Nuclear and mitochondrial genetic markers highly conserved between Chinese and Philippine Schistosoma japonicum

Geographical isolates of S. japonicum, and particularly isolates from China and the Philippines, were examined at the molecular level for genetic divergence. Sequences from both nuclear and mitochondrial genomes were selected as markers of evolutionary divergence and S. mekongi and S. mansoni were included in the study for comparison purposes. Restriction fragment length polymorphism (RFLP) and PCR-RFLP analysis of the rDNA repeat unit and sequence analysis of the second internal transcribed spacer region (ITS2) within the rDNA repeat and the cytochrome c oxidase I (COI) gene of the mitochondrial genome were performed. No intra-specific variation in S. japonicum was found in the rDNA repeat and only very slight variation was detected within the COI sequence. A survey of the entire genome, using random amplified polymorphic DNA (RAPD) analysis, again showed that Chinese and Philippine S. japonicum are remarkably similar at the DNA sequence level. We were thus unable to obtain direct molecular evidence in support of previous findings, particularly those based on isoenzyme analysis, that a very high level of intra-specific variation exists in S. japonicum.