Objective To analyze the epidemic tendency of Microtus fascus plague during 2000-2008 in Sichuan province. Methods To investigate the plague each year according to "overall Plan of the Plague in the Whole Nation" and "Surveillance Program of Sichuan Province Plague". Results There were plague epidemic from 2000 to 2008, with the average density as 312.41/ha. 42.57% of the Microtus fuscus were infected by body Fleas. The Fleas Index was 0.88 and the Index for nest Fleas of Microtas fuscus was 55.89. Six kinds of animals were infected by not only the Microtus fuscus but also herd-dog, sand fox, Tibetan sheep, domestic cats and Cricetulus longicaulatus as well. The positive rate of live Microtus fuscus was 0.32% but 22.99% in the dead Microtus fuscus. The overall positive rate on serological test was 6.70%. There were 4 Sections, 11 species and 19 kinds Fleas identified and carrying 3 kinds of fleas, Callopsylla sparsilis, Amphipsylla tntua tutua and Rhadinopsylla dahurica vicina, with the overall infection rate as 0.054%. Conclusion Plague among Microtus fuscus showed a continuous epidemic in Sichuan province during 2000-2008.

Objective To analyzed the variant information on the indices regarding fleas from natural foci of Microtus plague in Sichuan epidemic area during 2000 to 2008.Methods Statistical and analytical methods were used on the surveillance data regarding Microtus fuscus plague.Results There were 19 flea species identified and the share of Callopsylla sparsilis was 62.79 percent while the share of Amphipsylla tuta tuta was 30.90 percent on Microtus fuscus plague.The infection rate of fleas and the flea index were the highest in October and the lowest in December and March.Species as Callopsylla sparsilis,Amphipsylla tuta tuta and Rhadinopsylla dahurica vicina could naturally infect the Yersinia pestis.Conclusion Microtus fuscus plague could become epidemic when animals and flea species were infected.We should emphasis on plague monitoring program so as to prevent the occurrence of the disease.

Objective To explore the existence of natural loci on Marmota himalayana plague in Sichuan province and to provide basis for prevention and control of the disease. Methods Both epidemiological investigation and laboratory tests were used to provide the host animal and fleas of the vectors with Yersinia pestis carriers. Results 30 species of animals were found to belong to 10 orders. Ochotona curzoniae and M.himalayana were the most common ones while 7 species of the fleas belonged to 7 genera and 3 families. M.himalayana was the main reservoirs while Callopsylla dolabris and Oropsylla silantiewi served as vectors. The 13 Y.pestis were identified from 43 Marmota samples. 8 samples were identified under IHA, with the highest titer of herding-dogs serum as 1 : 10 240. 19 samples were F1 antigen positive using RIHA and the highest titer of M.himalayana serum was 1:409 600. The major foci was 4545 km2, distributed at Dege county in Sichuan province. Conclusion We have confirmed the existence of natural foci on M. Himalayana plague in Sichuan province.

Objective Throush identify biochemical characteristics and virulence factors of 2 strains suspected Yersinia pestis(Y.pestis)isolated from the dead Marmota himalayana(M.himalayana)to confirm the nature epidemic focus in Dege County,Sichuan Province.Methods Y.pestis was analyzed by specific staining and shape,culturing characteristics,splitting-test by bacteriophage,test of biochemical characteristics and glycolysis ability,virulence factors,virulence,nutritional requirement,plasmid,genetic test and genetic type. Results The tested strains were Gram staining bacilus.The main biochemical characteristics were Arabinose(+)、 Rhamnose(-),Maltose(+),Melibiose(-),Glycerol(+),Denitrification(+).The virulence factors with FI+.VW+, Pgm+,Pst I+;and with the common 6.0×106,45.0×106,65.0×106 plasmids,also with the virulence-relative plasmid gene.Both their absolutely lethal dose(LD100)in mice were 50 bacteria.The nutritional requirement appeared which were depended on Phenylalanine and Methionine.With the Genomovar 5 genotype characteristics of M.himalayana plague foci of Qinghai-Tibet plateau.The difference between tested strains and Yersinia pseudotubercuosis on the 3 different culture medium was obvious.The tested strains had a Y.pestis' specific 3a fragment,Pst I and FI-Ag,at 22 ℃,the strains could be split by bacteriophage completely.Conclusions According to the diagnostic criteria of plague in China,the 2 suspected strains isolated from Dege County,Sichuan Province ale confirmed as Y.pestis.both with powerful virulenceand with the characteristics of the Y.pestis of M.himahtyana in Qinghai-Tibet plateau plague natural focus.