Aroapyrgus costaricensis, hydrobiid snail host of paragonimiasis in Costa Rica.

A small freshwater hydrobiid snail found in narrow shallow steams at various altitudes in Costa Rica is the intermediate host of Paragonimus mexicanus. Based on the morphology of its shell and soft parts the snail is assigned to the species Aroapyrgus costaricensis (Mörch). It is easily maintained in the laboratory; the female is ovoviviparous, carries up to 40 embryos in its brood pouch, and young-to-young cycle is about 10 weeks. Natural infection rates with rediae and cercariae of Paragonimus mexicanus are less than 1%, the majority of the naturally infected snails are of medium size (about 2 mm in height), but all sizes (ages) can be experimentally infected. The microcercous cercairae of P. mexicanus emerge from A. costaricensis in late afternoon and evening, about 2 months after exposure to the miracidia.