Strongyloides stercoralis is a nematode with a complicated life cycle that involves parasitic and free-living forms. It can cause autoinfection, which is the ability to complete a full life cycle within humans and therefore multiplies. Multiple migratory cycles can lead to recurrent infection. Only complete cure can eliminate the risk of complications, so accurate diagnostic methods must be employed.
Endemic to the Caribbean, Latin America, Europe, Asia, and sub-Saharan Africa, strongyloidiasis mainly affects tropical and sub-tropical regions. It is estimated that S. stercoralis affects 30 to 100 million people worldwide. It is often underdiagnosed and more appropriate and sensitive diagnostic tests would yield a higher global incidence.
The life cycle of S. stercoralis has three components: direct, indirect, and autoinfection. In the direct cycle, the rhabditiform larva from stool matures into filariform larvae in the soil and penetrates the skin to travel to the lungs and eventually the gastrointestinal system. The indirect cycle follows, where eggs are excreted and returned to the soil to live as free-living adults or develop into filariform larvae or reinvade the host through the perianal skin. This reinvasion characterizes the autoinfection cycle, where the infective filariform larva completes its formation in the host’s intestines.
Minor and chronic Strongyloides infection is commonly clinically unapparent in healthy individuals. Some experience gastrointestinal symptoms such as nausea, vomiting, constipation, and abdominal pain, skin problems including pruritis or dermatitis, or respiratory symptoms such as a cough, apnea, or dyspnea. Others can have malabsorption which can mimic tropical sprue clinically and radiographically. Immunocompromised or patients on immunosuppressive treatment are at risk for more severe complications such as disseminated infection and enterococcal meningitis.
The gold standard for diagnosis is based on identifying rhabditiform larvae on direct stool examination under microscopy, or by culturing on agar plates. Serial and repeat stool examination is necessary because the parasitic output is often limited and dependent on the occurrence of larvae in the stool. Therefore, examining multiple stool samples is recommended to identify uncomplicated strongyloidiasis. Hyperinfection is readily diagnosed as filariform larvae in high numbers can be visualized. Other serologic tests using recombinant antigen and enzyme-linked immunosorbent assay are more sensitive and specific, but available only in special laboratories.
Many studies show that the best treatment for uncomplicated strongyloidiasis is a drug called Ivermectin. The recommended treatment regimen consists of 200 mg/kg for 2 consecutive days. For uncomplicated strongyloidiasis, the treatment is ivermectin daily until larvae can no longer be detected in stool, urine, or sputum for two weeks.
The differential diagnoses include:
The prognosis in Strongyloidiasis depends on if complications develop. Strongyloidiasis can result in dermatologic, gastrointestinal, renal, pulmonary, and neurologic complications and even death.
The goal in strongyloidiasis is to eradicate the infection, decrease morbidity, and prevent complications.
Parasite pathways are different from the human host and allow selective interference by chemotherapeutic agents. The effectiveness of anthelmintic agents against larvae is poor; they are more effective in established infection.
The diagnosis and management of Strongyloides infection is done with a multidisciplinary team that includes an infectious disease expert, gastroenterologist, emergency department physician and pharmacist. The key is to get rid of all larvae with ivermectin. Once discharged, the patients need to follow up by the nurse practitioner and primary physician to ensure that all body fluids have no larvae. Patients also need to be educated about hand washing and maintaining personal hygiene. For those with a simple infection of the GI tract, the outcomes are good but in patients with multiple organ infestation, the prognosis guarded.
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