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ObjectiveTo analyze the community structure and dynamics of parasitic fleas on the body surface of host animals and nested fleas in different seasons in the natural foci of wild rat plague in Yulong County，Yunnan Province， to explore the relationship between seasonal fluctuation of fleas and the prevalence of plague among animals， so as to provide evidence for plague prevention and control in the natural foci. MethodsNanxi Village， Huangshan Town， the core area of plague epidemic in Yulong County， was selected as the monitoring sample area in December 2019 （winter）， August 2020（summer）， October 2020（autumn） and March 2021（spring）. Host animals were captured by rattrap at night and rat nests were excavated for collecting parasitic fleas on host animals and rat nest fleas in different seasons. Excel 2010 and SPSS 26.0 software were used to analyze the data， and Chi square test was used to compare the rate. Community ecological indicators were used to analyze the community structure and species diversity of the host animals and their parasitic fleas. ResultsA total of 355 vector fleas were captured， belonging to 7 species of 5 genera in 2 families. 441 small animals were captured and 138 rat body fleas were detected with the flea infection rate of 14.51% and the flea index 0.31. 96 effective rat holes were excavated and 217 fleas were detected with the flea infection rate of 35.42% and the flea index 2.26. Among the four seasons， the flea infection rates of rat body and rat nests were higher in summer and winter， showing a significant difference in general （χ2=15.851， P<0.01； χ2=16.398， P<0.01）. The dominant species of flea community were Ctenophthalmus quadratus， Stenischia humilis， Neopsylla specialis and Frontopsylla spadix， with a dominance index of 0.434， 0.254， 0.180 and 0.110， respectively. The diversity and evenness of rat body fleas showed a distribution characteristic of decreasing， increasing and then decreasing again with season changes， and both were the highest in spring， while the ecological dominance showed an opposite trend. The diversity and evenness of rat nest fleas showed a distribution characteristic of increasing first and then decreasing in summer， autumn and winter， with the highest in autumn， while the ecological dominance was diametrically opposite. ConclusionThe fleas community structure is relatively stable in Yulong County， but the number of species in the community is unevenly distributed by seasons， and the status of dominant species is prominent. Local authorities should carry out timely preventive deratization and depulization measures according to the results of daily monitoring， so as to effectively avoid the prevalence and spread of plague among animals in plague foci.
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Objective:To study the basic situation of Yunnan Province Suncus murinus carrying plague phage and to explore its epidemiological significance. Methods:From 2015 to 2018, a survey of plague host animals was carried out in 10 investigation sites in the historical plague foci, new plague foci (after 1982) and stubborn plague foci of domestric mouse in Yunnan Province. The plague phage was isolated and cultured from the intestinal specimens of Suncus murinus. The growth of plaque was observed by double-layer plate method, and the morphology and structure of plague phage were observed under electron microscope. At the same time, intestinal samples were taken to detect the structural gene caf1 of F1 antigen of Yersinia pestis. Results:In this study, a total of 157 Suncus murinus were captured and 16 strains of plague phage were isolated, with a total isolation rate of 10.19%. There was no difference in plague phage isolation rate between historical plague foci (10.00%, 1/10) and stubborn plague foci (16.22%, 12/74), new plague foci (4.11%, 3/73, χ 2 = 0.00, P = 0.965; Fisher test, P = 1.000). However, there was a difference in plague phage isolation rate between stubborn plague foci and new plague foci (χ 2 = 5.88, P = 0.015). There was no significant difference in the isolation rate of plague phage among different sex, growth period and habitat ( P > 0.05). The plaque morphology of the isolated plague phage was diverse, of which four strains were myotavirus phages; and all samples were negative for F1 antigen structural gene caf1. Conclusions:Suncus murinus is widely distributed in the domestic mouse plague foci in Yunnan Province, and the animals carry a certain number of plague phage. Regular surveillance of Suncus murinus and their plague phage has a certain guiding significance for the surveillance and early warning of plague in Yunnan Province.
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Objective:To investigate and determine the epidemic scope of plague natural foci in Yulong County of Yunnan Province, and to assess its epidemic risk, so as to providing basis for monitoring, prevention and control of plague.Methods:In 2017, 2 - 3 natural villages were selected from 8 villages and towns in Yulong County according to geographical landscape, altitude, population and area. During October and November, small mammal hosts and their parasitic fleas were captured by the night trap (cage) method, Yersinia pestis was isolated from host animal organs, and plague F1 antigen and antibody were detected by colloidal gold test. Plague specific antigen was detected by reverse indirect hemagglutination test (RIHA) in self-dead small mammals. Animal serum from dogs, cats and mice were collected for detection of plague F1 antibody by indirect hemagglutination test (IHA). Results:A total of 1 019 host animals including self-dead small mammals were collected, belonging to 22 species, 12 genera, 6 families, 4 orders. Among them, 1 016 small mammals were captured by tools and 996 were outdoors, with the capture rate of 25.28% (996/3 940). The dominant species of small mammals outdoors were Apodemus chevrieri, Rattus (R.) rattus, Eothenomys miletus and Crocidura attenuate, which accounted for 30.32% (302/996), 22.09% (220/996), 17.37% (173/996) and 12.35% (123/996). The common species were Niviventer confucianus, R.nitidus and R.norvegicus, which accounted for 8.13% (81/996), 4.02% (40/996) and 1.81% (18/996). A total of 20 small mammals of 9 species were captured indoors in the residential area, and the capture rate was 1.11% (20/ 1 800). The dominant species were R.norvegicus, R.nitidus and Mus musculus, which accounted for 30.00% (6/20), 25.00% (5/20) and 10.00% (2/20). Eighteen small mammals of 8 species were infected with 67 parasitic fleas, belonging to 5 species, 5 genera, 3 families. The total flea infection rate was 1.77% (18/1 019) and the total flea index was 0.070. Among them, 49 parasitic fleas from 4 small mammals of 3 species were collected indoors. The flea infection rate was 19.05% (4/21) and the flea index was 2.333. Leptopsylla segnis had the highest flea infection rate of 9.52% (2/21) and flea index of 0.571. Ctenocephalides felis had the highest flea index of 1.571 and flea infection rate of 4.76% (1/21). They were the main flea species on the body surface of small mammals in residential areas. There were 14 small mammals infected with parasitic fleas outdoors, and 18 fleas in 5 species were collected with flea infection rate of 1.40% (14/998) and flea index of 0.018. Among them, Leptopsylla segnis had the highest flea infection rate was 0.50% (5/998) and the flea index was 0.005. The flea infection rate of Neopsylla specialis specialis was 0.40% (4/998), and the flea index was 0.004. Ctenophthalmus quadratus had the highest flea index of 0.007, and the flea infection rate ranked the third with 0.30% (3/998). The flea infection rate and flea index of Frontopsylla spadix spadix were the lowest, which were 0.20% (2/998) and 0.002, respectively. Ctenophthalmus quadratus, Leptopsylla segnis and Neopsylla specialis specialis were the dominant parasitic fleas on the surface of outdoor small mammals. A total of 419 indicator animal sera were collected, including 402 dog sera. One of them was positive by IHA, with a positive rate of 0.25% (1/402). Seventeen serum samples were collected from cats and mice, and IHA test results were negative. Yersinia pestis was isolated and cultured from the organs of small mammals and the detection of Yersinia pestis by colloidal gold test was negative. RIHA test of self-dead small mammals was negative. Conclusion:A plague indicator animal positive spot is newly found in the plague natural foci in Yulong County, and the plague epidemic monitoring, prevention and control in this region should be strengthened.
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Objective:To investigate whether the squirrels in Yunnan Province carried Yersinia pestis phages and their epidemiological significance. Methods:From 2015 to 2018, plague host animals were investigated in five of Yunnan plague foci and non-plague foci. The spleen, liver and intestinal specimens of the squirrels captured in the investigation were taken and stored at low temperature for later use. Intestinal specimens with PBS solution, were filtered by 0.22 μm and added to LB liquid medium containing 100 μl suspension of plague vaccine strain (EV76) and then oscillated in a constant temperature gas bath at 28 ℃ and 220 r/min for 18 to 24 h. The double-layer plate method was used to isolate and observe the growth of plaque. The morphology and structure of Yersinia pestis phages were observed under electron microscope. Meanwhile, spleen, liver and intestinal specimens were taken for detection of Yersinia pestis specific marker gene caf1. Results:A total of 10 squirrels were captured (8 Callosciurus erythraeus and 2 Dremomys pernyi), and four Yersinia pestis phages were isolated (2 in Callosciurus erythraeus and 2 in Dremomys pernyi). Two were isolated from non-plague foci (Yongshan County), two from house rats plague foci (Mile County and Xinping County), and none was isolated from wild radents plague foci (Jianchuan County and Eryuan County). By naked eye observation, two bacteriophages from the plague foci produced transparent plaques and grew well, while two bacteriophages from non-plague foci produced translucent plaques and with poor growth. By electron microscopy, these Yersinia pestis phages were of typical Myoviridae family, their head diameter was about 40 nm, muscle tail was about 120 nm, and tail filament cluster was slightly visible at the end of muscle tail. And all the 10 samples of squirrels were negative of plague-specific caf1 gene. Conclusions:The proportion of plague phages carried by Yunnan squirrels is relatively high. Although the detection of caf1 is negative. Squirrels may be a carrier of plague transmission due to the existence of Yersinia pestis phages.
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Objective To evaluate the effect of schistosomiasis control in Yunnan Province since achieving the transmission control standards,so as to provide the evidence for formulating the next prevention and control strategy. Methods The schistoso-miasis epidemic monitoring reports,annual reports,relevant information about Oncomelania hupensis snails,and schistosomiasis patient conditions were collected and analyzed for epidemic condition and characteristics of schistosomiasis in Yunnan Province from 2009 to 2012. Results The various epidemic monitoring indicators all decreased. In 2012,compared with 2009,the preva-lence reduced by 33.33%after correction;the number of villages with schistosomiasis patients reduced by 55.56%;the adjusted positive rate of livestock stool tests reduced by 45.45%;the number of villages with infected cow reduced by 42.25%;the actual area with snails reduced by 13.58%;the density of living snails reduced by 25.66%,and no schistosome infected snails were found in 2012. Conclusion There still exist schistosome infections in human and animals in some local areas of Yunnan Prov-ince,and it is difficult to achieve the standard of schistosomiasis transmission interrupted in a short period.