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micrograph of Strongyloides larvae

Strongyloides sp. filariform larvae.
Credit: CDC/Dr. Mae Melvin


Strongyloidiasis is a parasitic disease. It is found in tropical and subtropical areas but also can be found in temperate regions, including the southern United States. The disease usually occurs in rural areas, institutional settings, and among lower socioeconomic groups. According to the Centers for Disease Control and Prevention, the global prevalence of Strongyloides is unknown, but experts estimate that there are between 3 to 100 million infected people worldwide.


Strongyloidiasis is caused by a parasitic roundworm called Strongyloides stercoralis, that mainly infects humans. This roundworm has different types of life cycles. At times, the larvae (immature stage) of the parasite may develop rapidly into the infective stage in the intestine where they penetrate the intestinal lining instead of passing out of the body in the feces, as occurs normally. This modification of the life cycle, called internal autoinfection, explains persistent strongyloidiasis, which can last as long as 40 years in people who have moved to areas where the infection is not generally found

Autoinfection may produce heavy infections and severe disease, especially in people with reduced immunity such as those receiving corticosteroids or other immunosuppressive medicines, or those with acquired immune deficiency due to retroviruses such as human T cell lymphotropic virus-1 (HTLV-1).


People become infected when they come in contact with soil containing the roundworms. After a short feeding period and development in the soil, the larvae penetrate human skin, enter the blood stream, and pass through the right side of the heart to the lungs. From the lungs, the parasites go up the windpipe into the mouth, are swallowed, and reach the upper part of the small intestine where they develop into mature worms.


Many Strongyloides infections are mild and go unnoticed. Moderate infections may cause a burning pain in your abdomen. You may have nausea and vomiting and alternating diarrhea and constipation. Severe infections result in anemia, weight loss, and chronic diarrhea. Strongyloidiasis in severely immunocompromised people can cause a variety of symptoms, including an ARDS-like pneumonia (Acute Respiratory Distress Syndrome).


Your healthcare provider can use blood tests to help diagnose strongyloidiasis, but those tests are prone to error. You may need to also have repeated stool examinations.


Ivermectin, given in a single dose for one or two days, has become the medicine of choice. Albendazole, given twice daily for seven days, is also effective. Disease that has spread through the body often requires longer treatment.


Following good personal hygiene practices and wearing shoes when walking on soil can help prevent you from being infected with strongyloidiasis


NIAID conducts and supports basic and clinical research on the prevention, control, and treatment of a variety of parasitic diseases, including some caused by parasitic roundworms. Research on a vaccine to prevent strongyloides infection is underway in NIAID labs.

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Last Updated September 21, 2015