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Causal Agent:

Ascaris lumbricoides is the largest nematode (roundworm) parasitizing the human intestine. (Adult females: 20 to 35 cm; adult male: 15 to 30 cm.)

Life Cycle:

Ascaris lumbricoides

Adult worms The number 1 live in the lumen of the small intestine. A female may produce approximately 200,000 eggs per day, which are passed with the feces The number 2. Unfertilized eggs may be ingested but are not infective. Fertile eggs embryonate and become infective after 18 days to several weeks The number 3, depending on the environmental conditions (optimum: moist, warm, shaded soil). After infective eggs are swallowed The number 4, the larvae hatch The number 5, invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs The number 6. The larvae mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed The number 7. Upon reaching the small intestine, they develop into adult worms The number 1. Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female. Adult worms can live 1 to 2 years.

Life cycle image and information courtesy of DPDx.