Strongyloidiasis - Strongyloides Stercoralis

The strongyloidiasis is a worm infestation caused by nematodes (helminths) Strongyloides stercoralis, very common in tropical and subtropical regions, including Brazil. The Strongyloides stercoralis often inhabit the small intestine of infected individuals and in most patients with healthy immune system does not cause significant symptoms.

Strongyloides stercoralis
Strongyloides stercoralis

Transmission and life cycle strongyloides stercoralis

Human infection occurs when skin penetration by infective larvae of Strongyloides stercoralis, usually by direct contact with the soil contaminated with human feces. Walking barefoot is one of the most important risk factors to defile. In addition to skin invasion, estrogiloidíase can also be acquired by the oral route through ingestion of contaminated water or when the patient ingests food prepared by infected hands not washed properly after a bowel movement.

After penetration in the skin, the larvae migrate to the lungs. Once in the lungs, they migrate toward the upper airways, being unconsciously swallowed to reach near pharynx, falling into the gastrointestinal system.

When they reach the small intestine, the mature larvae and evolve only for the way of adult females, measuring about 2 mm in length. Each adult female can live up to five years, producing eggs and releasing new larvae still inside the intestines. The new larvae are excreted together with the faeces, restarting the transmission cycle of the worm.

Larvae released to the environment along with the stool can contaminate other people or develop into adult life in the environment, this time becoming male or female (as in the intestine, the larva becomes always a female in adulthood).

From the time of infection until the new release of larvae feces usually be an interval of 3 to 4 weeks. Therefore, once infected, the patient becomes a potential transmitter about 1 month.


The Strongyloides stercoralis is the only helminth able to complete their life cycle within the host. Not all larvae born in the intestine will be excreted in the faeces. Some of them can penetrate the lining of the colon or the skin of the perianal region and return to the bloodstream, heading toward the lungs. Thus, if the patient is self-infecting, making possible the continuation of parasitosis.

In patients with an intact immune system, this cycle of infection is self-limited. However, if the patient is immunocompromised, there may be process mass self-infections causing a hyperinfection above by Strongyloides stercoralis, and disseminated strongyloidiasis.

Disseminated strongyloidiasis is that the worm can affect extra-intestinal organs such as the central nervous system, heart, urinary tract, glands, etc. All organs and tissues may be invaded.

Symptoms of strongyloidiasis

Most patients infected with Strongyloides stercoralis does not have significant symptoms. In some cases, the only clue to the parasitism is an increase in the number of eosinophils (eosinophilia) in blood count.

When symptoms of strongyloidiasis, the most common framework is abdominal pain, usually around the stomach, like gastritis pain, which may or may not be accompanied by vomiting, nausea, diarrhea or loss of appetite.

Skin lesions in larval penetration site are also a common finding. The most common site is the feet. These lesions are small sores that can itch a lot. In some cases, injuries have snakelike, showing the larval migration path under the skin.

Respiratory symptoms occur in about 10% of patients during the migration phase of the larvae through the lungs. Cough, sore throat, shortness of breath, fever and even spitting blood are some of the possible symptoms. Tables similar to asthma or pneumonia may also occur.

The severe cases usually occur in patients with weakened immune systems. The patient with hyperinfection syndrome presents many of the symptoms described above and more severely. Mortality in these cases is very high. Although a parasite, strongyloidiasis, these cases may promote the occurrence of infections widespread natural bacteria in the intestines.

Risk factors for serious strongyloids

As explained above, healthy patients often have mild frames of strongyloidiasis with no or few symptoms. However, in immunosuppressed patients, infection with Strongyloides stercoralis can become a dramatically serious condition. Among the people most at risk are:
  • Alcoholics.
  • Cancer patients.
  • Patients using immunosuppressive drugs.
  • Patients using corticosteroids.
  • HIV positive patients.
  • Patients with diabetes mellitus.
  • Transplant patients.
  • Elderly.
  • Diabetics with poorly controlled disease.

Diagnosis of strongyloidiasis

In most cases, the diagnosis of strongyloidiasis is done by stool testing looking for larvae in feces. However, this test has a high false negative rate. Blood tests can be an alternative with higher diagnosis rates.

Treatment strongyloidiasis

Treatment with two doses of ivermectin with 24 hours interval between one another, is the treatment of choice for strongyloidiasis, with a success rate close to 100%. Cambendazol, Albendazole and Thiabendazole are also effective alternatives. After the end of treatment, it is recommended to carry out a parasitological examination after the 7th, 14th and 21st days.

If symptoms persist, even if the 3 control EPF are negative, should be considered in treatment failure. Blood tests can be used to help clear up the doubt.
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