Molecular evolution and genetic diversity analysis of SFTS virus based on next-generation sequencing

SFTS virus(SFTSV)is a novel bunyavirus,which was discovered as the etiological agent of severe fever with thrombocytopenia syndrome(SFTS)in China in 2009,and was now prevalent in at least 25 provinces in China.SFTS was subsequently identified in South Korea and Japan in 2012.To explore themolecular evolution and genetic characteristics of this newly identified pathogen,we reported 72 whole genome sequences of SFTSV,and built a dataset of SFTSV genome sequences containing 292 L-segment,302 M-segment and 502 S-segment.We clearly divided SFTSV into six genotypes,Genotype A-F.It was found that genotype F was the dominant epidemic genotype of Japan,South Korea,and Zhejiang province of China.The coalescent analysis supported that SFTSV originated in the early 18th century from Zhejiang province,and Genotype F was the most primitive one.Henan,Hubei,and Anhui provinces which are located in Dabie Mountain area weremainly epidemic of Genotype A,which emerged relatively late but distributed widely.A total of 37 recombination events were identified,making SFTSV with a high recombination frequency(L segment 5.1%,Msegment 3.6%,S segment 0.8%)among negative-strand segmented RNA viruses.It was identified that 19 reassortant strains belonged to 12 reassortment forms of SFTSV genome containing 6 newly identified forms.The reassortment virus and recombination in tick were both found for the first time.We also found many of genotype-specific mutation sites,7 of which could be considered as potential molecular marker for genotype classification.This study promoted a more comprehensive understanding of the phylogeny and origin,and the genetic diversity of SFTSV,and it could help the studies of other newly discovered tick-borne bunyavirus as reference data and research ideas.

Immunogenicity and protective efficacy of an inactivated SFTS vaccine candidate in mice

Severe fever with thrombocytopenia syndrome(SFTS),caused by a novel identified bunyavirus SFTS virus(SFTSV),was an emerging viral infectious disease that was firstly reported in China.There are no licensed vaccines and therapeutics against SFTSV currently.B‐Propiolactone(BPL)inactivated whole virions of SFTSV strain AH12 were prepared as experimental vaccine in different antigen dose with or without Al(OH)3 adjuvant.The experimental SFTS vaccine was a satisfying immunogen,which could efficiently trigger the development of high levels of SFTSV NP‐specific IgG antibodies and neutralizing antibodies against SFTSV Strain HB29 in BALB/c and C57/BL6 mice,and could induce SFTS virus‐specific cellular immune responses to a certain extent.A single dose of vaccine was immunogenically insufficient in BALB/c mice;the second and third dose resulted in significant boost in antibody response.The use of Al(OH)3 adjuvant resulted in higher antibody titers.The mediate‐dose of vaccine could induce as high and equivalent level of antibody titer as that of high‐dose.The experimental SFTS vaccine in mediate‐and high antigen dose with adjuvant resulted in solid protection of C57/BL6 mice against wild‐type SFTSV challenge with markedly accelerated virus clearance from blood and spleen compared with controls.The experimental SFTS vaccine prepared in this study could efficiently elicit virus specific humoral and cellular immune responses in both BALB/c and C57/BL6 mice,and could protect C57/BL6 mice against SFTS virus challenge.These results supplied evidence that inactivated vaccine was a promising vaccine candidate for the prevention of SFTSV infection.