Molecular Epidemiological Characteristics Of Tick-borne Spotted Fever Group Rickettsiae In Inner Mongolia

Ticks are important zoonotic vectors,which are distributed all over the world.Ticks can carry nearly 168 pathogens including the spotted fever group rickettsiae(SFGR),which seriously affected the public health and the development of animal husbandry,playing an important role in the prevention and control of infectious diseases.In recent years,with the rapid development of some diagnostic technologies,more and more new tick-borne pathogens have been being discovered everywhere.Although China had been committed to the prevention and control of tick-borne diseases,there are still many areas and some remote areas with little attention and lack of monitoring.It is a certain risk of tick-borne diseases transmission.Ticks have a wide range of host,distribution and diversity of tick species,suggesting that our findings are only the tip of the iceberg.China has a vast territory,many areas and some remote areas have little attention,there is always a huge hidden danger.Therefore,the monitoring of tick-borne diseases should be strengthened,and the monitoring area should be further expanded,which can prevent "trouble" before it happens.This experiment focused on Inner Mongolia,and the the infection situation of tick-borne spotted fever group rickettsia was investigated in six areas of Erguna City,Xilinhot City,Arshan City,pastures around Arrihashat Port,Manzhouli City,and Ebuduge Port.Objective:Further to understand the infection situation of tick-borne spotted fever group rickettsiae in Inner Mongolia,and master the infection rate,distribution characteristics and genotype diversity of SFGR,and provide scientific basis for the prevention and control of spotted fever disease.Methods:In the May and June,2019-2020,we collected ticks in the six regions with the dragging method.Total DNA from ticks and ticks pathogens were extracted.According to the SFGR specific primer recorded in the literature,the omp A gene of SFGR outer membrane protein was amplified by PCR.The positive samples were sequenced,the sequenced results were reverse spliced by CLC(Main Work Bench V5.0 software)and constructed phylogenetic trees with representative positive specimens and reference sequence of SFGR by maximum likelihood method in MEGA7 software.Bootstrap was set to 1000.Statistical analysis determine the relationship between infection rate and tick species,area,male and female.Chi-square test was used for statistical analysis,and P < 0.05 was used to determine that the difference was statistically significant.Results:1.A total of 1404 adult ticks were collected,including Dermacentor silvarum 523(37.3%),Dermacentor nuttalli 146(10.4%),Ixodes persulcatus455(32.4%),Haemaphysalis conicinna 280(20.0%).2.According to the place and different ticks,SFGR was detected in 695 tick samples randomly,including Erguna City 530,Manzhouli City 19,Arshan City 80,Xilinhot City 23,pastures around Arrihashat Port 10,and Ebuduge Port 33.and the total SFGR positive rate was 37.7%.Four species were detected including Rickettsia raoultii,Rickettsia sibirica,Rickettsia heilongjiangii and Candidatus Rickettsia tarasevichiae.The positive rate of R.raoultii was the highest in this region,which was 26.6%,and was distributed in all 6 regions.3.The distribution of SFGR was different in different regions.The largest number of SFGR species were found in Erguna City,with 3 species.Statistical analysis showed that in Inner Mongolia regional SFGR infections were statistically significant difference(?~2=67.050,P<0.05).The infection rate was the highest in Manzhouli city,followed by the pastures around Arriha Saudi port.4.For different ticks,SFGR infections were statistically significant differences(?~2=128.639,P<0.05),and the highest SFGR infections rate of Dermacentor nuttalli was 81.1%.The number and species of rickettsia,which carried by different tick species were different.5.The difference of SFGR infections rate was not related to gender(?~2=0.042,P>0.05).6.The molecular phylogenetic tree analysis based on omp A gene showed 4 rickettsia with the close relationship between the SFGR which were found in heilongjiang,jilin,Russia and Mongolia,the homologous were 99.78%-100%.The branch of R.raoultii divided into two small branches with the sequence differences,may be two kinds of different plant types,which were prevalent in Erguna,Arshan and Xilinhot,and both Ixodes persulcus and Dermacentor silvarum of Erguna can detect the two kinds of different plant types.And it should further judgment by other genes.XLHT-CY-10,EEGN-QG-60,EEGN-SL-100 and AES-SL-30 were more closely related to Tomks,Dns14 and Shangzhi-23 strains of R.raoultii,while XLHT-CY-11,EEGN-QG-1,EEGN-SL-98 and AES-SL-14 were more closely related to Dns28,M198 and M30 strains of R.raoultii,and the homology were 99.78%-100%.Conclusion:1.It confirmed that the area of Inner Mongolia had species diversity.The four kinds of ticks were the main ticks in the area.The Dermacentor nuttalli covered the 5 areas,with the most areas.2.It confirmed that the area of Inner Mongolia had genotype diversity of SFGR.The SFGR infection was common.The area had four SFGR,which were closely related to the rickettsia found in Heilongjiang province,Mongolia and Russia.R.raoultii genotype was the endemic strain in this region.3.The distribution and species of rickettsia were different in different areas,and the infection rate was also different.The infection rate of SFGR in Manzhouli City was the highest,followed by the pastures around Arriha Saudi Port.Relevant departments should strengthen prevention and control.4.The infection rate of tick-borne spotted fever group rickettsiae in this area was not related to the sex of ticks.5.R.raoultii was genetic diversity in the region.There may be two different strains of R.raoultii,which are prevalent in Erguna,Arshan and Xilinhot,and both Ixodes persulcus and Dermacentor silvarum of Erguna can detect the two kinds of different plant types.