Larvae in stool develop into free-living adults or infective filariform larvae in the soil. The infective larvae penetrate skin to enter circulation, then pass to the lungs and finally to the upper small intestine, where they develop into adults. Adult worms produce eggs from which first-stage or rhabditiform larvae may hatch during transit through the bowel. In addition, infections can result in autoinfection when rhabditiform larvae develop to infective larvae while still within the bowel.
Humans are the primary host.
In endemic areas, children often have asymptomatic strongyloidiasis. A Loeffer-like pulmonary syndrome with eosinophilia may occur on passage of larvae through the lungs, but it is generally milder than that seen in ascariasis and hookworm infections. Inpatients with severe malnutrition or immunosuppression, disseminated strongliodosis can manifest as acute abdominal distress, paralytic ileus, asthma, or sprue-like disease. Only a few cases support a linkage between strongyliodasis and retroviral infections. The diagnosis must be considered in any patient from an endemic region who is to be treated with immunosuppressive agents.