Strongyloidiasis, an
infection by the small intestinal nematode Strongyloides stercoralis, is encountered
worldwide but is most common in tropical climates.
In immunocompetent
individuals S. stercoralis can produce asymptomatic infections or a
moderate clinical picture of diarrhea, some cases become chronic. In
immunocompromised patients, a disseminated disease may appear, sometimes
fatal.
S. stercoralis is a complex organism that has three life
cycles.
In one, parasitic parthenogenic females live in the human small
intestine and lay eggs that hatch in the mucosal epithelium, releasing
rhabdoid larvae.
These larvae become infective within the intestine or on
the perianal skin and invade human hosts directly (the autoinfection
cycle).
Alternatively, rhabdoid larvae pass in the faeces, become
infective larvae in the soil, and later penetrate human skin (the direct
development cycle).
In the third possible cycle (the indirect development
cycle), rhabdoid larvae passed in the faeces become free-living adults in
the soil eventually produce infective larvae.
These infective larvae
penetrate the skin, enter blood vessels, and pass to the lungs, where they
invade alveolar spaces.
They ascend the trachea, descend the esophagus,
and mature to become parthenogenetic females in the small intestine.
Invading larvae
cause transient dermatitis.
Larvae migrating through the lungs may
provoke cough , hemoptysis , and dyspnea, but most infections do not lead to
pulmonary symptoms.
Severe infection of the intestine is debilitating and
causes vomiting, diarrhea, and constipation.
This is often associated with
the autoinfective cycle.
In patients with suppressed immunity, infective
larvae are more likely to penetrate the intestinal mucosa and invade the
body.
This "hyperinfection" strongyloidiasis may cause
malabsorption and
hypoproteinemia with anasarca, and may be severe enough to kill the
patient.
Obstruction from paralytic ileus and from thickening and
immobility of the colon are characteristic of persistent hyperinfection.
Female worms and rhabdoid larvae living in jejunal crypts cause mild eosinophilia and
chronic inflammation.
By contrast, patients with hyperinfection may have
ulceration, edema, congestion, fibrosis, and severe inflammation of the
intestine.
In such cases, filariform larvae invade both the small and
large intestine and may travel to any organ.
Larvae in tissues
may cause no reaction or may provoke microabscesses or granulomas.
The diagnosis is
made by identifying larvae in the stool. Larvae may occasionally be in
sputum, pleural effusions and urine.
Chemotherapy is generally
unsatisfactory, but thiabendazole may be useful.
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