Strongyloidiasis is a human parasitic disease caused by the nematode called Strongyloides stercoralis, or sometimes the closely related S. fülleborni. These helminths belong to a group of nematodes called roundworms. These intestinal worms can cause a number of symptoms in people, principally skin symptoms, abdominal pain, diarrhea and weight loss, but also many other specific and vague symptoms in disseminated disease, and severe life-threatening conditions through hyperinfection. In some people, particularly those who require corticosteroids or other immunosuppressive medication, Strongyloides can cause a hyperinfection syndrome that can lead to death if untreated. The diagnosis is made by blood and stool tests. The medication ivermectin is widely used to treat strongyloidiasis.
Strongyloidiasis is a type of soil-transmitted helminthiasis. Low estimates postulate it to affect 30–100 million people worldwide, mainly in tropical and subtropical countries, while higher estimates conservatively extrapolate that infection is upwards to or above 370 million people. It belongs to the group of neglected tropical diseases, and worldwide efforts are aimed at eradicating the infection.
Signs and symptoms
Strongyloides infection occurs in five forms. As the infection continues and the larvae matures, there may be respiratory symptoms (Löffler's syndrome). The infection may then become chronic with mainly digestive symptoms. On reinfection (when larvae migrate through the body) from the skin to the lungs and finally to the small intestine, there may be respiratory, skin and digestive symptoms. Finally, the hyperinfection syndrome causes symptoms in many organ systems, including the central nervous system.
Uncomplicated disease
Frequently asymptomatic. Gastrointestinal system symptoms include abdominal pain and diarrhea and/or conversely constipation. Pulmonary symptoms (including Löffler's syndrome) can occur during pulmonary migration of the filariform larvae. Pulmonary infiltrate may be present through radiological investigation. Dermatologic manifestations include urticarial rashes in the buttocks and waist areas as well as larva currens. Eosinophilia is generally present. Strongyloidiasis can become chronic and then become completely asymptomatic.
Disseminated disease
Disseminated strongyloidiasis occurs when patients with chronic strongyloidiasis become immunosuppressed. There is a distinction to be made between dissemination and hyperinfection. It is mainly a semantic distinction. There can be mild dissemination where the worm burden is relatively lower yet causes insidious symptoms, or extreme dissemination that the term hyperinfection is used to describe. Thus hyperinfection of varying levels of severe dissemination may present with abdominal pain, distension, shock, pulmonary and neurologic complications, sepsis, haemorrhage, malabsorption, and depending on the combination, degree, number, and severity of symptoms, is potentially fatal. The worms enter the bloodstream from the bowel wall, simultaneously allowing entry of bowel bacteria such as Escherichia coli. This may cause symptoms such as sepsis (bloodstream infection), and the bacteria may spread to other organs where they may cause localized infection such as meningitis. Dissemination without hyperinfection may present to a lesser degree the above and many other symptoms.
Dissemination can occur many decades after the initial infection and has been associated with high dose corticosteroids, organ transplant, any other instances and causes of immunosuppression, HIV, lepromatous leprosy, tertiary syphilis, aplastic anemia, malnutrition, advanced tuberculosis and radiation poisoning. It is often recommended that patients being started on immunosuppression be screened for chronic strongyloidiasis; however, this is often impractical (screen tests are often unavailable) and in developed countries, the prevalence of chronic strongyloidiasis is very small, so screening is usually not cost-effective, except in endemic areas. The reality of global travel and need for modern advanced healthcare, even in the so-called "developed world", necessitates that in non-endemic areas there is easily accessible testing and screening for neglected tropical diseases such as strongyloidiasis.
It is important to note that there is not necessarily any eosinophilia in the disseminated disease. Absence of eosinophilia in an infection limited to the gastrointestinal tract may indicate poor prognosis. Eosinophilia is often absent in disseminated infection. Steroids will also suppress eosinophilia, while leading to dissemination and potential hyperinfection.