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USAID's NTD Program
USAID's NTD Program

Roundworm: Ascariasis

Life Cycle

Figure illustrating the lifecycle of roundworm.  
Source: CDC  

Step 1: Adult worms live in the lumen of the small intestine. A female may produce up to 200,000 eggs per day, which are passed in the feces.

Step 2 and 3: Fertile eggs embryonate and become infective after 18 days to several weeks, depending on the environmental conditions (optimum: moist, warm, and shaded soil).

Step 4: The eggs of the worm are found in soil contaminated by human feces or in uncooked food contaminated by soil containing eggs of the worm. Humans are infected when they ingest the contaminated soil found in their food, on their fingers, or in their drinks.

Step 5: The eggs hatch into larvae within the person’s intestine.

Step 6: The larvae penetrate the intestine wall and reach the lungs through the blood stream.

Step 7: 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. Upon reaching the small intestine, they develop into adult worms. The female adult worm, which can grow to more than 30 cm in length, lays eggs that are then passed into the feces. If soil is polluted with human or animal feces containing eggs, the cycle begins again. An adult ascaris may live up to one and a half years. Humans are the only reservoir, but the eggs may remain viable in soil for years.

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