Life Cycle
Microscopy of Ascaris lumbricoides

Adult worms  live in the lumen of the small intestine. A female may produce up to 240,000 eggs per day, which are passed with the feces . Fertile eggs embryonate and become infective after 18 days to several weeks , depending on the environmental conditions (optimum: moist, warm, shaded soil). After infective eggs are swallowed , the larvae hatch , invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs . The larvae mature further in the lungs (10-14 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 . 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. 
(Used with permission:  DPDx, the CDC Parasitology Website)


Infection with Ascaris lumbricoides often causes no symptoms.  Infections with a large number of worms may cause abdominal pain or intestinal obstruction.  Adults feed on the contents of the small intestine and in heavy infections this may compound problems in malnourished individuals (especially children). 

Migration of larvae may cause localized reactions in various organs.  Penetration of the larvae from capillaries into the lungs can lead to Loeffler's pneumonia, in which pools of blood and dead epithelial cells clog air spaces in the lungs.  Resulting bacterial infections can be fatal.

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