Genetic Diversity Analysis Of Dermacentor Nuttalli Of Inner Mongolia And Identification Of Rickettsia

Objective Dermacentor nuttalli(Acari:Ixodidate),is widely distributed across northern China,Eastern Siberia and Mongolia,and is generally found in arid grassland areas suitable for grazing cattle and sheep.D.nuttalli spreads a variety of pathogens and brings great harms to the health of humans and animals.Therefore,exploring the genetic diversity of D.nuttalli and the infection of Rickettsia in Inner Mongolia Autonomous region is not only helpful to understand the living condition and spreading rules of D.nuttalli,but also clarify the species of Rickettsia in Inner Mongolia.So as to lays an effective theoretical foundation for the distribution,prevention and control of ticks and tick-borne diseases.Methods(1)In this study,16S r RNA,cytochrome c oxidase subunit?(CO?)and internal transcribed spacer 2(ITS2)were used to analyze the population genetic diversity of Dermacentor nuttalli in Ordos,Hohhot,Chifeng and Hulunbuir regions of Inner Mongolia Autonomous region.(2)In this study,the glt A gene and omp A gene fragments of Rickettsia were amplified by PCR to detect the infection of Rickettsia carried by D.nuttalli in four geographical populations in Inner Mongolia.The obtained haplotype reference sequence analysis results of glt A gene and omp A gene,download the sequences of Rickettsia with higher and lower homology respectively to construct a phylogenetic tree,using neighbor-join method and Kimura-2 parameter model.Results(1)There were 16 haplotypes with16S r RNA gene,including 6 shared haplotypes,the haplotype diversity was 0.764,and the nucleotide diversity was 0.05788.There were 37 haplotypes and 9shared haplotypes in COI gene.The haplotype diversity and nucleotide diversity were 0.838and 0.06907 respectively.There were 80 haplotypes and 3 shared haplotypes of ITS2 gene.The haplotype diversity and nucleotide diversity were 0.968 and 0.26746 respectively.Analysis of F_ST value of D.nuttalli using three genes showed that the F_ST value of CO?gene between Chifeng and Ordos were more than 0.15,and the F_ST values of 16S r RNA and ITS2 genes were both less than 0.15.Analysis of molecular variance(AMOVA)on three genes of D.nuttalli indicated that the variation within populations was greater than that between populations.The construction of haplotype network map and phylogenetic tree showed that there was gene communication among different geographical populations,there was no influence of geographical isolation,and the haplotypes of different geographical populations were in a mixed pattern.In the neutral test of the four populations.The Fu's Fs value of CO?was not significant,and the Tajima's D value and Fu's Fs value of 16S r RNA and ITS2 genes were not significant,indicating that there was no expansion recently.The mismatch analysis maps of the three genes of D.nuttalli showed double peaks,which indicated that the population did not expanded recently,which was consistent with the results of neutral test.(2)Among the 408 D nuttalli,207 were infected with Rickettsia,and the total infection rate was 50.74%.Among them,the infection rate in Hulunbuir was the highest(85.14%).The phylogenetic tree of glt A gene showed that haplotypes G1-G7,G9 and R.raoultii are on the same branch,and the haplotypes G8,G10 and R.sibirica are on the same branch.The phylogenetic tree of omp A gene showed that the haplotype O1-O15,O18 and R.raoultii are on the same branch,and the haplotypes O16,O19 and R.sibirica are on the same branch.Conclusion(1)The analysis of16S r RNA,CO?gene and ITS2 gene of D.nuttalli in Inner Mongolia showed high haplotype diversity and high nucleotide diversity(Hd>0.5,Pi>0.005),indicating that this is a large and stable population through evolution.The degree of genetic differentiation of D.nuttalli population is very small,but the population genetic diversity is high,which can adapt to different geographical environment.(2)There are two genotypes of Rickettsia in Inner Mongolia,which are R.raoultii and R.sibirica.