This infestation is caused by nematode worms of the genus Strongyloides spp. – the great majority being from S. stercoralis. This helminth is present throughout most tropical and subtropical countries. Larvae penetrate intact skin, especially the feet (as with hookworm infection). Their eggs mature and hatch in the lower gastrointestinal tract and larvae can immediately re-enter the circulation in the colo-rectum or perianal region, setting up an auto-infection cycle. Therefore, infection can continue for the remaining lifespan of the individual. Severe malnutrition may be a predisposing factor to infection, as was the case in prisoners of war in south-east Asia during the Second World War.

Whilst an infected patient is frequently asymptomatic, heavy infection can cause intestinal malabsorption with resulting weight loss. During the migratory phase an itchy linear rash (larva currens) may be present on the lower abdomen, buttocks, and groins; this gives rise to recurrent transient itching.

Treatment is with ivermectin (currently not licensed in the UK but prescribable).