An intestinal nematode, Strongyloides stercoralis.
Filariform larvae found in contaminated soil penetrate human skin. Person-to-person transmission is rare but documented.
Endemic in the tropics and subtropics and in limited foci in the southeastern United States, Europe, Australia, and Japan. Estimates of global prevalence vary between 3 million and 100 million. Most documented infections in the United States occur in immigrants, refugees, and military veterans who have lived in endemic areas for long periods of time. Risk for short-term travelers is low, but infections can occur.
Most infections are asymptomatic. With acute infections, a localized, pruritic, erythematous papular rash can develop at the site of skin penetration, followed by pulmonary symptoms (a Löffler-like pneumonitis), diarrhea, abdominal pain, and eosinophilia. Migrating larvae in the skin cause larva currens, a serpiginous urticarial rash.
Immunocompromised people, especially those receiving systemic corticosteroids, those with human T-cell lymphotropic virus type 1 infection, those with hematologic malignancies, or who have had organ transplants, are at risk for hyperinfection or disseminated disease, characterized by abdominal pain, diffuse pulmonary infiltrates, and septicemia or meningitis from enteric gram-negative bacilli. The death rate from untreated disseminated strongyloidiasis is very high. Unexplained eosinophilia may be a presenting sign.
Rhabditiform larvae on microscopic examination of stool, either directly or by culture on agar plates. Repeated stool examinations or examination of duodenal contents may be necessary. Hyperinfection and disseminated strongyloidiasis are diagnosed by examining stool, sputum, cerebrospinal fluid, and other body fluids and tissues, which typically contain high numbers of larvae. Serologic testing is available through commercial laboratories and through the National Institutes of Health and CDC (www.dpd.cdc.gov/dpdx; 404-718-4745; firstname.lastname@example.org).
Treatment of choice for both chronic and disseminated disease or hyperinfection is ivermectin. The alternative is albendazole, although associated with slightly lower cure rates. Prolonged or repeated treatment may be necessary in patients with hyperinfection and disseminated disease, and relapse can occur.
No vaccine or preventative drugs are available. Protective measures include wearing shoes when walking in areas where humans may have defecated. It may be reasonable to perform serologic testing on patients who have been at high risk for Strongyloides infection and who will either be placed on immunosuppressive drug regimens or who will undergo procedures that involve immunosuppression such as transplantation. If indicated, these patients should be treated before immunosuppression. Further information may be found on the CDC website.