Question
Ascaris lumbricoides.
Answer
Ascaris lumbricoides is the largest intestinal nematode infecting humans, and the most common human helminth infection worldwide.
Morphology: adult worms are large, pinkish-white, cylindrical roundworms — females up to 35–40 cm, males slightly smaller (15–30 cm) with a curved posterior end; a female can lay up to 200,000 eggs daily.
Transmission and life cycle: a soil-transmitted helminth, transmitted by faecal-oral ingestion of embryonated eggs from contaminated soil/food/water. Ingested eggs hatch in the small intestine, releasing larvae that penetrate the intestinal wall, enter the bloodstream, and undergo a hepato-pulmonary migration — passing through the liver, then the lungs, where they break into alveoli, ascend the bronchial tree/trachea, and are swallowed, returning to the small intestine to mature into adult worms over 2–3 months. Adult worms live free in the intestinal lumen (not attached to mucosa).
Pathogenesis/clinical features:
- Pulmonary phase (Löffler’s syndrome) — cough, dyspnoea, wheeze, and eosinophilic pneumonitis during larval lung migration, with marked peripheral eosinophilia.
- Intestinal phase — usually asymptomatic with light infection; heavy worm burden can cause abdominal discomfort, malnutrition (competition for nutrients), and intestinal obstruction (a bolus of worms), particularly in children.
- Complications from aberrant migration — biliary/pancreatic duct obstruction (cholangitis, pancreatitis), appendicitis, or, rarely, migration through the mouth/nose (triggered by fever, anaesthesia, certain drugs).
Laboratory diagnosis: stool microscopy for characteristic fertilized (mammillated, bile-stained, oval) or unfertilized eggs; adult worms occasionally passed spontaneously or visualized on imaging (barium studies).
Treatment: albendazole or mebendazole (single dose); surgical intervention for obstructive complications.
Prevention: sanitation (proper faecal disposal), food/water hygiene, hand hygiene, and periodic deworming programmes in endemic areas.