Ascariasis pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Imtiaz Ahmed Wani, M.B.B.S

Pathophysiology

. The pathogenesis of ascariasis involves the following processes:

• The eggs are primarily transmitted from hand to mouth, but they may also be ingested in raw fruits and vegetables grown in soil contaminated with the eggs of ascaris. Ascaris infection occurs about 9-12 days after egg ingestion.
• Following ingestion of the eggs, the fertilized ova hatch in the small intestine and the larvae penetrates the intestinal mucosa.
• The larvae then proceeds to the lungs via the venous circulation and migrates through the alveoli and the bronchial tree, resulting in pulmonary ascariasis.
• The larvae are subsequently swallowed and return to the intestines where maturation into adult worms occur. The adult worms have a life span of 10-24 months within the human host. The adult male worms are 10-30cm long, while the adult female worms are larger and they measure up to 40cm long. Intestinal obstruction associated with perforation, volvulus and intussusception can occur in patients with large worm burdens. Worms can also migrate into the biliary tree resulting in biliary colic and pancreatitis. Migration of worms into the appendix can result in acute appendicitis.
• The fecund female worm produces a very high output of eggs (about 200,000 eggs/day), and eggs are passed out of the intestine with the feces and they can survive for years in warm, moist, shaded soil. At temperatures of 5-10⁰C, the eggs of ascaris can remain viable for as long as two years.

* 1- Adult worms live in the lumen of the small intestine. A female may produce approximately 200,000 eggs per day, which are passed with the feces. * 2- Unfertilized eggs may be ingested but are not infective. * 3- Fertile eggs embryonate and become infective in 5-10 days depending on the environmental conditions (optimum: moist, warm, shaded soil). * 4- Infective eggs are swallowed * 5- The larvae hatch, invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs . * 6- The larvae mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat * 7- The larvae are then swallowed. Upon reaching the small intestine, they develop into adult worms. The female ascaris begin depositing eggs in 8-10 weeks . Adult worms can live 1 to 2 years.

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