Excystment in vitro of Notocotylus attenuatus (Trematoda: Notocotyloidea) metacercariae

Optimum in vitro excystation of Notocotylus attenuatus (Rudolphi, 1809) metacercarial cysts occurred following pretreatment of the cyst for 2 hr in N,N',N'-polyoxyethylene(10)-N-tallow-1,3-diaminopropane/water solution (1:2), a second pretreatment (15 min) in 1.0% HCl acid-1.0% pepsin (pH 2.0), and then 2 hr treatment in an excystation medium containing 0.5% trypsin plus 0.5% bile salts in Earle's balanced salt solution adjusted with 7.5% NaHCO₃ to pH 7.8-8.0. The rate of excystation was rapid and reached 71.7% by 1 hr, increasing to 78.7% after 2 hr. Storage of metacercarial cysts for up to 12 wk at 4 C in Locke's 1:1 solution did not alter cyst viability. In vitro excystation was influenced by structures in the mucoid envelope of the cyst, including a funnel-shaped cavity and the narrow tube. This is the first report of N. attenuatus from North America.