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Ascaris Lumbricoides

  • Author: Aaron Dora-Laskey, MD; Chief Editor: Jeter (Jay) Pritchard Taylor, III, MD  more...
Updated: May 18, 2016


Intestinal nematode infections affect one fourth to one third of the world's population. Of these, the intestinal roundworm Ascaris lumbricoides is the most common. While the vast majority of these cases are asymptomatic, infected persons may present with pulmonary or potentially severe gastrointestinal complaints. Ascariasis predominates in areas of poor sanitation and is associated with malnutrition, iron-deficiency anemia, and impairments of growth and cognition.

Ascaris lumbricoides is shown in the image below.

Adult Ascaris lumbricoides. Adult Ascaris lumbricoides.


A lumbricoides is the largest of the intestinal nematodes affecting humans, measuring 15-35 cm in length in adulthood. Infection begins with the ingestion of embryonated (infective) eggs in feces-contaminated soil or foodstuffs. Once ingested, eggs hatch, usually in the small intestine, releasing small larvae that penetrate the intestinal wall. Larvae migrate to the pulmonary vascular beds and then to the alveoli via the portal veins usually 1-2 weeks after infection, during which time they may cause pulmonary symptoms (eg, cough, wheezing). During the time frame of pulmonary symptoms, eggs are not being shed, and thus diagnosis via stool ovas and parasites is not possible. Eggs are not shed in stool until roughly 40 days after the development of pulmonary symptoms.

After migrating up the respiratory tract and being swallowed, they mature, copulate, and lay eggs in the intestines. Adult worms may live in the gut for 6-24 months, where they can cause partial or complete bowel obstruction in large numbers, or they can migrate into the appendix, hepatobiliary system, or pancreatic ducts and rarely other organs such as kidneys or brain. From egg ingestion to new egg passage takes approximately 9 weeks, with an additional 3 weeks needed for egg molting before they are capable of infecting a new host.

Life cycle of Ascaris lumbricoides. Life cycle of Ascaris lumbricoides.



United States

In the United States, approximately 4 million people are believed to be infected.[1] High-risk groups include international travelers, recent immigrants (especially from Latin America and Asia), refugees, and international adoptees. Ascariasis is indigenous to the rural southeast, where cross-infection by pigs with the nematode Ascaris suum is thought to occur. (Children aged 2-10 years are thought to be more heavily infected in this and all other regions.)


Worldwide, 1.4 billion people are infected with A lumbricoides, with prevalence among developing countries as low as 4% in Mafia Island, Zanzibar,[2] to as high as 90% in some areas of Indonesia. Local practices (eg, termite mound–eating in Kenya[3] ) may predispose to ascariasis in some populations. Further risk factors include other forms of geophagia and cat/dog ownership. In some regions, Ascaris infection is thought to contribute significantly to the burden of abdominal surgical emergencies.


The rate of complications secondary to ascariasis ranges from 11-67%, with intestinal and biliary tract obstruction representing the most common serious sequelae. Although infection with A lumbricoides is often asymptomatic, it is responsible for an estimated 730,000 cases of bowel obstruction annually, 11,000 of which are fatal.[4] In one series of pregnant patients in Bangladesh, biliary ascariasis was responsible for a plurality (28%) of nonobstetric etiologies of acute abdomen.[5]

Owing to similarities in the means of infection, many individuals infected with Ascaris are also co-infected with other intestinal parasites.  


No racial predilection is known. A genetic predisposition has been described in a study of families from Nepal.[6]


Male children are thought to be infected more frequently, owing to a greater propensity to eat soil.


Children, because of their habits (eg, directly or indirectly consuming soil), are more commonly and more heavily infected than adults. Neonates may be infected by transplacental infection. Frequently, families may be infected and reinfected in group fashion due to shared food and water sources as well as hygiene practices.

Contributor Information and Disclosures

Aaron Dora-Laskey, MD Clinical Assistant Professor, Department of Emergency Medicine, Wright State University, Boonshoft School of Medicine

Aaron Dora-Laskey, MD is a member of the following medical societies: American Academy of Emergency Medicine

Disclosure: Nothing to disclose.


Eric L Weiss, MD, DTM&H Medical Director, Office of Service Continuity and Disaster Planning, Fellowship Director, Stanford University Medical Center Disaster Medicine Fellowship, Chairman, SUMC and LPCH Bioterrorism and Emergency Preparedness Task Force, Clinical Associate Professor, Department of Surgery (Emergency Medicine), Stanford University Medical Center

Eric L Weiss, MD, DTM&H is a member of the following medical societies: American College of Emergency Physicians, American College of Occupational and Environmental Medicine, American Medical Association, American Society of Tropical Medicine and Hygiene, Physicians for Social Responsibility, Southeastern Surgical Congress, Southern Oncology Association of Practices, Southern Clinical Neurological Society, Wilderness Medical Society

Disclosure: Nothing to disclose.

Ugo Anthony Ezenkwele, MD, MPH Vice Chief of Emergency Medicine, Woodhull Medical and Mental Health Center; Associate Professor of Clinical Emergency Medicine, Department of Emergency Medicine, New York University School of Medicine

Ugo Anthony Ezenkwele, MD, MPH is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, National Medical Association, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Jon Mark Hirshon, MD, MPH, PhD Professor, Department of Emergency Medicine, University of Maryland School of Medicine

Jon Mark Hirshon, MD, MPH, PhD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Emergency Physicians, American Public Health Association, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Chief Editor

Jeter (Jay) Pritchard Taylor, III, MD Assistant Professor, Department of Surgery, University of South Carolina School of Medicine; Attending Physician, Clinical Instructor, Compliance Officer, Department of Emergency Medicine, Palmetto Richland Hospital

Jeter (Jay) Pritchard Taylor, III, MD is a member of the following medical societies: American Academy of Emergency Medicine, South Carolina Medical Association, Columbia Medical Society, South Carolina College of Emergency Physicians, American College of Emergency Physicians, American Medical Association, Society for Academic Emergency Medicine

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Chief Editor for Medscape.

Additional Contributors

Mark Louden, MD Assistant Professor of Clinical Medicine, Division of Emergency Medicine, Department of Medicine, University of Miami, Leonard M Miller School of Medicine

Mark Louden, MD is a member of the following medical societies: American College of Emergency Physicians

Disclosure: Nothing to disclose.


The authors and editors of Medscape Reference gratefully acknowledge the medical review of this article by Joseph U Becker, MD.

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Adult Ascaris lumbricoides.
Life cycle of Ascaris lumbricoides.
Ascaris lumbricoides egg.
Adult Ascaris lumbricoides in biliary system.
The roundworm Ascaris lumbricoides causes ascariasis. Worms can reach 10-30 cm in length. Clinical disease results from effects of pulmonary larval migration, intestinal obstruction, or migration through the biliary tree.
Ascaris lumbricoides egg in feces (formalin-ethyl acetate sedimentation method).
Endoscopic retrograde cholangiogram shows long, linear, filling defect in common bile duct. Image courtesy of
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