The life cycle of a typical trematode begins when the egg is immersed in water or from the adult worms in the definitive host. Some trematode eggs hatch in water, others are eaten by the first intermediate host and hatch within that host, so there are many different routes that a trematode could take to infect a host. Following this, the miracidium, which is free - swimming ciliated larva that a parasite moves from the egg to host stage, hatches which then also goes to find the mollusc host as the first intermediate host. This is where either a rediae or sporocyst will form depending on the host and if there is competition between the two. This eventually forms into a motile cercariae. The cercariae then either infects vertebrates through the skin of a host or is ingested and aims to locate the second intermediate host. When in the vertebrate host, the cercariae can then form into an adult, metacercariae or mesocercariae, depending on the life cycle, or is rejected through feces or urine. Then the metacercariae and second intermediate host has to be ingested by the definitive host for the life cycle to be completed.
miracidium is a larval stage in the development of
trematode trematode trematode