Strongyloidiasis: Symptoms, Treatments, Medications and Prevention

Strongyloidiasis is a parasitic infection caused by the nematode (roundworm) Strongyloides stercoralis. It is a soil-transmitted helminth that infects humans, primarily through direct contact with contaminated soil. Unlike most parasitic infections, Strongyloidiasis can persist in the host for many years due to the parasite’s ability to complete its life cycle within the human body, causing chronic infections. In immunocompromised individuals, the infection can become severe and life-threatening, leading to a condition known as disseminated strongyloidiasis or hyperinfection syndrome.

What is Strongyloidiasis?

The Causative Agent: Strongyloides stercoralis

Strongyloides stercoralis is a parasitic roundworm (nematode) that primarily infects the human intestines. Unlike many other parasites, S. stercoralis can complete part of its life cycle within the human host, leading to autoinfection (reinfection by the larvae). This characteristic allows the parasite to persist in the host for decades, leading to chronic infections and, in some cases, severe complications.

Life Cycle of Strongyloides stercoralis

The life cycle of Strongyloides stercoralis is complex and includes both free-living and parasitic stages. The parasite is unique in its ability to undergo autoinfection, allowing the infection to perpetuate within the human host without the need for external reinfection. The key stages of the life cycle are as follows:

1. Infective larvae (filariform): Humans become infected when the filariform larvae penetrate the skin, usually through contact with contaminated soil.
2. Migration through the body: After penetrating the skin, the larvae enter the bloodstream and travel to the lungs, where they ascend the bronchial tree and are swallowed.
3. Development in the intestines: Once in the intestines, the larvae develop into adult females, which embed themselves in the intestinal wall and begin producing eggs through parthenogenesis (asexual reproduction).
4. Egg hatching and larvae release: The eggs hatch in the intestines, releasing rhabditiform larvae (non-infective larvae) that are excreted in the stool.
5. Autoinfection or external life cycle: Some of the rhabditiform larvae can develop into infective filariform larvae within the host, leading to autoinfection. Alternatively, they are excreted in the feces, where they can either develop into free-living adults in the soil or become infective larvae that can penetrate the skin of a new host.

Mode of Transmission

Humans become infected with Strongyloides stercoralis when their skin comes into direct contact with contaminated soil, usually when walking barefoot or handling soil. The larvae penetrate the skin and begin their life cycle within the body. Other less common modes of transmission include:

• Person-to-person transmission: Transmission through direct contact with fecal matter from an infected individual, though rare.
• Autoinfection: The larvae can develop into infective forms within the body, perpetuating the infection without the need for external exposure.
• Transplant-related transmission: In rare cases, Strongyloides can be transmitted through organ transplants from an infected donor.

Who is at Risk of Strongyloidiasis?

Geographic Risk Factors

Strongyloidiasis is primarily found in tropical and subtropical regions, where warm and humid environments facilitate the development of larvae in the soil. The disease is also present in some temperate areas, particularly in regions with poor sanitation and hygiene. The highest prevalence rates are found in:

• Southeast Asia: Countries like Thailand, Vietnam, and Cambodia report high rates of infection.
• Sub-Saharan Africa: Several countries in West, Central, and East Africa have endemic strongyloidiasis.
• Latin America and the Caribbean: Countries such as Brazil, Peru, and parts of Central America and the Caribbean are endemic.
• Southern United States: Areas with warm, moist climates, particularly the southeastern states, have reported cases of strongyloidiasis.

Occupational and Behavioral Risk Factors

Certain occupations and behaviors increase the risk of exposure to contaminated soil and therefore the risk of contracting strongyloidiasis.

1. Agricultural Workers

People who work in agriculture, particularly those involved in farming or irrigation, are at high risk of infection due to frequent contact with soil. In tropical regions, this risk is compounded by the use of human feces as fertilizer in some agricultural practices.

2. People Living in Poverty

Strongyloidiasis is more common in communities with poor sanitation and limited access to clean water. Open defecation and inadequate sewage systems contribute to the contamination of soil with human waste, increasing the likelihood of infection.

3. Children

Children who play outdoors, particularly in areas with contaminated soil, are more susceptible to infection. In many endemic regions, children often go barefoot, which increases the risk of skin penetration by the larvae.

4. Immunocompromised Individuals

People with weakened immune systems, such as those with HIV/AIDS, organ transplant recipients, or individuals receiving corticosteroids or immunosuppressive therapies, are at a higher risk of developing severe strongyloidiasis. In these individuals, the infection can progress to a disseminated or hyperinfection state, leading to life-threatening complications.

5. Travelers and Military Personnel

Travelers and military personnel visiting or stationed in endemic areas are at risk of infection, especially if they engage in activities that involve contact with soil, such as hiking or farming.

Symptoms of Strongyloidiasis

The symptoms of strongyloidiasis can range from asymptomatic to severe, depending on the individual’s immune status and the severity of the infection. Many people with chronic infection experience few or no symptoms, while others may develop significant gastrointestinal, dermatological, and respiratory issues. In immunocompromised individuals, the infection can become severe and widespread.

Early Symptoms: Skin Reactions

When the infective larvae penetrate the skin, they often cause localized skin reactions. This is one of the earliest signs of infection.

1. Itchy Rash (Larva Currens)

• Larva currens: A characteristic itchy, serpiginous (snake-like) rash that appears at the site where the larvae penetrate the skin.
• Localized redness and swelling: The rash is typically found on the feet, ankles, or buttocks, and may cause significant itching.

Gastrointestinal Symptoms

Once the larvae mature into adult worms in the intestines, they can cause a range of gastrointestinal symptoms.

1. Abdominal Pain and Discomfort

• Cramps and bloating: Many infected individuals experience abdominal pain, cramping, and bloating.
• Diarrhea: Chronic diarrhea is a common symptom of strongyloidiasis and may alternate with periods of constipation.
• Nausea and vomiting: Some individuals may experience nausea, vomiting, and general gastrointestinal distress.

2. Weight Loss

Chronic infection can lead to unintentional weight loss due to malabsorption of nutrients and prolonged gastrointestinal symptoms.

Respiratory Symptoms

During the migration of larvae through the lungs, some individuals may experience respiratory symptoms, particularly in the early stages of infection.

1. Cough

• Dry cough: A persistent, dry cough is common as the larvae pass through the lungs.
• Wheezing and shortness of breath: In more severe cases, individuals may develop wheezing, shortness of breath, and chest discomfort.

Severe Complications: Hyperinfection and Disseminated Strongyloidiasis

In immunocompromised individuals, strongyloidiasis can progress to a more severe form known as hyperinfection syndrome or disseminated strongyloidiasis. In these cases, the larvae spread throughout the body, causing widespread damage to organs and tissues.

1. Hyperinfection Syndrome

This occurs when the normal life cycle of the parasite is accelerated, leading to an overwhelming number of larvae in the intestines and lungs. Symptoms include:

• Severe abdominal pain
• Profound diarrhea
• Nausea and vomiting
• Severe respiratory symptoms: Including shortness of breath, wheezing, and coughing up blood (hemoptysis).
• Sepsis: Hyperinfection can lead to septicemia (blood poisoning), which can be life-threatening.

2. Disseminated Strongyloidiasis

In disseminated strongyloidiasis, the larvae spread to multiple organs beyond the gastrointestinal and respiratory tracts, including the liver, kidneys, central nervous system, and skin.

• Multi-organ failure: Infected individuals can develop organ dysfunction, leading to multi-organ failure.
• Neurological complications: Larvae can invade the brain, causing encephalitis or meningitis.
• Severe skin rashes: Disseminated larvae can cause widespread skin rashes and even purpura (bleeding under the skin).

Disseminated strongyloidiasis is often fatal if not promptly treated.

Diagnosis of Strongyloidiasis

Diagnosing strongyloidiasis can be challenging, especially in individuals with chronic or asymptomatic infections. The diagnosis typically involves a combination of clinical evaluation, laboratory tests, and sometimes imaging studies.

1. Clinical Evaluation

Healthcare providers will assess the patient’s history, including travel to endemic areas, occupational exposure, and the presence of immunosuppressive conditions. If the patient reports suggestive symptoms (such as abdominal pain, chronic diarrhea, or rash), further diagnostic testing is required.

2. Laboratory Tests

1. Stool Examination

Microscopic examination of stool samples is the most commonly used diagnostic method for strongyloidiasis. However, detecting the larvae can be difficult, especially in light infections, because the number of larvae in the stool may be low.

• Stool concentration techniques: Techniques like the Baermann method or agar plate culture are used to increase the likelihood of detecting larvae in stool samples.
• Multiple samples: Because larvae may not be consistently excreted, multiple stool samples over several days may be necessary to confirm the diagnosis.

2. Serological Tests

Antibody detection tests (serology) are useful for diagnosing chronic strongyloidiasis, especially in individuals who do not have detectable larvae in their stool. These tests measure the presence of antibodies to Strongyloides antigens.

• Enzyme-linked immunosorbent assay (ELISA): This is the most commonly used serological test for detecting antibodies to Strongyloides. It is particularly useful for screening asymptomatic individuals in endemic areas.

3. Polymerase Chain Reaction (PCR)

PCR testing can detect the DNA of Strongyloides stercoralis in stool, blood, or other body fluids. PCR is a highly sensitive method, especially in cases of low parasite burden.

3. Imaging Studies

In cases of disseminated strongyloidiasis, imaging studies such as chest X-rays or CT scans may be used to evaluate the extent of infection in the lungs or other organs. Imaging is particularly helpful in identifying complications like pneumonia or brain involvement.

Treatments for Strongyloidiasis

Antiparasitic Treatment

The treatment of strongyloidiasis focuses on using antiparasitic medications to eliminate the larvae and adult worms from the body. Early and effective treatment is crucial, especially in immunocompromised individuals or those with severe infections.

1. Ivermectin

Ivermectin is the drug of choice for treating strongyloidiasis. It works by paralyzing the worms, which are then expelled from the body. Ivermectin is highly effective against both the adult worms and larvae of Strongyloides stercoralis.

• Dosage: The typical dosage is 200 mcg/kg, administered once daily for one to two days. In cases of hyperinfection or disseminated strongyloidiasis, a longer course may be required.
• Side effects: Ivermectin is generally well-tolerated, with mild side effects such as dizziness, nausea, and diarrhea.

2. Albendazole

Albendazole is an alternative antiparasitic medication that can be used to treat strongyloidiasis, though it is less effective than ivermectin.

• Dosage: Albendazole is typically given at 400 mg twice daily for 7 days. In some cases, a longer course may be needed.
• Side effects: Common side effects include nausea, abdominal pain, and headache.

Supportive Treatment

In individuals with severe or disseminated strongyloidiasis, supportive care may be necessary to manage complications and improve outcomes.

1. Treatment for Respiratory Symptoms

Patients with significant respiratory involvement may require oxygen therapy or even mechanical ventilation in cases of severe respiratory failure.

2. Treatment of Sepsis

In individuals with hyperinfection syndrome or disseminated strongyloidiasis, sepsis can occur. These patients may require antibiotics, fluid resuscitation, and other supportive measures to treat systemic infections.

3. Management of Immunosuppression

For individuals on immunosuppressive therapy (such as corticosteroids or chemotherapy), reducing or discontinuing these medications, if possible, may help control the infection and reduce the risk of hyperinfection.

Most Common Medications for Strongyloidiasis

The most commonly prescribed medications for treating strongyloidiasis include:

1. Ivermectin

Ivermectin is the first-line treatment for strongyloidiasis due to its high efficacy and safety profile. It is especially effective in cases of chronic infection and hyperinfection.

2. Albendazole

Albendazole is an alternative treatment for strongyloidiasis, particularly for individuals who cannot tolerate ivermectin. It is also used in combination with ivermectin in some cases of severe infection.

3. Corticosteroids

In cases of hyperinfection or disseminated strongyloidiasis, corticosteroids may be used to manage inflammatory responses caused by the parasite. However, corticosteroids can also exacerbate the infection if not carefully managed, so their use requires close monitoring.

Where is Strongyloidiasis Most Prevalent?

Strongyloidiasis is primarily found in tropical and subtropical regions, but it also occurs in some temperate areas. The distribution of strongyloidiasis is closely linked to environmental and socioeconomic factors, such as climate, sanitation practices, and access to healthcare.

1. Southeast Asia

Countries like Thailand, Vietnam, and Cambodia report high rates of strongyloidiasis, particularly in rural and agricultural regions where contact with contaminated soil is common.

2. Sub-Saharan Africa

Strongyloidiasis is prevalent in several countries in West, Central, and East Africa. Poor sanitation, limited access to clean water, and high levels of poverty contribute to the high transmission rates in these regions.

3. Latin America and the Caribbean

In Brazil, Peru, and parts of Central America, strongyloidiasis remains a significant public health issue. Rural communities and indigenous populations are particularly affected due to limited access to healthcare and sanitation.

4. Southern United States

In the southern United States, especially in rural and economically disadvantaged areas, there are reports of endemic strongyloidiasis. The warm, humid climate and poor living conditions in some regions contribute to the persistence of the parasite.

5. Eastern Europe

In some parts of Eastern Europe, particularly among economically disadvantaged communities or marginalized populations, strongyloidiasis continues to be a concern, although the prevalence is lower than in tropical regions.

Prevention of Strongyloidiasis

Preventing strongyloidiasis requires a combination of public health interventions, improved sanitation, and personal protective measures. Reducing transmission of the parasite is critical, especially in endemic areas.

1. Improved Sanitation and Hygiene

One of the most effective ways to prevent strongyloidiasis is to improve access to sanitation facilities and clean water. Key measures include:

• Building latrines: Providing communities with hygienic latrines prevents open defecation, reducing the contamination of soil with Strongyloides larvae.
• Proper sewage disposal: Ensuring proper disposal of human waste through sewage systems helps prevent environmental contamination.

2. Wearing Protective Footwear

Since the primary mode of transmission is through skin contact with contaminated soil, wearing shoes or sandals can significantly reduce the risk of infection. Individuals working in agriculture or other soil-related activities should always wear protective footwear.

3. Health Education

Educating communities in endemic regions about the risks of strongyloidiasis and the importance of good hygiene practices can help reduce the spread of the infection. Key messages include:

• Washing hands: Frequent handwashing with soap and clean water, especially before eating and after using the toilet, can help prevent the ingestion of contaminated soil.
• Avoiding direct contact with soil: Encouraging the use of gloves when handling soil or gardening in areas where strongyloidiasis is common.

4. Mass Drug Administration (MDA)

In regions with high prevalence rates, mass drug administration (MDA) programs may be implemented as part of public health campaigns to reduce the burden of strongyloidiasis. These programs typically involve administering ivermectin to large groups of people at regular intervals.

• School-based deworming: In areas where children are at high risk, regular treatment with ivermectin or albendazole can help control the disease and prevent long-term complications.

5. Screening and Prophylaxis for High-Risk Individuals

In areas with endemic strongyloidiasis, individuals at high risk, such as immunocompromised individuals or those undergoing organ transplants, should be screened for the infection before starting immunosuppressive therapy. Prophylactic treatment with ivermectin may be recommended for those at risk of developing severe strongyloidiasis.