Pathogenic ecology and epidemiological significance of Tibetan-sheep plague in Qinghai plateau

Abstract

Objective To analyze the pathogenic ecology characteristics of Tibetan-sheep plague in Qinghai plateau.Methods Total 14 Yersinia pestis strains were separated from 1975 to 2009,which were conducted biochemical test,toxicity test,virulence factor evaluation,plasmid analysis,different region (DFR) genotyping,infection spectrum of host and media.Results All the strains' biovars were antique; the ecotype was Qinghai-Tibet Plateau.78.57％ (11/14) of Yersinia pestis strains contained all the four virulence factors-Fr1 (F1),pesticin Ⅰ (Pst Ⅰ),virulence antigen (VW) and pigmentation (Pgm).Toxicity test showed minimum lethat dose (MLDs) were all under 1 000,so these strains were velogenic strains.Each strain contained 3 kinds of plasmid 6 × 106,45 × 106,65 × 106 or 6 × 106,45 × 106,52 × 106.65 × 106 and 52 × 106 had classification significance;strains in Yushu County,Nangqian County and Zhiduo County carried 65 × 106 plasmid,and the ones in Delingha region carried 52 × 106 plasmid.The DFR genotyping showed strains in Yushu County and Zhiduo County were genomovar 5,one strain in Nangqian County was genomovar 5 and the other was genomovar 7,and strains in Delingha region were genomovar 8.Condusions All the strains separated from Tibetan-sheep plague have the characteristics of Qinghai-Tibet plateau plague's pathogen.Tibetan-sheep's participation in plague has developed many new characteristics in Qinghai plague.Therefore,we should strengthen the monitoring of Tibetan sheep plague,especially in the marmot plague-endemic areas. Key words: Plague; Pathogenic ecology; Sheep; Epidemiology