Intermediate Hosts (Snails)

Intermediate Hosts

An Intermediate host is an organism serving as a host for a portion of the life cycle during which it transforms into an infective stage for it’s next host. In the case of swimmer’s itch causing trematode parasites, freshwater snails serve as the intermediate host. It is at this stage that the parasite undergoes asexual reproduction and multiplies exponentially. It transforms into a stage called a cercariae that migrates through the snail’s body and exits through the headfoot (head portion of the snail). This is a free-swimming stage that is then infective to birds, and is the stage that will enter human skin as well. Snails can maintain these infections for weeks, to even months, and can release hundreds of cercariae per day.