Abstract:

To obtain the single-sex cercaria for relevant research of schistosomiasis a single miracidium or multiple miracidia were used to infect one snail (one-to-one or multiple-to-one models). The released cercaria from each infected snail were used to infect a mouse. Immature adult worms or schistosomula were collected from each infected mouse 3 weeks after infection and the sex of the worms was identified under microscope. The genotype variation was determined by PCR with 6 short tandem repeats (STRs) primers (RRPS, M5A, MPA, 2AAA, MF1 and J5N). Among 4 mice infected with "one-to-one"cercaria, single-sex worms were obtained in all mice, one mouse with female and three mice with male worms. However, among 43 mice infected with cercaria from "multiple-to-one"snails, 19 contained female worms (44.2%), 7 contained male worms (16.3%) and 17 contained mixed-sex worms (39.5%). STR analysis with 6 pairs of microsatellite primers, better than electrophoresis analysis of PCR products, showed the nearly identical genotype for worms collected from "one-to-one" groups and different genotypes for worms collected from "multiple-to-one" groups. Minor genetic variation was detected between single-sex worms collected from "one-to-one" groups possibly due to the mutation(s) occurred during self-reproduction and development in snail. Worms from "multiple-to-one" groups showed significant genetic polymorphism in terms of different STR patterns, even for the single-sex worms compared to those collected from "one-to-one" groups. In conclusion, single-sex cercaria can be obtained by infecting a snail with single miracidium ("one-to-one" model) with nearly identical genotype. Even though the single-sex cercaria are possibly obtained by the multiple-to-one infection model, the genotype is mixed and complicated.

Key words: Schistosoma japonicum, Single-sex cercaria, Miracidium, Snail