Résumé
@#Abstract: Objective To understand the phenotypic and genetic characteristics of Yersinia pestis strains isolated from Himalayan marmot natural focus area and domestic rat plague focus area in southern China, and provide reference for mastering the pathogenic characteristics of Yersinia pestis of two plague foci. Methods A total of 412 of Yersinia pestis strains isolated from Himalayan marmot plague focus and domestic rat plague focus of southern China were subjected to to sorbitol fermentation assays, virulence factor, different region (DFR) typing, and clustered regularly interspaced palindromic repeats (CRISPR) typing. Results The biochemical types of Y. pestis from the two plague foci showed distinct regional distribution features. Five biochemical phenotypes were identified in Yersinia pestis isolated from Himalayan marmot natural focus area, while only one biochemical phenotype was identified in strains isolated from the domestic rat plague focus of Southern China. Most of the Yersinia pestis isolated from the two plague foci were capable of producing the virulence factors of Fl and PstI. Among the strains from Himalayan marmot focus, 70.53% (201/285) were VW-positive, 75.09% (214/285) were Pgm-positive, 20.00% (57/285) of the strains were Pgm-negative, and 5.26% (15/285) were Pgm mixed-type strains. Among strains from domestic rat plague focus of southern China, 37.80% (48/127) were VW-positive, 29.13% (37/127) were Pgm-positive, 58.27% (74/127) were Pgm-negative, and 12.60% (16/127) were Pgm mixed-type strains. DFR typing revealed 22 genotypes of Y. pestis from the Himalayan marmot plague focus, with the main genotypes being type 5, 7, 8, 10, 19, 32 and 49. All strains from domestic rat plague focus area in southern China belonged to type 9. CRISPR typing revealed that all strains from the Himalayan marmot natural focus were classified into 7 CRISPR gene clusters and 14 CRISPR genotypes, with the main genotypes being G7, G22, G26-a1'and G22-A1'. All strains from domestic rat plague focus area in southern China belonged to CRISPR genotype G30, with the gene cluster being Ca8. Conclusions The phenotypes and genotypes of the Yersinia pestis of Himalayan marmot plague focus are diverse, with an obvious characteristics of geographical distribution. The phenotype and genotype of the Yersinia pestis of domestic rat plague focus of Southern China are single. DFR and CRISPR genotyping methods with phenotypic characteristics can effectively identify the Yersinia pestis isolated from the two plague foci, thereby meeting the needs of identification and traceability research.
Résumé
Objective To study the epidemiological significance of community-structural difference regarding both small mammal and flea communities on Rattus ftavipectus in Dehong and Baoshan areas,Yunnan province,during 1982 to 1996.Methods Methodologies as cluster analysis,communities dominated constitution and species diversity were used for data analysis.Results 75 490 small mammals of 27 species could be divided into three types:Ⅰ.Ruili habitat-communities dominated bv R.flavipectus (54.41%)and Suncus murinus(33.37%): Ⅱ.Longchuan and Yingiiang habitat-communities dominated by R.flavipectus(62.99%),S.murinus(23.25%)and Mus musculus(10.06%);Ⅲ.Baoshan habitat-community dominated by R.flavipectus(48.07%),S.murinus(19.56%)and Crocidura attenuats(14.37%).The captured 61 122 fleas of 11 species on R.flavipectus could be divided into three types: i.Ruili habitat-communities dominated by Xenopsylla cheopis(83.51%)and Lentistivslius ferinus(13.86%);ii.Longchuan and Yingjiang habitats X.cheopis(74.42%)and L.segnis(22.94%); iii.Baoshan habitat-communities dominated by L.segnis(70.62%)and X.cheopis(22.70%).There had been 1471 strains of Y.pestis isolated from the hosts of 7 species and vectors of 5 species in Dehong areas for the ten year period.36 strains of Y.pestis were isolated from host of one species and vectors of 2 species in Baoshan area for ten years.The constitution ratio of R.flavipectus and X.cheopis was higher in Dehong area with average as 58.70%and 78.97%respectively.However.the diversities of species among host and vector communities were low,with average as 1.010 and 0.625.On the contrary,the constitution ratios of R.flavipectus and X.cheopis were lower in Baoshan area.with an average as 48.07%and 22.70%respectively but the diversities of species among host and vector community were higher with the averages as 1.471 and 0.829 respectively.The main dominative flea species from 'group ii'to 'group iii'in the flea community had changed from X.cheopis to L.segnis.Conclusion The species diversity index of host and vector community was higher in Baoshan area,while the constitution ratio of main host and vector community was lower.This findings seemed to be the important factor of the decrease of plague prevalence in Baoshan area.