Strongyloides stercoralis is a very small nematode (2 mm × 0.4 mm) which parasitises the mucosa of the upper part of the small intestine, often in large numbers, causing persistent eosinophilia. The eggs hatch in the bowel but only larvae are passed in the faeces. In moist soil, they moult and become the infective filariform larvae. After penetrating human skin, they undergo a development cycle similar to that of hookworms, except that the female worms burrow into the intestinal mucosa and submucosa. Some larvae in the intestine may develop into filariform larvae, which may then penetrate the mucosa or the perianal skin and lead to autoinfection and persistent infection. Patients with Strongyloides infection persisting for more than 35 years have been described. Strongyloidiasis occurs in the tropics and subtropics, and is especially prevalent in the Far East.
The classic triad of symptoms consists of abdominal pain, diarrhoea and urticaria. Cutaneous manifestations, either urticaria or larva
currens (a highly characteristic pruritic, elevated, erythematous lesion advancing along the course of larval migration), are characteristic and occur in 66% of patients.
Systemic strongyloidiasis (the Strongyloides hyperinfection syndrome), with dissemination of larvae throughout the body, occurs in association with immune suppression (intercurrent disease, HIV and HTLV-1 infection, corticosteroid treatment). Patients present with severe, generalised abdominal pain, abdominal distension and shock. Massive larval invasion of the lungs causes cough, wheeze and dyspnoea; cerebral involvement has manifestations ranging from subtle neurological signs to coma. Gram-negative sepsis frequently complicates the picture.
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