Abstract: Objective  To investigate genetic diversity in the elastase gene among eight Schistosoma japonicum populations, and whether natural selection occur.  Methods  S. japonicum populations were collected from the provinces of Anhui（Tongling and Guichi）, Hunan（Yueyang）, Hubei（Shashi）, Sichuan（Xichang）, Yunnan（Eryuan）, Taiwan （Puye） in China, and the Philippines. The elastase gene from different populations was amplified by PCR and then sequenced. Watterson’s θ, Tajima’s π, dN/dS ratio, Tajima’s D and fixation index（Fst） of each population were calculated. The phylogenetic networks based on the elastase gene were constructed by median-joining algorithm.  Results  A total of 73 elestase gene sequences（GenBank No. KF297654-KF297681）were obtained from 8 populations. The sequence analysis indicated that higher genetic diversity was found in the populations from the middle and lower reaches of the Yangtze River（i.e. Tongling City of Anhui, Yueyang City of Hunan）, while there was no genetic variations in Hubei or Philippines populations. The value of Tajima’s D was positive in Hunan population, while negative in the other populations. The dN/dS ratio was higher than 1 in Tongling population, whereas lower than 1 in Taiwan population. Significant genetic differentiations were observed between Taiwan population and other populations.  Conclusion   The genetic diversity of the elastase gene among S. japonicum populations is very high, and a high level of gene flow has been detected among the populations from the middle and lower reaches of the Yangtze River. The S. japonicum elastase gene might have been under a positive selection. The level of genetic divergence is the highest between Taiwan population and others.

Key words: Schistosoma japonicum, Elastase, Genetic diversity, Natural selection