2. After the Aswan High Dam was built on the Nile River, the rate of parasitic blood-fluke (a worm-like microorganism) infection doubled in the human population near the dam. As a result of building the dam, the flow of the Nile changed. This changed the habitat, which resulted in an increase in its population of a certain aquatic snail. The snails, which were infected, released larvae of the fluke. These larvae then infected humans. The role of the snail in this relationship may be described as a (1) Host (3) Producer (2) Parasite (4) Decomposer