Q.Explain the extra-intestinal migration route of Ascaris larvae in the human body.

[!TLDR] Ascaris larvae migrate through the liver, heart and lungs before returning to the intestine.

After hatching in the small intestine, the Ascaris larva bores into gut blood vessels, travels via the portal circulation to the liver, then via the heart to the lungs, breaks into the alveoli, moults, migrates up the airway to the pharynx, and is swallowed again to mature in the small intestine. …

Unlike most intestinal parasites, the larva of Ascaris lumbricoides does not develop directly into an adult within the gut after hatching; instead it undertakes an elaborate journey through several organs before returning to the intestine, known as the extra-intestinal migration route. After a swallowed embryonated egg hatches in the small intestine, the released first-stage larva bores actively through the intestinal wall into the surrounding blood vessels of the gut. It is then carried passively by the portal blood circulation first to the liver, and from there via the hepatic vein, the inferior vena cava, and the right side of the heart into the pulmonary circulation, arriving finally at the capillaries of the lungs. In the lungs, the larva breaks out of the pulmonary capillaries into the air-filled alveoli, where it moults (sheds its cuticle) twice as it continues to grow, before migrating upward through the bronchioles, bronchi and trachea into the pharynx (throat). On reaching the pharynx, the larva is swallowed a second time, carrying it back down in …

• Assuming the Ascaris larva develops directly into an adult in the intestine without any migration — the extra-intestinal (liver-heart-lung-throat) journey is an essential part of its life cycle. …