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Ascariasis

Ascariasis is an intestinal infection caused by the roundworm Ascaris lumbricoides. People acquire it by swallowing infective eggs from soil, food or water contaminated with human feces; light infections may cause no symptoms, while heavy worm burdens can impair nutrition or obstruct the intestine or biliary tract.

At a glance

Quick facts

Condition snapshot
Cause
Ascaris lumbricoides
Transmission
Fecal–soil–oral
Person-to-person
Not directly
Diagnosis
Stool microscopy in established infection
Treatment
Anthelmintic medicine
Severe complication
Intestinal / biliary obstruction

Names & terminology

How this entity may be named or searched

Ascariasis
Infection with the large intestinal roundworm Ascaris lumbricoides.
Soil-transmitted helminthiasis
Ascariasis is grouped with trichuriasis and hookworm infections because transmission depends on fecal contamination of soil.
Pulmonary phase
Larvae migrate through the lungs before returning to the intestine, so cough or eosinophilic lung symptoms can occur early.
Important transmission point
Fresh stool does not directly transmit mature Ascaris infection; eggs require time in soil to become infective.

Structured entity profile

Clinical profile

Condition data
ParasiteAscaris lumbricoidesAdult worms live in the small intestine.
TransmissionIngestion of mature eggsContaminated soil, produce, hands or water are common pathways.
Early phaseLarval lung migrationTransient cough, wheeze or eosinophilia can occur.
Established phaseIntestinal infectionMany people are asymptomatic; heavy burden causes more disease.
DiagnosisStool ova microscopyEggs appear after adult worms mature; imaging may identify complications.
TreatmentDeworming medicineAlbendazole or mebendazole are commonly used according to local guidance.

Overview

Ascaris eggs are passed in the feces of infected people and mature in soil under favorable conditions. Infection occurs after mature eggs are swallowed. Larvae hatch in the intestine, migrate through the bloodstream to the lungs, ascend the airways, are swallowed, and then mature into adult worms in the small intestine. Because the eggs need environmental maturation, ascariasis is not usually transmitted directly from one person to another through immediate contact. [1] [2]

Clinical illness depends strongly on worm burden and age. Light infection may be silent. Children with repeated or heavy infections can experience abdominal symptoms, impaired nutritional status and growth effects. A large number of adult worms can form a bolus that obstructs the intestine, and migrating worms can enter the bile or pancreatic ducts. [1] [2]

Symptoms and warning signs

During larval lung migration, some people develop cough, wheeze, chest discomfort, fever or transient eosinophilic pulmonary infiltrates. Later intestinal symptoms can include abdominal pain, nausea, poor appetite or seeing a worm in stool or vomit. Severe abdominal pain, persistent vomiting, abdominal distension or jaundice can indicate obstruction or migration into the biliary system. [2] [3]

SYMPTOM MATRIX

Symptoms depend on the stage and number of worms

Heavy infections carry the greatest risk of nutritional and obstructive complications.

Parasitic infection
Often absent or mild
  • No symptoms
  • Intermittent abdominal discomfort
  • Nausea or reduced appetite
  • Visible worm passed in stool
Pulmonary / heavy infection
  • Cough or wheeze during larval migration
  • Eosinophilia
  • Poor growth or nutritional effects in children
  • Biliary-type pain or jaundice
Urgent complications
  • Severe cramping abdominal pain
  • Persistent vomiting or distension
  • Failure to pass stool/gas with illness
  • Jaundice with severe upper-abdominal pain
  • Signs of pancreatitis or cholangitis

Heavy worm burdens can cause intestinal or biliary obstruction and may require procedural or surgical care.

Diagnosis

Established intestinal ascariasis is usually diagnosed by identifying characteristic eggs on stool microscopy. A stool test can be negative early after infection, before adult female worms begin producing eggs, and infections with only male worms may also be missed. Eosinophilia can occur during larval migration but is not specific. [2] [3]

Ultrasound, radiography, CT, MRI or endoscopy may reveal adult worms or complications when obstruction or biliary/pancreatic migration is suspected. The history of residence or travel in areas with poor sanitation and exposure to contaminated soil or produce adds context but cannot replace testing. [2] [3]

Diagnostic pathway

Confirm intestinal infection and look for obstruction when symptoms are severe

The diagnostic approach changes when worms have migrated into the biliary or pancreatic ducts.

Parasitology
1Assess exposure and severityReview sanitation exposure, travel/residence and symptoms of pulmonary or intestinal disease.
2Test stoolUse ova-and-parasite microscopy for established intestinal infection.
3Check complicationsUse blood tests and imaging when obstruction, biliary disease or pancreatitis is suspected.
4Treat and address reinfection riskDeworm appropriately and reduce fecal-soil exposure through sanitation and hygiene.
Routine diagnosisStool ova microscopyafter worms mature
Complication imagingUS / CT / endoscopywhen obstruction suspected

A negative early stool test does not completely exclude recent infection because eggs are not produced immediately.

Why ascariasis can cause both lung and intestinal symptoms

The Ascaris life cycle includes tissue migration. After eggs hatch, larvae cross the intestinal wall and travel to the lungs before being coughed up and swallowed. This creates a short pulmonary phase followed by the longer intestinal adult-worm phase. The timing explains why cough and eosinophilia can precede a positive stool examination. [2] [3]

Complications of heavy worm burden

High-intensity infection can impair nutritional intake and growth, especially in children. Tangled adult worms may obstruct the intestine. Adult worms can also migrate into the biliary tree, gallbladder or pancreatic duct, causing biliary colic, cholangitis, cholecystitis or pancreatitis. These complications require hospital-level assessment rather than routine deworming alone. [1] [2]

Treatment and management

Uncomplicated ascariasis is treated with an anthelmintic medicine. WHO preventive-treatment programs commonly use albendazole or mebendazole in populations where soil-transmitted helminths are endemic, and clinicians use similar medicines for individual infection according to age, pregnancy status and local guidance. [1] [2]

Mechanical complications need a different plan. Intestinal obstruction may require bowel rest, fluids and surgical review; biliary or pancreatic worms may require endoscopic extraction or other procedures in addition to antiparasitic therapy. Treating one episode does not provide durable immunity, so reinfection remains possible when sanitation exposure continues. [2] [3]

Treatment & care hub

Deworm uncomplicated infection; escalate obstruction

Medication clears worms, but severe mechanical complications may need procedures.

Anthelmintic care
DewormingCore

Use an effective anthelmintic

Albendazole or mebendazole are commonly used according to patient factors and local guidance.

ObstructionUrgent

Treat mechanical complications

Bowel or biliary obstruction can require hospital care, endoscopy or surgery.

NutritionSupportive

Address growth and nutritional impact

Children with heavy or recurrent infection may need nutritional assessment and broader preventive care.

PreventionCommunity + individual

Reduce fecal–soil exposure

Sanitation, hand hygiene and safe food preparation reduce reinfection.

Diagnose→Deworm→Treat complications→Prevent reinfection

Mass drug administration is a public-health strategy for endemic communities; individual treatment should follow age- and pregnancy-appropriate guidance.

Prevention and sanitation

Prevention depends on interrupting contamination of soil with human feces: access to safe sanitation, handwashing, safe water and careful washing or cooking of produce are central. In endemic areas, WHO recommends periodic preventive chemotherapy for at-risk groups when prevalence thresholds are met, because reinfection is common. [1]

Follow-up after treatment

Symptoms usually improve after effective therapy, but persistent abdominal, biliary or respiratory symptoms should prompt reassessment for another diagnosis, treatment failure or a complication. Routine test-of-cure practices vary by setting; population control programs focus on repeated preventive treatment and reinfection reduction rather than proving eradication after every dose. [1] [2]

Global helminth burden

Soil-transmitted helminths affect about 1.5 billion people worldwide

This WHO estimate includes Ascaris, Trichuris and hookworms together; it is not an ascariasis-only prevalence figure.

WHO — Soil-transmitted helminth infections ↗
People with soil-transmitted helminth infections~1.5 billionWHO group estimate
Share of world population~24%
Ascarisone of the main species
Important: The 1.5-billion estimate is for the combined soil-transmitted helminth group, not for ascariasis alone.

Common questions

Frequently asked questions

Reference content

Sources

  1. WHO — Soil-transmitted helminth infections — Fact sheet
  2. CDC — About Ascariasis
  3. CDC DPDx — Ascariasis — Laboratory Identification of Parasites

This article is based on trusted medical sources and is awaiting clinician review. It is not a substitute for personalized medical advice.