Through what organism is schistosomiasis primarily spread?

Schistosomiasis is primarily spread through freshwater snails, specifically those in the genus Biomphalaria and Bulinus. These snails serve as intermediate hosts for the parasitic flatworms known as schistosomes. The life cycle of schistosomes involves the transformation of larvae, known as cercariae, which are released into the water when the snails are disturbed or when they reach maturity. Upon release, these cercariae can penetrate human skin when a person comes into contact with contaminated freshwater, leading to infection.

Understanding this lifecycle highlights the importance of controlling freshwater snail populations in areas where schistosomiasis is endemic to mitigate the disease's spread. The other choices, such as freshwater plants, fish, and crustaceans, do not play a role in the transmission of schistosomiasis, as they do not support the life cycle of the schistosome parasites.