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Strongyloidiasis -ˌlȯi-ˈdī-ə-səs

(Threadworm Infection)

By Richard D. Pearson, MD

Strongyloidiasis is infection caused by the roundworm Strongyloides stercoralis, which enters the body when bare skin comes in contact with soil contaminated with the worm.

  • Usually, people are infected when they walk barefoot on contaminated soil.

  • Most people with this infection do not have any symptoms, but some have a rash, cough, wheezing, abdominal pain, diarrhea, and weight loss.

  • Rarely, a severe, life-threatening infection develops in people who have a weakened immune system because of a disorder (such as cancer) or drugs that suppress the immune system.

  • Doctors diagnose the infection by finding larvae in a stool sample or by detecting antibodies to the threadworm in blood.

  • Ivermectin or albendazole is used to treat the infection.

Strongyloidiasis occurs in warm, moist areas such as the subtropics and tropics, including rural areas of the southern United States. Strongyloides worms are sometimes called threadworms. However, pinworms are also sometimes called threadworms.

Adult Strongyloides worms live in the small intestine. The females produce eggs, which hatch and release larvae. Most of the larvae are excreted in stool. After a few days in soil, larvae develop into a form that can cause infection. If threadworm larvae come in contact with a person's bare skin, they penetrate it. Then they travel through the bloodstream to the lungs and up the respiratory tract to the throat, are swallowed, and end up in the small intestine.

The larvae that do not come in contact with people may develop into adult worms that can reproduce for several generations before their larvae come in contact a person.

Some of the larvae in the small intestine can re-infect the person. These larvae can either penetrate the wall of the intestine and re-enter the person's bloodstream directly or be excreted in stool and penetrate the skin around the anus. In both cases, the larvae travel through the bloodstream to the lungs and then to the throat and back to the intestine to cause another infection—called autoinfection (infection of self).

Hyperinfection syndrome

Rarely, a severe infection (called hyperinfection syndrome) develops in people who have a weakened immune system because of a disorder, such as cancer, or drugs that suppress the immune system (immunosuppressants), such as prednisone or drugs used to prevent rejection of an organ transplant. This syndrome also occurs in people with AIDS, but less often than might be expected.

Hyperinfection syndrome causes widespread disease that can affect organs such as the brain, liver, or heart, which are not usually affected by threadworm infections. Strongyloides larvae may bacteria from the digestive tract with them. When the larvae travel through the body, these bacteria can cause infections in the bloodstream or brain and spinal fluid.

Symptoms of Threadworm Infection

Most people with a threadworm infection do not have symptoms. When symptoms occur, they usually involve the skin, lungs, and/or digestive tract.

People who have an autoinfection develop a rash caused by the larvae as they travel through the skin. The rash often occurs around the anus. As the larvae travel, the rash can rapidly spread to the thighs and buttocks, causing intense itching.

Severe infections may cause lung and/or digestive symptoms. Some people cough and wheeze. Some have abdominal pain and tenderness, diarrhea, nausea, and vomiting. They may lose their appetite. They may not absorb nutrients normally, resulting in weight loss.

Hyperinfection syndrome

People with hyperinfection syndrome often have severe symptoms involving the lungs and/or digestive tract. Lung symptoms include severe shortness of breath and coughing up blood. Digestive tract symptoms include intestinal blockage and/or bleeding.

Infection may be fatal in people with a weakened immune system, even when they are treated.

Diagnosis of Threadworm Infection

  • Examination of a stool sample

  • For hyperinfection syndrome, examination of a sputum (phlegm) sample and chest x-rays

  • Blood tests to detect antibodies to the threadworm

Doctors can sometimes see larvae when they examine a stool sample under a microscope. Often, they must examine many samples.

If doctors suspect hyperinfection syndrome, they also examine a sputum sample for larvae and take chest x-rays to look for evidence of lung infection.

Blood tests to check for antibodies to the threadworm (particularly a test called enzyme immunoassay) are usually done. ( Antibodies are proteins produced by the immune system to help defend the body against attack, including that by parasites.) However, these tests cannot distinguish between new and old infections or sometimes between threadworm and other roundworm infections.

Prevention of Threadworm Infection

Prevention of hookworm infections involves the following:

  • Using latrines or toilets

  • Preventing the skin from directly contacting the soil (for example, by wearing shoes and using a tarp or other barrier when seated on the ground)

Treatment of Threadworm Infection

  • Ivermectin or albendazole (drugs used to eliminate worms—antihelminthic drugs)

For most infections, ivermectin is given once a day for 2 days, or albendazole is given twice a day for 7 days.

For hyperinfection syndrome, both drugs may be used. If people are unable to take drugs by mouth, a rectal preparation is used. People with this infection may need to take drugs for a longer time.

To determine whether the infection is eliminated, doctors examine stool samples for larvae or do blood tests to check for antibodies to the worm.

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