Strongyloides stercoralis
Strongyloides stercoralis infects 30 to 100 million people worldwide. It is endemic in the southeastern United States, South America, sub-Saharan Africa, and Southeast Asia.
The worms live in the soil and infect humans when larvae penetrate the skin, travel in the circulation to the lungs, and then travel up the trachea to be swallowed.
Female worms reside in the mucosa of the small intestine, where they produce eggs by asexual reproduction (parthenogenesis). Most of the larvae are passed in the stool and then may contaminate soil to continue the cycle of infection.
In immunocompetent hosts, S. stercoralis may cause diarrhea, bloating, and occasionally malabsorption. Unlike other parasitic worms, S. stercoralis larvae hatched in the gut can invade the colon mucosa and reinitiate infection (autoinfection).
Immunocompromised hosts, particularly people on prolonged corticosteroid therapy, can have very high levels of disseminated worms due to uncontrolled autoinfection. This hyperinfection can be complicated by sepsis caused by bacteria from the intestine, which are carried into the host’s blood by the invading larvae.
Morphology
In mild strongyloidiasis, worms, mainly larvae, are present in the duodenal crypts but are not seen in the underlying tissue. There is an eosinophil-rich infiltrate in the lamina propria with mucosal edema.
Hyperinfection with S. stercoralis results in invasion of larvae into the colonic submucosa, lymphatics, and blood vessels, with an associated mononuclear infiltrate.
There are many adult worms, larvae, and eggs in the crypts of the duodenum and ileum. Worms of all stages may be found in other organs, including skin and lungs, and may even be found in large numbers in sputum.
Pathology
strongyloidiasis
eosinophilic granulomatous enterocolitis