Epidemic Distribution And Genome Evolution Of Shigella In My Country

Shigellosis caused by Shigella is the most widely distributed, highest incidence of intestinal infectious disease, and so far, no effective vaccines are aviable. Therefore, it is still a major global public health threat. Shigella bacteria are serologically grouped into four species (S. dysenteriae, S. flexneri, S. boydii and S. sonnei), and each exhibits unique epidemiological characteristics. For instance, S. sonnei is the most common species found in developed countries, while S. flexneri is the predominant species in developing countries. Previous study showed that, in the1990s,S. flexneri are responsible for86%of shigellosis in China,and the predominant serotype is S. flexneri2a. However, no data are available for the causative species and serotypes of shigellosis in China’s mainland during the past decade.A total of131eligible articles were analyzed in this study. Meta-analysis showed that S. flexneri (76.2%,95%Cl,73.7%-78.5%) and S. sonnei (21.3%,95%Cl,19.0%-23.7%) were the two major causative agent of shigellosis in China’s mainland during2001-2010. Stratified analyses showed that a lower rate of S. flexneri cases and a higher rate of S. sonnei cases were observed in studies from the top10economic provinces as compared to other provinces, indicating the differences in the proportions of the two Shigella species were likely associated with local economic status. This study systematically reviewed the status of circulating species/serotypes of Shigella in China’s mainland during the past decade, and provided valuable information for the shigellosis prevention and control of China. In addition, it revealed the potential association between dominant species and local economy for the explanation of the epidemiologic features of Shigella.In an attempt to seeking genomic phylogeny of the predominant Shigella species in China, we further collected33clinical S. flexneri samples from seven provinces during the past15years. By using the high-throughput sequencing technology, we made a phylogenomic analysis of the S. flexneri clones circulated in China. We estimated a genome-wide substitution rate of9.2×10-7(95%HPD,8.9×10-7-9.5×10-7). Majority of the currently circulating S. flexneri serotype2a strains were recently evolved from a single clone since1990s, and they were phylogeneticly distinct from the widely used reprentative strain301(isolated in the1980s). Therefore, genomic studies on the currently circulating clone of S. flexneri are required to further elucidate the characteristics and evolutionary pattern of Shigella in China.