Detection Of Rickettsia In Dermacentor Nuttalli And The Effect On Host Genetic Diversity

Dermacentor nuttalli(Acari: Ixodida),is widely distributed and found in Heilongjiang,Jilin,Inner Mongolia,Liaoning,Hebei and other regions in China.And it is considered as a common species in the northern region.As a vector of many pathogens,it threatens the health of human and animal.Rickettsia is a Gram-negative bacterium that is strictly intracellularly parasitic,as a pathogen of vertebrates,it can cause a variety of diseases such as spotted fever,endangering human health and affecting the development of animal husbandry.The tick-Rickettsia relationship provides a theoretical basis foundation for the investigation of the distribution of tick-borne diseases,the control of tick-borne diseases and the analysis of tick population.The main aim of this study is to focus on the identification and diagnosis of Rickettsia at the molecular level and the influence of this relationship on tick.In this study,the 16 S rRNA,ompA and gltA gene fragments of Rickettsia were amplified using PCR.The infection of Rickettsia was detected in the total of 118 tick samples from four different geographical locations including Inner Mongolia,Jilin,Heilongjiang,Hebei.The detection rate of Rickettsia based on the three gene fragments was the same.The number of samples infected with Rickettsia was 63,and the total infection rate was 53.39%(63 / 118).The highest infection rate was recorded for Inner Mongolia with 80%(24 / 30).The infection rate for other locations were 50%(15 / 30),46.42%(13 / 28)and 36.67%(11 / 30),in Hebei,Heilongjiang,and Jilin respectively.The BLASTn comparison results revealed that more than 99% homology of two of the 16 S rRNA genes with R.raoultii.In addition to this,the phylogenetic analysis showed that Rickettsia strains were formed a sister cluster with the R.raoultii strains,suggesting that they are closely related species.Analysis of genetic diversity in Rickettsia population revealed that high haplotype diversity(Hd: 16 S rRNA: 0.70302;ompA: 0.583;gltA: 0.60665)and low level of nucleotide diversity(Pi: 16 S rRNA: 0.00165;ompA: 0.00297;gltA: 0.00249).These indices indicating high genetic variation,diversity,viability and adaptability to the environmental changes in spite of low level of the accumulation of population variation.The population genetic differentiation coefficient among geographical populations of Rickettsia showed that the overall Fst value of the Rickettsia population was more than 0.25,indicating that the genetic differentiation among the geographic populations was high.The AMOVA analysis verified that Rickettsia possesses intra-population variation.Additionally,the genetic structure,the hyplotype network map and phylogenetic tree of Rickettsia strains were analyzed.The results of mixing haplotype of different geographical populations emphasized that there was no clear and obvious clustering based on the geographical pattern.Assessment of three DNA fragments(COI,16 S rRNA,ITS2)of D.nuttalli divided tick population into two groups including infected and uninfected based on the infection of Rickettsia.Subsequently,the analysis of haplotype distribution revealed that these two groups shared a large number haplotypes in the whole population(COI: 64.70%;16S rRNA: 41.17%;ITS2: 60%).Our genetic and population diversity of these two groups indicated that the haplotype diversity(Hd),nucleotide diversity(Pi)and average nucleotide difference(K)of COI gene in the infected group was greater than uninfected group.The genetic diversity of geographical populations of these two groups showed this trend appeared in Hebei and Inner Mongolia regions.Furthermore,the infection of Rickettsia had a certain effect on the genetic diversity of D.nuttalli COI gene but there was not significant difference between two groups.In contrast,this phenomenon was not discovered in the analysis of 16 S rRNA gene and ITS2 gene.The result of FsT value of two given groups of D.nuttalli for ITS2 gene showed ranging from 0.05 to 0.15 in Inner Mongolia and Hebei locations,suggesting a certain level of genetic differentiation between these two groups in these two locations.Moreover,the results of haplotype network map and phylogenetic analysis of two groups of D.nuttalli based on the Rickettsia infection indicated that there was not segregate and independent clustering between these two groups.