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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.

eFigure 330.1.

Strongyloides stercoralis life cycle.

Figure 330-1.

Parasitic female Strongyloides stercoralis (red arrow) on intestinal biopsy.

(Source: Courtesy of Colin Rudolph.)

Figure 330-2.

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.)

Clinical Manifestations

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 may produce transient pruritic papules ...

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