Investigation For Coxiella Burnetii Infection Of Wild Small Mammals In The Plague Natural Foci Of Western Yunnan

ObjectivesTo determine the infection status and differences for Coxiella burnetii of wild small mammals in the Plague Natural Foci of Western Yunnan,analyze the genetic polymorphism of Coxiella burnetii,offer baseline level for the infection of Coxiella burnetii of wild small mammals,evaluate the risk of occurrence and epidemic of Q fever in wild small mammals and humans,and provide scientific basis for the effective prevention and control of Q fever.MethodsFrom December 2015 to October 2016,the research group used the night trapping method to catch wild small mammals and obtained 2524 liver and spleen samples in different seasons,different elevation gradients and different geographical landscapes in Yulong,Jianchuan and Lianghe.DNA was extracted from samples of the liver and spleen by using magnetic beads method.This experiment adopts the nested PCR to amplify conservative sequence ComⅠ of Coxiella burnetii,which was used for molecular biological detection.Chi-square test and Exact probability method were used to compare and analyze the prevalence rates of Coxiella burnetii infections of wild small mammals from the aspects of the species,gender,habitat,altitude gradient,and season of different foci with the application of Excel 2010 and SPSS 17.0 software.The homology of positive DNA amplification sequences of Coxiella burnetii was analyzed and the phylogenetic tree was constructed by using software Megalign and MEGA7.0 to explore its evolutionary origin.Results1.The dection for Coxiella burnetii of wild small mammals included 2524 DNA samples in the plague natural foci of western Yunnan,23 positive samples were tested from 2524 DNA samples,the positive rate of Coxiella burnetii was 0.91%,and the wild small mammals were tested positive for Coxiella burnetii including Apodemus chevrieri 0.64%(5/780),Apodemus draco 2.19%(6/274),Rattus tanezumi 0.54%(1/184),Niviventer confucianus 3.64%(2/55),Mus pahari 1.37%(1/73),Eothenomys miletus 1.03%(5/485),Suncus murinus 4.08%(2/49),Hylomys suillus 1.96%(1/51).2.The positive rate of Coxiella burnetii infection of wild small mammals was 0.34% in the Yulong plague natural foci,the positive rate of Coxiella burnetii infection of wild small mammals was 1.46% in the Jianchuan plague natural foci,and the positive rate of Coxiella burnetii infection of wild small mammals was 0.80% in the Lianghe plague natural foci.The positive rate of Coxiella burnetii infection of wild small mammals in the Jianchuan plague natural foci was higher than that in the Yulong plague natural foci(P<0.05).3.The positive rate of Coxiella burnetii infection of wild small mammals in the altitudinal gradient of more than 2450 m was higher than that of below 2450 m in the Jianchuan plague natural foci(P<0.05).4.The positive rate of Coxiella burnetii infection of wild small mammals in spring was higher than that in autumn in the plague foci of western Yunnan(P<0.05).The positive rate of Coxiella burnetii infection of wild small mammals in the winter was higher than that in other seasons in the Yulong plague natural foci(P<0.05);and the positive rate of Coxiella burnetii infection of wild small mammals in the spring was higher than that in the summer and winter in the Jianchuan plague natural foci(P<0.05).5.There was no statistical difference in the infection of Coxiella burnetii in different kinds of wild small mammals(P>0.05);there was no significant difference in the infection of Coxiella burnetii between male and female small mammals(P>0.05);there was no statistical difference in the infection for Coxiella burnetii of wild small mammals in different habitats(P>0.05);there was no statistical difference in the infection for Coxiella burnetii of wild small mammals in different altitude gradient of Yulong and Lianghe plague natural foci(P>0.05);and there was no statistical difference in the infection for Coxiella burnetii of wild small mammals in different seasons in the Lianghe plague natural foci(P>0.05).6.Homology and phylogenetic analysis have proved that sequence for ComⅠ of Coxiella burnetii in wild small mammals in western Yunnan plague foci was highly homologous to the related reference sequence of Genebank,whereas,the gene similarity on Coxiella burnetii Com I sequences of some samples from wild small mammals in Yulong plague natural foci was different from those of other regions,and there was no significant difference among the rest of samples.Conclusions1.The positive rate of Coxiella burnetii infection in the plague natural foci of western Yunnan was low(0.91%),and the species of wild small mammals tested positive of Coxiella burnetii infection were Apodemus chevrieri,Apodemus draco,Rattus tanezumi,Niviventer confucianus,Mus pahari,Eothenomys miletus,Suncus murinus and Hylomys suillus.2.The positive rate of Coxiella burnetii infection of wild small mammals in Jianchuan plague natural foci was higher than that in Yulong plague natural foci.The positive rate of Coxiella burnetii infection of wild small mammals in the altitudinal gradient of more than 2450 m was higher than that of below 2450 m in the Jianchuan plague natural foci.3.The positive rate of Coxiella burnetii infection of wild small mammals in the plague natural foci of western Yunnan in the spring was higher than that of the autumn.The positive rate of Coxiella burnetii infection of wild small mammals in Yulong plague natural foci in the winter was higher than that of other seasons,while the positive rate of Coxiella burnetii infection of wild small mammals in Jianchuan plague natural foci in the spring was higher than that of the summer and winter.4.ComⅠ gene segment of Coxiella burnetii in the wild small mammals in the plague foci of western Yunnan presented highly conservative popularity and distribution;the gene similarity of Coxiella burnetii of some samples of wild small mammals in Yulong plague natural foci was different from that of other regions.