Detection of bird schistosomes in lakes by PCR and filter-hybridization

Many lakes around the world are contaminated with bird schistosome cercariae, which penetrate into human skin, causing an itching dermatitis called "swimmers' itch." Bathers could be forewarned from exposure to the larvae and ecological examinations could be performed, when a sensitive method to detect the parasites in aquatic systems, where lots of organisms hinder microscopic examinations, would be available. For this purpose we cloned, sequenced, and analyzed a 396bp tandem repeated DNA sequence from Trichobilharzia ocellata (ToSau3A), and employed it for developing molecular detection assays. It hybridized with less than 100pg DNA from different Trichobilharzia species (T. ocellata, Trichobilharzia franki, and Trichobilharzia regenti), but not with 10ng DNA from other related or sympatric trematodes. A PCR assay, amplifying this sequence with the same specificity, detected 100fg T. ocellata DNA, 1 cercaria in 0.5g plankton, and 2 cercariae in 0.5g host snail tissues.