Which statement correctly describes schistosome immunity?

• A. Intact worms evade immune responses; eggs are attacked.
• B. Eggs evade immune responses; worms are attacked.
• C. Larvae evade immune responses; eggs are attacked.
• D. Miracidia evade immune responses; Cercariae are attacked.

Answer: (A)

In schistosome immunity, the host’s defenses are most actively directed against the eggs, while the adult worms evade attack. The parasites’ adults have a tegument, a thick surface layer, that acts as a shield and can shed antigens, helping intact worms slip past immune surveillance and survive for years in the bloodstream. The eggs, however, are highly antigenic and are deposited in tissues like the liver and intestines, where they trigger strong immune recognition and granulomatous inflammation. This combination—adult worms evading the immune system and eggs provoking the immune response—is the best description of how schistosome immunity works. The other scenarios don’t fit the usual pattern: the immune system largely reacts to eggs rather than the larvae or sure-stage forms in the ways those options suggest.