About Strongyloidiasis Infection
Strongyloidiasis is a disease caused by a nematode, or a roundworm, in the genus Strongyloides. Though there are over 40 species within this genus that can infect birds, reptiles, amphibians, livestock and other primates, Strongyloides stercoralis is the primary species that accounts for human disease. It sometimes infects primates, dogs and cats, and some dog and primate infecting strains have been shown to be capable of causing human infection. We do not know if cat-infecting strains can infect humans or not. The larvae are small; the longest reach about 600 µm in length—making them very difficult to see with the naked eye.
Strongyloides stercoralis is classified as a soil-transmitted helminth. This means that the primary mode of infection is through contact with soil that is contaminated with free-living larvae. When the larvae come in contact with skin, they are able to penetrate it and migrate through the body, eventually finding their way to the small intestine where they burrow and lay their eggs. Unlike other soil-transmitted helminths such as hookworm and whipworm, whose eggs do not hatch until they are in the environment, the eggs of S. stercoralis hatch into larvae in the intestine. Most of these larvae will be excreted in the stool, but some of the larvae may mature and immediately re-infect the host either by burrowing into the intestinal wall, or by penetrating the skin around the anus. This characteristic of S. stercoralis is termed auto-infection. The significance of auto-infection is that unless treated for S. stercoralis, persons may remain infected throughout their lifetime.
In addition to contact with soil and auto-infection, there have been rare cases of person-to-person transmission in the following:
- Organ transplantation
- Institutions for people with cognitive disability requiring assistance with daily living
- Long-term care facilities
- Daycare centers
In the United States, S. stercoralis infection has classically been associated with uniformed-service veterans who returned from tropical regions such as Southeast Asia and the South Pacific during World War II or the Vietnam wasr. Small domestic studies have shown focal locations of infection in rural Appalachia. The highest rates in the United States have been documented in immigrant populations.
Strongyloides is more commonly found in areas that are relatively warm and moist, in rural areas, and areas associated with agricultural activity, but it can occur anywhere. It is found more frequently in socio-economically disadvantaged persons and in institutionalized populations.
The majority of people infected with Strongyloides do not have symptoms. Those who do develop symptoms often have non-specific, or generalized complaints. Some people develop abdominal pain, bloating, heartburn, intermittent episodes of diarrhea and constipation, a dry cough, and skin rashes. Rarely people will develop arthritis, kidney problems, and heart conditions.
Strongyloidiasis can be severe and life-threatening in persons who
- Are taking corticosteroids (oral or intravenous) for asthma or chronic obstructive pulmonary disease (COPD) exacerbations, lupus, gout, or other conditions requiring steroids for immunosuppression or symptomatic relief;
- Are infected with the virus HTLV-1;
- Have hematologic malignancies such as leukemia or lymphoma; or
- Are transplant recipients.
Most people do not know when their exposure occurred. For those who do, a local rash can occur immediately. The cough usually occurs several days later. Abdominal symptoms typically occur approximately 2 weeks later, and larvae can be found in the stool about 3 to 4 weeks later.
See your health care provider.
Strongyloides infection is best diagnosed with a blood test. Microscopic examination of stool is another option for diagnosis, but it might not find the worms in all infected people.
Safe and effective drugs are available to treat infection with Strongyloides.
The best way to prevent Strongyloides infection is to wear shoes when you are walking on soil, avoid contact with fecal matter or sewage, and clean up after dogs. Proper sewage disposal and fecal management are keys to prevention.