Objective:To explore the biochemical characteristics, virulence factors and other phenotypes of the strains of Yersinia pestis isolated in Jianchuan County Yunnan Province in 2017, and to analyze the nature and source of the new plague epidemic. Methods:Three strains of Yersinia pestis (JC109 rat, JC109 fleas and JC113) isolated from Daqing Village, Jinhua Town, Jianchuan County, Dali Prefecture, Yunnan Province in 2017, and 2 associated strains of Yersinia pestis (LJ01 in Yulong County, Lijiang City and LJ04 in Gucheng District of Lijiang City), 5 control strains ( Yersinia pestis JC1332, LJ485, BN2636, EV-76 and Yersinia pseudotuberculosis PST-1), preserved by the Central Laboratory of Yunnan Institute for Endemic Disease Control and Prevention were collected. The biochemical characteristics and ecotypes of Yersinia pestis were analyzed by using arabinose, rhamnose, denbiose, maltose and glycerol fermentation experiments and nitrate reduction experiments. Combining pigmentation factor (pgm), virulence antigen (VW) detection and nutritional requirements test results to determine the virulence of Yersinia pestis. Results:The Yersinia pestis JC109 rat, JC109 fleas and JC113 all fermented arabinose, maltose and glycerol, but didn't ferment rhamnose and denbiose; and the nitrate reduction test was positive. The ecological type belonged to the Himalayan Marmot plague strain of Qinghai-Tibet plateau. The virulence factors pgm and VW tests were positive, the nutritional requirement type was phenylalanine dependent and glutamate independent. It had the same phenotype as the LJ01 strain, but different from the JC1332 strain. Conclusions:The newly isolated strains in Jianchuan County are the same as those in the Lijiang Yulong wild rodent plague foci. This outbreak may have been imported from the Lijiang Yulong wild rodent plague foci to the south.

Objective To investigate whether the host animals of Yulong plague foci carry Yersiniapestis phage,and to identify isolated plague phage.Methods Rodent specimens were collected in 5 villages of Yulong plague foci in spring and autumn of 2016,respectively.Vaccine strain EV76 was used as breeding bacteria.Phage was isolated from the specimens by double-layer plate method and plaque morphology was identified.Results ① Totally 409 samples collected in spring failed in phage isolation.A total of 40 of Yersinia pestis phages were isolated from 444 samples in autumn,and the total isolation rate was 9.01％ (40/444).② The Yersinia pestis phages were isolated in all of 5 villages,and the isolation rate was of no significant difference (x2 =5.055,P ＞ 0.05).③ Of the 40 strains of phage,37 strains were isolated from Apodemus chevrieri,2 strains from Eothenomys Miletus and 1 strain from Crocidura Dracula.④Based on the appearance,the plaque of the phage was divided into three:large (diameter 1.5-2.5 mm),middle (0.5-＜ 1.5 mm) and small (＜ 0.5 mm).Conclusion There is a higher number of plague phage in the host animals of the plague foci in Yulong County of Yunnan Province,the plaques are diverse in morphology,and their biological characteristics may be polymorphic.

Objective:To evaluate the practical value of the up-converting phosphor technology (UPT) in the field fast detection of plague, and to provide scientific basis for its promotion and application in the field work of plague monitoring.Methods:In September 2020, a total of 116 samples (including 4 samples for epidemic determination) were collected at the plague epidemic site in Menghai County, Yunnan Province, including 24 human blood and lymphatic fluid samples, 83 rat liver and muscle samples, and 9 rat blood samples. In March 2023, a total of 12 rat liver and muscle samples were collected from Lijiang City for on-site monitoring of plague outbreak (all of them were outbreak determination samples). All of the above samples were tested for Yersinia pestis antibody and antigen using the up-converting phosphor technology. At the same time, haemagglutination test, real-time fluorescence quantitative PCR and bacterial culture were conducted to compare the detection process and results of different experimental methods, the advantages and disadvantages of the up-converting phosphor technology for detecting Yersinia pestis were analyzed, and the feasibility of using this detection method in the field of plague epidemic monitoring was judged. Results:The plague epidemic samples site in Menghai County, Yunnan Province were tested by up-converting phosphor technology, and 19 samples were found to be positive for Yersinia pestis (1 antibody-positive and 18 antigen-positive). Among the samples determined, 4 samples with positive results of Yersinia pestis were detected by up-converting phosphor technology, and the results of their haemagglutination test, real-time fluorescence quantitative PCR and bacterial culture were all positive. All samples from Lijiang City were tested by up-converting luminescence technology, two samples were positive for Yersinia pestis(antigen-positive). The results of haemagglutination test and real-time fluorescence quantitative PCR were positive, and one sample was positive for bacterial culture. The time required for up-converting phosphor technology, haemagglutination test, real-time fluorescence quantitative PCR, and bacterial culture were 0.5, 4.0, 2.5 and 72.0 h, respectively. Conclusions:The results of Yersinia pestis detection by up-converting phosphor technology are basically consistent with the results of haemagglutination test, real-time fluorescence quantitative PCR and bacterial culture, but the time used is relatively short. When the number of samples is large, this method can be used preferentially in the field work of plague outbreak monitoring, which can quickly complete the preliminary judgement of plague outbreak, and save a lot of time and economic resources for the next step of plague prevention and control work.

Objective: To investigate whether plague phages were present in the indicator animals of plague foci in Yunnan Province, and to explore their epidemiological significance. Methods: Anus swabs were collected from indicator animals (dogs or cats) of the 41 plague affected villages in 26 towns of 10 cities (counties, districts) of Yunnan plague foci from November of 2015 to March of 2018. The Yersinia pestis phages were isolated by plague vaccine strain EV76. The isolation of plague phages from different plague foci, the isolation of plague phages from different canine species (cats), the polymorphism of plaque and the host spectrum of phages were analyzed. Results: A total of 1 014 indicator animals (1 003 dogs and 11 cats) were studied, and 102 of plague phages were isolated. In the 10 cities (counties, districts), plague phages were only not isolated from Lancang County, and the plague phages were isolated from the other 9 cities (counties, districts). The separation rates from high to low were as follows: Yiliang County (21.00%, 21/100), Menghai County (19.23%, 25/130), Yuanjiang County (11.63%, 10/86), Midu County (11.50%, 13/113), Wenshan County (10.10%, 10/99), Mile Country (7.07%, 7/99), Lianghe County (6.67%, 7/105), Baoshan Longyang District (4.90%, 5/102) and Gengma County (3.81%, 4/105). Of the 102 plague phages, 75 were isolated from the native dogs (Chinese pastoral dogs, 9.32%, 75/805), 20 from the pug dogs (13.70%, 20/146), 5 from the wolf dogs (17.24%, 5/29), 1 from Samoye (1/4) and 1 from Alaska dog (1/2). The plaque of the phage was divided by five appearance of complete lysis (the plate was clear), large (2.5-4.0 mm), big (1.5-< 2.5 mm), middle (0.5-< 1.5 mm) and small (< 0.5 mm). The representative phages were all of the Myoviridae family. Most of the phages could lysis the strains of Yersinia pestis, and some phages could lysis Shigella and type 5 Yersinia pseudotuberculosis (PST5). Conclusion The plague phages are present in the plague foci of Yunnan, and the phages are polymorphic.