What is the pathophysiology of strongyloidiasis?

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

The life cycle of Strongyloides stercoralis is complex and unique among the intestinal nematodes. This worm has 2 types of life cycles—a free-living life cycle (rhabditiform larvae) and a parasitic life cycle (filariform infective larvae)—with 3 developmental stages: adult, rhabditiform larva, and filariform larva.

The first type of life cycle allows development of nonparasitic adults, both males and females, in the soil, which can indefinitely maintain infestation of the soil. This free-living phase is occasionally termed the heterogonic life cycle.

The second type of life cycle allows noninfective new larvae to molt in the human host into infective filariform larvae. Infective larvae can penetrate the intestine and set up a new cycle, commonly termed the hyperinfective or autoinfective cycle. In this setting, unlike in other intestinal nematodes of humans, the larvae can increase in numbers without reinfection from outside. This life-cycle variation is responsible for the decades-long persistence of infection in untreated hosts.

The adult female worm is a minute, slender, almost transparent worm that measures approximately 2.2-2.5 mm long and has a diameter of 50 µm. The adult female worm lives in tunnels between the enterocytes in the small bowel of humans.

A parasitic male exists, but it is found only in experimentally infected dogs and has no role in human infections. Parasitic males are shorter and broader than females and are easily eliminated from the intestine. Only adult females are found in infected humans.

Humans are the principal host of S stercoralis. Dogs, cats, and other mammals can also harbor the worm and may serve as reservoir hosts.


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