|
Ascariasis
is infection with Ascaris lumbricoides.
Light infections may be asymptomatic. Early symptoms are pulmonary
(cough, wheezing); later symptoms are GI, with cramps or abdominal
pain from obstruction of GI lumina (intestines or biliary or pancreatic
ducts) by adult worms. Chronically infected children may develop
malnutrition. Diagnosis is by identifying eggs or adult worms in
stool, adult worms that migrate from the nose or mouth, or larvae in
sputum during the pulmonary migration phase. Treatment is with albendazole, mebendazole,
or pyrantel pamoate.
Etiology
and Pathophysiology
Ingested eggs hatch in the duodenum, and the resulting larvae penetrate the wall of the small bowel and migrate via the portal circulation through the liver to the heart and lungs. Larvae lodge in the alveolar capillaries, penetrate alveolar walls, and ascend the bronchial tree into the oropharynx. They are swallowed and return to the small bowel, where they develop into adult worms, which mate and release eggs into the stool. The life cycle is completed in about 2 to 3 mo; adult worms live 1 to 2 yr.
A tangled mass of worms from heavy infection can produce bowel obstruction, particularly in children. Aberrantly migrating individual adult worms occasionally obstruct the biliary or pancreatic ducts, causing cholecystitis or pancreatitis; cholangitis, liver abscess, and peritonitis are less common. Fever from other illnesses or certain drugs (eg, albendazole , mebendazole , tetrachloroethylene) may provoke aberrant migration.
Ascariasis occurs worldwide. It is concentrated in tropical and subtropical areas with poor sanitation, but transmission occurs in rural areas of the southeastern US. Ascariasis is the most prevalent intestinal helminth infection in the world. Current estimates suggest that > 1.3 billion people are infected, of whom about 20,000 (mostly children) die each year from bowel or biliary obstruction. An estimated 4 million people in the US are infected.
Symptoms,
Signs, and Diagnosis
Larvae migrating through the lungs may produce cough, wheezing, and occasionally hemoptysis or other respiratory symptoms. Adult worms in small numbers usually do not produce GI symptoms, although passage of an adult worm by mouth or rectum may bring an otherwise asymptomatic patient to medical attention. Bowel or biliary obstruction causes cramping abdominal pain, nausea, and vomiting. Jaundice is uncommon. Even moderate infections can lead to malnutrition in children. The pathophysiology is unclear and may include competition for nutrients, impairment of absorption, and depression of appetite.
Diagnosis is by microscopic detection of eggs in stools. Occasionally, larvae can be found in the sputum during the pulmonary phase. Eosinophilia can be marked while larvae migrate though the lungs but usually subsides later in infection when adult worms reside in the intestine. Chest x-ray during the pulmonary phase may show infiltrates (Löffler's pneumonia).
Treatment
and Prevention
All infections should be treated. Albendazole (400 mg po once), mebendazole (100 mg po bid for 3 days), or ivermectin (150 μg/kg once) are effective. Mebendazole and albendazole should not be used in pregnancy. Recent data suggest that nitazoxanide is also effective at a dose of 500 mg bid for 3 days in adults; 100 mg q 12 h for 3 days in children 1 to 3 yr; and 200 mg q 12 h for 3 days in children 4 to 11 yr. Obstructive complications may respond to anthelmintic therapy or require surgical or endoscopic extraction of adult worms.
Prevention requires adequate sanitation. Uncooked or unwashed vegetables should be avoided in areas where human feces are used as fertilizer.
Last full review/revision November 2005
Content last modified November 2005
| 
