Genetic diversity and selection of three nuclear genes in Schistosoma japonicum populations

Background: The blood fluke, Schistosoma japonicum still causes severe disease in China, the Philippines and Indonesia. Although there have been some studies the molecular epidemiology of this persistent and harmful parasite, few have explored the possibility and implications of selection in S. japonicum populations. Methods: We analyzed diversity and looked for evidence of selection at three nuclear genes (SjIpp2, SjFabp and SjT22.6) in 13 S. japonicum populations. Results: SjT22.6 was found to exhibit high nucleotide diversity and was under positive selection in the mountainous region of mainland China. As a tegumental protein, its secondary and tertiary structure differed between S. japonicum strains from the mountainous and lakes regions. In contrast, SjIpp2 and SjFabp had relatively low levels of nucleotide diversity and did not show significant departure from neutrality. Conclusions: As a tegument-associated antigen-encoding gene of S. japonicum, SjT22.6 has high nucleotide diversity and appears to be under positive selection in the mountainous region of mainland China.