Ascariasis is infection with the nematode (worm) Ascaris lumbricoides or occasionally with the nematode Ascaris suum(a closely related parasite of pigs). 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. Light infections may be asymptomatic. Chronically infected children may develop undernutrition. Diagnosis is by identifying eggs or adult worms in stool, adult worms that migrate from the nose, mouth, or rectum, or rarely larvae in sputum during the pulmonary migration phase. Treatment is with albendazole, mebendazole, or ivermectin (or pyrantel pamoate in pregnant women).
Ascariasis is the most common intestinal helminth (parasitic worm) infection worldwide, but most infections occur in tropical and subtropical areas with limited sanitation and high rates of fecal contamination of soil, water, and food.
Global prevalences is estimated to be 819 million (1). Prevalence is highest in school-aged children (2). In the United States, most cases occur in refugees, immigrants, or travelers to endemic tropical areas.
Infection contributes to undernutrition. Deaths are mostly due to bowel or biliary tract obstruction in children.
Human to human transmission is fecal-oral by ingestion of fecal material containing fertile eggs of Ascaris lumbricoides in contaminated food or water or through contact with hands that have touched contaminated dirt or other materials.
Human infection can also be caused by ingesting the fertilized eggs of Ascaris suum (a closely related parasite of pigs) in pig feces. Eggs are ingested by handling infected pigs or from consuming contaminated raw or undercooked vegetables or fruits.
(See also Approach to Parasitic Infections.)
General references
1. Magalhães L, Nogueira DS, Gazzinelli-Guimarães PH, et al. Immunological underpinnings of Ascaris infection, reinfection and co-infection and their associated co-morbidities. Parasitology. Published online April 12, 2021. doi:10.1017/S0031182021000627
2. Silver ZA, Kaliappan SP, Samuel P, et al. Geographical distribution of soil transmitted helminths and the effects of community type in South Asia and South East Asia - A systematic review. PLoS Negl Trop Dis. 2018;12(1):e0006153. Published 2018 Jan 18. doi:10.1371/journal.pntd.0006153
Pathophysiology of Ascariasis
Ingested A. lumbricoides eggs hatch in the duodenum, and the resulting larvae penetrate the wall of the small intestine 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 intestine, where they develop into adult worms, which mate and release eggs into the stool.
Adult females range from 20 to 35 centimeters (8 to 14 inches), and adult males range from 15 to 30 centimeters (6 to 12 inches) in length. The life cycle is completed in approximately 2 to 3 months; adult worms live 1 to 2 years.
Image from the Centers for Disease Control and Prevention, Global Health, Division of Parasitic Diseases and Malaria.
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 medications (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. After an initial exposure, people in endemic areas develop T-helper cell type 2 (Th2) cell–mediated immunity that is associated with decreased worm burden and symptoms (1).
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.
Symptoms and signs reference
1. McSharry C, Xia Y, Holland CV, Kennedy MW. Natural immunity to Ascaris lumbricoides associated with immunoglobulin E antibody to ABA-1 allergen and inflammation indicators in children. Infect Immun. 1999;67(2):484-489. doi:10.1128/IAI.67.2.484-489.1999
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 gross visualization of adult worms in stool or emerging from the nose, mouth, or rectum. Occasionally, larvae can be found in sputum during the pulmonary phase. 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 radiograph during the pulmonary phase may show infiltrates, which in the presence of eosinophilia leads to the diagnosis of Löffler syndrome.
Treatment of Ascariasis
Albendazole, mebendazole, or ivermectin
For pregnant women, pyrantel pamoate
All intestinal Ascaris infections should be treated.
Pyrantel pamoate is also efficacious and is recommended treatment in pregnant women. Benzimidazoles are potentially teratogenic, and if their use is considered in pregnant women, the risk of treatment must be balanced with risk of untreated disease (1).
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 lightAscaris 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 anthelmintics or require surgical or endoscopic extraction of adult worms.
For pulmonary infections, treatment is symptomatic; it includes bronchodilators and corticosteroids. Anthelmintics are typically not used.
Treatment reference
1. Keiser J, Utzinger J. Efficacy of current drugs against soil-transmitted helminth infections: systematic review and meta-analysis. JAMA. 2008;299(16):1937-1948. doi:10.1001/jama.299.16.1937
Prevention of Ascariasis
Prevention of ascariasis requires adequate sanitation.
Preventive strategies include
Washing hands thoroughly with soap and water before handling food, after possible contact with feces or contaminated dirt, and after handling pigs
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 small intestine, and larvae migrate first to the lungs and then back to the small intestine, 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 migrating from the nose, mouth, or rectum.
Treat with albendazole, mebendazole, or ivermectin or pyrantel pamoate in pregnant women; obstructions may require surgical or endoscopic extraction of the worms.
