Analysis of Yersinia pestis detection result of Citellus undulates and parasitic fleas in Gurt, Usu in Xinjiang, 2013

Objective To observe immunological and bacteriological dynamic and distribution of Yersinia pestis in Citellus undulates in Gurt plague natural focus in Usu, Xinjiang in 2013. Methods In the focus,Citellus undulates was captured with cram frame and blood from heart was collected and serum was isolated from June to August 2013. Indirect hemagglutination test (IHA) and enzyme-linked immunosorbent assay (ELISA) were taken to detect F1 antibody against Yersinia pestis of Citellus undulates, and the accuracy of two methods was conducted. Parasitic fleas were collected and classified. Yersinia pestis was isolated with four-step method (microscopic examination, cultivation for Yersinia pestis, bacteriovirus test and animal experiment) from liver, spleen of mice and parasitic fleas. Results Totally 436 Citellus undulates were captured and 2 801 parasitic fleas were collected. Positive rate of F1 antibody was 19.0% (83/436) and 4.4% (19/436) by ELISA and IHA, geometric mean titer (GMT) was 1∶26.92 and 1∶23.17, respectively. The positive rate and GMT of ELISA was higher than IHA (χ2 = 45.44,t = 1.96,P < 0.01 or < 0.05). The positive rate of F1 antibody was 20.2% (38/188), 25.9% (33/127) and 9.9% (12/121) from June, July to August, respectively, and the difference between months was statistically significant (χ2 = 10.67,P < 0.01). Totally 32 strains of Yersinia pestis were isolated. From June to August, the isolated strains were accounted for 81.3% (26/32), 12.5% (4/32) and 6.3% (2/32), respectively, the difference between months was statistically significant (χ2 = 20.60,P < 0.01). The ratio of strains isolated from 3 kinds of samples was 56.3% (18/32) of the fleas, 25.0% (8/32) of self-dead rodents and 18.8% (6/32) of the captured rodents, the difference between samples was statistically significant (χ2 = 18.46,P < 0.01). Conclusions ELISA is better than IHA for detecting sera F1 antibody, and testing accuracy can be improved by combination of the two methods. Strain detection rate is higher in June, and positive rate of self dead rodents is higher than that of captured rodents and fleas. More attention should be paid to strains isolation from the fleas in plague surveillance. Searching for self dead rodents is an effective way for strains isolation. Key words: Citellus undulates; Parasitic fleas; Yersinia pestis; Antibodies