How are the fluke larvae transferred from the snail (invertebrate host) to the vertebrate host?

The eggs of the fluke are passed into water supplies from feces and urine of infected people. After hatching the parasite actively swims and invades the body of a snail, usually by penetrating through the snail's foot. The parasite requires the presence of certain species of snails (e.g., Oncomelania, Biomphalaria, Bulinus) to transform (and multiply) itself into an infective stage, called cercaria.