Overwhelming strongyloidiasis: an unappreciated opportunistic infection

Abstract

Strongyloides stercoralis is an intestinal nematode which infects a large portion of the world's population. Individuals with infection confined to the intestinal tract are often asymptomatic but may have abdominal pain, weight loss, diarrhea, and other nonspecific complaints. Enhanced proliferation of the parasite in compromised hosts causes an augmentation of the normal life-cycle. Resultant massive invasion of the gastrointestinal tract and lungs is termed the hyperinfection syndrome. If the worm burden is excessive, parasitic invasion of other tissues occurs and is termed disseminated strongyloidiasis. A variety of underlying conditions appear to predispose to severe infections. These are primarily diseases characterized by immunodeficiency due to defective T-lymphocyte function (Table 1). Individuals with less severe disorders become compromised hosts because of therapeutic regimens consisting of corticosteroids or other immunosuppressive medication. The debilitation of chronic illness or malnutrition also predisposes to systemic stronglyloidiasis. The diagnosis of strongyloidiasis can be readily made by microscopic examination of concentrates of upper small bowel fluid, stool, or sputum. Important clues suggesting this infection include unexplained gram-negative bacillary bacteremia in a compromised host who may have vague abdominal complaints, an ileus pattern on X-ray, and pulmonary infiltrates. Eosinophilia is helpful, if present, but should not be relied upon to exclude the diagnosis. The treatment of systemic infection due to Strongyloides stercoralis with either thiabensazole 25 mg/kg orally twice daily is satisfactory if the diagnosis is made early. Because of several unusual features of this illness in compromised hosts, the standard recommendation for 2 days of therapy should be abandoned in such patients. Immunodeficiency, corticosteroids, and bowel ileus reduce drug efficacy. Thus a longer treatment period of at leuch as blind loops or diverticula necessitate longer treatment. Stool specimens and upper small bowel aspirates should be monitored regularly and treatment continued several days beyond the last evidence of the parasite. In particularly difficult situations where either worm eradication is impossible or reinfection is probable, short monthly courses of antihelminthic therapy seem to be effective in averting recurrent systemic illness. Finally, prevention of hyperinfection or dissemination due to Strongyloides stercoralis can be accomplished by screening immunocompromised hosts with stool and upper small bowel aspirate examinations. These would be especially important prior to initiating chemotherapy, or before giving immunosuppressive medications or corticosteroids to patients with nonneoplastic conditions such as systemic lupus erythematosus, nephrotic syndrome, or renal allografts.