The Nasty Truth About Strongyloidiasis

Written by Jacquelyn Cafasso | Published on August 7, 2012
Medically Reviewed by Brenda B. Spriggs, MD, MPH, FACP

What is Strongyloidiasis?

Strongyloidiasis is infection by a roundworm calledStrongyloides stercoralis (S. stercoralis). The S. stercoralis roundworm is a parasite. A parasite is an organism that lives in the body of a different species from which it obtains nutrients. The infected organism is called the host.

According to the Centers for Disease Control and Prevention, S. stercoralis infection is uncommon in the United States (CDC). The roundworm is usually found in warm climates, such as tropical and subtropical countries. It is more common in rural areas and institutional settings, such as mental hospitals. Most of the roundworm infections in North America are spread by travelers who have visited or lived in South America or Africa (CDC).

Usually, strongyloidiasis causes no symptoms. S. stercoralis infection can be prevented through good personal hygiene.

What Causes Strongyloidiasis?

Strongyloidiasis is caused by the parasitic roundworm S. stercoralis. This worm infects mainly humans. It is most often found in tropical and subtropical climates, but it can occasionally be found in more temperate climates. This may include parts of the southern United States and Appalachia. Once a human comes in contact with S. stercoralis, the infection follows the lifecycle of the worm.

The worm’s lifecycle includes the following stages:

  • The tiny worms penetrate the skin and enter the bloodstream.
  • The worms then move through the bloodstream and pass through the right side of the heart and into the lungs.
  • The parasites travel from the lungs up the windpipe and into the mouth.
  • The infected person unknowingly swallows the worms into his or her stomach.
  • The worms move into the small intestine of the human host.
  • The worms lay eggs, which hatch into larvae.
  • The larvae are expelled from the host’s body in his or her feces.
  • The larvae can infect the body by penetrating the skin around the anus or they can develop into mature worms and infect another host on contact.

The worms can also live and reproduce in the soil without a host.

Rarely, the worms can modify their lifestyle such that the larvae penetrate the intestine of the host rather than pass out of the body through the feces. This type of infection can be serious in patients with weakened immune systems, such as those with the HIV/AIDS virus.

Who Is at Risk for Strongyloidiasis?

Those who travel to or live in South America, Africa, or other tropical regions are at risk for infection. You are at a much higher risk if you travel to rural areas, areas with unsanitary living conditions, or areas without adequate public health services. If you don’t practice good personal hygiene, you are also at an increased risk.

What Are the Symptoms of Strongyloidiasis?

In most cases, strongyloidiasis causes no symptoms. If symptoms are present, they may include:

  • upper abdominal pain or burning
  • diarrhea or alternating diarrhea and constipation
  • cough
  • rash
  • red hives near the anus
  • vomiting
  • weight loss

How Is Strongyloidiasis Diagnosed?

According to the National Institutes of Health (NIH), the following tests may be performed to diagnose an infection with S. stercoralis (NIH):

Duodenal Aspiration

In this test, your doctor will take fluid from the first section of the small intestine to examine under a microscope for the presence of S. stercoralis.

Sputum Culture

In a sputum culture, your doctor analyzes fluid that comes from the lungs or airways for S. stercoralis.

Stool Sample Exam

This test checks for S. stercoralis larvae in the feces. You may require repeat testing for accurate results.

Complete Blood Count (CBC) Test With Differential

A blood count may help to rule out other causes of symptoms.

Blood Antigen Test

This blood analysis tests for antigens to S. stercoralis. This test is conducted when an infection is suspected but the parasite cannot be found in a duodenal aspiration or in several stool samples. Antibody test results cannot be used to tell the difference between a past and current S. stercoralis infection.

The most common methods of diagnosis are microscopic examinations of duodenal or stool samples.

What Is the Treatment for Strongyloidiasis?

The goal of treatment is to eliminate the worms. The medicine of choice to treat strongyloidiasis is a single dose of the anti-parasitic medication Ivermectin, given for one or two days. Ivermectin works by killing the worms in your small intestine.

In addition, your doctor may prescribe two courses of albendazole administered 10 days apart. Thiabendazole twice a day for two or three days is also an effective treatment (NIAID).

Longer or repeated courses of medication may be required if the infection is widespread.

What Are the Possible Complications?

The following complications may occur during an S. stercoralis infection:

Eosinophilic Pneumonia

This occurs when your lungs swell due to an increase in eosinophils. Eosinophils are a type of white blood cell that your body produces when the worms enter your lungs.


Malnutrition occurs if your intestines cannot properly absorb nutrients from the foods you eat while you’re infected with the worms.

Disseminated Strongyloidiasis

Disseminated strongyloidiasis involves widespread distribution of the parasite to other organs of your body. This occurs in people taking immunosuppressive medicines or people with immune deficiency caused by a virus. It occurs when S. stercoralis changes its lifecycle, penetrates the intestines, and re-enters the bloodstream (NIAID). Symptoms include: abdominal pain and swelling, shock, pulmonary and neurological complications, and septicemia (infection in the blood).

What Can Be Expected in the Long Term?

With proper medical treatment, the prognosis for strongyloidiasis is very good. Patients can expect to make a full recovery, and the parasites should be fully eliminated. Occasionally, the treatment will need to be repeated.

However, severe or widespread infections in people with a weakened immune system are dire. The infection can be fatal in these patients if a diagnosis is delayed.

How Can I Prevent Strongyloidiasis?

Strongyloidiasis cannot always be prevented. However, exercising good personal hygiene and using sanitary facilities when traveling to warm or tropical climates can reduce your risk of becoming infected.

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