Health Library



Intestinal parasite - strongyloidiasis; Roundworm - strongyloidiasis


Strongyloidiasis is an infection with the roundworm Strongyloides stercoralis (S stercoralis).



S stercoralis is a roundworm that is fairly common in warm, moist areas. In rare cases, it can be found as far north as Canada.

People catch the infection when their skin comes in contact with soil that is contaminated with the worms.

The tiny worm is barely visible to the naked eye. Young roundworms can move through a person's skin and into the bloodstream to the lungs and airways.

They then move up to the throat, where they are swallowed into the stomach. From the stomach, the worms move to the small intestine, where they attach to the intestinal wall. Later, they produce eggs, which hatch into tiny larvae (immature worms) and pass out of the body.

Unlike other worms, these larvae can re-enter the body through the skin around the anus, which allows an infection to grow. Areas where the worms go through the skin can become red and painful.

This infection is uncommon in the United States, but it does occur in the southeastern US. Most cases in North America are brought by travelers who have visited or lived in South America or Africa.

Some people are at risk for a severe type called strongyloidiasis hyperinfection syndrome. In this form of the condition, there are more worms and they multiply more quickly than normal. It can occur in people who have a weakened immune system. This includes people who have had an organ or blood-product transplant, and those who take steroid medicine or immune-suppressing drugs.




Most of the time, there are no symptoms. If there are symptoms, they may include:

  • Abdominal pain (upper abdomen)
  • Cough
  • Diarrhea
  • Rash
  • Red hive-like areas near the anus
  • Vomiting
  • Weight loss


Exams and Tests


The following tests may be done:

  • Blood antigen test for S stercoralis
  • Complete blood count with differential
  • Total eosinophil count in the blood (eosinophils are a type of white blood cell)
  • Duodenal aspiration (removing a small amount of tissue from the first part of the small intestine) to check for S stercoralis
  • Sputum culture to check for S stercoralis
  • Stool sample exam to check for S stercoralis




The goal of treatment is to eliminate the worms with anti-worm medicines.

Sometimes, people with no symptoms are treated. This includes people who take drugs that suppress the immune system, such as those who are going to have, or have had, a transplant.


Outlook (Prognosis)


With proper treatment, the worms can be killed and full recovery is expected. Sometimes, treatment needs to be repeated.

Infections that are severe (hyperinfection) or that have spread to many areas of the body (disseminated infection) often have a poor outcome, especially in people with a weakened immune systems.


Possible Complications


Possible complications include:

  • Disseminated strongyloidiasis, especially in people with HIV or an otherwise weakened immune system
  • Strongyloidiasis hyperinfection syndrome, also more common in people with a weakened immune system
  • Eosinophilic pneumonia
  • Malnutrition due to problems absorbing nutrients from the gastrointestinal tract


When to Contact a Medical Professional


Call for an appointment with your health care provider if you have symptoms of strongyloidiasis.




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




Bogitsh BJ, Carter CE, Oeltmann TN. Intestinal nematodes. In: Bogitsh BJ, Carter CE, Oeltmann TN, eds. Human Parasitology. 4th ed. Waltham, MA: Elsevier Academic Press; 2012:chap 16.

Maguire JH. Intestinal nematodes (roundworms). In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, Updated Edition. 8th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 288.

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    Strongyloidiasis, creeping eruption on the back


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    Digestive system organs


    • Strongyloidiasis, creeping eruption on the back

      Strongyloidiasis, creeping eruption on the back


    • Digestive system organs

      Digestive system organs


    Tests for Strongyloidiasis


      Review Date: 11/14/2016

      Reviewed By: Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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