Merck Manual

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Ascariasis

By

Richard D. Pearson

, MD, University of Virginia School of Medicine

Last full review/revision Mar 2019| Content last modified Mar 2019
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Ascariasis is infection with Ascaris lumbricoides or occasionally Ascaris suum (a closely related parasite of pigs). Light infections may be asymptomatic. Early symptoms are pulmonary (cough, wheezing); later symptoms are gastrointestinal, with cramps or abdominal pain due to obstruction of gastrointestinal 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.

Ascariasis occurs worldwide. It is concentrated in tropical and subtropical areas with poor sanitation. Ascariasis is the most common intestinal helminth infection in the world. Prevalence is highest in children aged 2 to 10 years and decreases in older age groups. Current estimates suggest that 800 million to 1.2 billion people are infected worldwide, and ascariasis contributes to malnutrition in many of those. In addition, an estimated 2,000 infected people (mostly children) die each year of bowel or biliary obstruction.

In the United States, most cases occur in refugees, immigrants, or travelers to endemic tropical areas.

Humans are infected with A. lumbricoides when they ingest its eggs, often in food contaminated by human feces. Infection can also occur when hands or fingers with contaminated dirt on them are put in the mouth.

Humans can also be infected with A. suum, a closely related roundworm of pigs, when they ingest eggs from handling pigs or from consuming undercooked vegetables or fruits contaminated with pig feces.

Pathophysiology

Ingested A. lumbricoides 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 months; adult worms live 1 to 2 years.

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.

Symptoms and Signs

Ascaris larvae migrating through the lungs may cause cough, wheezing, and occasionally hemoptysis or other respiratory symptoms in people without prior exposure to Ascaris.

Adult worms in small numbers usually do not cause gastrointestinal 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 of ascariasis is by microscopic detection of eggs in stool or observation of adult worms in stool or emerging from the nose or mouth. Occasionally, larvae can be found in sputum during the pulmonary phase, or later in infection, adult worms may be seen in radiographic studies of the gastrointestinal tract.

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, which in the presence of eosinophilia leads to the diagnosis of Löffler syndrome.

Treatment

  • Albendazole, mebendazole, or ivermectin

All intestinal infections should be treated.

Albendazole 400 mg orally once, mebendazole 100 mg orally twice a day for 3 days or 500 mg orally once, or ivermectin 150 to 200 mcg/kg orally once is effective. Albendazole, mebendazole, and ivermectin may harm the fetus, and risk of treatment in pregnant women infected with Ascaris must be balanced with risk of untreated disease. Before treatment with ivermectin, patients should be assessed for coinfection with Loa loa if they have traveled to areas of central Africa where Loa loa is endemic because ivermectin can cause severe reactions in patients with loiasis and high microfilarial levels.

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 be effectively treated with anthelmintic drugs or require surgical or endoscopic extraction of adult worms.

When the lungs are affected, treatment is symptomatic; it includes bronchodilators and corticosteroids. Anthelmintic drugs are typically not used.

Prevention

Prevention of ascariasis requires adequate sanitation.

Preventive strategies include

  • Washing the hands thoroughly with soap and water before handling food

  • Washing, peeling, and/or cooking all raw vegetables and fruits before eating

  • Not eating uncooked or unwashed vegetables in areas where human feces is used as fertilizer

  • Not defecating outdoors

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; masses of adult worms may obstruct the intestines and single worms may migrate into and obstruct bile or pancreatic ducts.

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

  • Treat with albendazole, mebendazole, or ivermectin; obstructions may require surgical or endoscopic extraction of the worms.

Drugs Mentioned In This Article

Drug Name Select Trade
ALINIA
ALBENZA
No US brand name
STROMECTOL
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