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Ascariasis

by Richard D. Pearson, MD

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 due to obstruction of GI lumina (intestines or biliary or pancreatic ducts) by adult worms. Chronically infected children may develop undernutrition. 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 ivermectin.

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 resulting from heavy infection can obstruct the bowel, 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 due to other illnesses or certain drugs (eg, albendazole, mebendazole, tetrachloroethylene) may trigger aberrant migration.

Etiology

Ascariasis occurs worldwide. It is concentrated in tropical and subtropical areas with poor sanitation, but transmission also occurs in rural areas of the southeastern US. Ascariasis is the most prevalent intestinal helminth infection in the world. Current estimates suggest that about 1 billion people are infected, and about 20,000 infected people (mostly children) die each year of bowel or biliary obstruction. An estimated 4 million people in the US are infected.

Symptoms and Signs

Larvae migrating through the lungs may cause cough, wheezing, and occasionally hemoptysis or other respiratory symptoms. Adult worms in small numbers usually do not cause 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 undernutrition in children. The pathophysiology is unclear and may include competition for nutrients, impairment of absorption, and depression of appetite.

Diagnosis

  • Microscopic examination of stool

  • Identification of adult worms in stool or emerging from the nose,mouth, or rectum

Diagnosis is by microscopic detection of eggs in stool or observation of adult worms emerging from the nose or mouth. Occasionally, larvae can be found in sputum during the pulmonary phase.

Eosinophilia can be marked while larvae migrate though the lungs but usually subsides later when adult worms reside in the intestine. Chest x-ray during the pulmonary phase may show infiltrates (Löffler syndrome).

Treatment

  • Albendazole, mebendazole, or ivermectin

All infections should be treated. Albendazole 400 mg po once, mebendazole 100 mg po bid for 3 days or 500 mg po once, or ivermectin 150 to 200 mcg/kg po once is effective. Albendazole, mebendazole, and ivermectin are pregnancy category C drugs, and risk of treatment in pregnant women infected with Ascaris must be balanced with risk of untreated disease. Nitazoxanide is effective for mild Ascaris infections but less effective for heavy infections. Piperazine, once widely used, has been replaced by less toxic alternatives.

Obstructive complications may respond to anthelmintic therapy or require surgical or endoscopic extraction of adult worms.

Prevention

Prevention requires adequate sanitation. Uncooked or unwashed vegetables should be avoided in areas where human feces are used as fertilizer.

Key Points

  • Ascariasis is the most prevalent intestinal helminth infection in the world.

  • Eggs hatch in the intestines, and larvae migrate first to the lungs and then to the intestines, where they mature.

  • Larvae in the lungs may cause cough and wheezing; adult worms may obstruct the intestines.

  • Diagnose by microscopic examination of the stool; occasionally, adult worms are seen.

  • Treat with albendazole, mebendazole, or ivermectin.

Resources In This Article

Drugs Mentioned In This Article

  • Drug Name
    Select Trade
  • No US brand name
  • ALBENZA
  • STROMECTOL
  • ALINIA

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