Strongyloidiasis is an infection caused by the roundworm Strongyloides stercoralis.

Causes, incidence, and risk factors

S. stercoralis is fairly common in warm moist areas. Rarely it can be found as far north as Canada.

This tiny worm is barely visible to the naked eye. Its life cycle is very similar to the hookworm:

  1. Young roundworms penetrate the skin.
  2. They migrate through the bloodstream to the lungs and up the large airways.
  3. The worms are swallowed.
  4. The young worms mature and bury themselves into the intestinal wall.
  5. Adult roundworms begin producing eggs in the intestines.

Exposure occurs when skin has direct contact with contaminated soil. Unlike the hookworm life cycle, where the eggs must pass in the feces and mature in wet soil, the roundworm eggs hatch and the larvae can infect others even at the time they are passed in the feces.

Because of this, the larvae may move through the skin near the anus after being passed in the stool and repeat the cycle. A person becomes more heavily infected with each cycle. Areas where the larvae go through the skin may become red and painful.

The incidence is low in the US. Most of the disease seen in North America is brought by travelers who have visited or lived in South America and Africa.

The main risk factor for infection involves contact with soil contaminated with S. stercoralis.


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

Signs and tests

  • Increased cells called eosinophils in blood  
  • Stool exam (larvae of S. stercoralis present)  
  • Duodenal aspiration (larvae present in duodenal fluid)  
  • Antigen test positive for S. stercoralis  
  • S. stercoralis in sputum when it moves to the lung

The goal of treatment is to eliminate the worms with anti-worm medications (anthelminthics) such as ivermectin or thiabendazole.

Expectations (prognosis)

Full recovery with eradication of parasites is expected with adequate treatment. Sometimes treatment needs to be repeated.

Infections that are widespread often have a poor prognosis, especially in patients with weakened immune systems.


  • Acute pulmonary eosinophilia (Loeffler’s syndrome)  
  • Malabsorption  
  • Disseminated strongyloidiasis, especially in patients with HIV or an otherwise compromised immune system

Calling your health care provider
Call for an appointment with your health care provider if symptoms of strongyloidiasis are present.

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

Johns Hopkins patient information

Last revised: December 8, 2012
by Brenda A. Kuper, M.D.

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