Objective To analyze the changes in the species and densities of the hosts and vectors of plague in Yuxi, Yunnan province, China, with understanding its epidemic pattern, and to provide scientific evidence for preventing and controlling plague. Methods According to the National Plague Surveillance Protocol and Yunnan Provincial Plague Surveillance Protocol, we collected the surveillance data of the hosts, vectors, pathogeny, and serology from seven counties and two districts of Yuxi from 1985 to 2018. We calculated the densities of plague hosts, rate of flea infestation, and flea index by Excel 2010 software, and estimated the Pearson correlation coefficient between Rattus tanezumi density and Xenopsylla cheopis by R3.5.1 software. Results There were two human plague outbreaks in Yuxi, 1985-2018, involving 11 confirmed cases of bubonic plague (9 cases in Yuanjiang county and 2 cases in Xinping county). A total of 59 331 myomorphous rodents were captured, involving 21 species of 13 genera of 6 families of 3 orders, and the overall capture rate was 3.78% (95% confidence interval:3.75%-3.81%). The dominant species was R. norvegicus, accounting for 57.80% of the total number. A total of 55 137 parasitic fleas were collected, involving 8 species of 8 genera of 5 subfamilies of 4 families. The rate of flea infestation was 28.36%, and the overall flea index was 0.83. The dominant species was X. cheopis, accounting for 46.32% of the total number. Indirect hemagglutination assay detected 11 positive serum samples out of 35 412 samples from host animals, and yielded 100% positive results for 11 serum samples of suspected plague patients. Reverse indirect hemagglutination assay detected 4 out of 7 organ samples from rodent. Four strains of Yersinia pestis were isolated from 89 968 host animals examined, and the test was negative for all 33 028 fleas examined. There was no significant association of R. tanezumi density and X. cheopis (r=-0.09, P=0.658). Conclusion During the recent twenty years, the species and densities of plague hosts and vectors were kept at relatively stable levels, and plague was in a relatively silent period in its epidemic foci. However, the main host R. tanezumi and the main vector X. cheopis are still maintained in a certain number, demanding strengthened plague surveillance and improved surveillance quality for timely detection and prevention of the occurrence and spread of human plague.
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