The Strongyloides life cycle is more complex than that of most nematodes with its alternation between free-living and parasitic cycles, and its potential for autoinfection and multiplication within the host. 1. Rhabditiform larvae are excreted in the stool into the soil. 2. There, the rhabditiform larvae can become free-living adults or become infective filariform larvae that penetrate human skin (6). 3. Adult worms mate, and the females produce eggs. 4. Rhabditiform larvae hatch from the eggs. 5. These larvae can develop into free-living adults (2) or into infective filariform larvae (6). 6. The filariform larvae penetrate human skin. 7. The larvae migrate via the bloodstream to the lungs, break through pulmonary capillaries, ascend the bronchial tree to the pharynx, are swallowed, then reach the small intestine, where they mature into adults. 8. In the small intestine, the adult female worms produce eggs. 9. Eggs hatch into rhabditiform larvae. Most of the larvae are excreted in stool. 10. Some larvae become filariform larvae in the large intestine, penetrate the intestinal wall (internal autoinfection) or perianal skin (external autoinfection), and follow the normal infective cycle.
Image from the Centers for Disease Control and Prevention Image Library.