Merck Manual

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Chelsea Marie

, PhD, University of Virginia;

William A. Petri, Jr

, MD, PhD, University of Virginia School of Medicine

Reviewed/Revised Sep 2022
Topic Resources

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 rarely larvae in sputum during the pulmonary migration phase. Treatment is with albendazole, mebendazole, or ivermectin.

Ascariasis, the most common intestinal helminth infection in the world, occurs worldwide but is concentrated in tropical and subtropical areas with poor sanitation. Prevalence is highest in children aged 2 to 10 years and decreases in older age groups. Current estimates suggest that about 500 million people are infected worldwide, and ascariasis contributes to malnutrition in areas with poor sanitation. It is estimated that ascariasis is responsible for 2,000 to 10,000 deaths worldwide annually, most of which are due to bowel or biliary tract obstruction in children.

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 ascaris (A. suum) from pigs when they ingest eggs from handling pigs or from consuming undercooked vegetables or fruits contaminated with pig feces. Whether A. suum is a distinct species from A. lumbricoides is debated.

Pathophysiology of Ascariasis

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 of adult worms.

Symptoms and Signs of Ascariasis

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 of Ascariasis

  • 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. Adult worms may be seen in radiographic studies of the gastrointestinal tract.

Treatment of Ascariasis

  • Albendazole, mebendazole, or ivermectin

All intestinal Ascaris 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 lived in 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 of Ascariasis

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 or pig feces is used as fertilizer

  • Not defecating outdoors except in latrines with proper sewage disposal

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 adult 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
Emverm, Vermox
Sklice, Soolantra, Stromectol
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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