• Parasitic flatworms


  • Begins with an egg, found in faeces, sputum, or urine of definitive host. Can be non-embryonated (immature) or embryonated (ready to hatch). Hatch in environment (water) or within a host (typically mollusc).

  • Miracidium (pleural: miracidia): hatchling, a free-swimming ciliated larvae. No mouth, cannot eat, therefore need to find a host quickly if hatch in the environment.

  • Grow and develop within intermediate host into an elongated sac-like structure called a sporocyst.

  • Cercaria (plural: cercariae): larval form of trematode (develops within geminal cells of sporocyst). May or may not have swimming tail. Motile cercaria finds and settles in a host where it will become either depending on the species, an:

    • adult (fully developed mature stage capable of sexual reproduction)

    • metacercariae (cercaria encysted and resting, only when there are 3 intermediate host cycles) or

    • mesocercariae (encysted stage either on vegetation or in a host tissue on the 2nd intermediate host. Parasite able to infect definitive host by consuming 2nd intermediate host that has metacercariae on/in it)

Life-cycle stages of Schistosoma Japonicum



  • Schistosoma spp, Exposure to fresh water (skin penetration)

Lung / tissue flukes

  • Paragominas spp. (lung fluke), raw or undercooked crab or other crustaceans

Liver flukes


  • Fasciolopsis, metagonimus etc.