Studies on the fresh water cercariae in Leyte Island, Philippines. I. Collection of snails.

During the past two years of 1975 and 1976, approximately sixteen thousand specimens of fresh water snails were examined for the presence of cercariae in Leyte Island, Philippines. These snails comprised about 14 species belonging to 7 families, and ultimately 43 species of cercariae were found, namely, 6 species from Oncomelania quadrasi, 13 species from Thiaridae, 9 species from Viviparidae and Pilidae, 8 species from Planorbidae, and 7 species from Lymnaeidae and Bulinidae. As a total, out of 15,925 snails examined, 761 or 4.78% were found infected with cercariae. Up to the present, 22 species of cercariae had been reported from the Philippines, and almost all of them are from Luzon Island only. Therefor, except for the cercaria of Schistosoma japonicum, all of the cercariae in the present study are new discoveries, and most of them are considered as new species. In this paper, the historical review on the cercarial study in the Philippines was made first, then dates and localities of snail collection in the present study were shown in details with some map and table, and general method of cercarial observation was described for the benefit of succeeding reports of this series.