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Strongyloidiasis

Updated : September 16, 2023





Background

Strongyloidiasis, also known as strongyloidiasis or threadworm infection, is a parasitic disease caused by the nematode Strongyloides stercoralis. This parasite infects humans and certain other primates. Strongyloidiasis is primarily a tropical and subtropical disease but can also occur in temperate regions. It is most prevalent in areas with poor sanitation and limited access to clean water.

The primary transmission mode is through direct skin contact with contaminated soil, often in areas with poor sanitation. In addition to soil, the infection can be transmitted through organ transplantation, blood transfusion, or vertically from mother to child during childbirth if the mother is infected.

Epidemiology

Strongyloidiasis is endemic to regions encompassing Latin America, the Caribbean, Europe, Asia, and sub-Saharan Africa, with a primary prevalence in tropical and subtropical areas. It is estimated that Strongyloides stercoralis affects a substantial global population, ranging from 30 to 100 million individuals. This parasitic infection often goes undiagnosed, and improving diagnostic tests could reveal an even higher incidence worldwide.

Environmental factors play a significant role in endemic areas, where individuals frequently come into close contact with sand and soil due to occupational requirements, live near farm animals, face overcrowding, and have limited access to proper sanitation. Consequently, socio-economically disadvantaged populations are more vulnerable to infection. Children are particularly affected, largely due to poor adherence to personal hygiene practices.

Additionally, occupational exposure makes males twice as likely to contract the infection. Interestingly, S. stercoralis larvae, eggs, and even adult nematodes have been identified in certain soil-grown vegetables and tap water. While strongyloidiasis is found on all continents, it has been notably identified in the United States, specifically focusing on regions like Appalachia and the southeastern United States.

Anatomy

Pathophysiology

The infection begins when the filariform larvae of S. stercoralis penetrate the host’s intact skin upon contact with contaminated soil. These larvae then migrate through the host’s body via the bloodstream and lymphatic system. As they travel, they can cause mechanical damage to host tissues, particularly during their passage through the lungs. In the lungs, the larvae move through the pulmonary capillaries and into the alveoli. This migration can result in symptoms such as coughing and wheezing, often mistaken for respiratory infections.

The host’s immune system may mount an initial response during this phase. Once the larvae are swallowed and reach the gastrointestinal tract, they mature into adult worms in the small intestine. They establish themselves by burrowing into the intestinal mucosa, where they can feed on host tissues and lay eggs. The eggs hatch into rhabditiform larvae, excreted in the host’s stool. A unique feature of strongyloidiasis is autoinfection.

Some larvae within the host’s intestines can reinvade the host’s body through the perianal skin or mucous membranes, leading to a continuous cycle of infection. This autoinfection can persist for years or even decades, making chronic strongyloidiasis possible. The host’s immune response is critical in the pathophysiology of strongyloidiasis. While the initial infection may induce a mild immune response, chronic infections can lead to parasite immune suppression or evasion.

This can result in the persistence of the infection and contribute to its underdiagnosis. In cases where the host’s immune system is compromised, such as in individuals with HIV/AIDS, corticosteroid therapy, or other immunosuppressive conditions, strongyloidiasis can progress to hyperinfection syndrome or disseminated strongyloidiasis. During these severe forms of the infection, the parasite can disseminate throughout the body, affecting various organs and leading to life-threatening complications, including sepsis.

Etiology

Strongyloides stercoralis is a nematode with a complex life cycle that encompasses both parasitic and free-living stages. A notable characteristic of this parasite is its capability for autoinfection, allowing it to complete a full life cycle within the human host, leading to multiplication.

Recurrent infections can occur due to multiple migratory cycles. To eliminate the risk of complications, it is imperative to achieve a complete cure, underscoring the importance of employing accurate diagnostic methods.

Genetics

Prognostic Factors

The prognosis for strongyloidiasis varies from good in mild cases to serious in severe or immunocompromised individuals. Early diagnosis and appropriate treatment are critical for a favorable outcome. Individuals with chronic or recurrent infections may require ongoing medical care to ensure complete resolution of the infection.

Clinical History

In individuals with asymptomatic chronic strongyloidiasis, the most common way it comes to attention is through the incidental discovery of peripheral eosinophilia. However, during the acute stage of infection, those affected may experience a pruritic, edematous, and petechial rash at the site where the larvae penetrated the skin. One of the more distinctive rashes of this infection is known as larva migrans or currens. It occurs due to the migration of the filariform larva beneath the skin, triggering a hypersensitivity reaction in the host.

This results in a transient linear and serpiginous rash with erythematous features that move at a rate of 2-10 centimeters per hour. While the duration of this rash can vary from hours to days, it can also be a recurring process during the course of parasitic autoinfection. Chronic strongyloidiasis may manifest with nonspecific symptoms affecting multiple organ systems, particularly the gastrointestinal, dermatological, and respiratory systems. Common gastrointestinal symptoms include heartburn, abdominal bloating, constipation or diarrhea, and a decreased appetite.

These symptoms typically appear about two weeks after the initial infection. Respiratory symptoms like a chronic dry cough or wheezing, often resembling asthma, can also occur. Constitutional symptoms like a low-grade fever, weight loss, and anemia may present as the sole features of the infection. Furthermore, the migration of larvae through pulmonary capillaries can lead to alveolar hemorrhage, while their presence in alveolar spaces provokes an eosinophilic inflammatory response, resulting in clinical evidence of pneumonitis.

Physical Examination

Larva currens is a distinctive and pathognomonic rash associated with strongyloidiasis. It appears as a raised, serpiginous, erythematous (red) rash that moves rapidly and causes itching. The rash is caused by the migration of larvae beneath the skin. Patients usually have gastrointestinal symptoms such as abdominal pain and discomfort, diarrhea, which can be watery or bloody, nausea and vomiting, and loss of appetite, and dehydration can be observed through sunken or dry skin.

In severe cases or individuals with compromised immune systems, strongyloidiasis can lead to a condition known as disseminated strongyloidiasis, which involves the spread of the parasite to other organs beyond the gastrointestinal and respiratory systems. In these cases, physical examination findings may include signs of Septicemia such as hypotension, tachycardia, and altered mental status.

Age group

Associated comorbidity

Associated activity

Acuity of presentation

Differential Diagnoses

Asthma

Acute respiratory distress syndrome

Cholera

Chronic Obstructive Pulmonary Disease

Diverticulitis

Loeffler Syndrome

Peritonitis

Laboratory Studies

Imaging Studies

Procedures

Histologic Findings

Staging

Treatment Paradigm

Initial Approach

Numerous studies have consistently demonstrated that the optimal approach for treating uncomplicated strongyloidiasis involves the use of Ivermectin. The recommended treatment protocol entails administering 200 mcg/kg of Ivermectin for two consecutive days. In cases of uncomplicated strongyloidiasis, the treatment course typically consists of daily Ivermectin administration until no larvae can be detected in stool, urine, or sputum for a period of two weeks.

Intensive Care

Immunocompromised individuals may necessitate intensive care management when dealing with disseminated strongyloidiasis infection. Considering contact isolation is advisable due to the potential presence of infective larvae in sputum, stool, and vomit. Patients experiencing hyperinfection syndrome frequently exhibit conditions such as sepsis, shock, and acute respiratory distress syndrome (ARDS).

by Stage

by Modality

Chemotherapy

Radiation Therapy

Surgical Interventions

Hormone Therapy

Immunotherapy

Hyperthermia

Photodynamic Therapy

Stem Cell Transplant

Targeted Therapy

Palliative Care

Lifestyle Modifications

Eradicating Strongyloides can be challenging, as the parasite can persist in individuals for extended periods, even after treatment.

Consequently, continued treatment is often necessary, even if symptoms have resolved. To prevent reinfection, it is advisable to wash clothes and bedding with enzyme-based laundry detergent and dry them in hot weather conditions. 

Anthelmintic Therapy

Patients with hyperinfection or disseminated strongyloidiasis should receive oral Ivermectin until two consecutive weeks of stool or sputum examinations yield negative results. In cases where patients have malabsorption issues or cannot tolerate oral therapy, rectal administration is the preferred route. Particular attention should be given to reducing or discontinuing immunosuppressive medications in these individuals. 

For patients with hyperinfection syndrome, it is advisable to implement contact precautions and isolation measures due to the potential presence of larvae in all body fluids. It is also recommended to screen family members for the infection, and healthcare workers should adhere to universal precautions. 

The use of steroids and leukotriene inhibitors should be avoided, as leukotrienes may play a role in immune response against Strongyloides infection. Additionally, Albendazole and thiabendazole are also effective treatment options. The optimal treatment duration remains unclear. It is worth noting that Albendazole can suppress bone marrow function, possibly leading to pancytopenia. 

Medication

Media Gallary

References

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Strongyloidiasis

Updated : September 16, 2023




Strongyloidiasis, also known as strongyloidiasis or threadworm infection, is a parasitic disease caused by the nematode Strongyloides stercoralis. This parasite infects humans and certain other primates. Strongyloidiasis is primarily a tropical and subtropical disease but can also occur in temperate regions. It is most prevalent in areas with poor sanitation and limited access to clean water.

The primary transmission mode is through direct skin contact with contaminated soil, often in areas with poor sanitation. In addition to soil, the infection can be transmitted through organ transplantation, blood transfusion, or vertically from mother to child during childbirth if the mother is infected.

Strongyloidiasis is endemic to regions encompassing Latin America, the Caribbean, Europe, Asia, and sub-Saharan Africa, with a primary prevalence in tropical and subtropical areas. It is estimated that Strongyloides stercoralis affects a substantial global population, ranging from 30 to 100 million individuals. This parasitic infection often goes undiagnosed, and improving diagnostic tests could reveal an even higher incidence worldwide.

Environmental factors play a significant role in endemic areas, where individuals frequently come into close contact with sand and soil due to occupational requirements, live near farm animals, face overcrowding, and have limited access to proper sanitation. Consequently, socio-economically disadvantaged populations are more vulnerable to infection. Children are particularly affected, largely due to poor adherence to personal hygiene practices.

Additionally, occupational exposure makes males twice as likely to contract the infection. Interestingly, S. stercoralis larvae, eggs, and even adult nematodes have been identified in certain soil-grown vegetables and tap water. While strongyloidiasis is found on all continents, it has been notably identified in the United States, specifically focusing on regions like Appalachia and the southeastern United States.

The infection begins when the filariform larvae of S. stercoralis penetrate the host’s intact skin upon contact with contaminated soil. These larvae then migrate through the host’s body via the bloodstream and lymphatic system. As they travel, they can cause mechanical damage to host tissues, particularly during their passage through the lungs. In the lungs, the larvae move through the pulmonary capillaries and into the alveoli. This migration can result in symptoms such as coughing and wheezing, often mistaken for respiratory infections.

The host’s immune system may mount an initial response during this phase. Once the larvae are swallowed and reach the gastrointestinal tract, they mature into adult worms in the small intestine. They establish themselves by burrowing into the intestinal mucosa, where they can feed on host tissues and lay eggs. The eggs hatch into rhabditiform larvae, excreted in the host’s stool. A unique feature of strongyloidiasis is autoinfection.

Some larvae within the host’s intestines can reinvade the host’s body through the perianal skin or mucous membranes, leading to a continuous cycle of infection. This autoinfection can persist for years or even decades, making chronic strongyloidiasis possible. The host’s immune response is critical in the pathophysiology of strongyloidiasis. While the initial infection may induce a mild immune response, chronic infections can lead to parasite immune suppression or evasion.

This can result in the persistence of the infection and contribute to its underdiagnosis. In cases where the host’s immune system is compromised, such as in individuals with HIV/AIDS, corticosteroid therapy, or other immunosuppressive conditions, strongyloidiasis can progress to hyperinfection syndrome or disseminated strongyloidiasis. During these severe forms of the infection, the parasite can disseminate throughout the body, affecting various organs and leading to life-threatening complications, including sepsis.

Strongyloides stercoralis is a nematode with a complex life cycle that encompasses both parasitic and free-living stages. A notable characteristic of this parasite is its capability for autoinfection, allowing it to complete a full life cycle within the human host, leading to multiplication.

Recurrent infections can occur due to multiple migratory cycles. To eliminate the risk of complications, it is imperative to achieve a complete cure, underscoring the importance of employing accurate diagnostic methods.

The prognosis for strongyloidiasis varies from good in mild cases to serious in severe or immunocompromised individuals. Early diagnosis and appropriate treatment are critical for a favorable outcome. Individuals with chronic or recurrent infections may require ongoing medical care to ensure complete resolution of the infection.

In individuals with asymptomatic chronic strongyloidiasis, the most common way it comes to attention is through the incidental discovery of peripheral eosinophilia. However, during the acute stage of infection, those affected may experience a pruritic, edematous, and petechial rash at the site where the larvae penetrated the skin. One of the more distinctive rashes of this infection is known as larva migrans or currens. It occurs due to the migration of the filariform larva beneath the skin, triggering a hypersensitivity reaction in the host.

This results in a transient linear and serpiginous rash with erythematous features that move at a rate of 2-10 centimeters per hour. While the duration of this rash can vary from hours to days, it can also be a recurring process during the course of parasitic autoinfection. Chronic strongyloidiasis may manifest with nonspecific symptoms affecting multiple organ systems, particularly the gastrointestinal, dermatological, and respiratory systems. Common gastrointestinal symptoms include heartburn, abdominal bloating, constipation or diarrhea, and a decreased appetite.

These symptoms typically appear about two weeks after the initial infection. Respiratory symptoms like a chronic dry cough or wheezing, often resembling asthma, can also occur. Constitutional symptoms like a low-grade fever, weight loss, and anemia may present as the sole features of the infection. Furthermore, the migration of larvae through pulmonary capillaries can lead to alveolar hemorrhage, while their presence in alveolar spaces provokes an eosinophilic inflammatory response, resulting in clinical evidence of pneumonitis.

Larva currens is a distinctive and pathognomonic rash associated with strongyloidiasis. It appears as a raised, serpiginous, erythematous (red) rash that moves rapidly and causes itching. The rash is caused by the migration of larvae beneath the skin. Patients usually have gastrointestinal symptoms such as abdominal pain and discomfort, diarrhea, which can be watery or bloody, nausea and vomiting, and loss of appetite, and dehydration can be observed through sunken or dry skin.

In severe cases or individuals with compromised immune systems, strongyloidiasis can lead to a condition known as disseminated strongyloidiasis, which involves the spread of the parasite to other organs beyond the gastrointestinal and respiratory systems. In these cases, physical examination findings may include signs of Septicemia such as hypotension, tachycardia, and altered mental status.

Asthma

Acute respiratory distress syndrome

Cholera

Chronic Obstructive Pulmonary Disease

Diverticulitis

Loeffler Syndrome

Peritonitis

Initial Approach

Numerous studies have consistently demonstrated that the optimal approach for treating uncomplicated strongyloidiasis involves the use of Ivermectin. The recommended treatment protocol entails administering 200 mcg/kg of Ivermectin for two consecutive days. In cases of uncomplicated strongyloidiasis, the treatment course typically consists of daily Ivermectin administration until no larvae can be detected in stool, urine, or sputum for a period of two weeks.

Intensive Care

Immunocompromised individuals may necessitate intensive care management when dealing with disseminated strongyloidiasis infection. Considering contact isolation is advisable due to the potential presence of infective larvae in sputum, stool, and vomit. Patients experiencing hyperinfection syndrome frequently exhibit conditions such as sepsis, shock, and acute respiratory distress syndrome (ARDS).

Eradicating Strongyloides can be challenging, as the parasite can persist in individuals for extended periods, even after treatment.

Consequently, continued treatment is often necessary, even if symptoms have resolved. To prevent reinfection, it is advisable to wash clothes and bedding with enzyme-based laundry detergent and dry them in hot weather conditions. 

Patients with hyperinfection or disseminated strongyloidiasis should receive oral Ivermectin until two consecutive weeks of stool or sputum examinations yield negative results. In cases where patients have malabsorption issues or cannot tolerate oral therapy, rectal administration is the preferred route. Particular attention should be given to reducing or discontinuing immunosuppressive medications in these individuals. 

For patients with hyperinfection syndrome, it is advisable to implement contact precautions and isolation measures due to the potential presence of larvae in all body fluids. It is also recommended to screen family members for the infection, and healthcare workers should adhere to universal precautions. 

The use of steroids and leukotriene inhibitors should be avoided, as leukotrienes may play a role in immune response against Strongyloides infection. Additionally, Albendazole and thiabendazole are also effective treatment options. The optimal treatment duration remains unclear. It is worth noting that Albendazole can suppress bone marrow function, possibly leading to pancytopenia. 

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