As little as a single S. japonicum or S. mekongi egg (Fig. 2) mixed artificially in 100 mg of uninfected mouse or rat feces could be clearly detected. Similarly, a single S. japonicum or S. mekongi cercaria inoculated into an aliquot derived from 10 pooled non-infected N. aperta or O. nosophora snail samples could be detected. No fluorescence signal was detected when evaluated with the defined DNA controls (1 μg) other than S. japonicum and S. mekongi (see Materials and Methods).