What is the pathophysiology of stage 3 of the Strongyloides stercoralis life cycle in strongyloidiasis?

Updated: Jun 20, 2019
  • Author: Pranatharthi Haran Chandrasekar, MBBS, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Answer

When they reach the small bowel, they molt twice and mature into adult females (2 mm × 0.05 mm in diameter). (All parasitic adult worms are female.) The parasitic females produce eggs via parthenogenesis. Each adult female may live up to 5 years and continue the reproductive cycle. Their eggs hatch into noninfective rhabditiform larvae within the intestine, which may then be passed through the stool into the environment, where they mature into adult males and females (see the image below). Compared with hookworms, adult Strongyloides organisms lie embedded in the intestinal folds. The traditional migratory pathway is now perceived to exist in conjunction with an equally significant direct migration from the skin to the duodenum.

Strongyloides is the only helminth to secrete larvae (and not eggs) in feces. Typically, larvae appear in feces approximately 1 month (about 28 days) after skin penetration, but the incubation period is unknown. As long as the patient is infected, which can be for several decades, the infection is communicable. The excreted rhabditiform larvae may again live freely in soil or be transformed into filariform larvae awaiting another human host. Alternatively, they may cause autoinfection.

Third stage, life cycle of Strongyloides stercoral Third stage, life cycle of Strongyloides stercoralis. Illustration by Tessa Kalman.

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