Life Cycle
Ascaris lumbricoides, or "roundworm", infections in humans occur when an ingested infective egg releases a larval worm that penetrates the wall of the duodenum and enters the blood stream. From here, it is carried to the liver and heart, and enters pulmonary circulation to break free in the alveoli, where it grows and molts. In 3 weeks, the larvae pass from the respiratory system to be coughed up, swallowed, and thus returned to the small intestine, where they mature to adult male and female worms. Fertilization can now occur and the female produces as many as 200,000 eggs per day for a year. These fertilized eggs become infectious after 2 weeks in soil; they can persist in soil for 10 years or more.
The eggs have a lipid layer, that makes them resistant to the effects of acids and alkalis as well as other chemicals. This resilience helps to explain why this nematode is such a ubiquitous parasite.
Read more about this topic: Ascaris Lumbricoides
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