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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Intestinal Nematodes

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Ascariasis : Clinical Aspects

Clinical manifestations may result from either the migration of the larvae through the lung or the presence of the adults in the intestinal lumen.

ASCARIASIS : CLINICAL ASPECTS

MANIFESTATIONS

Clinical manifestations may result from either the migration of the larvae through the lung or the presence of the adults in the intestinal lumen. Pulmonary involvement is usu-ally seen in communities where transmission is seasonal; the severity of symptoms is re-lated to the degree of hypersensitivity induced by previous infections and the intensity of the current exposure. Fever, cough, wheezing, and shortness of breath are common. Labo-ratory studies reveal eosinophilia, oxygen denaturation, and migratory pulmonary infil-trates. Death from respiratory failure has been noted occasionally.

If the worm load is small, infections with adult worms may be completely asympto-matic. They come to clinical attention when the parasite is vomited up or passed in the stool. This situation is most likely during episodes of fever, which appear to stimulate the worms to increase motility. Most physicians who have worked in developing countries have had the disconcerting experience of observing an ascarid crawl out of a patient’s mouth, nose, or ear during an otherwise uneventful evaluation of fever. Occasionally, an adult worm migrates to the appendix, bile duct, or pancreatic duct, causing obstruction and inflammation of the organ. Heavier worm loads may produce abdominal pain and malabsorption of fat, protein, carbohydrate, and vitamins. In marginally nourished chil-dren, growth may be retarded. Occasionally a bolus of worms may form and produce in-testinal obstruction, particularly in children. Worm loads of 50 are not uncommon, and as many as 2000 worms have been recovered from a single child. In the United States, where worm loads tend to be modest, obstruction occurs in 2 per 1000 infected children per year. The mortality in these cases is 3%. Estimates of deaths from ascariasis range from 8000 to 100,000 annually worldwide.

DIAGNOSIS

The diagnosis is generally made by finding the characteristic eggs in the feces. The ex-treme productivity of the female ascarid generally makes this task an easy one, except when the atypical-appearing unfertilized eggs predominate. The pulmonary phase of as-cariasis is diagnosed by the finding of larvae and eosinophils in the sputum.

TREATMENT AND PREVENTION

Albendazole, mebendazole and pyrantel pamoate are highly effective; the first two are preferred if T. trichiura is also present. Community-wide control of ascariasis can be achieved with mass therapy administered at 6-month intervals. Ultimately, control re-quires adequate sanitation facilities.

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