Study On Pathogenic Characteristics And Transmission Vectors Of Borrelia Garinii SZ

Borrelia burgdorferi sensu lato, is the causative agent of Lyme disease which is a natural focidisease caused by tick bitting. The microbe survives in a complex enzootic cycle involving tick vectorsbelonging to the Ixodes ricinus species complex and a variety of mammalian hosts, usually smallrodents and birds. The natural infections by B. burgdorferi s.l were recorded from at least40Ixodid tickspecies. Vector competences for transmitting B. burgdorferi s.l were experimentally confirmed for12tick species, such as Ixodes ricinus complex. Molecular analysis indicates that the B. burgdorferi s.l.complex comprises at least20different genotypes. The symptoms and severity of the disease vary in B.burgdorferi genospecies. B. garinii is primarily associated with neuroborreliosis, B. afzelii withacrodermatitis chronic athrophicans and B. burgdorferi s.s is prevalent in Lyme arthritis. Due to thegenetic polymorphisms and antigenic heterogeneity of different genotypes and even pathogenic of thedifferent region isolates within the same genotypes are also quite different. Therefore, as more and morestrains were isolated, it is necessary to study the pathogen vectors and pathogenicity of these isolates,this may play a good reference for the pathogenesis, clinical symptoms, prevention and treatment ofLyme disease.B. garinii is the main genotype found in China which B. garinii SZ was isolated from Dermacentorticks collected in Shangzhi County of Heilongjiang Province. The kinetics of spirochete disseminationand the severity of the disease were evaluated in a murine model, in which the B. burgdorferi B31and B.afzelii BO23were used for comparison. The data obtained by real-time PCR and the histopathologyindicated the correlations of spirochete burden and disease severity in mice tissues in infections causedby B. garinii SZ, B. burgdorferi B31and B. afzelii BO23. The B. garinii SZ strain is highly pathogenicand can trigger multi-system pathological damage in mice.In order to explore the transmission vectors of B. garinii SZ, In the present study, Haemaphysalisqinghaiensis, H. longicornis and Rhipicephalus sanguineus ticks were used to withstand the similarexperiments for analyzing the susceptibly of the tick species to transmit two genospecies of spirochetes.The larva, nymph of H.qinghaiensis, H. longicornis and R. sanguineus ticks could acquire spirochetesafter engorged on rabbits infected by Borrelia garinii SZ or B. burgdorferi B31. However, thecapabilities of the three tick species for maintaining and transmission spirochetes were different. H.qinghaiensis was able to maintain and transmit B. garinii SZ to next stage tick during molting, but not B.burgdorferi B31. Subsequently, the next stage ticks could transmit the pathogen to naive rabbits andmice via feeding. In H. longicornis ticks, spirochetes could not survive posterio to the digestion periodof blood and during the molting process. The nymphs of R. sanguineus were able to maintain andtransmit B. burgdorferi B31to next stage during molting, but not B. garinii SZ. H. qinghaiensis shouldbe considered to be a vector of Lyme disease in Northern China. This experiment suggested thatdifferent genospecies of Borrelia could be transmitted by different tick species.To date, whole-genome sequences have been reported from26B. burgdorferi isolates. To further understand the genomic information and genetic polymorphisms of B. burgdorferi isolates in China, thewhole genome sequence of B. garinii SZ which carries numerous plasmids, both10circular and9linearplasmids. The902,487-bp linear chromosome (28.2%GC content) contains820open reading frames,33tRNAs, and4complete rRNAs. The plasmid cp32-10contains one CRISPR with four repeats.The symptoms and severity of disease varied among B. burgdorferi genospecies. The differences indisease severity in B. burgdorferi B31-and B. garinii SZ-infected mice were particularly significant inthe brain, heart, liver and spleen tissues. Borrelia species possessed plasmids that were required forpathogenesis and essential for mammalian infection. In this study, we investigated the correlationsbetween the plasmid contents, pathogenesis, and tissue tropism. Using specific primers for each plasmid,PCR and real-time RT-PCR were applied to quantify the tissue-specific expression of the plasmidcontents from B. burgdorferi B31-and B. garinii SZ-infected mice. The results suggested that cp26,cp32-9, lp28-2, lp28-3, lp28-4, and lp56might contribute to the tropisms in certain mouse tissues.It is hypothesized that genes differentially expressed between Borrelia isolates encode potentialbacterial factors which might contribute to the disease diversity. In present study highthroughputsequencing technology was used to characterize the comparative transcriptional profiling of B.burgdorferi B31and B. garinii SZ during in vitro culture. A total of731genes were differentiallyexpressed between B. burgdorferi B31and B. garinii SZ isolates, it was found that lipoproteins andpurine transport proteins were important for contributing to the differential transcriptional landscapeobserved in the B. burgdorferi B31and B. garinii SZ isolates. These observations supported thehypothesis that global changes in gene expression were able to drive the differences in pathogenicity ofborrelia. Additionally, this study provided novel information for studying specific mechanisms of targetgenes and their potential usefulness for the diagnosis and control of Lyme disease.The findings revealed the transmission vectors and pathogenic characteristics of B. garinii SZ, andthat the vectors, pathogenicity, tissue tropism, genome and transcriptome of B. garinii SZ comparedwith the international standard strains (B. burgdorferi B31) have significant differences. However thepathogenesis remains to be further explored. Although H. qinghaiensis can confirm to transmit B.garinii SZ and R. sanguineus can transmit B. burgdorferi B31. However, to determine whether theseticks are the competence vectors of Lyme disease also need the correlation between natural infectionand evidence of the population infection. In order to determine the ability of different tick speciestransmission different genotypes of Borrelia burgdorferi and to clarify their position and role in thespread of Lyme disease, a lot of works need to be done in the future research. These studies areavailable for pathogenesis, clinical symptoms, prevention and treatment of Lyme disease.