Systematic review of severe fever with thrombocytopenia syndrome: virology, epidemiology, and clinical characteristics

Abstract

Severe fever with thrombocytopenia syndrome (SFTS) was firstly discovered in China in 2010, followed by several reports from many other countries worldwide. SFTS virus (SFTSV) has been identified as the causative agent of the disease and has been recognized as a public health threat. This novel Bunyavirus belongs to the Phlebovirus genus in the family Bunyaviridae. This review also describes the different aspects of virology, pathogenesis, epidemiology, and clinical symptoms on the basis of the published article surveillance data and phylogenetic analyses of viral sequences of large, medium, and small segments retrieved from database using mega 5.05, simplot 3.5.1, network 4.611, and epi information system 3.5.3 software. SFTS presents with fever, thrombocytopenia, leukocytopenia, and considerable changes in several serum biomarkers. The disease has 10~15% mortality rate, commonly because of multiorgan dysfunction. SFTSV is mainly reported in the rural areas of Central and North-Eastern China, with seasonal occurrence from May to September, mainly targeting those of ≥50 years of age. A wide range of domesticated animals, including sheep, goats, cattle, pigs, dogs, and chickens have been proven seropositive for SFTSV. Ticks, especially Haemaphysalis longicornis, are suspected to be the potential vector, which have a broad animal host range in the world. More studies are needed to elucidate the vector-animal-human ecological cycle, the pathogenic mechanisms in high level animal models and vaccine development.

Figure 1

Schematic diagram of the structure and genome of the SFTSV ,. SFTSV genome included L, M, and S segments. The antisense RNA and the encoded ORFs are represented in orange and blue boxes respectively. In L, M, and S genomic RNAs, only the first 20 Nts of both the 5′ and 3′ termini of each segment are shown. The first 15 Nts of both the 5′ and 3′ termini of each segment are paired and conserved except for the mismatches A–C/G or C–U in red color and C–C or G–G in blue color. Note: The data were sourced from the report of Li et al. and processed in photoshop 7.0

Figure 2

Phylogenetic relationship of Chinese SFTSV and other Phlebovirus strains based on sequences of L gene fragment. Evolutionary relationships of 21 taxa were inferred by the neighbor joining and maximum-likelihood methods using MEGA 5.05 software

Figure 3

Similarity plot analysis of Chinese SFTSV strains and the other Phlebovirus species, with a window size of 200 bp and a step size of 20 bp. The plot were done using SIMPLOT 3.5.1 software (an interactive 32-bit software program) based on the sequence homology versus position of Chinese SFTSV strains to a panel of other Phleboviruses in database

Figure 4

Median-joining network depicting the relationship of Chinese SFTSV strains and other Phlebovirus species in database. The common ancestor was inferred based on network of L gene mutations using the NETWORK 4.611 software reported by Bandelt et al.

Figure 5

Geographic distribution of 571 SFTS confirmed cases and 59 deaths from Chinese SFTS surveillance in 2011, as processed in EPI information 3.5 software

Figure 6

Age distribution of 649 SFTS confirmed cases from Chinese SFTS surveillance in 2012. Note: The data were sourced from Chinese SFTS surveillance and processed in excel 2010 and spss 17.0

Figure 7

Weekly distribution of 275 SFTS confirmed cases in China during 2012. Note: The data were sourced from Chinese SFTS surveillance and processed in excel 2010 and spss 17.0

Figure 8

Clinical symptom percentages among 352 SFTS cases and 11 fatal cases from China. Note: The data were sourced from References , , and and processed in excel 2010 and spss 17.0