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- Ascaris lumbricoides: largest intestinal nematode (roundworm) that is a human pathogen.
- Soil-transmitted helminth, ova develop on warm, humid soil before becoming infective.
- Adult worms live in lumen of small intestine, ova excreted in stools.
- Life cycle: humans ingest infective ova that hatch and release larvae. Larvae invade intestinal mucosa and travel from portal to systemic circulation to lungs in about 4 days. Larvae penetrate through alveoli, ascend the trachea, and are reingested, then mature in intestines and live for 10 to 24 months .
- Ova are hardy. They can sustain freezing and live up to 6 years in moist soil. Adult female worms can produce 200,000 ova/day.
- Endemic in warm, humid areas especially where human excreta is used as fertilizer, contaminated wastewater is used for irrigation, or geophagy (deliberate/regular consumption of soil) is practiced.
- Infection most common in young, but affects all ages, and can cause malnutrition. Transmission: hand to mouth.