Classification: ICD-9 127.2; ICD-10 B78
Syndromes and synonyms: Larva currens.
Agent: Strongyloides stercoralis, a minute nematode roundworm (up to 2.2 mm long). S. fuelleborni (not shown on the map) is a less common agent and can cause human disease in Africa and Papua New Guinea (‘swollen belly syndrome’ in infants).
Reservoir: For S. stercoralis: mainly humans, although infections in non-human primates and dogs have been described. S. fuelleborni is mainly found in in monkeys, but human-to-human transmission may occur in some geographical regions.
Transmission: Mainly skin contact with fecally contaminated soil, but oral transmission cannot be excluded.
Cycle: S. stercoralis has a free-living (asexual) and parasitic (sexual) lifecycle. Free-living filariform (L3) larvae in the soil penetrate the skin, enter the bloodstream, reach the lungs, travel up to the throat, and are swallowed. In the duododenal wall they mature into adult female worms, produce eggs that hatch immediately, thus only larvae (L1) are excreted. These non-infectious (L1) larvae develop further in the soil into either adult worms or infectious (L3) larvae. Some non-infectious L1 larvae may develop faster into infectious L3 larvae in the human intestine and penetrate the perianal skin or colon wall. This process of auto-infection may lead to hyperinfection in immunocompromised individuals.
Incubation period
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