Strongyloidiasis: Symptoms, Types, Causes and Treatment

Strongyloidiasis is a parasitic infection that remains one of the most overlooked tropical diseases worldwide, despite its potentially severe consequences. Caused by the helminth Strongyloides stercoralis, this disease can persist silently for decades, erupting with life-threatening complications—especially in people with weakened immune systems. In this article, we unravel the complex picture of strongyloidiasis, detailing its symptoms, types, causes, and modern treatment approaches. Let’s explore how this “hidden” infection can impact human health and what can be done to diagnose and manage it effectively.

Symptoms of Strongyloidiasis

While strongyloidiasis often lurks beneath the surface, causing few or no symptoms, it can also present with a range of clinical features. Awareness of these manifestations is vital for timely diagnosis, especially in at-risk individuals.

Symptom	Frequency/Significance	Notes/Details	Source(s)
Abdominal pain	Common	Present in over half of cases	3 4 9
Diarrhea	Common	May be intermittent or chronic	3 4 9
Urticaria	Notable	Persistent, itchy rash, often on trunk	4 9
Vomiting	Common	Especially in children and severe cases	3 9
Fever	Occasional	Seen in up to 40% of symptomatic cases	3
Eosinophilia	Common laboratory sign	May be the only clue in asymptomatic cases	1 2 11
Respiratory symptoms	Severe/advanced	Cough, wheezing, ARDS in hyperinfection	5 7 11
Sepsis	Life-threatening	In immunocompromised or hyperinfection	2 5 7

Table 1: Key Symptoms

Common Presentations in Chronic and Acute Infection

Most people with strongyloidiasis remain asymptomatic—over 60% never experience noticeable symptoms, and the infection may only be suggested by an elevated eosinophil count in blood tests 1 11. When symptoms do occur, they often involve the gastrointestinal tract:

• Abdominal pain is the most frequently reported complaint, sometimes accompanied by bloating and discomfort 3 4 9.
• Diarrhea can be persistent or intermittent, sometimes alternating with episodes of constipation 4.
• Vomiting is also seen, particularly in children and those with heavier infections 3.
• Urticaria, a persistent and intensely itchy rash (often on the trunk or buttocks), is a classic—though not universal—feature 4 9.

Respiratory and Systemic Manifestations

In severe cases, especially among immunosuppressed individuals (such as those taking corticosteroids), the infection can disseminate:

• Respiratory symptoms like cough, wheezing, shortness of breath, and even acute respiratory distress syndrome (ARDS) may signal hyperinfection or disseminated disease 5 7 11.
• Sepsis or meningitis can develop if the larvae invade other organs and carry gut bacteria into the bloodstream 2 5 7.
• Fever is less common but can occur, especially in severe or disseminated cases 3.

Laboratory Clues

• Eosinophilia (increased eosinophils in blood) is a frequent finding and may be the only indication in silent infections 1 2 11.
• However, in severe or hyperinfected cases, eosinophilia may be absent, possibly due to immune suppression 2 7.

Types of Strongyloidiasis

Strongyloidiasis is not a one-size-fits-all disease. Its clinical spectrum can be divided into distinct types—each with its own risks and implications.

Type	Main Features	Risk Factors/Triggers	Source(s)
Uncomplicated (chronic)	Often asymptomatic or mild GI/skin signs	Endemic exposure, immunocompetent	1 6 11
Hyperinfection	Increased GI and lung parasite burden	Immunosuppression (esp. steroids)	2 7 8 11
Disseminated	Parasites spread to multiple organs	Severe immune suppression	5 7 8 11

Table 2: Clinical Types of Strongyloidiasis

Uncomplicated (Chronic) Strongyloidiasis

This is the most common form—especially in endemic regions. Many people harbor the parasite for years or decades without symptoms, or with only mild, intermittent gastrointestinal or skin complaints 1 6. Chronic infection may go unnoticed, but it carries the risk of sudden worsening if the immune system is compromised 11.

Hyperinfection Syndrome

• Hyperinfection refers to an accelerated autoinfection cycle, with huge numbers of larvae migrating within the gastrointestinal tract and lungs 2 7.
• It is most often triggered by immunosuppressive therapies, especially corticosteroids, but also by other immunosuppressants or conditions like HTLV-1 infection 2 8 11.
• Symptoms intensify, with severe diarrhea, vomiting, abdominal pain, and new or worsening respiratory symptoms (cough, wheeze, or even ARDS) 5 7.

Disseminated Strongyloidiasis

• Disseminated strongyloidiasis is the most severe form, where larvae invade organs beyond the usual gut-lung cycle—such as the brain, liver, skin, or urinary tract 5 7 8 11.
• This form can result in overwhelming sepsis, meningitis, multi-organ failure, and a high risk of death (case fatality rates up to 60-70%) 7 8.

Risk Factors for Severe Disease

• Immunosuppression: Steroids are the leading trigger, but transplant recipients, cancer patients, and those with HIV or HTLV-1 are also at risk 2 8 11.
• Delayed diagnosis: Due to non-specific or mild early symptoms, the severe forms are often missed until advanced 3 6 7.

Causes of Strongyloidiasis

Understanding how strongyloidiasis is acquired and who is at risk is essential for prevention and control.

Cause/Factor	Description	Details/Implications	Source(s)
Strongyloides stercoralis	Parasitic nematode (roundworm)	Main agent of human infection	1 6 11
Soil exposure	Contact with contaminated soil	Barefoot walking, poor sanitation	1 9 10 11
Autoinfection	Internal re-infection cycle	Permits lifelong, persistent infection	1 6 11
Immunosuppression	Steroids, transplant, cancer, HTLV-1	Major risk for hyperinfection/dissemination	2 7 8 11
Zoonotic reservoirs	Dogs, possibly flies	Potential but unclear role in human disease	10

Table 3: Causes and Risk Factors

The Parasite and Its Transmission

Strongyloidiasis is caused by the parasitic roundworm Strongyloides stercoralis (and to a lesser extent, S. fuelleborni) 1 6 11. Humans acquire the infection primarily through skin contact with soil contaminated by infective larvae, especially in areas with poor sanitation and warm, humid climates 1 9 10 11. Walking barefoot and inadequate hygiene practices increase the risk.

Unique Lifecycle: Autoinfection

Unlike most intestinal worms, Strongyloides can perpetuate its lifecycle entirely within the human host. This autoinfection mechanism allows the parasite to survive for decades, leading to chronic, sometimes lifelong infections 1 6 11. Larvae in the intestine can penetrate the gut wall or perianal skin and start a new cycle—without ever leaving the host.

Risk Factors for Acquisition and Progression

• Endemic regions: Highest prevalence is in tropical and subtropical areas, but cases occur globally, including in temperate zones with poor sanitation 1 10 11.
• Immunosuppression: The risk of severe disease (hyperinfection or dissemination) is dramatically increased by:
  • Corticosteroid therapy (even short-term or moderate doses) 2 7 8 11
  • Organ transplantation
  • Cancer chemotherapy
  • HTLV-1 infection
  • Advanced HIV/AIDS 2 7 10 11
• Zoonotic and environmental reservoirs: Dogs and, in some studies, flies, may serve as reservoirs, though their precise role is not fully understood 10.

Prevention Strategies

• Wearing shoes in endemic areas
• Improving sanitation and hygiene
• Screening at-risk populations before administering immunosuppressive therapies 11 15

Treatment of Strongyloidiasis

Once diagnosed, strongyloidiasis can be effectively treated—if the right medications are used and the risk of severe disease is recognized.

Treatment	Efficacy/Preference	Notes/Considerations	Source(s)
Ivermectin	Drug of choice; highly effective	Preferred over albendazole, thiabendazole	12 13 14 15
Albendazole	Alternative	Less effective than ivermectin	13
Thiabendazole	Alternative	Similar efficacy but more side effects than ivermectin	13
Multiple vs. single-dose ivermectin	Single dose preferred	No added benefit from multiple doses in chronic cases	14
Severe/Disseminated disease	May require prolonged/combination therapy	Optimal regimen not fully defined	12 13 14
Screening before immunosuppression	Essential for prevention	Especially in migrants, endemic exposures	11 15

Table 4: Treatment Options

First-Line Therapies

• Ivermectin is the gold-standard treatment, demonstrating higher cure rates and better tolerability than either albendazole or thiabendazole for uncomplicated infections 12 13.
• A single oral dose of ivermectin (200 μg/kg) is generally sufficient for non-disseminated cases. Large clinical trials have found no additional benefit to multiple dosing in these patients, and side effects may be higher with more doses 14.
• Albendazole and thiabendazole are alternatives, but are less effective (albendazole) or have more adverse effects (thiabendazole) 13.

Treating Severe Cases

• In hyperinfection or disseminated strongyloidiasis, therapy often requires prolonged and sometimes higher or repeated doses of ivermectin, sometimes combined with other anti-helminthics 12 13.
• There is limited evidence on the optimal regimen for severe disease, and management is often guided by expert opinion and individual response 12.
• Supportive care—addressing sepsis, respiratory failure, and multi-organ complications—is critical 5 7 8.

Preventive Measures and Screening

• Screening all individuals with a history of exposure in endemic regions—especially before starting immunosuppressive therapy—is universally recommended 11 15.
• In high-risk cases where testing is delayed or unavailable, empiric treatment should be considered to prevent severe outcomes 11 15.
• Improved access to ivermectin and better diagnostics are crucial barriers to effective public health management 9 15.

Special Considerations

• Children, migrants, and immunosuppressed patients require careful evaluation and, if at risk, prompt treatment—even if asymptomatic 1 10 11 15.
• Adverse events with ivermectin are generally mild (dizziness, nausea), and serious effects are rare 13 14.

Conclusion

Strongyloidiasis is a complex, often hidden infection that can have devastating consequences if left undiagnosed and untreated. Here’s what you need to remember:

• Symptoms are often absent or non-specific, but can include abdominal pain, diarrhea, urticaria, and, in severe cases, respiratory symptoms or sepsis.
• Types range from silent, chronic infection to life-threatening hyperinfection and disseminated disease, especially in immunosuppressed people.
• Causes involve the Strongyloides stercoralis parasite, with infection acquired via contact with contaminated soil and perpetuated by unique autoinfection cycles; immunosuppression is the key risk for severe disease.
• Treatment with ivermectin is highly effective for most cases, but severe forms require prompt, often prolonged therapy, and preventive screening is vital for at-risk groups.

Key Takeaways:

• Chronic strongyloidiasis can persist for decades and is often asymptomatic 1 6 11.
• Severe, life-threatening disease is most likely in immunosuppressed individuals—screening and early treatment are critical 2 7 11 15.
• Ivermectin is the treatment of choice; albendazole and thiabendazole are alternatives but less preferred 12 13 14.
• Public health efforts must focus on raising awareness, improving diagnostics, and ensuring access to effective therapy 9 15.

By increasing clinical suspicion, screening those at risk, and ensuring access to effective treatment, the burden and deadly consequences of strongyloidiasis can be greatly reduced.