Evolution and epidemiology of pathogenic Yersinia

Human pathogenic Yersinia species belongs to Yersinia enterocolitica. Yersinia pseudotuberculosis and Yersinia pestis. Recently by using two clock rates E. coli was calibrated, and it was established that the Yersinia common ancestor (nonpathogenic Yersinia) arose 0.42 to 1.87 million years ago, and that Y. enterocolitica and Y. pseudotuberculosis diverged 41 to 186 million years ago. The same analysis established that Y. pestis is a clone which emerged from Y. pseudotuberculosis very recently, i.e., within the last 1,500 to 20,000 years. The three currently existing pathogenic Yersinia species can be separated into two clearly distinct groups based on their clinical and epidemiological features : Y. enterocolitica and Y. pseudotuberculosis on one hand, and Y. pestis on the other. The drastically different modes of transmission, clinical symptoms, and outcomes were observed between these two groups, and also between Y. enterocolitica and Y. pseudotuberculosis. The differences of pathogenicity, reservoir, modes of transmission and history of evolution among these three species influenced their epidemiological features, which were also influenced by the cross protectivity by V antigen. Y. enterocolitica, which is classified into low pathogenicity, is prevalent mainly among domestic animals and can be transported by the trade of food, such as pork, around the world. Y. pseudotuberculosis and Y. enterocolitica serotype 0:8, which have high pathogenicity, are prevalent mainly among wild animals. They might have been transported to Japan from the Asian Continent by the migration of infected wild animals due to the change of climate in the ice age. Three pandemic waves of plague were caused by different biovar of Y. pestis. The spread of plague in the first and the second waves could have been brought about by trade and travel from the focal areas of Y. pestis. The third pandemic wave could have resulted from the marine transportation of. Y pestis-infected rodents at the end of the 19th century. This review will endeavor to explain the relationships between evolution and epidemiology among the three pathogenic species of Yersinia.