The Strongyloides life cycle is complex and not completely understood. It resembles that of the hookworms in that larvae migrate via the bloodstream to the lungs and eventually to the small intestine. The administration of corticosteroids may disrupt the usual cycle of autoinfection, resulting in disseminated infection.
Section of duodenal mucosa showing the very small adult worms
of Strogyloides stercoralis in the crypts of the mucosa.
Fecal smear showing Strongyloides stercoralis
larvae. Larvae demonstrated in feces or duodenal fluid are
the basis for diagnosis of infection. Rhabditiform larvae exit in the feces, and transform either into free-living adult nematodes or filariform larvae, which must penetrate the skin of their host in order to complete their life cycle.
Rhabditiform larva of S. stercoralis in faeces.
At this magnification it is very difficult to distinguish from the larvae of hookworm.
Strongyloides stercoralis in a tissue section from the small intestine of a renal transplant patient with abdominal pain and diarrhea. With heavy infections, there may be severe intestinal damage, but this is unusual. Peripheral eosinophilia of 50% to 75% may be seen, especially in immunocompetent hosts. Immunocompromised promised patients or those with chronic illness often have much less eosinophilia.
Higher magnification showing adult S. stercoralis in crypt in jejunal mucosa.
Strongyloidiasis. Ulcerated jejunal mucosa showing adult and larval forms of Strogyloides stercoralis.
Massive invasion of a lymph node by larvae
of S. stercoralis indisseminated infection
in an immunocompromised patient.
Strongyloides larva in bronchoalveolar lavage fluid of a bone marrow transplant patient who presented with bilateral pulmonary infiltrates. Autoinfection is probably the mechanism that allows for persistent infection in those individuals from an endemic area. Parasite and host are able to survive without problems until the host is immunosuppressed, at which time the larvae then begin to proliferate and disseminate to multiple organs. Mortality is very high in the hyperinfection syndrome.