In the western United States the primary host are mainly raccoons (Procyon lotor) with the possibility of minks (Neovison vison) as well. Adult Metagonimoides oregonensis are found in the intestines of these mammals. Through the parasite's eggs in the primary host's fecal matter transmission to another host is made easy. Prosobranch snails which are found in rivers and streams are then infected with miracidia from the fecal matter from the primary hosts. It is unknown if a prosobranch snail needs to ingest the miracidia to become infected, or if the miracidia are free-swimming. This is how our first intermediate host becomes infected.
