Strongyloidiasis in Immunosuppressed Patients: A Silent Threat with Lethal Potential

Introduction

Strongyloidiasis, an infection caused by the soil-transmitted helminth Strongyloides stercoralis, is often asymptomatic in immunocompetent individuals but can become life-threatening in immunosuppressed patients. This parasite has a unique ability to replicate within the human host, allowing chronic infection for decades. In patients receiving corticosteroids, chemotherapy, or undergoing organ transplantation, this infection can transform into disseminated strongyloidiasis or hyperinfection syndrome—a rapidly fatal condition without prompt diagnosis and treatment.

Epidemiology and Transmission

Strongyloides stercoralis is endemic in tropical and subtropical regions, including parts of Southeast Asia, Latin America, sub-Saharan Africa, and pockets of the southeastern United States. Transmission occurs primarily through skin contact with contaminated soil. The infective filariform larvae penetrate the skin, migrate through the lungs, ascend the bronchial tree, and are swallowed into the gastrointestinal tract where they mature and reproduce (CDC, 2023).

A key feature of Strongyloides is its autoinfective lifecycle. Unlike most helminths, S. stercoralis can reinfect the host without external exposure, establishing chronic infections that may remain dormant for years until immunosuppression triggers uncontrolled proliferation.

Pathophysiology in Immunosuppressed Hosts

In immunocompetent individuals, the immune system limits parasite burden. However, in patients receiving immunosuppressive therapies—particularly corticosteroids, which suppress eosinophilic and Th2 immune responses—larvae replication increases exponentially. This can lead to hyperinfection syndrome, where the number of migrating larvae overwhelms the pulmonary and gastrointestinal systems, or disseminated strongyloidiasis, where larvae invade distant organs, including the liver, brain, and skin (Buonfrate et al., 2013).

Moreover, steroid use enhances female worm fertility and may upregulate receptors that facilitate larval migration, exacerbating disease severity.

Clinical Manifestations

While strongyloidiasis may be asymptomatic or present with mild gastrointestinal symptoms in healthy hosts, immunosuppressed individuals can develop severe complications:

• Hyperinfection syndrome: Intense GI and respiratory symptoms, including vomiting, diarrhea, abdominal pain, cough, and dyspnea.

• Disseminated strongyloidiasis: Invasion of nontraditional sites like the CNS, skin, or kidneys. Patients may develop septicemia due to translocation of enteric bacteria via larval migration.

A notable feature is Gram-negative sepsis (e.g., E. coli, Klebsiella), often triggered by bacterial hitchhiking on larvae through tissue planes and the bloodstream.

Diagnosis

Diagnosis is challenging, especially in non-endemic areas where clinical suspicion is low. Available diagnostic tools include:

• Stool microscopy: Limited sensitivity; multiple samples often needed.

• Serologic testing (ELISA for IgG): High sensitivity but limited in immunosuppressed patients due to poor antibody response.

• Sputum, bronchoalveolar lavage, or duodenal aspirates: May reveal larvae in cases of hyperinfection.

• Molecular diagnostics (PCR): Emerging as sensitive alternatives in specialized labs.

Eosinophilia is a helpful clue in immunocompetent individuals but may be absent in hyperinfection syndrome.

Treatment

Ivermectin is the treatment of choice, with doses typically given daily until symptoms resolve and stool/sputum exams are negative for at least two weeks. In disseminated disease, treatment duration is longer, and parenteral options may be considered for patients who cannot tolerate oral medications (Requena-Méndez et al., 2013).

For patients undergoing organ transplantation or high-dose steroid therapy, empiric treatment prior to immunosuppression is often recommended if strongyloidiasis is suspected based on epidemiologic exposure or eosinophilia.

Prevention and Screening

Given the high mortality of disseminated disease, screening for strongyloidiasis is essential before initiating immunosuppressive therapy in at-risk individuals. This includes:

• Patients from endemic areas

• Those with prior eosinophilia of unclear cause

• Candidates for corticosteroid therapy, chemotherapy, or transplantation

Empiric ivermectin treatment is cost-effective and safe, particularly in cases where confirmatory testing is delayed or unavailable.

Conclusion

Strongyloidiasis may remain silent for years but can rapidly evolve into a fatal illness in immunosuppressed patients. Its unique autoinfective cycle makes it unlike any other helminth, and its clinical consequences demand high suspicion and early intervention. For clinicians managing transplant recipients, oncology patients, or individuals receiving high-dose steroids, proactive screening and preemptive treatment can mean the difference between life and death.

References

Buonfrate, D., Requena-Méndez, A., Angheben, A., Muñoz, J., Gobbi, F., Van Den Ende, J., & Bisoffi, Z. (2013). Severe strongyloidiasis: A systematic review of case reports. BMC Infectious Diseases, 13(1), 78. https://doi.org/10.1186/1471-2334-13-78

Centers for Disease Control and Prevention (CDC). (2023). Strongyloides – Biology. https://www.cdc.gov/dpdx/strongyloidiasis/index.html

Requena-Méndez, A., Buonfrate, D., Gomez-Junyent, J., Zammarchi, L., Bisoffi, Z., & Muñoz, J. (2013). Evidence-based guidelines for screening and management of strongyloidiasis in non-endemic areas. The American Journal of Tropical Medicine and Hygiene, 88(3), 422–426. https://doi.org/10.4269/ajtmh.2012.12-0487

Assessed and Endorsed by the MedReport Medical Review Board