Strongyloidiasis
At a Glance
Strongyloidiasis is a parasitic disease caused by a roundworm that enters the body through the skin, migrates to the intestines, and can reproduce internally to cause a long-lasting infection involving the gut, lungs, and skin.
This condition occurs in people of all ages but is most common in children and adults living in or traveling to tropical and subtropical regions, as well as those in rural areas with limited sanitation.
It is typically a chronic condition that can persist for a lifetime if untreated due to the parasite's ability to reinfect the host, but it is treatable with medication and manageable with appropriate medical care.
The outlook is generally excellent with curative treatment, though the infection can be life-threatening if it progresses to hyperinfection syndrome in individuals with weakened immune systems.
How It Affects You
Strongyloidiasis is a parasitic infection caused by the roundworm Strongyloides stercoralis, which can persist in the human body for decades through a unique cycle of autoinfection. The microscopic larvae penetrate the skin and migrate through the bloodstream to the lungs before eventually settling in the small intestine. While many people have no symptoms, those who do often experience a combination of effects:
- Digestive issues including abdominal pain, bloating, diarrhea, and nausea.
- Respiratory symptoms such as a dry cough, wheezing, or throat irritation during the migration phase.
- Skin manifestations specifically a red, itchy, rapidly moving rash known as larva currens, often found on the buttocks, thighs, or trunk.
Causes and Risk Factors
Underlying Causes
Strongyloidiasis is caused by the parasitic roundworm Strongyloides stercoralis. Unlike most other worms, this parasite has a unique life cycle that allows it to reproduce within the human host, a process called autoinfection. The infection begins when microscopic larvae found in contaminated soil penetrate bare skin. These larvae migrate through the bloodstream to the lungs, move up the windpipe, are swallowed, and settle in the small intestine where they lay eggs. The hatched larvae can then either be excreted in stool or burrow back into the intestinal wall or perianal skin to restart the cycle, maintaining the infection for decades.
Risk Factors and Triggers
The primary risk factor is direct skin contact with soil contaminated by human waste, which often occurs when walking barefoot in tropical or subtropical climates. People working in farming, coal mining, or sanitation services are at higher risk. A critical risk factor for severe disease is a weakened immune system. Specifically, the use of corticosteroid medications (such as prednisone) or infection with the HTLV-1 virus can trigger a massive multiplication of the parasite, leading to a dangerous state called hyperinfection.
Prevention Strategies
Primary prevention focuses on avoiding contact with contaminated soil. This includes wearing shoes when walking outdoors, using gloves when gardening, and ensuring proper disposal of human waste and sewage. For individuals who have lived in endemic areas, the most important step to reduce severity is medical screening for the parasite before starting immunosuppressive therapies like chemotherapy or corticosteroids. Treating the latent infection before suppressing the immune system prevents the potentially fatal complications of hyperinfection.
Diagnosis, Signs, and Symptoms
Signs and Symptoms
Many people with strongyloidiasis have no symptoms at all, or symptoms that are mild and vague. When they do occur, they typically involve the skin, lungs, and digestive system. Digestive symptoms are the most common and include upper abdominal burning or pain, bloating, intermittent diarrhea, and nausea. Respiratory symptoms may include a dry cough, wheezing, or throat irritation, often mimicking asthma. A distinctive sign of this condition is a specific skin rash called larva currens (racing larva), which appears as a red, raised, itchy line that moves rapidly across the skin—sometimes centimeters per hour—usually on the buttocks, groin, or trunk.
Diagnostic Tests
Diagnosing strongyloidiasis can be difficult because the number of worms in the body is often low. Standard stool exams frequently miss the parasite. Clinicians often use a specialized blood test (serology) to detect antibodies against the parasite, which is generally more sensitive than stool tests. Specialized stool culture methods, such as agar plate culture, may be used to track the tracks of bacteria moved by the larvae. Blood tests may also show a high level of eosinophils, a type of white blood cell associated with parasitic infections, though this is not always present.
Differential Diagnosis
Because the symptoms are nonspecific, this condition is often confused with other digestive or respiratory disorders. It may be misdiagnosed as peptic ulcer disease, irritable bowel syndrome (IBS), asthma, or general hives. The rash can be mistaken for other insect bites or allergic reactions, but the rapid speed at which the red line moves is unique to strongyloidiasis.
Treatment and Management
Medications and Procedures
The goal of treatment is the complete elimination of the parasite to prevent future complications. The most effective medication is ivermectin, an antiparasitic drug usually taken as a single dose or over two days. Albendazole is an alternative option but is generally considered less effective. For patients with hyperinfection syndrome, treatment is much more aggressive, requiring hospitalization, prolonged courses of antiparasitic medication, and the reduction or cessation of immune-suppressing drugs if possible.
Management and Follow-up
Successful management involves confirming that the parasite has been eradicated. Because symptoms can resolve even if a few worms remain, follow-up testing is essential. Clinicians typically repeat blood tests or stool exams several months after treatment to ensure the infection is cleared. Patients are advised to monitor for any returning rash or digestive issues. No special diet is required, but good hygiene practices are encouraged to prevent reinfection from the environment.
When to Seek Medical Care
You should see a doctor if you experience unexplained abdominal pain, persistent diarrhea, or a moving, itchy rash, especially if you have ever traveled to or lived in a tropical area. It is vital to inform your healthcare provider about your travel history or past residence in warm climates. Seek emergency care immediately if you have a known history of this infection or risk factors and develop severe shortness of breath, coughing up blood, or signs of overwhelming infection (sepsis), as these could indicate hyperinfection.
Severity and Prognosis
Severity and Disease Course
Strongyloidiasis ranges from a completely asymptomatic condition to a severe, life-threatening emergency. In the uncomplicated chronic form, the disease is generally mild to moderate, causing intermittent discomfort that can wax and wane for years. The worm's ability to autoinfect the host means the disease does not resolve on its own and can persist for decades. The course changes dramatically if the host's immune system is compromised; this can lead to hyperinfection syndrome, where larvae invade numerous organs including the lungs, liver, and central nervous system.
Prognosis and Complications
For healthy individuals who receive treatment, the prognosis is excellent, and the cure rate is high. Life expectancy is normal, and long-term complications are rare once the parasite is gone. However, for those who develop hyperinfection syndrome or disseminated strongyloidiasis, the condition is severe and carries a high mortality rate even with treatment. Complications in these severe cases can include bacterial meningitis, pneumonia, and sepsis, as the traveling larvae carry gut bacteria into the bloodstream. Early diagnosis and treatment before immunosuppression occurs are the most important factors for a good outcome.
Impact on Daily Life
Impact on Daily Activities
For most people, chronic strongyloidiasis is a background nuisance rather than a disability. However, unpredictable bouts of abdominal pain, urgent diarrhea, or intense itching can disrupt work, sleep, and social activities. The characteristic rash can be embarrassing and uncomfortable. Some individuals experience anxiety related to the knowledge of having a parasitic infection. Recognizing that the condition is curable often helps alleviate this stress.
Questions to Ask Your Healthcare Provider
Being proactive can help ensure you get the right care. Consider asking the following questions at your appointment:
- Could my past travel or residence in tropical areas explain my symptoms?
- What specific tests are best for detecting this parasite, given that stool tests often miss it?
- If I need to take steroids or other immune-suppressing drugs in the future, should I be tested for this first?
- How will we know for sure that the infection is gone after I take the medication?
- Do my family members need to be tested even if they do not have symptoms?
Common Questions and Answers
Q: Is strongyloidiasis contagious from person to person?
A: Direct person-to-person transmission is rare. The infection is primarily spread through contact with contaminated soil. However, it can occasionally be transmitted through organ transplants or rarely through intimate contact.
Q: Can I get this infection from my pets?
A: It is possible but uncommon. Dogs can carry a strain of Strongyloides, and while transmission to humans is rare, it is a potential risk. Veterinary care for pets helps reduce this possibility.
Q: How long does it take to get cured?
A: The medication typically works quickly, often killing the worms within a few days. However, doctors usually monitor you for several months to ensure no larvae survived to restart the cycle.
Q: Why did I get tested for this before my kidney transplant or chemotherapy?
A: Doctors test for this because these procedures weaken the immune system. If you have a silent infection, suppressing your immune system could cause the worms to multiply out of control, leading to a dangerous hyperinfection.
Q: Can the infection come back after treatment?
A: Reinfection from the environment is possible if you are exposed to contaminated soil again. However, once the internal autoinfection cycle is broken by medication, the original infection does not return on its own.