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
Famous quotes containing the words life and/or cycle:
“Without poets, without artists, men would soon weary of nature’s monotony. The sublime idea men have of the universe would collapse with dizzying speed. The order which we find in nature, and which is only an effect of art, would at once vanish. Everything would break up in chaos. There would be no seasons, no civilization, no thought, no humanity; even life would give way, and the impotent void would reign everywhere.”
—Guillaume Apollinaire (1880–1918)
“The lifelong process of caregiving, is the ultimate link between caregivers of all ages. You and I are not just in a phase we will outgrow. This is life—birth, death, and everything in between.... The care continuum is the cycle of life turning full circle in each of our lives. And what we learn when we spoon-feed our babies will echo in our ears as we feed our parents. The point is not to be done. The point is to be ready to do again.”
—Paula C. Lowe (20th century)