Cause
Strongyloidiasis is caused by a parasitic roundworm called Strongyloides stercoralis, that mainly infects humans. This roundworm has different types of life cycles. At times, the larvae (immature stage) of the parasite may develop rapidly into the infective stage in the intestine where they penetrate the intestinal lining instead of passing out of the body in the feces, as occurs normally. This modification of the life cycle, called internal autoinfection, explains persistent strongyloidiasis, which can last as long as 40 years in people who have moved to areas where the infection is not generally found.
Autoinfection may produce heavy infections and severe disease, especially in people with reduced immunity such as those receiving corticosteroids or other immunosuppressive medicines, or those with acquired immune deficiency due to retroviruses such as human T cell lymphotropic virus-1 (HTLV-1).