae remain infective within the earthworm, Lumbricus terrestris. Pig feces containing infective As. suum eggs were fed to earthworms that were then allowed to purge their intestines and eliminate ascarid eggs. Although exposed earthworms were examined using direct dissection, agar, and digestion techniques, no As. suum larva was recovered from the earthworms. Twenty-five exposed earthworms were administered to each of 3 helminth-free pigs, but no As. suum larva was isolated from the liver, the lungs, or the small intestine on days 4, 7, and 11 postinoculation. No intermediate or paratenic host role for L. terrestris in the As. suum life cycle was demonstrated. Unexpectedly, unidentified nematode larvae were isolated from both the earthworms and the lungs of the earthworm-fed pigs. These earthworms were imported from Canada and were usually sold to anglers for fish bait, suggesting that the human-mediated transport of intermediate or paratenic hosts may introduce parasites to new geographic regions.
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