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Given certain conditions, the first-stage larvae can develop into a free-living (nonparasitic) generation of males and females. The fertilized eggs laid by the females of this generation develop into infective third-stage larvae. This capacity for exogenous reproduction explains the enormous potential for contamination of a given environment with Strongyloides larvae. Third-stage larvae are highly sensitive to desiccation, but remain viable for two to three weeks in the presence of sufficient moisture.

The parasitic part of the life cycle is similar to that of the hookworms in that Strongyloides also penetrate the host's skin and the larvae reach their target localization in the small intestine by way of lung and tracheal migration. The prepatent period is at least 17 days. Strongyloides larvae can also be occasionally transmitted via mother's milk.

The potential for autoinfection with this organism is worthy of mention. The first-stage larvae can transform into infectious larvae during the intestinal passage or in the anal cleft and penetrate into the body through the large intestine or perianal skin. Continuous autoinfection can maintain an unnoticed infection in an immunocompetent person for many years (see below).

Humans are the main reservoir hosts of S. stercoralis; infections can also be transmitted from monkeys or dogs, but this route of infection is insignificant.

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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