Ascaris lumbricoides, or "roundworm", infections in humans occurs when an ingested infective egg releases a larval worm that penetrates the wall of the duodenum and enters the bloodstream. From here, it is carried to the liver and heart, and enters pulmonary circulation to break free in the alveoli, where it grows and molts. In 3 weeks, the larvae pass from the respiratory system to be coughed up, swallowed, and thus returned to the small intestine, where they mature to adult male and female worms. Fertilization can now occur and the female produces as many as 200,000 eggs per day for a year. These fertilized eggs become infectious after 2 weeks in soil; they can persist in soil for 3 years or more.

A small child at the clinic presenting with vomiting, diarrhea, and anemia vomited this worm up while at the clinic. We were able to give him the necessary medication to eradicate the problem.