Strongyloidiasis - Causes, Symptoms and Treatments
Strongyloidiasis, also called threadworm infection, is a parasitic intestinal infection caused by the helminth Strongyloides stercoralis. This worldwide infection is endemic in the tropics and subtropics. Susceptibility to strongyloidiasis is universal. Infection doesn't confer immunity, and immunocompromised people may suffer overwhelming disseminated infection. Because the threadworm's reproductive cycle may continue in an untreated individual for up to 45 years, autoinfection is highly probable. Most patients with strongyloidiasis recover, but debilitation from protein loss may result in death.
Causes of Strongyloidiasis:
Transmission to humans usually occurs through contact with soil that contains infective S. stercoralis filariform larvae; such larvae develop from non infective rhabdoid (rod-shaped) larvae in human feces. The filariform larvae penetrate the human skin, usually at the fect, then migrate by way of the lymphatic system to the bloodstream and the lungs.
Once they enter into pulmonary circulation, the filariform larvae break through the alveoli and migrate upward to the pharynx, where they are swallowed. Then, they lodge in the small intestine, where they deposit eggs that mature into noninfectious rhabdoid larvae. Next, these larvae migrate into the large intestine and are excreted in feces, starting the cycle again. The threadworm life cycle-which begins with penetration of the skin and ends with excretion of rhabdoid larvae-takes 17 days.
In autoinfection, rhabdoid larvae mature within the intestine to become infective filariform larvae.
Signs and symptoms of Strongyloidiasis:
The patient's resistance and the extent of infection determine the severity of symptoms. Some patients have no symptoms, but many develop an erythematous maculopapular rash at the site of penetration that produces swelling and pruritus and that may be confused with an insect bite. As the larvae migrate to the lungs, pulmonary signs develop, including minor hemorrhage, pneumonitis, and pneumonia; later, intestinal infection produces frequent, watery, and bloody diarrhea, accompanied by intermittent abdominal pain.
Severe infection can cause malnutrition from substantial fat and protein loss, anemia, and lesions resembling ulcerative colitis, all of which invite secondary bacterial infection. Ulcerated intestinal mucosa may lead to perforation and, possibly, potentially fatal dissemination, especially in patients with malignancy or immunodeficiency diseases or in those who receive immunosuppressants.
Diagnosis of Strongyloidiasis:
Diagnosis requires observation of S. stercoralis larvae in a fresh stool specimen (2 hours after excretion, rhabdoid larvae look like hookworm larvae). During the pulmonary phase, sputum may show many eosinophils and larvae; marked eosinophilia also occurs in disseminated strongyloidiasis.
Other helpful tests include:
1. chest X-ray - positive during pulmonary phase of infection
2. hemoglobin - as low as 6 to 10 g
3. white blood cell count with differential (eosinophil count 450 to 700/ul).
Treatment of Strongyloidiasis:
Because of potential autoinfection, treatment with thiabendazole is required for 2 to 3 days (total dose not to exceed 3 g). Other drugs available for treatment are albendazole and ivermectin. Patients also need protein replacement, blood transfusions, and I.V. fluids. Retreatment is necessary if S. stercoralis remains in stools after therapy. Glucocorticoids are contraindicated because they increase the risk of autoinfection and dissemination.
Special considerations and Prevention Tips of Strongyloidiasis:
1. Keep accurate intake and output records, especially if treatment includes blood transfusions and I.V. fluids. Ask the dietary department to provide a high-protein diet. The patient may need tube feedings to increase caloric intake.
2. Wear gloves when handling bedpans or giving perineal care, and dispose of feces promptly.
3. Because direct person-to-person transmission doesn't occur, isolation is not required. Label stool specimens for laboratory as contaminated.
4. Warn the patient that thiabendazole may cause mild nausea, vomiting, drowsiness, and giddiness.
5. In pulmonary infection, reposition the patient frequently, encourage coughing and deep breathing, and administer oxygen, as ordered.
6. Check the patient's family and close contacts for signs of infection. Emphasize the need for follow-up stool examination, continuing for several weeks after treatment.
7. To prevent reinfection, teach the patient proper hand-washing technique.
8. Stress the importance of washing hands before eating and after defecating, and of wearing shoes when in endemic areas.
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