Which stage of Schistosoma is most commonly targeted by the immune response in schistosomiasis?

• A. Eggs
• B. Worms
• C. Cercariae
• D. Miracidia

Answer: (A)

In schistosomiasis, the immune response in humans is driven primarily by the eggs deposited by adult worms. As these eggs become trapped in tissues such as the liver, intestines, or bladder, they secrete antigens that provoke a strong, localized immune reaction, especially a Th2-type response with granuloma formation around the eggs. This granulomatous inflammation and subsequent tissue remodeling are responsible for most of the disease’s clinical pathology, including fibrosis and organ dysfunction. While the larval stages (cercariae and miracidia) and the adult worms can evoke immune responses, they are not the main source of ongoing pathology in established infection. Therefore, the eggs are the stage most commonly targeted by the host immune response.