MLVA distribution characteristics of Yersinia pestis in China and the correlation analysis

Two hundred and thirteen Y. pestis strains collected from different plague foci in China and a live attenuated vaccine strain of Y. pestis (EV76) were genotyped using multiple-locus variable-number tandem repeat analysis (MLVA) on 14 loci. A total of 214 Y. pestis strains were divided into 85 MLVA types, and Nei's genetic diversity indices of the various loci ranged between 0.02 - 0.76. Minimum spanning tree analysis showed that Y. pestis in China could be divided into six complexes. It was observed that Microtus strains were different from the other three biovar strains. Each plague focus had its own unique MLVA types.The strains isolated from Yulong, Yunnan province had a unique MLVA type, indicating a new clone group. Our results suggest that Yulong strains may have a close relationship with strains from the Qinghai-Tibet Plateau plague focus.Plague is an infectious disease caused by Yersinia pestis, a naturally occurring bacterium found primarily in wild rodents. It is highly transmissible and brings a high mortality, leading to major public health disasters throughout the history of humanity [1]. In the early 1990s, the incidence of human plague increased significantly [2], with outbreaks occurring in Africa [3] and India [4]. WHO has classified plague as a reemerging infectious disease for the past 20 years, and Y. pestis has been identified as a bioterrorism agent, posing as a significant threat to human health and safety [5]. In November 2005, a natural focus of human plague was discovered in Yulong, Yunnan province, China[6]. In this study, we compared Y. pestis isolated from the Yulong focus to strains from other areas.Y. pestis couldn't be separated by serotype and phage-type, but could be classified into three biovars: Antiqua, Mediaevalis and Orientalis, according to their ability to ferment glycerol and to reduce nitrate as described by Devignat in the 1950s [7]. Recently, a new biovar Microtus was proposed based on whole genome sequencing and genetic