Author(s): Susan Montgomery, Rebecca Chancey, Mary Kamb

Infectious Agent

Strongyloidiasis is caused by an intestinal nematode, Strongyloides stercoralis.

Transmission

Transmission occurs when filariform larva, found in contaminated soil, penetrate human skin. Person-to-person transmission is rare but has been documented. Autoinfection can occur, leading to persistent infection if untreated.

Epidemiology

Strongyloidiasis is endemic to the tropics and subtropics; it has limited foci elsewhere, including Appalachia and the southeastern United States. Estimates of global prevalence range from 30–100 million. Most documented infections in the United States occur in immigrants, refugees, and military veterans living in Strongyloides-endemic areas for long periods. Risk for short-term travelers is low, but infections can occur.

Clinical Presentation

Most acute and chronic infections are asymptomatic or have minimal symptoms. In acute infections, a localized, pruritic, erythematous papular rash can develop at the site of skin penetration, followed by pulmonary symptoms (a Löffler-like pneumonitis; for more details, see Sec. 5, Part 3, Ch. 13, Soil-Transmitted Helminths), abdominal pain, diarrhea, and eosinophilia. In chronic infections, migrating larvae in the skin can occasionally cause larva currens, a serpiginous urticarial rash on the perineum or upper thighs.

Immunocompromised people, especially those receiving systemic corticosteroids, those infected with human T cell lymphotropic virus type 1, and those with hematologic malignancies or who have had hematopoietic stem cell or organ transplants are at risk for hyperinfection or disseminated disease, characterized by abdominal pain, diffuse pulmonary infiltrates, and septicemia or meningitis from enteric bacteria. Untreated hyperinfection and disseminated strongyloidiasis are associated with high mortality rates.

Diagnosis

Suspect strongyloidiasis in symptomatic patients who have a history of skin contact (i.e., bare feet) with soil in tropical or subtropical regions. Laboratory diagnosis usually involves blood and stool testing. Although common in intestinal strongyloidiasis, peripheral blood eosinophilia is often absent in hyperinfection and disseminated strongyloidiasis.

Rhabditiform larvae can be visualized on microscopic examination of stool, either directly or by culture on agar plates. Repeated stool examinations or examination of duodenal contents might be necessary. Hyperinfection and disseminated strongyloidiasis are diagnosed by examining cerebrospinal fluid, sputum, stool, and other body fluids and tissues, which typically contain high numbers of filariform larva.

Serologic testing is available through commercial laboratories; diagnostic assistance is available from the Centers for Disease Control and Prevention (CDC)’s Division of Parasitic Diseases and Malaria DPDx laboratory (dpdx@cdc.gov), and the Parasitic Diseases Hotline for Healthcare Providers (404-718-4745; parasites@cdc.gov).

Treatment

The treatment of choice for acute, chronic, and disseminated disease or hyperinfection is ivermectin. The alternative is albendazole, but it is associated with lower cure rates. Because of the potential for relapse, patients with hyperinfection, disseminated disease, or co-infection with human T cell lymphotropic virus 1 might need prolonged or repeated treatment.

Prevention

No vaccines or drugs are available to prevent infection. To protect against Strongyloides infection, travelers should wear shoes when walking in areas where humans might have defecated. Perform serologic testing for patients at risk for Strongyloides infection who will be placed on corticosteroids or other immunosuppressive drug regimens, or who will undergo procedures that involve immunosuppression (e.g., transplantation). If indicated, treat these patients for strongyloidiasis before initiating immunosuppressive therapy. Consider empiric treatment in people deemed at risk of strongyloidiasis who require immediate immunosuppression.

CDC website: About Strongyloides