Strongyloidiasis overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]
Overview
Strongyloidiasis is a human parasitic disease caused by the nematode (roundworm) Strongyloides stercoralis or sometimes S. fülleborni. The primary mode of infection is through contact with soil that is contaminated with free-living larvae. It can cause a variety of symptoms, most commonly skin lesions, abdominal pain, diarrhea, and weight loss. In some people, particularly those who require corticosteroids or other immunosuppressive medications, Strongyloides can cause a hyperinfection syndrome that can lead to death if left untreated. The disease may be complicated by disseminated strongyloidiasis (especially in immunosuppressed patients), eosinophilic pneumonia, and malnutrition. The diagnosis is made by blood and stool tests. Ivermectin is the drug of choice in the treatment of strongyloidiasis.
Historical Perspective
Strongyloides was first discovered in 1876 by the French physician Louis Alexis Normand while working in the naval hospital in Toulon; he identified the adult worms and sent them to Arthur Réné Jean Baptiste Bavay, chief health inspector, who observed that the worms were the adult forms of the larvae found in stool. In 1883, the German parasitologist Rudolf Leuckart made initial observations on the life cycle of parasite. Belgian physician Paul Van Durme described the mode of infection through the skin. The German parasitologist Friedrich Fülleborn described autoinfection and the mechanism by which strongyloidiasis involves the intestine. Strongyloidiasis was investigated further during the 1940s, as persons who had acquired the infection abroad and then received immunosuppression developed hyper-infestation syndrome.
Classification
Strongyloidiasis may be classified as acute or chronic based on the duration of symptoms and as hyper infection syndrome or disseminated strongyloidiasis based on the organ system involvement.
Pathophysiology
Strongyloides is classified as a soil-transmitted helminth. The primary mode of infection is through contact with soil that is contaminated with free-living larvae. When the larvae come in contact with skin, they are able to penetrate it and migrate through the body, eventually finding their way to the small intestine where they burrow and lay their eggs. Unlike other soil-transmitted helminths such as hookworm and whipworm, whose eggs do not hatch until they are outside the body, the eggs of Strongyloides hatch into larvae in the intestine. Most of these larvae will be excreted in the stool, but some of the larvae may molt and immediately re-infect the host either by burrowing into the intestinal wall or by penetrating the perianal skin. This characteristic of Strongyloides is termed auto-infection. The significance of auto-infection is that if left untreated, persons may remain infected throughout their lifetime.
Causes
Strongyloidiasis is a human parasitic disease caused by the nematode (roundworm) Strongyloides stercoralis or sometimes S. fülleborni.
Differentiating Strongyloidiasis from other Diseases
Strongyloidiasis can mimic other worm infections like Ascaris lumbricoides, Trichuris trichiura, hookworm infections (Necator americanus and Ancylostoma duodenale), Enterobius vermicularis (pinworm) and gastrointestinal pathologies such as peptic ulcer disease, intussusception in children, and bile duct stone.
Epidemiology and Demographics
The global prevalence of Strongyloides is unknown, but experts estimate that there are between 30–100 million infected persons worldwide, mainly in tropical and subtropical countries. Strongyloidiasis is more common in the pediatric age group (ages 2-10 years).
Risk Factors
Strongyloides is found more frequently in the socioeconomically disadvantaged, institutionalized populations, and in rural areas. Activities that increase contact with the soil increase the risk of becoming infected, such as walking with bare feet or contact with human waste or sewage. Occupations that increase contact with contaminated soil such as farming and coal mining, and a history of infection with Human T-Cell Lymphotropic Virus-1 (HTLV-1) also increase the risk of infection.
Screening
Most fatal infections caused by S.stercoralis can be prevented by early detection and treatment of asymptomatic chronic infections. Screening is highly recommended to detect latent S.stercoralis infection before the start of chemotherapy or immunosuppression/steroid therapy in patients at risk. Repeated stool examination for ova and parasites or agar culture of stool may be the most appropriate approach.
Natural history, Complications and Prognosis
If strongyloidiasis is left untreated, the infection can disseminate and transform into hyperinfection syndrome which has a mortality rate of 90%. Complications that can develop as a result of strongyloidiasis are disseminated strongyloidiasis (especially in patients with HIV or an otherwise suppressed immune system), eosinophilic pneumonia, malnutrition, and malabsorption. With appropriate treatment, people should make a full recovery. Treatment needs to be repeated often. Infections that are severe or widespread often have a poor outcome, especially in people with a suppressed immune system.
Diagnosis
History and symptoms
Strongyloides infection occurs in five forms. On acquiring the infection, 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), there may be respiratory, skin, and digestive symptoms. Finally, hyper infection syndrome causes symptoms in many organ systems, including the central nervous system.
Physical examination
The physical examination findings in strongyloidiasis vary and are usually dependent on the worm burden and the involved organ.
Laboratory findings
The gold standard for the diagnosis of strongyloidiasis is serial stool examination. Duodenal aspirate is more sensitive than stool examination. Duodenal biopsy may reveal parasites in the gastric crypts, duodenal glands, or eosinophilic infiltration in the lamina propria. In disseminated cases of strongyloidiasis, larvae can be detected in sputum by simple wet-mount of bronchoalveolar lavage (BAL). Immunodiagnostic tests for strongyloidiasis are indicated when the infection is suspected and the organism cannot be demonstrated by duodenal aspiration, string tests, or by repeated examinations of stool. Enzyme immunoassay (EIA) is currently recommended because of its greater sensitivity (90%). Cross-reactions in patients with filariasis and some other nematode infections can occur. Antibody test results cannot be used to differentiate between past and current infection.
Chest and Abdominal X-rays
Radiographs can be useful investigations in the diagnosis of strongyloidiasis. A chest X-ray can reveal varying sizes of oval or round infiltrates (Löffler's syndrome). Plain abdominal radiographs and contrast studies may reveal worm masses in bowel loops.
CT
There are no specific CT findings associated with strongyloidiasis. However, in cases of abdominal obstruction due to worm burden, CT can demonstrate collapsed loops of the bowel distally and radial distribution of several dilated, fluid-filled bowel loops.
MRI
There are no specific MRI findings associated with strongyloidiasis.
Ultrasound
There are no specific ultrasound findings associated with strongyloidiasis.
Other Imaging Findings
There are no other specific imaging findings associated with strongyloidiasis infection.
Other diagnostic tests
Upper and lower GI endoscopy, skin biopsy, and BAL fluid examination are some other diagnostic tests that are employed in diagnosing strongyloidiasis when there is a negative stool exam.
Treatment
Medical Therapy
The drug of choice for the treatment of uncomplicated strongyloidiasis is ivermectin with albendazole as the alternative. All patients who are at risk of disseminated strongyloidiasis should be hospitalized.
Surgery
Strongyloidiasis is usually managed with medical therapy. However, surgery may be indicated when medical management fails or complications arise.
Primary Prevention
The prevention of strongyloidiasis is best achieved through improvements in personal hygiene and environmental sanitation.
Secondary Prevention
Secondary preventive measures of strongyloidiasis are similar to primary preventive measures.