Strongyloidiasis is an intestinal parasitic infection caused
by the roundworm Strongyloides stercoralis. Strongyloides has
a unique ability to replicate within its host and behave as a potentially
fatal opportunistic pathogen in patients who are immunocompromised,
particularly in those receiving corticosteroids. The global prevalence
of strongyloidiasis is estimated to be 30 to 100 million cases.1Strongyloides infections
are endemic in most tropical regions of the world, with hyperendemic
areas in Brazil and central Africa. Endemic foci are also found
in certain temperate areas such as the south-central United States (especially
eastern Kentucky and rural Tennessee) and both western and eastern
Europe. Most infections diagnosed in temperate climates were acquired
by travel in the tropics. Humans are the principal host, but dogs,
cats, and other animals may be reservoirs.2
Infection is acquired when third-stage filariform larvae, which
are usually found in contaminated soil or in human stool, penetrate
the human skin, enter a blood or lymphatic vessel, and proceed to
the lungs (eFig. 330-1).
Larvae break into the alveolar spaces and migrate through bronchi,
trachea, esophagus, and stomach to reach the duodenum, where female
worms complete their maturation. Males are nonparasitic and pass
with the stools after migration is completed. Adult females establish
themselves in the lamina propria of the small intestine, where they
lay a small number of eggs that hatch to produce sluggishly moving
rhabditiform larvae (Fig. 330-1). In a favorable
external environment, the rhabditiform larvae molt
again into the long, slender, and swift filariform larvae, which
is the skin-penetrating, infective form of the parasite (Fig. 330-2). While still in the intestine,
rhabditiform larvae become filariform and repenetrate the colonic
mucosa or perianal skin, thus starting a new parasitic generation
within the same host. This endogenous cycle, known as autoinfection, allows
the virtually indefinite persistence of the parasite in its host.
In the presence of certain conditions, particularly corticosteroid
therapy and profound malnutrition, the internal replication of parasites
may increase dramatically (ie, hyperinfection), and large numbers
of filariform larvae, as well as adults, may disseminate to extraintestinal
sites and produce a fatal outcome.
Strongyloides stercoralis life cycle.
Parasitic female Strongyloides stercoralis (red
arrow) on intestinal biopsy.
(Source: Courtesy of Colin Rudolph.)
Filariform larva of Strongyloides. Filariform
larva is the infective form that penetrates the skin.
(Source: Levinson W. Review of Medical
Microbiology and Immunology. 10th ed. New York: McGraw-Hill,
2008. Provider: CDC.)
Strongyloidiasis is usually characterized by marked eosinophilia,
and the diagnosis should be considered in any child from endemic
areas with unexplained eosinophilia. Many infections are asymptomatic.
Initial skin penetration by filariform larvae ...