What Is Strongyloidiasis?
Strongyloidiasis is infection by a roundworm, or nematode, called
Strongyloides stercoralis. The S. stercoralis roundworm
is a type of 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.
S. stercoralis infection is uncommon in the United
States. The roundworm is usually found in warm climates like tropical and
subtropical countries. It’s more common in rural areas and institutional
settings. According to the Centers for
Disease Control and Prevention, most of the roundworm infections in North
America are spread by travelers who have visited or lived in South America or
Usually, strongyloidiasis causes no symptoms. S.
stercoralis infection can generally be prevented through good personal
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
- a cough
- a rash
- red hives near the anus
- weight loss
What Causes Strongyloidiasis?
Strongyloidiasis is caused by the parasitic roundworm S.
stercoralis. This worm infects mainly humans. It’s 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 person 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 your skin and enter
- The worms then move through your bloodstream and
pass through the right side of your heart and into the lungs.
- The parasites travel from the lungs up the windpipe
and into your mouth.
- You unknowingly swallow the worms, and they
travel into your stomach.
- The worms move into your small intestine.
- The worms lay eggs that hatch and become larvae.
- The larvae are expelled from your body in your feces.
- The larvae can infect your body by penetrating
the skin around your anus, or they can develop into mature worms and infect
The worms can also live and reproduce in the soil without a host.
Rarely, the worms can penetrate the intestine of the host as
larvae rather than pass out of the body through the feces.
Who Is at Risk for Strongyloidiasis?
You’re at an increased risk for infection if:
- you travel to or live in South America, Africa,
or other tropical regions
- you live in or travel to rural areas, areas with
unsanitary living conditions, or areas without adequate public health services
- you don’t practice good personal hygiene
- you have a weakened immune system, such as can
occur from HIV or AIDS
How Is Strongyloidiasis Diagnosed?
The following tests may be performed to diagnose an infection
with S. stercoralis:
- During a duodenal aspiration, your doctor will
take fluid from the first section of your small intestine to examine under a
microscope for the presence of S. stercoralis.
- Your doctor can use a sputum culture to analyze
fluid from your lungs or airways for S. stercoralis.
- You doctor can use a stool sample for ova and parasites
to check for S. stercoralis larvae in
the feces. You may need to repeat the test to get accurate results.
- A complete blood count test with differential may
help to rule out other causes of symptoms.
- A blood antigen test can help your doctor look
for antigens to S. stercoralis. This test is done when your doctor
suspects you have an infection but they can’t find the parasite in a duodenal
aspiration or in several stool samples. The test results can’t 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 called ivermectin.
This drug works by killing the worms in your small intestine.
Also, your doctor may prescribe two courses of albendazole to
be taken 10 days apart. Taking thiabendazole twice per day for two or three
days is also an effective treatment.
You may need longer or repeated courses of medication if the
infection is widespread.
What Are the Possible Complications?
An S. stercoralis infection can cause the following
Eosinophilic pneumonia 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
Malnutrition occurs if your intestines can’t properly absorb
nutrients from the foods you eat while you’re infected with the worms.
Disseminated strongyloidiasis involves widespread distribution of
the parasite to other organs of your body. This can occur if you’re taking
immunosuppressive medicines or if you have an immune deficiency caused by a
virus. It happens when S. stercoralis changes its lifecycle, enters
the intestines, and re-enters the bloodstream. The symptoms include:
- abdominal pain and swelling
- pulmonary and neurological complications
- infection of the blood
What Can Be Expected in the Long Term?
With proper medical treatment, the prognosis for strongyloidiasis
is very good. You 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 very serious. The infection can be fatal in these people
if a diagnosis is delayed.
How Can I Prevent Strongyloidiasis?
Strongyloidiasis can’t 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.