| The northeast forest area is the largest natural forest in China,and it is one of the main natural foci of related tick-borne diseases.Ticks,as a specific blood-sucking parasitic insect in vitro,can spread a variety of pathogens(viruses,spirochetes,Rickettsia,etc.)by biting humans and livestock,which seriously threatens human health and livestock production.In recent years,the incidence of tick-borne diseases has increased,which has a great impact on public health.As one of the border provinces in Northeast China,Heilongjiang Province has complex topography,abundant forest resources,and provides a good habitat for tick survival and reproduction.In addition,Heilongjiang Province and the Russian Far East are connected by waterways,roads,and railways,which provding conditions for tick-borne diseases to be introduced.To understand the distribution of tick-borne pathogens in border areas of Heilongjiang Province,to carry out investigation on tick-borne pathogens and to master accurate and convenient detection methods of tick-borne pathogens can provide scientific basis for formulating control strategies for tick-borne infectious diseases in this area.This research(1)Systematically analyzed the epidemiological characteristics of tick-borne encephalitis(TBE)in China based on the data of tick-borne encephalitis cases(2007-2017)collected through the China Information System for Diseases Control and Prevention;(2)Established a Reverse-transcription Recombinase-aided Amplification Assay for the Rapid Detection of the Far-Eastern Subtype of Tick-borne Encephalitis Virus;(3)Based on the previous two studies,molecular screening of seven pathogens:Tick-borne encephalitis virus(TBEV),Severe fever with thrombocytopenia syndrome virus(SFTSV),Omsk Hemorrhagic Fever virus(OHFV),Langat virus,(LGTV),Powassan virus(POWV),Borrelia burgdorferi sensulato(B.b.s.l),Spotted Fever Group Rickettsia(SFGR)were carried out in tick specimens collected from the border areas of Heilongjiang Province(Jiamusi,Yichun and Daxing'anling district).The results showed that:(1)A total of 3165 tick-borne encephalitis cases were reported from 2007 to 2017 in China.The high-incidence provinces were Inner Mongolia Autonomous Region.Heilongjiang Province and Jilin Province,which are all in the northeast of China.The total number of tick-borne encephalitis cases in the three provinces accounted for 98.4%of the total cases in China.Among them,Hulunbeier City,Yanbian Korean Autonomous Prefecture,Mudanjiang City,Daxing'anling district and Yichun City are the high-incidence cities.Most cases occur in spring and summer;the patients have obvious occupational characteristics and mainly are farmers,unemployed workers,household workers and workers.Since 2014,the proportion of unemployed workers and household workers has increased year by year,while the proportion of farmers has declined year by year;the sex ratio of men to women is 2.05:1,and the age group of 40-49 years old is the peak population of the disease.(2)The Reverse-transcription Recombinase-aided Amplification Assay has a good specificity for the Rapid Detection of the Far-Eastern Subtype of Tick-borne Encephalitis Virus.The analytical limit of detection of the assay was 20 copies per reaction of the TBEV synthetic transcript and 3 plaque-forming units(pfu)per reaction of TBEV titers.(3)TBEV,OHFV,SFTSV,LGTV and POWV were all negative in 2530 tick specimens collected from Daxing'anling District,Yichun and Jiamusi in Heilongjiang Province;Among 1185 tick specimens in Jiamusi area,21 were positive for Borrelia burgdorferi sensulato,with a positive rate of 8.9%.For 141 positive specimens of spotted fever group Rickettsia,the positive rate was 59.5%.The positive rates of B.b.s.l and SFGR in Ixodes persalcatus specimens were higher than those in Dermacentor silvarum;B.b.l.s positive specimens belonged to B.garinii and B.afzelii genotypes,while SFGR positive specimens belonged to Candidatus R.tarasevichiae,R.heilongjianges and R.raoultii genotypes.In summary,Heilongjiang Province is one of the provinces with the highest incidence of tick-borne encephalitis in China.The positive rates of TBEV,SFTSV,OHFV,LGTV and POWV in specimens collected in Jiamusi,Yichun and Daxing'anling district are low.Considering that no cases of OHFV,LGTV and POWV have been reported in China,we maintain that these three viruses have not yet been introduced into the region.Ticks collected in Jiamusi City carry spotted fever group Rickettsia and Borrelia burgdorferi,indicating that the risk of spotted fever and Lyme disease is relatively high in this area.The Reverse-transcription Recombinase-aided Amplification Assay for the Rapid Detection of the Far-Eastern Subtype of Tick-borne Encephalitis Virus provides a new method for the rapid detection of tick-borne encephalitis virus,a supplement for the isothermal detection of tick-borne encephalitis virus in China,and technical support for the field and the screening of tick-borne encephalitis in areas with poor medical conditions.At the same time,the basic data obtained from the screening of tick-borne pathogens have certain reference value for the prevention and control of tick-borne diseases in border areas of Heilongjiang Province. |
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