Experimental Infection of Hosts for Echinostome Metacercariae

In order to obtain metacercariae experimentally, we attempted to infect laboratory-reared snails [Biomphalaria glabrata (Say, 1818)] and fish (Poecilia reticulata Peters, 1859). These species were used as experimental hosts due to their availability in the laboratory and previous knowledge on the involvement of snails and fish as second intermediate hosts of echinostomes. The behavior of cercariae in the presence of these potential hosts was observed under a stereomicroscope. After 24hs of exposure to cercariae, the snails and fish were necropsied. We also searched for metacercariae in samples of insects, fishes, snails, and tadpoles collected in the same water bodies where snails were found infected.
Metacercariae found in tadpoles collected in the stream where snails were found infected were used for an experimental infection study. We suspected they could be of the same species based on the number of excretory corpuscles. Aiming to obtain adult parasites for taxonomic identification, a sub-sample of 50 metacercariae was orally administered to one specimen of a dexamethasone-immunosuppressed (50 mg/kg) male Swiss mouse. The infected mouse was maintained on a 12/12h light–dark cycle and allowed access to food and water ad libitum. Coproparasitological examinations by the sedimentation technique were conducted daily, starting from seven days post-infection. The mouse was euthanized via barbituric overdose (sodium pentobarbital, injected intraperitoneally) and necropsied for the search of adult parasites 14 days post-infection.