Overview
Definition:
Strongyloidiasis is a parasitic infection caused by the nematode Strongyloides stercoralis, endemic in tropical and subtropical regions
In immunocompromised individuals, particularly those on corticosteroids, it can lead to hyperinfection syndrome or disseminated disease, which are life-threatening.
Epidemiology:
Affects millions worldwide, with higher prevalence in Southeast Asia, sub-Saharan Africa, and Latin America
Immigrants from endemic areas are at increased risk
Pediatric cases can present with varied symptoms, often mimicking other childhood illnesses, leading to delayed diagnosis.
Clinical Significance:
The critical aspect for pediatricians is identifying asymptomatic carriers in immigrant children who may later develop severe, potentially fatal hyperinfection syndrome when immunosuppressed (e.g., by steroids for asthma, autoimmune diseases, or cancer chemotherapy)
Proactive screening is paramount to prevent this.
Clinical Presentation
Symptoms:
Many infections are asymptomatic
Symptomatic patients may experience: Cough, wheezing, or dyspnea due to larval migration through the lungs
Gastrointestinal symptoms including abdominal pain, diarrhea, nausea, and vomiting
Skin manifestations such as pruritic rashes or tracks (larva currens).]
Signs:
In asymptomatic carriers, physical examination may be normal
In hyperinfection/disseminated disease: Fever
Abdominal distension and tenderness
Signs of pneumonia or acute respiratory distress syndrome
Eosinophilia is typically present in uncomplicated infection but may be absent in severe disseminated disease due to immune suppression.
Diagnostic Criteria:
No single definitive diagnostic criterion exists for initial screening in asymptomatic individuals
Diagnosis relies on identifying the parasite or its antigens
In hyperinfection syndrome, a combination of clinical suspicion, radiographic evidence of pulmonary or disseminated disease, and parasite identification (often in sputum, stool, or other body fluids) is key.
Diagnostic Approach
History Taking:
Crucial elements include: Travel history to or origin from endemic regions
History of immunosuppressive therapy, particularly corticosteroids, recent or planned
Co-existing medical conditions requiring immunosuppression
Any gastrointestinal, respiratory, or dermatological symptoms, even if mild or intermittent.
Physical Examination:
A thorough systemic examination focusing on: Respiratory system for crackles, wheezes, or signs of consolidation
Abdomen for tenderness, guarding, or distension
Skin for characteristic rashes or larva currens
Rectal examination may be considered.
Investigations:
Standard stool microscopy for larvae (e.g., Baermann technique, Harada-Mori culture) has low sensitivity, especially in low-parasitemic states
Serological tests (ELISA for antibodies against S
stercoralis) are more sensitive but may be positive long after infection
Repeated stool examinations, examination of duodenal fluid, sputum, or even pleural/peritoneal fluid can be diagnostic
Complete blood count to assess for eosinophilia and leukocytosis
Chest X-ray or CT scan to evaluate pulmonary involvement.
Differential Diagnosis:
Other helminthic infections (e.g., Ascaris, hookworm)
Pneumonia of various etiologies
Inflammatory bowel disease
Irritable bowel syndrome
Allergic bronchopulmonary aspergillosis (in asthmatics)
Other causes of eosinophilia.
Management
Initial Management:
For children identified as carriers from endemic areas who are initiating or on corticosteroids: Treatment with an antiparasitic agent is indicated prior to or concurrently with immunosuppression.
Medical Management:
The drug of choice is Ivermectin
For children: Usual dose is 200 mcg/kg orally once daily for 2-5 days
Dosing for pediatric patients requires careful calculation based on weight
Alternatives include Albendazole (400 mg BID for 7 days) or Mebendazole (100 mg BID for 3 days), but ivermectin is generally preferred for its efficacy and safety profile, especially in immunocompromised individuals
Treatment of hyperinfection/disseminated disease requires prolonged courses of ivermectin, often with supportive care.
Surgical Management:
Rarely indicated, primarily for management of complications such as bowel obstruction or perforation in disseminated disease.
Supportive Care:
Includes management of secondary bacterial infections, fluid and electrolyte balance, nutritional support, and respiratory support (oxygen therapy, mechanical ventilation if needed) in cases of hyperinfection syndrome.
Complications
Early Complications:
Hyperinfection syndrome: characterized by autoinfection and massive larval proliferation leading to symptoms in multiple organ systems, including gastrointestinal, pulmonary, and dermatological manifestations
Disseminated strongyloidiasis: involves widespread organ involvement with high mortality, often associated with Gram-negative sepsis due to larval transport of bacteria.
Late Complications:
Chronic symptoms including intermittent abdominal pain, malabsorption, and failure to thrive
Recurrent pulmonary infections.
Prevention Strategies:
Systematic screening of immigrants from endemic areas, especially before initiating immunosuppressive therapy
Education of healthcare providers on the risks of Strongyloides hyperinfection
Prompt diagnosis and treatment of identified carriers
Judicious use of corticosteroids and awareness of their potential to unmask latent infections.
Prognosis
Factors Affecting Prognosis:
The degree of immunosuppression, the extent of larval dissemination, and the promptness of treatment are key prognostic factors
Untreated hyperinfection or disseminated strongyloidiasis carries a very high mortality rate.
Outcomes:
With appropriate and timely treatment with ivermectin, prognosis is generally good for uncomplicated infections and many cases of hyperinfection
Disseminated disease in severely immunocompromised individuals remains challenging.
Follow Up:
Follow-up stool examinations are recommended to confirm eradication, especially in immunocompromised patients
Patients on long-term immunosuppression should be monitored for recurrent symptoms
Consultation with infectious disease specialists may be beneficial for complex cases.
Key Points
Exam Focus:
Recognize the association between immigrant status, steroid use, and potential for life-threatening Strongyloides hyperinfection syndrome
Know the diagnostic gold standard (larval identification), limitations of serology, and the preferred treatment (Ivermectin)
Remember pediatric dosing of ivermectin.
Clinical Pearls:
Always consider Strongyloides in immigrants presenting with unexplained GI, pulmonary, or dermatological symptoms, especially if they are, or will be, on steroids
Low sensitivity of single stool O&P
Consider serology if stool is negative but suspicion is high, particularly prior to immunosuppression
If serology is positive, treat even without symptoms before steroids.
Common Mistakes:
Overlooking the possibility of Strongyloidiasis in asymptomatic immigrants
Delaying screening or treatment before initiating steroid therapy
Relying solely on single stool O&P for diagnosis
Incorrect dosing of Ivermectin in pediatric patients.