Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at December 30, 2016

Strongyloidiasis is a parasitic infection caused by a species of roundworm. As part of its life cycle, the worm penetrates the skin, settles into the body, and lays eggs there. While it is usually not a serious condition and can be treated with commonly available drugs, it can be dangerous in immunosuppressed patients or those who let it go untreated. 


Definition & Facts

Strongyloidiasis is caused by contact with a tiny roundworm, Strongyloides stercoralis. The largest larva of this species is no bigger than a grain of sand. S. stercoralis is uncommon in the United States, and is more commonly found in warm, moist climates and in rural areas. It is most frequently seen in Southeast Asia, Latin America, and sub-Saharan Africa; an estimated 30-100 million people worldwide suffer from strongyloidiasis.

Once infestation has occurred, the worms may pass into the lungs and throat, where they will be swallowed and pass into the small intestine, or they may go to the small intestine directly. There, they lay eggs, which hatch into larva that are excreted with the host's feces. The larvae can then infest someone else, or re-infest the host. 

Symptoms & Complaints

Many people infested with S. stercoralis do not manifest any symptoms, it is possible to have strongyloidiasis for many years without it being diagnosed. Unlike many other roundworms, S. stercoralis can survive in the human body for up to 30 years.

The most common symptom is a light rash on the site where the worms entered the body. If the worms pass through the lungs, they can cause wheezing and shortness of breath. In the intestines, they can cause diarrhea, constipation, heartburn, bloating, and/or cramps.

Once the initial infestation has passed, symptoms can become very mild and intermittent. In patients with weakened or suppressed immune systems, however, the worms can pass into body parts that are not part of their normal life cycle, such as the urinary tract, heart, or nervous system.

Additional symptoms include severe abdominal pain, bloody diarrhea, blood in sputum, fever, chills, nausea, difficulty breathing, and severe rashes. Untreated, this form of infestation can cause death from internal bleeding, respiratory failure, or dehydration, and the stress on the body can also leave it open to more serious bacterial infections


The most common way to be infested with S. stercoralis is by skin contact with soil that is infested with the roundworm, such as walking barefoot over a patch of dirt. It is also possible, but very rare, to be infested by contact with someone who is already infested, or by receiving organ transplants from an infested host.

The host's feces will also contain the worms, so contact with feces or sewage can also spread the infestation. S. stercoralis eggs and larvae can also remain in the large intestine after the first infestation, and re-infest the host after the condition is seemingly cured. 

Diagnosis & Tests

Since the symptoms are so vague and generalized, strongyloidiasis can be difficult to diagnose and easy to mistake for other mild respiratory disorders or gastrointestinal disorders. The most widely used way to diagnose this condition is by examining the stools, and even this can be unreliable. Since the larvae are so small, they are easily overlooked even with microscopic examination, and it usually requires multiple stool samples to confirm the presence of S. stercoralis. 

A biopsy of the lower intestine is more likely to provide quicker results, although care must be taken to avoid internal bleeding. Another method is aspiration of the lower intestine which involves removing fluids or matter directly from the intestine for examination.

If the worms may have infested the lungs, the doctor may perform a bronchoalvelolar lavage, where part of the lungs is washed with fluid through an endoscope and then the fluid is collected for examination. There are also blood tests that check for antibodies produced by parasitic infestation, but it's difficult to tell the results apart from those produced by other, more common, parasites such as hookworms. While some laboratories are capable of doing blood tests sensitive enough to identify S. stercoralis, most doctors still rely on physical examination to find the worms. 

Treatment & Therapy

Once strongyloidiasis has been diagnosed, the usual treatment is a course of an antiparasitic drug such as ivermectin or albendazole. Ivermectin normally only takes a single dose to work, while albendazole must be taken for a week. If, for whatever reason, the patient cannot take the drugs orally, they can be administered in suppository form. These are well-known drugs that should have no major contraindications or side effects. However, they only kill the adult worms, not the larvae.

To prevent re-infestation, the doctor should examine the patient's stools two to four weeks after the medicine has been administered to verify that there are no larvae present. If there are, the dosage can be repeated. Patients who have developed severe strongyloidiasis may also need support therapies, such as respiratory aids, intravenous fluids, and blood transfusion for internal bleeding, as well as antibiotics if bacteria have invaded the weakened body. 

Prevention & Prophylaxis

The easiest way to avoid strongyloidiasis is, of course, to avoid exposure to the worm in the first place. Avoiding touching soil with bare skin, and avoiding all contact with feces and/or sewage are crucial.

Proper disposal of sewage and fecal matter is important to prevent the spread of the disease. While it is uncommon to be infested by contact with another person, it's important to take precautions, such as gloves and protective garments, when dealing with a person who might be infected. Because of the severe and potentially lethal effects strongyloidiasis can have on a weakened immune system, doctors must be careful to rule it out before administering any drugs that will affect the immune system.