Ascaris Lumbricoides (Ascariasis)



Ascaris lumbricoides is a large parasitic nematode (roundworm), 15 to 40 cm in length, which infects humans via eggs found in soil.


  • Geographic distribution: South America, sub-Saharan Africa, China, and East Asia
  • All ages may be affected; however, children are more frequent hosts owing to oral behavior and tend to have a higher worm burden.
  • Ascariasis is more common where sanitation is poor and population is dense.
  • Eggs are viable in the soil for >6 years in temperate climates.
  • It is the most prevalent helminth infection in the world.
  • 800 million cases worldwide and estimated 400 million children infected
    • Around 51 million children suffer severe morbidity, mostly from moderate and heavy worm loads.


Infection control

  • Sanitary disposal of human excrement, not using human feces as fertilizer, and hand washing has the potential to eliminate this infection.
  • In communities with high transmission of Ascaris, community-wide mass drug delivery of anthelmintics is effective in controlling morbidity.


  • Fertilized eggs are ingested from soil contaminated with human feces.
  • Larvae hatch in the small intestine and migrate to cecum and colon.
  • Larvae invade the mucosa into the venous system and travel to the portal circulation, inferior vena cava, and finally, pulmonary capillaries.
  • During migration through the pulmonary vessels, an eosinophilic response is evoked.
  • Larvae penetrate the alveoli, are expelled by coughing, and swallowed back (days 10 to 14).
  • Larvae become adult worms in the small intestine (day 24).
  • Female worms excrete up to 200,000 eggs per day.
  • Ingestion to excretion takes 2 to 3 months.
  • Once in soil, fertilized eggs require 2 to 3 weeks of incubation in soil to become infectious and restart cycle.


Children commonly acquire this infection from playing in dirt contaminated with Ascaris eggs.


This infection may be associated with other soil-transmitted helminths:

  • Hookworm (Necator americanus, Ancylostoma duodenale)
  • Trichuris trichiura
  • Strongyloides stercoralis
  • Toxocara canis



  • Gastrointestinal symptoms include the following:
    • Abdominal distention
    • Pain
    • Nausea
    • Diarrhea
    • Decreased appetite
  • In the chronic phase, ascariasis is associated with the following:
    • Growth stunting
    • Cognitive delays
  • Severe respiratory symptoms during the pulmonary migratory stage, when larvae cause an inflammatory response (Löeffler syndrome), characterized by the following:
    • Dyspnea
    • Cough
    • Fever
    • Shifting pulmonary infiltrates
    • Eosinophilia
  • Severe presentation during the intestinal phase, when symptoms are due to the presence of worms:
    • Pain
    • Obstruction (2 per 1,000)
    • Peritonitis from perforation
    • Biliary colic, hepatitis, or pancreatitis from blockages due to worms
  • History of passage of large worms in the stool or vomitus is suggestive of ascariasis.
  • History of wheezing may precede passage of worms by 2 to 3 months.


  • Chest: may have rales or wheezing if Ascaris larvae are in the lungs
  • Abdomen
    • Distended
    • Auscultate and palpate for signs of obstruction or perforation.


Ascariasis should be considered in the differential diagnosis when a patient presents with pneumonia, peripheral eosinophilia, and/or intestinal obstruction in returned traveler or resident from an endemic area.



  • Microscopic examination of stool specimens will demonstrate the characteristic Ascaris eggs (round with thick shell).
  • During the pulmonary phase, may have peripheral eosinophilia and larvae in sputum but negative stool examinations
  • Serologic tests are unnecessary and are poorly specific to the diagnosis.
  • Molecular diagnostics (PCR) are becoming more widely available and are more sensitive test particularly in low-prevalence areas.
  • Chest radiograph, if cough is present, may demonstrate shifting pulmonary infiltrates.
  • Abdominal imaging, if abdominal signs or symptoms of obstruction or perforation




  • Oral
    • Albendazole
      • 400 mg, single dose
      • The World Health Organization (WHO) recommends 200 mg single dose for children <1 year old.
    • Mebendazole
      • 100 mg, b.i.d. for 3 days or 500 mg once
    • Ivermectin
      • 150 to 200 mcg/kg, single dose
    • Nitazoxanide
      • 100 mg b.i.d. for 3 days (12 to 47 months of age)
      • 200 mg b.i.d. for 3 days (4 to 11 years of age)
      • 500 mg b.i.d. for 3 days (12 years and above)
  • Alternatives (oral):
    • Pyrantel pamoate
      • 11 mg/kg to max 1 g per day for 3 days
    • Piperazine citrate
      • 75 mg/kg/24 h for 2 days; maximum, 3.5 g
      • Has been used historically for cases of intestinal obstruction (causes worm paralysis), but it is no longer available in the United States


Surgery or endoscopic retrograde cholangiopancreatography may be required for severe intestinal or biliary tract obstruction.

Ongoing Care


  • Treatment is highly effective.
  • Reexamination of stool specimens 2 weeks after therapy can be considered but is not essential.
  • Reinfection is common in endemic areas and has led to mass drug administration programs.


Warn parents about passage of worms in stool with treatment.


  • Once intestinal infection is detected and treated, the prognosis is excellent.
  • If obstructive or respiratory complications have occurred, the prognosis is less favorable.
  • The case fatality rate in cases with complications is up to 5%, most from obstruction.


  • Bronchopneumonia may be seen during the pulmonary migrational stage, producing fever, cough, dyspnea, wheeze, eosinophilia, and pulmonary infiltrates (Löeffler syndrome).
  • Heavy infestations may cause abdominal pain, malabsorption, and growth failure.
  • Children may experience obstruction (ileocecal), malabsorption, or intussusception.
  • Perforation or migration into the appendix, biliary, or pancreatic ducts may rarely occur.
  • Hepatitis, acute cholecystitis, or pancreatitis can occur. Liver abscess can occur if intrahepatic ducts are obstructed.

Additional Reading

  1. American Academy of Pediatrics. Ascaris lumbricoides infections. In: Kimberlin DW, Brady MT, Jackson MA, et al, eds. Red Book: 2015 Report of the Committee on Infectious Diseases. Elk Grove Village, IL: American Academy of Pediatrics; 2015:247–248. [PMID:20934531]
  2. Capello M, Hotez PJ. Intestinal nematodes. In: Long S, Pickering L, Prober C, eds. Principles and Practice of Pediatric Infectious Diseases. 4th ed. Churchill Livingstone/Elsevier; 2012:1326–1334. [PMID:18289159]
  3. Centers for Disease Control and Prevention. Parasites—ascariasis. Accessed January 27, 2017. [PMID:11386692]
  4. Dold C, Holland CV. Ascaris and ascariasis. Microbes Infect. 2011;13(7):632–637. [PMID:20934531]
  5. Hall A, Hewitt G, Tuffrey V, et al. A review and meta-analysis of the impact of intestinal worms on child growth and nutrition. Matern Child Nutr. 2008;4(Suppl 1):118–236. [PMID:26550552]
  6. Lamberton PH, Jourdan PM. Human ascariasis: diagnostics update. Curr Trop Med Rep. 2015;2(4):189–200. [PMID:18289159]
  7. Mitchell PD, Yeh HY, Appleby J, et al. The intestinal parasites of King Richard III. Lancet. 2013;382(9895):888. [PMID:24011545]
  8. O’Lorcain P, Holland CV. The public health importance of Ascaris lumbricoides. Parasitology. 2000;121(Suppl):S51–S71. [PMID:11386692]
  9. World Health Organization. Intestinal worms. Accessed January 27, 2017.



127.0 Ascariasis


  • B77.9 Ascariasis, unspecified
  • B77.0 Ascariasis with intestinal complications
  • B77.81 Ascariasis pneumonia
  • B77.89 Ascariasis with other complications


  • 50982003 Infection by Ascaris lumbricoides (disorder)
  • 1082721000119101 Pneumonia due to Ascaris (disorder)


  • Q: What are the long-term effects of untreated Ascaris infection in children?
  • A: Growth stunting and cognitive delays are the most common long-term effects of untreated infections. Given the prevalence of this infection in the world, this is a major cause of morbidity in the world.
  • Q: Which King of England, who was also the subject of a play by William Shakespeare, was infected with A. lumbricoides?
  • A: In 2012, the remains of Richard III were excavated and identified in Leicester, England. Further analysis of sediment samples from the sacral area suggested evidence of roundworm eggs (A. lumbricoides) and intestinal roundworm infection.


Amaya L. Bustinduy, MD, MPH, PhD, FRCPCH

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