Ascaris lumbricoides

Large Intestinal Roundworm

Physiology and Structure: 
  • A. lumbricoides are large (20cm to 35cm long), pink worms.
  • The egg releases a larval worm which penetrates the duodenal wall and enters the bloodstream which is then carried to the liver and heart and finally into the pulmonary circulation.
  • In the lungs, they break free and start to molt. 
  • The larvae would be coughed up, swallowed and returned to the small intestine. This process takes around 3 weeks.
  • The worms mature in the small intestine.
  • Up to 200,000 eggs can be produced in a day.
  • Fertilized eggs become infectious after 2 weeks of exposure to soil.


Ascaris lumbricoides









Lifecycle of Ascaris lumbricoides


Clinical Syndromes
  • Infections caused by the ingestion of a few eggs may produce no symptoms.
  • The ingestion of a single adult worm may be dangerous as it is able to travel into the bile duct and liver and destroy tissue.
  • Infections with many larvae would produce pneumonitis,similar to an asthma attack, when larvae migrate to the lungs.
  • Prolonged exposure would cause eosinophilia and oxygen desaturation.
  • Worms tangled in the intestines would cause obstruction, perforation and occulsion of the appendix.
  • Victims would also experience symptoms like abdominal tenderness, fever, distention and vomiting.


Treatment, Prevention and Control
  • Treatment of symptomatic infection with mebendazole is effective.
  • Patients who have mixed infection in the stool have to be treated for ascariasis to prevent the migration of worms and intestinal perforation.
  • Sanitary facilities should be maintained to prevent contamination of the soil with human feces.
  • Practice of using human feces as fertilizer should be avoided.