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Strongyloidiasis (threadworm infection) is a parasitic intestinal infection that occurs worldwide. It's endemic in the tropics and subtropics as well as areas associated with poor hygiene. Outbreaks also occur in facilities. Its incidence in the United States is low.

Susceptibility to strongyloidiasis is universal; infection doesn't confer immunity. Because the reproductive cycle of the threadworm may continue in the untreated host for as long as 45 years after the initial infection, auto infection is highly probable.

Most patients with strongyloidiasis recover completely, but debilitation from protein loss occasionally is fatal. Massive auto infection, especially in immunocompromised patients, also can be fatal.


Strongyloidiasis is caused by the helminth Strongyloides stercoralis. Transmission to humans usually occurs through contact with soil that contains infective S. stercoralis filariform larvae. Such larvae develop from noninfective rhabditoid (rod-shaped) larvae in human stool. The filariform larvae penetrate the human skin, usually at the feet, and then migrate by way of the lymphatic system to the blood-stream and the lungs.

After they enter the pulmonary circulation, the filariform larvae break through the alveoli and migrate upward to the pharynx, where they are swallowed. Then they lodge in the small intestine, where they deposit eggs that mature into noninfective rhabditoid larvae. Next, these larvae migrate into the large intestine and are excreted in stool, starting the cycle again. The threadworm life cycle, which begins with penetration of the skin and ends with excretion of rhabditoid larvae, takes 17 days.

In autoinfection, rhabditoid larvae mature in the intestine to become infective filariform larvae.

Signs and symptoms

  • Abdominal pain (upper abdomen, epigastric)
  • Cough
  • Diarrhea
  • Unintentional weight loss
  • Rash
  • Often asymptomatic
  • Periodic appearance of red hive-like appearing lesions near the anus
  • Unintentional weight loss
  • Vomiting

Diagnostic tests 

Observation of S.stercoralis larvae in a fresh stool specimen allows diagnosis (2 hours after excretion, rhabditoid larvae look like hookworm larvae). Repeated testing may be needed. During the pulmonary phase, sputum may show many eosinophils and larvae.


Because of the potential for autoinfection, the patient needs treatment with thiabendazole for 2 to 3 days. The total dose shouldn't exceed 3 g. He also may need protein replacement, blood transfusions, and I.V. fluids.

Treatment is necessary if S.stercoralis remains in stools after therapy. Corticosteroids are contraindicated because they increase the risk of autoinfection and dissemination and also predispose the patient to GI ulceration.


Good personal hygiene can reduce the risk of strongyloidiasis. Adequate public health services and sanitary facilities provide good control of infection.

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