Ascaris lumbricoides Life Cycle

1. Adult Ascaris nematodes (worms) live in the lumen of the small intestine.

2. A female may produce approximately 200,000 eggs/day; the eggs are excreted with feces. Unfertilized eggs may be ingested but are not infective.

3. In the environment, fertile eggs, depending on the conditions, embryonate and become infective after 18 days to several weeks; optimal conditions are moist, warm, shaded soil.

4. Infective eggs are swallowed.

5. In the small intestine, the eggs hatch into larvae.

6. Larvae penetrate the wall of the small intestine and migrate via the portal circulation through the liver, then via the systemic circulation to the lungs, where they mature further (in 10 to 14 days).

7. The larvae penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed. They then return to the small intestine, where they develop into adult worms.