Study On The Vertical Transmission Of Two Novel Rickettsiae In Vector Ticks In China

BackgroundSpotted fever group rickettsia?SFGR?is a short rod-shaped species of rickettsia and mainly transmitted by ticks,resulting in the Spotted fever group rickettsiosis.Rickettsial infection of humans and host animals caused by the bite of rickettsial ticks.Before 2012,a total of 9 species of SFGR were found in Chinese mainland,In 2012,our group discovered a new kind of rickettsiosis in Heilongjiang province,Candidatus Rickettsia tarasevichiae?CRT?.Differ from other rickettsial infection,all Candidatus Rickettsia tarasevichiae patients has not been any spots but a tick bite eschar and lymphadenalgia,we also identified the R.sibirica BJ-90,which caused multiple organ dysfunction in patients.It was followed by the discovery of Rickettsia raoultii,a milder form of the disease.Recently,reseachers have found a variety of novel rickettsiae in ticks,such as R.aeschimannii,R.massiliae,Candidatus R.gannanii,Candidatus R.barbariae,Rickettsia sp.tselentii and so on.Whether these novel rickettsiae cause disease in humans remain unclear.The appearance of novel rickettsia remind us that we must insist on the continuous monitoring of rickettsia.The distribution and transmission of rickettsia relative to the distribution of ticks,but selective pressure plays the leading role in it.Study confirmed that the rickettsia can be spread in the different development stages of vector ticks and maintain its pathogenicity,different susceptibility to rickettsia in the vetor ticks,have different influence on the tick development.The vector ticks microbial can directly influence the transmission of pathogens,the diversity of microbes associated with a variety of factors.Study on the novel rickettsiae and the relationship between the vector ticks microbial population help of tick-borne rickettsia disease risk prediction and evaluation of the epidemic,is a new field of rickettsial research.Does the infection of two novel rickettsiae in this study affect the reproductive development of vector ticks?The relationship between the trend of novel rickettsial transmission in the vector ticks and the microbial population carried by the ticks is an urgent scientific problem to be solved.Research purpose?1?To elucidate the effects of two novel rickettsiae on the development of vector ticks.?2?To specific the transovarial transmission and transstadial transmission of the vector ticks under laboratory conditions.?3?To understand the relationship between the diversity of tick microbial population and the vertical transmission of novel rickettsiaeMethodThe BALB/c mice and New Zealand white rabbit were used as hosts for laboratory feeding.Based on PCR sequencing to confirmed the infection of novel rickettsia in vector ticks and used the qPCR to detected the rickettsia loads.Used 2^-??Ct method to calculate the relative loads of rickettsia through different stages.The purpose of amplifying the different stages of the two vector ticks by using 16S rRNA V3-V4 high-variant region amplase sequencing was to find out the difference of the microbial population between the rickettsia-infected group and the uninfected group,find out the microflora possibly related to rickettsial,and analyze the relative factors of the change of rickettsial in the vector ticks.ResultCollected 300 Ixodes persulcatus,60 Dermacentor silvarum.The infection rate of CRT in engorged female Ixodes persulcatus ticks was 35%and infection rate of Rickettsia raoultii in engorged female Dermacentor silvarum ticks was 12.5%.The results showed that the Ixodes persulcatus hatching rate of the positive group was higher than the negative group,and the difference was statistically significant.By qPCR to detect Ixodes persulcatus 18 breeding series of rickettsia loads change,the first generation female as contrast,foldchange of eggs,larvae,nymphs,adults were 0.44,1.40,5.77,17.99,the trend of the different development stages of CRT was that the rickettsial load decreased during ovipositon and increased during transstadial transmission,and was significantly higher than that of the first-generation female tick when it developed into next generation.Rickettsia raoultii in Dermacentor silvarum,relative to female ticks,the foldchange of eggs,larvae,nymphs,adults were 0.03,0.12,0.15,0.42.During ovipositon period,the Rickettsia raoultii loads was decreased,increased during transstadial transmission,but after the generation of reproduction,the amount of rickettsial load was lower than that of the first generation;Comments by species,Ixodes persulcatus positive group for common of OTU number and specific OTU number were higher than negative group.Two groups shared the same change trend,it can be seen through the bloodsucking process,lead to tick higher microbial species richness in.The bacteria have siginificant differeces compared to negative groups are rickettsia,Enterobacter,spirochete,pallid bacillus,staphylococcus,glutamate bacillus.Dermacentor silvarum,the positive mutual OTU number was significantly lower than the negative group of OTU number,but by a bloodsucking and molting complete generation reproduction,positive group OTU number higher than negative group OTU number.ConclusionThe positive effect of CRT on the hatching rate during the development of ticks was confirmed,which promoted the hatching process.This study revealed the transmission of two novel rickettsial species in the vector ticks during the development stages.CRT was significantly higher than the first generation after transovarial transmission and transstadial transmission.Rickettsia raoultii was lower than the first generation.Through the analysis of microbial population diversity,we find the microflora with large difference between groups,analyze the mutual benefit and selection between pathogens and microorganisms.SignificanceSFGR has become an important global public health problem and a potential threat to human health.The research scheme adopted in this study based on mature theories and techniques of etiology,immunology and epidemiology,and the technical route confirmed by previous studies with strong feasibility.Demonstrated the two novel rickettsia influence on ticks life cycle and development fitness.This paper expounds the two novel rickettsia transovarial and transstadial transmission of different development stages in ticks.By 16S rRNA V3-V4 sequencing,obtain the microbial population of ticks and described the relationship between microbial populations and novel rickettsiae.To predict the popular trend of novel SFGR and provide theoretical basis for risk assessment.