Seroprevalence of antibodies against SFTS virus infection in farmers and animals, Jiangsu, China

The first reported cases of severe fever with thrombocytopenia syndrome virus from domestic sick camel to humans in China

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne disease with an increasing annual incidence rate. In this case report, we presented two patients infected with the SFTS virus, suggesting a potential direct transmission route from camels to humans through blood contact. Both patients developed symptoms after engaging in the slaughtering of one sick camel, while their family members living in the same environment or co-diners remained unaffected. Subsequent detection revealed a high viral load of SFTS virus, reaching 1010 viral RNA copies/ml, in the sample obtained from the sick camel. Metagenomic sequencing did not identify any other pathogens. The SFTS virus was successfully isolated from both patient and camel samples. The complete nucleotide sequences obtained from the infected patients demonstrated a remarkable 100% similarity to those found in the camel, and genetic evolution analysis classified the virus as genotype A. Additionally, partial sequences of the SFTS virus were identified in ticks captured from the camel rearing environment, however, these sequences showed only 95.9% similarity to those found in camel and humans. Furthermore, immunoglobulin M and immunoglobulin G antibodies were detected in serum samples collected from the patient. Our findings provide evidence that camel may serve as a competent reservoir for transmitting the SFTS virus to humans. Further in vitro investigations into SFTS virus infections in large animals are warranted to understand their role in viral maintenance and transmission.

First detection of Bandavirus dabieense in ticks collected from migratory birds in the Republic of Korea

The causative agent of severe fever with thrombocytopenia syndrome (SFTS) is Bandavirus dabieense, an emerging tick-borne zoonotic pathogen. Migratory birds have often been suggested as potential carriers of ticks that can transmit Bandavirus dabieense; however, their role remains unclear. The Republic of Korea (ROK) holds an important position as a stopover on the East Asian-Australasian Flyway. The present study aimed to investigate the potential involvement of migratory birds in the transmission of the SFTS virus (SFTSV) in the ROK. A total of 4,497 ticks were collected across various regions, including Heuksando and Daecheongdo, in the ROK, from bird migration seasons in 2022 and 2023. Genetic analysis of the SFTSV was performed for 96 ticks collected from 20 different species of migratory birds. Polymerase chain reaction (PCR) fragments of SFTSV were detected in one Haemaphysalis concinna nymph collected from a Black-faced Bunting (Emberiza spodocephala) and one Ixodes turdus nymph collected from an Olive-backed Pipit (Anthus hodgsoni) on Daecheongdo and Heuksando, respectively, during their northward migration in two spring seasons. This finding suggests that migratory birds can be considered as possible carriers and long-distance dispersers of ticks and associated tick-borne diseases. This study highlights the importance of clarifying the role and impact of migratory birds in the rapid expansion of tick-borne diseases, facilitating enhanced preparedness and the development of mitigation measures against emerging SFTS across and beyond East Asia.

Structural snapshots of phenuivirus cap-snatching and transcription

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a human pathogen that is now endemic to several East Asian countries. The viral large (L) protein catalyzes viral transcription by stealing host mRNA caps via a process known as cap-snatching. Here, we establish an in vitro cap-snatching assay and present three high-quality electron cryo-microscopy (cryo-EM) structures of the SFTSV L protein in biologically relevant, transcription-specific states. In a priming-state structure, we show capped RNA bound to the L protein cap-binding domain (CBD). The L protein conformation in this priming structure is significantly different from published replication-state structures, in particular the N- and C-terminal domains. The capped-RNA is positioned in a way that it can feed directly into the RNA-dependent RNA polymerase (RdRp) ready for elongation. We also captured the L protein in an early-elongation state following primer-incorporation demonstrating that this priming conformation is retained at least in the very early stages of primer extension. This structural data is complemented by in vitro biochemical and cell-based assays. Together, these insights further our mechanistic understanding of how SFTSV and other bunyaviruses incorporate stolen host mRNA fragments into their viral transcripts thereby allowing the virus to hijack host cell translation machinery.

Seroprevalence for severe fever with thrombocytopenia syndrome virus among the residents of Miyazaki, Japan: An epidemiological study

INTRODUCTION

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne infectious disease caused by the SFTS virus (SFTSV). The Miyazaki Prefecture has the highest number of SFTS cases in Japan and requires countermeasures for prevention. In this study, we aimed to conduct an epidemiological survey in Miyazaki Prefecture to determine the exposure conditions of SFTSV by measuring the seroprevalence among residents of Miyazaki and to evaluate the factors that influence the endemicity of SFTS.

METHODS

The survey was conducted between June 2014 and April 2019 in all 26 municipalities in Miyazaki Prefecture. SFTSV antibodies were detected using an enzyme-linked immunosorbent assay in the blood samples of 6013 residents (3184 men and 2829 women). A questionnaire-based survey of the living environment was also conducted.

RESULTS

Multiple logistic regression analysis revealed that age and occupation were significant factors related to the proportion of participants with an optical density (OD) value > 0.2 and a seroprevalence of 0.9 % (54/6013). Seven seropositive individuals (0.1 %) with an OD value of >0.4 were identified (three men and four women, aged 54-69 years), and all were asymptomatic. One participant had a higher OD than the positive control.

CONCLUSION

Although SFTS is endemic in Miyazaki Prefecture, Japan, its seroprevalence is relatively low. Since some risk areas in Miyazaki prefecture have been identified, it is important to enhance awareness of SFTS in residences and reduce contact with ticks, especially in high-risk areas.

Initial study and phylogenetic analysis of hard ticks (Acari: Ixodidae) in Nantong, China along the route of avian migration

The growing concern about migratory birds potentially spreading ticks due to global warming has become a significant issue. The city of Nantong in this study is situated along the East Asia-Australasian Flyway (EAAF), with numerous wetlands serving as roosting sites for migratory birds. We conducted an investigation of hard ticks and determined the phylogenetic characteristics of tick species in this city. We utilized three different genes for our study: the mitochondrial cytochrome oxidase subunit 1 (COX1) gene, the second internal transcribed spacer (ITS2), and the mitochondrial small subunit rRNA (12 S rRNA) gene. The predominant tick species were Haemaphysalis flava (H. flava) and Haemaphysalis longicornis (H. longicornis). Additionally, specimens of Haemaphysalis campanulata (H. campanulata) and Rhipicephalus sanguineus (R. sanguineus) were collected. The H. flava specimens in this study showed a close genetic relationship with those from inland provinces of China, as well as South Korea and Japan. Furthermore, samples of H. longicornis exhibited a close genetic relationship with those from South Korea, Japan, Australia, and the USA, as well as specific provinces in China. Furthermore, R. sanguineus specimens captured in Nantong showed genetic similarities with specimens from Egypt, Nigeria, and Argentina.

Parasitic Characteristics of Ticks (Acari: Ixodidae) Collected from Water Deer (Hydropotes inermis argyropus) and Spatiotemporal Distribution Prediction within Host-Influenced Cultivated Areas

Tick-borne diseases result from human-ixodid tick encounters, making it crucial to understand host-ixodid tick interactions and host-dependent distribution for epidemiology and prevention. This study examines water deer patterns and ixodid tick interactions in designated croplands of South Korea over two years, finding that the highest deer presence occurred in July and the lowest in May, during crop harvesting. Four tick species were identified, with Haemaphysalis longicornis being predominant (92.2%). Tick life stage analysis revealed peak nymphs and adults in July and larvae in October. Nymph abundance correlated positively with nearby water deer. MaxEnt biodiversity prediction results indicated wider water deer distribution in summer, reflecting their tendency to use multiple croplands. Areas with nymphs and adults aligned with predicted deer presence in summer, while larval areas aligned in autumn. Increased agroforestry expanded water deer habitats, enhancing tick dispersion. Prevention involved minimizing human-deer encounters by strategic land use in tick-prone areas. This comprehensive study provides insights into preventing severe fever with thrombocytopenia syndrome in agricultural workers, emphasizing the need for targeted interventions based on host behavior and tick life stages in different seasons.

Spatiotemporal distribution and environmental influences of severe fever with thrombocytopenia syndrome in Shandong Province, China

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease discovered in China in 2009. The purpose of this study was to describe the spatiotemporal distribution of SFTS and to identify its environmental influencing factors and potential high-risk areas in Shandong Province, China.

METHODS

Data on the SFTS incidence from 2010 to 2021 were collected. Spatiotemporal scan statistics were used to identify the time and area of SFTS clustering. The maximum entropy (MaxEnt) model was used to analyse environmental influences and predict high-risk areas.

RESULTS

From 2010 to 2021, a total of 5705 cases of SFTS were reported in Shandong. The number of SFTS cases increased yearly, with a peak incidence from April to October each year. Spatiotemporal scan statistics showed the existence of one most likely cluster and two secondary likely clusters in Shandong. The most likely cluster was in the eastern region, from May to October 2021. The first secondary cluster was in the central region, from May to October 2021. The second secondary cluster was in the southeastern region, from May to September 2020. The MaxEnt model showed that the mean annual wind speed, NDVI, cattle density and annual cumulative precipitation were the key factors influencing the occurrence of SFTS. The predicted risk map showed that the area of high prevalence was 28,120 km2, accounting for 18.05% of the total area of the province.

CONCLUSIONS

The spatiotemporal distribution of SFTS was heterogeneous and influenced by multidimensional environmental factors. This should be considered as a basis for delineating SFTS risk areas and developing SFTS prevention and control measures.

High Seroprevalence of Severe Fever with Thrombocytopenia Syndrome Virus Infection among the Dog Population in Thailand

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne zoonotic disease caused by the SFTS virus (SFTSV). In Thailand, three human cases of SFTS were reported in 2019 and 2020, but there was no report of SFTSV infection in animals. Our study revealed that at least 16.6% of dogs in Thailand were seropositive for SFTSV infection, and the SFTSV-positive dogs were found in several districts in Thailand. Additionally, more than 70% of the serum samples collected at one shelter possessed virus-neutralization antibodies against SFTSV and the near-complete genome sequences of the SFTSV were determined from one dog in the shelter. The dog SFTSV was genetically close to those from Thailand and Chinese patients and belonged to genotype J3. These results indicated that SFTSV has already spread among animals in Thailand.

Serologic and Molecular Prevalence of Severe Fever with Thrombocytopenia Syndrome Virus Among Poultry in the Republic of Korea

Background: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by Dabie bandavirus, which belongs to the genus Bandavirus, family Phenuiviridae, and order Bunyavirales. It has been found in tick species, various animals, and humans. The aim of this study was to detect RNA of antigens and antibodies against SFTS virus (SFTSV) among poultry such as chickens, ducks, and wild geese from five provinces in the Republic of Korea (ROK). Materials and Methods: A one-step reverse transcriptase (RT)-PCR and nested PCR were performed after viral RNA extraction. The phylogenetic tree was constructed after sequencing data were analyzed and aligned. An indirect enzyme-linked immunosorbent assay (ELISA) and a neutralization test (NT) were performed to test for IgG antibodies of SFTSV. Results: Of a total of 606 poultry serum samples collected, 568 and 539 serum samples were used to perform ELISA and NT, respectively. Of a total of 606 serum samples tested by RT-PCR targeting the S segment, 15 (2.5%) were positive for SFTSV. From the 15 positive serum samples for the SFTSV antigen, three from chickens, three from ducks, and one from wild geese were classified as genotype B-2; one from chickens was classified as genotype B-3; and three from chickens and four from wild geese were classified as genotype D. Of the 568 serum samples tested by ELISA, 83 (28.0%) from chickens, 81 (32.9%) from ducks, and 8 (30.8%) from wild geese were seropositive. Of the 539 serum samples for which an NT was performed, 113 (38.6%) from chickens and 75 (30.5%) from ducks were positive for SFTSV antibodies. Conclusions: The results of this study provide useful information regarding detection of SFTSV RNA and antibodies among poultry and the possibility of SFTSV transmission in various types of poultry, including chickens, ducks, and wild geese, in the ROK.

Epidemiology of Severe Fever with Thrombocytopenia Syndrome in Dogs and Cats in Taiwan

Severe Fever with Thrombocytopenia Syndrome (SFTS), caused by the SFTS Virus (SFTSV), is a global health threat. SFTSV in Taiwan has only been reported in ruminants and wild animals. Thus, we aimed to investigate the infection statuses of dogs and cats, the animals with closer human interactions. Overall, the SFTSV RNA prevalence was 23% (170/735), with dogs showing a 25.9% (111/429) prevalence and cats at 19.3% (59/306) prevalence. Noticeably, the prevalence in stray animals (39.8% 77/193) was significantly higher than in domesticated ones (17.2%, 93/542). Among the four categories analyzed, the highest SFTSV prevalence was found in the stray dogs at 53.9% (120/193), significantly higher than the 24.2% prevalence noted in stray cats. In contrast, domesticated animals exhibited similar prevalence rates, with 17.1% for dogs and 17.2% for cats. It is noteworthy that in the domesticated animal groups, a significantly elevated prevalence (45%, 9/20) was observed among cats exhibiting thrombocytopenia compared to those platelet counts in the reference range (4.8%, 1/21). The high infection rate in stray animals, especially stray dogs, indicated that exposure to various outdoor environments influences the prevalence of infections. Given the higher human interaction with dogs and cats, there is a need for proactive measures to reduce the risk associated with the infection of SFTSV in both animals and humans.

Molecular and Serological Survey of Severe Fever with Thrombocytopenia Syndrome Virus in Horses from the Republic of Korea

Background: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging zoonotic tick-borne disease in East Asia caused by the SFTS virus (SFTSV). It is to investigate the presence of SFTSV RNA and antibodies in horses from a slaughterhouse and equestrian centers in the Republic of Korea (ROK). A prevalence study of SFTSV-specific RNA and antibodies was designed from 889 horses in the ROK. Materials and Methods: Serum samples were collected from horses at a slaughterhouse and equestrian centers from 2018 to 2020. To detect the presence of SFTSV, RNA was extracted from the serum samples, and a nested reverse transcription-polymerase chain reaction (RT-PCR) was conducted. Sequencing data were analyzed, and a phylogenetic tree was constructed using the maximum-likelihood method with Molecular Evolutionary Genetics Analysis Version 7.0 software. The horse sera were also tested for SFTSV-specific immunoglobulin G antibodies using enzyme-linked immunosorbent assay (ELISA). Results: Twelve of 889 (1.3%) horse sera were positive for SFTSV RNA, and 452 of 887 (51.0%) horse sera were seropositive by ELISA. Among the RT-PCR-positive samples, 12 of the SFTSV S-segment sequences were classified as sub-genotypes B-2 (n = 6) and B-3 (n = 6). ELISA analysis was evaluated by comparison with neutralization test. We investigated SFTSV infection in horses over a 3-year period, but sampling was not performed evenly by season; continuous surveillance of SFTSV in horses is needed. Conclusions: We report the detection of SFTSV RNA and provide serological data on SFTSV prevalence in horses in the ROK. The detection of SFTSV-specific RNA and antibodies in horses, which are in close proximity to humans, suggests that SFTS is an emerging and important health issue, indicating that more attention to its relevance for equestrian workers is needed.

Population dynamics of hard ticks (Acari: Ixodidae) and their harboring rates of Severe Fever with Thrombocytopenia Syndrome (SFTS) virus in four landscapes of Gyeonggi Province, South Korea

Population dynamics of hard ticks and their harboring rates of fatal severe fever with thrombocytopenia syndrome (SFTS) were monitored from 2021 to 2022 in Gyeonggi-do, South Korea. Hard ticks were surveyed monthly using CO2-bait traps in four vegetation types, including grassland, grave, mountain trail, and shrub. From the 2-year monitoring, totals of 5,737 and 14,298 hard ticks were collected in 2021 and 2022, respectively, all of which belonged to the genus Haemaphysalis. Of these collected ticks, 97.9 and 98.3% of adults and nymphs were identified as Haemaphysalis longicornis. Generally, density peaks of H. longicornis nymphs and adults were observed from April to May and from June to July, respectively. For Haemaphysalis flava, adults showed density peaks in September, whereas no obvious seasonal patterns were observed for nymphs. The density peak of Haemaphysalis larvae was observed in August and September, followed by a density peak of adults. There was a large variation in the number of hard ticks collected among the four vegetation types, yielding no significant difference among them over the 2-year monitoring. Half of the collected ticks from each vegetation type were pooled into groups by species and developmental stage and subjected to analysis of SFTS virus harboring rates, which yielded no SFTS positive pool detected over the 2-year monitoring.

Natural circulation of tick-borne severe fever with thrombocytopenia syndrome virus in the city ecosystem, China

•Hedgehogs and Haemaphysalis longicornis ticks can maintain the natural circulation of SFTSV in the city ecosystem. •Hedgehogs and H. longicornis ticks are becoming common in Beijing. •Parthenogenetic H. longicornis ticks are discovered in Beijing.

Analysis of fatal cases of severe fever with thrombocytopenia syndrome in Jiangsu province, China, between 2011 and 2022: A retrospective study

Introduction

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by the SFTS virus (SFTSV), which has a high fatality rate. This disease has become increasingly prevalent in recent years in Jiangsu province, with a noticeable rise in its incidence. Notably, fatal cases have also been increasing. Our study aimed to analyze the epidemiological characteristics and risk factors associated with the fatal cases of SFTS in Jiangsu province from 2011 to September 2022.

Methods

A retrospective study was performed among 698 SFTS cases during 2011-2022 in Jiangsu Province, China. Cox regression analyses were used to determine the dependent and independent risk factors that affected patient survival time. ArcGIS 10.7 was used for the visualization of the geographical distribution of the deaths from SFTS.

Results

There were 698 SFTS cases reported, with an increasing incidence, over the 12-year period. Among these cases, 43 deaths were reported. Fatal cases of SFTS were reported in 12 district counties from 2011 to 2022. Notably, most of the deaths occurred in Lishui county of Nanjing City. The median age of those who died was 69 years, with age ranges from 50 to 83 years. Multivariable Cox regression analysis showed that older age (>70) and living in Lishui county were risk factors for death from SFTS in Jiangsu province. Therefore, older adults aged over 70 years and residing in Lishui county were the high-risk group for SFTS mortality.

Discussion

Over the past 12 years, we have observed a consistent rise in the incidence of SFTS, accompanied by a relatively high case fatality rate, making it a critical public health issue. Therefore, it is urgently necessary to study the impact of meteorological factors on SFTS epidemics and devise prevention and control strategies.

Research Progress of Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is a new infectious disease first discovered in Ta-pieh Mountains in central China in 2009. It is caused by a novel bunyavirus infection (SFTSV). Since the first discovery of SFTSV, there have been case reports and epidemiological studies on SFTS in several East Asian countries, such as South Korea, Japan, Vietnam and so on. With the rising incidence of SFTS and the rapid spread of the novel bunyavirus around the world, it is clear that the virus has a pandemic potential and may pose a threat to global public health in the future. Early studies have suggested that ticks are an important medium for the transmission of SFTSV to humans; in recent years, it has been reported that there is also human-to-human transmission. In endemic areas, potential hosts include a variety of livestock and wildlife. When people are infected with SFTV, the main clinical manifestations are high fever, thrombocytopenia, leukocytopenia, gastrointestinal symptoms, liver and kidney function damage, and even MODS, with a mortality rate of about 10-30%. This article reviews the latest progress of novel bunyavirus, including virus transmission vector, virus genotypic diversity and epidemiology, pathogenesis, clinical manifestation and treatment.

Epidemiological and spatiotemporal analysis of severe fever with thrombocytopenia syndrome in Eastern China, 2011-2021

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease, which is caused by severe fever with thrombocytopenia syndrome virus (SFTSV) with high fatality. Recently, the incidence of SFTS increased obviously in Jiangsu Province. However, the systematic and complete analysis of spatiotemporal patterns and clusters coupled with epidemiological characteristics of SFTS have not been reported so far.

METHODS

Data on SFTS cases were collected during 2011-2021. The changing epidemiological characteristics of SFTS were analyzed by adopting descriptive statistical methods. GeoDa 1.18 was applied for spatial autocorrelation analysis, and SaTScan 10.0 was used to identify spatio-temporal clustering of cases. The results were visualized in ArcMap.

RESULTS

The annual incidence of SFTS increased in Jiangsu Province from 2011 to 2021. Most cases (72.4%) occurred during May and August with the obvious peak months. Elderly farmers accounted for most cases, among which both males and females were susceptible. The spatial autocorrelation and spatio-temporal clustering analysis indicated that the distribution of SFTS was not random but clustered in space and time. The most likely cluster was observed in the western region of Jiangsu Province and covered one county (Xuyi county) (Relative risk = 8.18, Log likelihood ratio = 122.645, P < 0.001) located in southwestern Jiangsu Province from January 1, 2017 to December 31, 2021. The Secondary cluster also covered one county (Lishui county) (Relative risk = 7.70, Log likelihood ratio = 94.938, P < 0.001) from January 1, 2017 to December 31, 2021.

CONCLUSIONS

The annual number of SFTS cases showed an increasing tendency in Jiangsu Province from 2011 to 2021. Our study elucidated regions with SFTS clusters by means of ArcGIS in combination with spatial analysis. The results demonstrated solid evidences for the orientation of limited sanitary resources, surveillance in high-risk regions and early warning of epidemic seasons in future prevention and control of SFTS in Jiangsu Province.

Seroprevalence of severe fever with thrombocytopenia syndrome using specimens from the Korea National Health & Nutrition Examination Survey

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an acute febrile disease caused by bites from ticks infected with the SFTS virus. In Korea, SFTS patients are observed nationwide, including Jeju Island, but there are currently no data regarding the national prevalence of SFTS, including that of residents of 16 cities and provinces. This study aimed to investigate the seroprevalence of SFTS in Korea.

METHODOLOGY/PRINCIPAL FINDINGS

A total of 1500 participants were selected through random sampling from the 2014-2015 Korea National Health and Nutrition Examination Survey (KNHANES). An indirect immunofluorescence antibody assay (IFA) was performed to assess immunoglobulin (Ig) G and IgM antibody titers against SFTS virus.

RESULTS

Of the 1500 participants, 55 (3.7%) tested positive for IgG and 1 (0.1%) tested positive for IgM, with antibody titer of ≥ 1:32. Approximately 3.9% and 2.5% of participants in urban and rural areas, respectively, had a positive titer of ≥ 1:32. There was a significant correlation between SFTS incidence per 100,000 population and seroprevalence using an IgG titer ≥ 1:64 as the cut-off value.

CONCLUSION

This is the first study to investigate national SFTS seroprevalence in all 16 cities and provinces representing Korea. Our study will also provide useful guidelines for the development of preventive measures against SFTS.

Hedgehogs as Amplifying Hosts of Severe Fever with Thrombocytopenia Syndrome Virus, China

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tickborne bandavirus mainly transmitted by Haemaphysalis longicornis ticks in East Asia, mostly in rural areas. As of April 2022, the amplifying host involved in the natural transmission of SFTSV remained unidentified. Our epidemiologic field survey conducted in endemic areas in China showed that hedgehogs were widely distributed, had heavy tick infestations, and had high SFTSV seroprevalence and RNA prevalence. After experimental infection of Erinaceus amurensis and Atelerix albiventris hedgehogs with SFTSV, we detected robust but transitory viremias that lasted for 9-11 days. We completed the SFTSV transmission cycle between hedgehogs and nymph and adult H. longicornis ticks under laboratory conditions with 100% efficiency. Furthermore, naive H. longicornis ticks could be infected by SFTSV-positive ticks co-feeding on naive hedgehogs; we confirmed transstadial transmission of SFTSV. Our study suggests that the hedgehogs are a notable wildlife amplifying host of SFTSV in China.

Clinical features and epidemiology of severe fever with thrombocytopenia syndrome in dogs in the Republic of Korea: an observational study (2019-2020)

Severe fever with thrombocytopenia syndrome (SFTS) is a zoonotic disease with a high mortality rate for humans and cats. The clinical course and prognosis of SFTS in dogs remains unclear. In the present study, we investigated the clinical and epidemiological characteristics of SFTS virus (SFTSV) infection in dogs. All evaluated dogs exhibited an acute course and symptoms including fever (57.1%), anorexia (57.1%), depression (42.9%), and vomiting (35.7%). Thrombocytopenia was present in 45.5% of dogs, while jaundice was not observed. C-reactive protein, alanine transaminase, and alkaline phosphatase were elevated in some cases. Viral clearance occurred within 6 to 26 days. Phylogenetic analysis revealed that the SFTSV sequences were consistent with viruses circulating in the Republic of Korea. As dogs often live in close contact with humans, awareness of the clinical and epidemiological features of SFTS in dogs is crucial. Further large-scale studies are necessary to investigate SFTSV infection in dogs.

Meteorological factors and tick density affect the dynamics of SFTS in jiangsu province, China

Background

This study aimed to explore whether the transmission routes of severe fever with thrombocytopenia syndrome (SFTS) will be affected by tick density and meteorological factors, and to explore the factors that affect the transmission of SFTS. We used the transmission dynamics model to calculate the transmission rate coefficients of different transmission routes of SFTS, and used the generalized additive model to uncover how meteorological factors and tick density affect the spread of SFTS.

Methods

In this study, the time-varying infection rate coefficients of different transmission routes of SFTS in Jiangsu Province from 2017 to 2020 were calculated based on the previous multi-population multi-route dynamic model (MMDM) of SFTS. The changes in transmission routes were summarized by collecting questionnaires from 537 SFTS cases in 2018–2020 in Jiangsu Province. The incidence rate of SFTS and the infection rate coefficients of different transmission routes were dependent variables, and month, meteorological factors and tick density were independent variables to establish a generalized additive model (GAM). The optimal GAM was selected using the generalized cross-validation score (GCV), and the model was validated by the 2016 data of Zhejiang Province and 2020 data of Jiangsu Province. The validated GAMs were used to predict the incidence and infection rate coefficients of SFTS in Jiangsu province in 2021, and also to predict the effect of extreme weather on SFTS.

Results

The number and proportion of infections by different transmission routes for each year and found that tick-to-human and human-to-human infections decreased yearly, but infections through animal and environmental transmission were gradually increasing. MMDM fitted well with the three-year SFTS incidence data (P<0.05). The best intervention to reduce the incidence of SFTS is to reduce the effective exposure of the population to the surroundings. Based on correlation tests, tick density was positively correlated with air temperature, wind speed, and sunshine duration. The best GAM was a model with tick transmissibility to humans as the dependent variable, without considering lagged effects (GCV = 5.9247E-22, R² = 96%). Reported incidence increased when sunshine duration was higher than 11 h per day and decreased when temperatures were too high (>28°C). Sunshine duration and temperature had the greatest effect on transmission from host animals to humans. The effect of extreme weather conditions on SFTS was short-term, but there was no effect on SFTS after high temperature and sunshine hours.

Conclusions

Different factors affect the infection rate coefficients of different transmission routes. Sunshine duration, relative humidity, temperature and tick density are important factors affecting the occurrence of SFTS. Hurricanes reduce the incidence of SFTS in the short term, but have little effect in the long term. The most effective intervention to reduce the incidence of SFTS is to reduce population exposure to high-risk environments.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging vector-borne disease caused by SFTS virus. After the first case was detected in China in 2009, SFTS endemic areas have gradually increased, with more than 23 provinces and cities reporting SFTS cases. In order to explore the transmission mechanism of SFTS and explain the impact of meteorological factors and tick density on the transmission routes of SFTS, this study collected SFTS cases data, meteorological data and tick surveillance data in Jiangsu Province from 2017 to 2019 to investigate the study question. The multi-population and multi-route dynamic model established in the previous study was used to calculate the infection rate coefficients of various transmission routes of SFTS in Jiangsu Province, and the generalized additive model was established to further elaborate the influence of SFTS transmission mechanism.

Seasonal activity of Haemaphysalis longicornis and Haemaphysalis flava (Acari: Ixodida), vectors of severe fever with thrombocytopenia syndrome (SFTS) virus, and their SFTS virus harboring rates in Gyeonggi Province, South Korea

Seasonal activity of ticks, including disease vectors of fatal severe fever with thrombocytopenia syndrome (SFTS) virus, was monitored using CO₂-bait traps from April to November in 2019 and 2020 in a rural area in Gyeonggi-do, South Korea. Traps were deployed for 24 h once a month in four vegetation types: grassland, grave, mountain trail, and shrubs. A total of 4516 ticks were caught, all of which belong to the genus Haemaphysalis; larvae, nymphs, and adults were 41.9, 39.5, and 18.6%, respectively. The nymphs and adults belonged to two tick species, H. longicornis and H. flava, and H. longicornis was dominant, comprising 97.9% of the two stages collected. Larvae were identified only to the genus level due to difficulty of morphological distinction between species. For H. longicornis, nymph numbers peaked between April and June, followed by adults between June and July. Haemaphysalis larvae showed clear peaks in August. In general, H. longicornis nymphs and adults were most abundant in grassland, whereas larvae were so in the grave area. Collected ticks were pooled and subjected to PCR analysis to estimate SFTS virus harboring rate. In 2019, only one SFTS virus-positive sample was detected in June. However, a total of 18 SFTS-virus positive samples were detected from August to October in 2020.

The Prognostic Significance of C-Reactive Protein to Albumin Ratio in Patients With Severe Fever With Thrombocytopenia Syndrome

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with the high case-fatality rate, lacking effective therapies and vaccines. Inflammation-based indexes have been widely used to predict the prognosis of patients with cancers and some inflammatory diseases. In our study, we aim to explore the predictive value of the inflammation-based indexes in SFTS patients.

Methods

We retrospectively analyzed 82 patients diagnosed with SFTS. The inflammation-based indexes, including neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), platelet-to-lymphocyte ratio (PLR), systemic immune-inflammation index (SII), systemic inflammation response index (SIRI), aggregate index of systemic inflammation (AISI) and C-reactive protein to albumin ratio (CAR), were compared between the survival and death patients. Receiver operating characteristic (ROC) curves were used to compare the predictive ability of MLR, AISI, and CAR. The survival analysis was based on the Kaplan–Meier (KM) method. Multivariate logistic regression analysis was used to analyze the independent risk factors of poor prognosis in patients with SFTS.

Results

The CAR is higher in the death group while MLR and AISI were higher in the survival group. The ROC curve analysis indicated CAR exhibited more predictive value than the other indexes and the optimal cut-off value of CAR was equal to or greater than 0.14. KM survival curve showed that higher CAR was significantly correlated to the lower overall survival in SFTS patients. Multivariate logistic regression analysis indicated that CAR was an independent risk factor for poor prognosis in patients with SFTS.

Conclusion

The CAR is an independent risk factor for death in patients with SFTS and could predict the poor prognosis of SFTS patients. It could be used as a biomarker to help physicians to monitor and treat patients more aggressively to improve clinical prognosis.

Epidemiology, clinical characteristics, and treatment of severe fever with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease caused by a novel phlebovirus (SFTS virus, SFTSV) in the family Phenuiviridae of the order Bunyavirales. The disease causes a wide spectrum of clinical signs and symptoms, ranging from mild febrile disease accompanied by thrombocytopenia and/or leukocytopenia to hemorrhagic fever, encephalitis, multiple organ failure, and death. SFTS was first identified in China and was subsequently reported in South Korea and Japan. The case-fatality rate ranges from 2.7% to 45.7%. Older age has been consistently shown to be the most important predictor of adverse disease outcomes. Older age exacerbates disease mainly through dysregulation of host immune cells and uncontrolled inflammatory responses. Tick-to-human transmission is the primary route of human infection with SFTSV, and Haemaphysalis longicornis is the primary tick vector of SFTSV. Despite its high case-fatality rate, vaccines and antiviral therapies for SFTS are not currently available. The therapeutic efficacies of several antiviral agents against SFTSV are currently being evaluated. Ribavirin was initially identified as a potential antiviral therapy for SFTS but was subsequently found to inefficiently improve disease outcomes, especially among patients with high viral loads. Favipiravir (T705) decreased both time to clinical improvement and mortality when administered early in patients with low viral loads. Anti-inflammatory agents including corticosteroids have been proposed to play therapeutic roles. However, the efficacy of other therapeutic modalities, such as convalescent plasma, is not yet clear.

Vectors, Hosts, and the Possible Risk Factors Associated with Severe Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is a disease caused by infection with the SFTS virus (SFTSV). SFTS has become a crucial public health concern because of the heavy burden, lack of vaccines, effective therapies, and high-fatality rate. Evidence suggests that SFTSV circulates between ticks and animals in nature and is transmitted to humans by tick bites. In particular, ticks have been implicated as vectors of SFTSV, where domestic or wild animals may play as the amplifying hosts. Many studies have identified antigens and antibodies against SFTSV in various animals such as sheep, goats, cattle, and rodents. Besides, person-to-person transmission through contact with blood or mucous of an infected person has also been reported. In this study, we reviewed the literature and summarized the vectors and hosts associated with SFTS and the possible risk factors.

Infection with severe fever with thrombocytopenia virus in healthy population: a cohort study in a high endemic region, China

Background

Severe fever with thrombocytopenia (SFTS) caused by SFTS virus (SFTSV) was a tick-borne hemorrhagic fever that posed significant threat to human health in Eastern Asia. The study was designed to measure the seroprevalence of SFTSV antibody in healthy population residing in a high endemic region.

Methods

A cohort study was performed on healthy residents in Shangcheng County in Xinyang City from April to December in 2018, where the highest SFTS incidence in China was reported. Anti-SFTSV IgG was measured by indirect enzyme-linked immunosorbent assay and neutralizing antibody (NAb) was detected by using PRNT50. The logistic regression models were performed to analyze the variables that were associated with seropositive rates.

Results

Totally 886 individuals were recruited. The baseline seroprevalence that was tested before the epidemic season was 11.9% (70/587) for IgG and 6.8% (40/587) for NAb, which was increased to 13.4% (47/350) and 7.7% (27/350) during the epidemic season, and further to 15.8% (80/508) and 9.8% (50/508) post epidemic. The IgG antibody-based seropositivity was significantly related to the patients aged ≥ 70 years old [adjusted odds ratio (OR) = 2.440, 95% confidence interval (CI): 1.334–4.461 compared to the group of < 50 years old, P = 0.004], recent contact with cats (adjusted OR = 2.195, 95% CI: 1.261–3.818, P = 0.005), and working in tea garden (adjusted OR = 1.698, 95% CI: 1.002–2.880, P = 0.049) by applying multivariate logistic regression model. The NAb based seropositivity was similarly related to the patients aged ≥ 70 years old (adjusted OR = 2.691, 95% CI: 1.271–5.695 compared to the group of < 50 years old, P = 0.010), and recent contact with cats (OR = 2.648, 95% CI: 1.419–4.941, P = 0.002). For a cohort of individuals continually sampled with 1-year apart, the anti-SFTSV IgG were maintained at a stable level, while the NAb level reduced.

Conclusions

Subclinical infection might not provide adequate immunity to protect reinfection of SFTSV, thus highlighting the ongoing threats of SFTS in endemic regions, which called for an imperative need for vaccine development. Identification of risk factors might help to target high-risk population for public health education and vaccination in the future.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s40249-021-00918-0.

Seroepidemiological surveys of tick-borne encephalitis virus and novel tick-borne viruses in wild boar in Nagasaki, Japan

In Japan, tick-borne viruses such as tick-borne encephalitis virus (TBEV) and severe fever with thrombocytopenia syndrome virus have been identified in humans, animals, and ticks. In addition, novel tick-borne viruses have been isolated from ticks in Japan. This study aimed to determine the seroprevalence of TBEV and novel viruses, particularly Tofla virus (TFLV), Kabuto Mountain virus (KAMV), and Muko virus (MUV) in wild boar in Nagasaki, Japan. Enzyme-linked immunosorbent assays and neutralization tests were performed to detect antibodies against each virus. Wild boar serum tested positive for antibodies against KAMV, TFLV, and TBEV, but not MUV. This study revealed the seroprevalence of newly identified tick-borne viruses and TBEV in animals residing in the Nagasaki area. The seroprevalence of these viruses in sentinel animals may inform policies aimed at preventing tick-borne virus disease outbreaks.

Experimental infection of dogs with severe fever with thrombocytopenia syndrome virus: Pathogenicity and potential for intraspecies transmission

Severe fever with thrombocytopenia syndrome (SFTS) is caused by infection with Dabie bandavirus [formerly SFTS virus (SFTSV)] and is an emerging zoonotic disease. Dogs can be infected with SFTSV, but its pathogenicity and transmissibility have not been fully elucidated. In experiment 1, immunocompetent dogs were intramuscularly inoculated with SFTSV. In experiment 2, immunosuppressed dogs (immunosuppressed group; oral azathioprine 5 mg/kg/day for 30 days) were intramuscularly inoculated with SFTSV. Both immunosuppressed and immunocompetent contact dogs were co-housed with the SFTSV-inoculated dogs that had been immunosuppressed. Immunocompetent SFTSV-infected dogs did not show any clinical symptom. However, immunosuppressed SFTSV-infected dogs showed high fever and weight loss without lethality. In all SFTSV-infected dogs, viral RNA could be measured in the serum only after 3 days post infection (DPI) and neutralizing antibodies were detected in the serum beginning 9 DPI. SFTSV shedding in the urine and faeces of some infected dogs occurred between 4 and 6 DPI. The immunocompromised SFTSV-infected dogs showed thrombocytopenia beginning 3 DPI to the end of the experiment (24 DPI). We confirmed SFTSV transmission to one of three immunocompetent co-housed dogs. This dog showed a high fever, weight loss, and shed viral RNA by urine. Viral RNA and neutralizing antibodies were also detected in the serum. These results demonstrated that intramuscular inoculation with SFTSV induced minor clinical symptoms in dogs, and intraspecies SFTSV transmission in dogs can occur by contact.

Epidemiological and clinical characteristics of severe fever with thrombocytopenia syndrome in southern Anhui Province, 2011-2020

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever, and the causative pathogen, the SFTS virus (SFTSV), was first discovered in China in 2010. In this study, a retrospective analysis of 86 patients that diagnosed with SFTS from two five-year periods (2011-2015 and 2016-2020) that was performed to explore the changes in epidemiology, clinical characteristics, laboratory parameters and prognosis between those two periods. The results showed that there were significant differences in age, the proportion of farmers, geographical distribution, the incidence of multiple organ dysfunction, the decrease in thrombocyte count, and the elevations of serum AST and lipase levels between the two groups (p<0.05). Additionally, the case-fatality rate in the 2016-2020 group (16.7%) was higher than that in the 2011-2015 group (6.25%), although the difference was not significant. Our study shows that SFTS is broadly distributed across Anhui Province. The mortality rate is high. May to July was the peak of the epidemic, and farmers constituted a high-risk group. In recent years, thrombocytopenia has become more serious, and multiple organ dysfunction is more common. Clinicians need to further strengthen their knowledge of the changing epidemiological and clinical characteristics of this disease.

Survey of severe fever with thrombocytopenia syndrome virus in wild boar in the Republic of Korea

Severe fever with thrombocytopenia syndrome (SFTS) is caused by Dabie bandavirus that belongs to the genus Bandavirus in the family Phenuiviridae and order Bunyavirales and is transmitted by hard ticks. It has been detected in several tick species, various animals, and humans. The purpose of this study was to detect SFTS virus (SFTSV) antigen and antibody in wild boar in the Republic of Korea (ROK). A total of 768 sera samples were collected from wild boar in the ROK between January and December 2019. Viral RNA was extracted from sera using viral RNA extraction kit, and one-step RT-nested polymerase chain reaction (PCR) was performed to amplify the S segment of the SFTSV. The sequencing data were analyzed using Chromas and aligned using Clustal X. The phylogenetic tree was constructed using the maximum-likelihood method using MEGA7. In addition, wild boar sera were tested for IgG antibodies against SFTSV by enzyme-linked immunosorbent assay (ELISA) and immunofluorescence assay (IFA). Of a total of 768 sera samples, 40 (5.2%) were positive for SFTSV by RT-PCR targeting the S segment. Two hundred twenty-one (28.8%) and 159 (20.7%) of 768 sera samples were seropositive by ELISA and IFA, respectively. Based on both ELISA and IFA tests of the same samples, 110 (14.3%) wild boar sera samples were positive for SFTSV antibodies. Of a total of 40 positive serum samples by RT-PCR, 33 (82.5%) and 7 (17.5%) sera were classified as the genotype B-3 and D, respectively, by sequence analysis,. These results provide useful information that demonstrates the detection of antigen and antibody in wild boar sera samples for every month of a certain year throughout the ROK.

Factors and outcomes in Severe Fever with Thrombocytopenia Syndrome (SFTS): A systematic review

BACKGROUND

An emerging infectious zoonosis known as Severe Fever with Thrombocytopenia Syndrome (SFTS) is discovered mainly in Japan, South Korea and China. SFTS virus (SFTSV) which is recently recognised as bunyavirus is borne by ticks such as Haemaphysalis longicornis. It has the capabilities to spread as develop clusters and become a considerable public health threat as this virus could experience rapid evolution via gene mutation. Case fatality rate has been reported up to higher than 30%. The aim of this review is to determine the associated risk factors of SFTS and its outcome.

MATERIALS AND METHODS

Literature search was conducted using online databases PubMed, ScienceDirect, and Scopus. A total of 517 records were identified from searches in PubMed, ScienceDirect, and Scopus. From the final exclusions, a total of 26 studies were included for final analysis.

RESULTS

Associated risk factors to getting SFTS infection include occupation, history of bite from a tick, biological susceptibility, and owning of domestic animal. Fatality rates apart from single case reports range from 15.1% to 50% and are contributed by various factors including delay in hospital admission, high viral load, older age group and presence of comorbid and complication.

CONCLUSION

A seroprevalence study can be conducted amongst the high-risk occupation group such as farmers and agricultural workers, as well as testing cases where viral fever is suspected but available tests for other diseases turns out negative.

Severe Fever with Thrombocytopenia Syndrome in Cats and Its Prevalence among Veterinarian Staff Members in Nagasaki, Japan

In this study, we investigated severe fever with thrombocytopenia syndrome (SFTS) virus (SFTSV) infection in cats in Nagasaki, Japan. In total, 44 of 133 (33.1%) cats with suspected SFTS were confirmed to be infected with SFTSV. Phylogenetic analyses of SFTSV isolates from cats indicated that the main genotype in Nagasaki was J1 and that unique reassortant strains with J2 (S segment) and unclassified genotypes (M and L segments) were also present. There were no significant differences in virus growth in cell cultures or fatality in SFTSV-infected mice between the SFTSV strains that were isolated from recovered and fatal cat cases. Remarkably, SFTSV RNAs were detected in the swabs from cats, indicating that the body fluids contain SFTSV. To evaluate the risk of SFTSV infection when providing animal care, we further examined the seroprevalence of SFTSV infection in veterinarian staff members; 3 of 71 (4.2%) were seropositive for SFTSV-specific antibodies. Our results provide useful information on the possibility of using cats as sentinel animals and raised concerns of the zoonotic risk of catching SFTSV from animals.

Modelling the transmission dynamics of severe fever with thrombocytopenia syndrome in Jiangsu Province, China

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease that is regionally distributed in Asia, with high fatality. Constructing the transmission model of SFTS could help provide clues for disease control and fill the gap in research on SFTS models.

METHODS

We built an SFTS transmission dynamics model based on the susceptible-exposed-infectious-asymptomatic-recovered (SEIAR) model and the epidemiological characteristics of SFTS in Jiangsu Province. This model was used to evaluate the effect by cutting off different transmission routes and taking different interventions into account, to offer clues for disease prevention and control.

RESULTS

The transmission model fits the reported data well with a minimum R2 value of 0.29 and a maximum value of 0.80, P < 0.05. Meanwhile, cutting off the environmental transmission route had the greatest effect on the prevention and control of SFTS, while isolation and shortening the course of the disease did not have much effect.

CONCLUSIONS

The model we have built can be used to simulate the transmission of SFTS to help inform disease control. It is noteworthy that cutting off the environment-to-humans transmission route in the model had the greatest effect on SFTS prevention and control.

Severe fever with thrombocytopenia syndrome virus: emerging novel phlebovirus and their control strategy

An emerging infectious disease first identified in central China in 2009, severe fever with thrombocytopenia syndrome (SFTS) was found to be caused by a novel phlebovirus. Since SFTSV was first identified, epidemics have occurred in several East Asian countries. With the escalating incidence of SFTS and the rapid, worldwide spread of SFTSV vector, it is clear this virus has pandemic potential and presents an impending global public health threat. In this review, we concisely summarize the latest findings regarding SFTSV, including vector and virus transmission, genotype diversity and epidemiology, probable pathogenic mechanism, and clinical presentation of human SFTS. Ticks most likely transmit SFTSV to animals including humans; however, human-to-human transmission has been reported. The majority of arbovirus transmission cycle includes vertebrate hosts, and potential reservoirs include a variety of both domestic and wild animals. Reports of the seroprevalence of SFTSV in both wild and domestic animals raises the probability that domestic animals act as amplifying hosts for the virus. Major clinical manifestation of human SFTS infection is high fever, thrombocytopenia, leukocytopenia, gastrointestinal symptoms, and a high case-fatality rate. Several animal models were developed to further understand the pathogenesis of the virus and aid in the discovery of therapeutics and preventive measures.

Factors associated with spatial distribution of severe fever with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS) was firstly identified in mainland China in 2009 and the geographic distribution has expanded in recent years. In this study, we constructed ecological niche models (ENM) of SFTS with meteorological factors, environmental factor, and density of domestic animals using MaxEnt. We found four significant associated factors including altitude, yearly average temperature, yearly accumulated precipitation, and yearly average relative humidity which accounted for 94.1% percent contribution. SFTS occurrence probability was high when altitude was between -100 m and 100 m, and the probability was nearly 0 when altitude was beyond 3000 m. Response curves of SFTS to the yearly average temperature, yearly accumulated precipitation, and yearly average relative humidity were all reversed V-shape. SFTS occurrence probability was high where the yearly average temperature, yearly accumulated precipitation, and yearly relative humidity were 12.5-17.5 °C, 700-2250 mm and 63-82%, respectively. ENMs predicted that the potential high-risk areas were mainly distributed in eastern areas and central areas of China. But there were some predicted potential high-risk areas where no SFTS case was reported up to date. More researches should be done to make clear whether SFTS case had occurred in these areas.

Severe fever with thrombocytopenia syndrome virus: a systematic review and meta-analysis of transmission mode

Severe fever with thrombocytopenia syndrome (SFTS) is a disease with a high case-fatality rate that is caused by infection with the SFTS virus (SFTSV). Five electronic databases were systematically searched to identify relevant articles published from 1 January 2011 to 1 December 2019. The pooled rates with 95% confidence interval (CI) were calculated by a fixed-effect or random-effect model analysis. The results showed that 92 articles were included in this meta-analysis. For the confirmed SFTS cases, the case-fatality rate was 0.15 (95% CI 0.11, 0.18). Two hundred and ninety-six of 1384 SFTS patients indicated that they had been bitten by ticks and the biting rate was 0.21 (95% CI 0.16, 0.26). The overall pooled seroprevalence of SFTSV antibodies among the healthy population was 0.04 (95% CI 0.03, 0.05). For the overall seroprevalence of SFTSV in animals, the seroprevalence of SFTSV was 0.25 (95% CI 0.20, 0.29). The infection rate of SFTSV in ticks was 0.08 (95% CI 0.05, 0.11). In conclusion, ticks can serve as transmitting vectors of SFTSVs and reservoir hosts. Animals can be infected by tick bites, and as a reservoir host, SFTSV circulates continuously between animals and ticks in nature. Humans are infected by tick bites and direct contact with patient secretions.

Endemic and Emerging Arboviruses in Domestic Ruminants in East Asia

Epizootic congenital abnormalities caused by Akabane, Aino, and Chuzan viruses have damaged the reproduction of domestic ruminants in East Asia for many years. In the past, large outbreaks of febrile illness related to bovine ephemeral fever and Ibaraki viruses severely affected the cattle industry in that region. In recent years, vaccines against these viruses have reduced the occurrence of diseases, although the viruses are still circulating and have occasionally caused sporadic and small-scaled epidemics. Over a long-term monitoring period, many arboviruses other than the above-mentioned viruses have been isolated from cattle and Culicoides biting midges in Japan. Several novel arboviruses that may infect ruminants (e.g., mosquito- and tick-borne arboviruses) were recently reported in mainland China based on extensive surveillance. It is noteworthy that some are suspected of being associated with cattle diseases. Malformed calves exposed to an intrauterine infection with orthobunyaviruses (e.g., Peaton and Shamonda viruses) have been observed. Epizootic hemorrhagic disease virus serotype 6 caused a sudden outbreak of hemorrhagic disease in cattle in Japan. Unfortunately, the pathogenicity of many other viruses in ruminants has been uncertain, although these viruses potentially affect livestock production. As global transportation grows, the risk of an accidental incursion of arboviruses is likely to increase in previously non-endemic areas. Global warming will also certainly affect the distribution and active period of vectors, and thus the range of virus spreads will expand to higher-latitude regions. To prevent anticipated damages to the livestock industry, the monitoring system for arboviral circulation and incursion should be strengthened; moreover, the sharing of information and preventive strategies will be essential in East Asia.

Severe Fever with Thrombocytopenia Syndrome Associated with Manual De-Ticking of Domestic Dogs

Background: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease. SFTS is caused by the SFTS virus, a novel phlebovirus, and is spread by ticks. Methods: A 50-year-old man was admitted to our hospital with the chief complaint of fever and was diagnosed with confirmed SFTS. An epidemiological investigation was conducted, and immunofluorescent antibody assays (IFAs) were performed to determine the role of the patient's three dogs in the transmission. PCR assays were performed using ticks that were collected with the dragging and flagging method from the patient's dogs and home. Results: PCR results were positive, and IFA confirmed an increased antibody titer. Although the reverse transcription PCR results of the three dogs were negative for SFTS virus, one dog had an elevated SFTS IFA immunoglobulin G (IgG) titer of 1:1,024. Moreover, a number of ticks were observed in the area surrounding the dog cages. Based on the findings of the patient interview, the patient was likely to have acquired SFTS by blood splash because he removed or burst ticks from the dogs with his bare hands. Although no tick bites were reported, tick transmission could not be ruled out. Studies have shown that only one in three individuals with a diagnosis of SFTS recalls a tick bite; thus, a definite exclusion of tick transmission in this case was not possible. Conclusions: The epidemiological findings of our case suggest a possible relationship between tick infestation in domestic dogs and SFTS virus transmission to humans. However, there is no direct evidence supporting this viral transmission route. Future studies are needed to further investigate a potential route of SFTS transmission by exposure to engorged tick blood or pet dogs.

Seroprevalence of Severe Fever with Thrombocytopenia Syndrome in the Agricultural Population of Jeju Island, Korea, 2015-2017

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne zoonotic disease that is caused by the SFTS virus (SFTSV), and exhibits an overall mortality rate of approximately 20.0% in Korea. Most cases of this disease have been reported in Korea, East China, and Japan, and it mostly affects outdoor workers and farmers. This study aimed to investigate the seroprevalence of SFTSV among healthy farmers on Jeju Island, Korea.

MATERIALS AND METHODS

In this prospective cross-sectional study, we analyzed 421 blood samples obtained from 254 farmers (mean age, 59.9 years; 68.9% male) to determine the seroprevalence of SFTSV in 16 rural areas of the Jeju Special Self-Governing Province over a period of 3 years (January 2015-December 2017). We used an enzyme-linked immunosorbent assay to detect immunoglobulin (Ig) G antibodies against SFTSV in the collected samples.

RESULTS

The seroprevalence of the SFTSV IgG among farmers on Jeju Island was observed to be 2.4%. One subject showed seropositivity over the entire 3-year study period. The areas with the highest SFTSV IgG seropositivity rates were Seonheul-ri in Jocheon-eup, followed by Namwon-eup. Fruit farmers were at a higher risk of exposure to SFTSV than other farmers.

CONCLUSION

The seroprevalence of SFTSV in the healthy agricultural population of Jeju Island was not high. However, personal hygiene management should be implemented for the agricultural population in the endemic areas. Surveillance of mild or asymptomatic infections is required in the endemic regions.

Susceptibility of spotted doves (Streptopelia chinensis) to experimental infection with the severe fever with thrombocytopenia syndrome phlebovirus

Background

Severe fever with thrombocytopenia syndrome virus (SFTSV), an emerging human pathogen naturally transmitted by ticks, has spread widely since it was first detected in 2010. Although SFTSV-specific antibodies have been detected in wild birds, these natural reservoir and amplifying hosts for the virus have not been well studied.

Methodology/Principle findings

Here we report an experimental infection of spotted doves (Streptopelia chinensis) with two strains of SFTSV, JS2010-14, a Chinese lineage strain, and JS2014-16, a Japanese lineage strain, which represent the main viral genotypes currently circulating in East Asia. In these studies, we have determined that spotted doves are susceptible to SFTSV and the severity of the viremia is dose-dependent. When challenged with 10⁷ and 10⁵ PFU, all doves developed viremia which peaked 3–5 days post infection (dpi). Only a subset (25–62.5%) of the birds developed viremia when challenged at 10³ PFU. Virulence of SFTSV in spotted doves was strain dependent. Infection with 10⁷ PFU of strain JS2014-16 resulted in 12.5% mortality over 6.8 days and mean peak viremia titers of 10^6.9 PFU/mL in experimentally inoculated birds. All doves inoculated with 10⁷ PFU of the JS2010-14 strain survived infection with relatively lower mean viremia titers (10^5.6 PFU/mL at peak) over 6.1 days.

Conclusions/Significance

Our results suggest that spotted doves, one of the most abundant bird species in China, could be a competent amplifying host for SFTSV and play an important role in its ecology. Between the two SFTSV strains, the strain of the Japanese lineage caused mortality, higher viremia titers in infected birds over a longer time period than did the Chinese strain. Our observations shed light on the ecology of SFTSV, which could benefit the implementation of surveillance and control programs.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging human pathogen naturally transmitted by ticks. Our recent study has showed that some species of migratory birds, such as swan geese and spotted doves, can be parasitized by Haemaphysalis longicornis, an SFTSV vector, and antibodies against the SFTSV detected in these species. These data demonstrate that migratory birds are infected with SFTSV and may also play a role in the infection of ticks with SFTSV. Other studies have reported that migratory bird routes and the distribution of H. longicornis in East Asia overlap with the geographic distribution of SFTSV. Migratory birds are known to be carriers and transmitters of infectious agents, like the causative agents of influenza, West Nile encephalitis, and Lyme disease. Wild birds often travel long distances carrying various parasites, including ticks, which may be infected with viruses and bacteria. It is therefore reasonable to hypothesize that migratory birds may have played an important role in spreading SFTSV in two potential transmission scenarios: 1) birds are infected with the virus and transmit it back to ticks endemically or in a distal region, or 2) they are carriers of parasitic ticks that are infected with the virus. Here we report an experimental infection of spotted doves (Streptopelia chinensis) with two strains of SFTSV, JS2010-14 from a Chinese lineage and JS2014-16 from a Japanese lineage, which represent the main viral genotypes currently circulating in East Asia. We determined that spotted doves are susceptible to SFTSV and that the severity of the viremia was dose and strain dependent. Infection with the strain of JS2014-16 led to a death rate of 12.5% and higher viremia titers in experimentally inoculated birds while doves inoculated with the JS2010-14 strain survived infection with relatively lower virus titers in the blood. These findings provide novel insights for understanding the rapid spread of the virus in a short time span, in particular the SFTSV strains from the Japanese lineage (genotype E).

Prevalence of severe fever with thrombocytopenia syndrome virus in animals in Henan Province, China

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by severe fever with thrombocytopenia syndrome virus (SFTSV). SFTSV has been found in humans, ticks and animals, and SFTS has high mortality and increasing prevalence in East Asia. In the study, the samples (heart, liver, lung, kidney, spleen, brain tissue and serum) were collected from 374 domestic animals and 241 wild animals in Pingqiao District and Xinxian County of Xinyang in Henan Province, China. 275 (44.72%, 275/615) animals were positive for anti-SFTSV antibodies, the anti-SFTSV antibodies positive ratios of domestic and wild animals were 43.58% (163/374) and 46.47% (112/241), respectively. There was no significant difference in domestic and wild animals, but significant differences were detected among different species of animals (χ² = 112.59, P < 0.0001). Among 615 animals, 105 (17.07%, 105/615) animals were positive for SFTSV RNA, and only one SFTSV strain was isolated from heart tissue of a yellow weasel. The phylogenetic analysis shows that the sequence from animals belonged to the same group with viral sequences obtained from humans. The animals maybe play a reservoir host in maintaining the life cycle of SFTSV in nature.

A Cluster of Bunyavirus-Associated Severe Fever With Thrombocytopenia Syndrome Cases in a Coastal Plain Area in China, 2015: Identification of a Previously Unidentified Endemic Region for Severe Fever With Thrombocytopenia Bunyavirus

Background

Severe fever with thrombocytopenia syndrome (SFTS) is a typical tick-borne, natural focal disease. The natural foci of SFTS were considered to exist in hilly and mountainous areas before 2015. A cluster of 3 patients exposed to a patient with a fulminant disease consistent with SFTS occurred from July to August 2015 in Dongtai County, which is characterized by alluvial plains; this prompted investigation.

Methods

The epidemiological, clinical, and laboratory features of 4 patients in the cluster were analyzed. Serum samples from the indigenous healthy population and native domesticated animals were collected to conduct laboratory tests, along with small wild animals and ticks.

Results

In 3 secondary case patients, high fever, thrombocytopenia and leukopenia developed within 8-13 days after contact with blood or bloody secretions from the index patient; SFTS was then diagnosed by means of reverse-transcription polymerase chain reaction. Genomic sequencing and analysis of S and L segments of 2 viral strains isolated from 2 secondary case patients showed that they shared 99.8%-99.9% homology in nucleotide sequence. The seroprevalences among indigenous healthy population, native livestock, native poultry, and small wild animals was 0.74%, 17.54%, 6.67%, and 1.12%, respectively. Three questing ticks, 61 feeding ticks, and 178 small wild animals were collected in August 2015. Survey on tick density and seasonal fluctuation in 2016 showed that ticks were active from March to October. All ticks were identified as Haemaphysalis longicornis. Severe fever with thrombocytopenia bunyavirus (SFTSV)-specific RNA was detected in the ticks collected in 2016, and the minimum SFTSV infection rate in these ticks was 0.54% (1 of 185).Wild mammals and ticks collected in August 2015 tested negative for SFTSV-specific RNA.

Conclusions

Aside from hilly or mountainous area, a coastal plain was identified as the natural foci of SFTSV in Dongtai County, China. The involvement of migration in the evolution of SFTSV might lead to a transregional transmission event of SFTSV.

Environmental Risk Factors and Geographic Distribution of Severe Fever with Thrombocytopenia Syndrome in Jiangsu Province, China

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging natural focus, tick-borne disease caused by a novel bunyavirus named SFTS virus (SFTSV). The main purpose of this study was to analyze the environmental risk factors and geographic distribution of SFTS natural foci in Jiangsu Province. A retrospective space-time analysis by SaTScan software was used to detect clusters at the town level. The maximum entropy modeling method was applied to construct the ecological niche model and analyze the environmental risk factors, and then to draw the predicted risk map. The performance of the model was assessed using the area under the curve (AUC) and known occurrence locations. During the years 2010-2016, a total of 140 laboratory-confirmed indigenous SFTS cases occurred in Jiangsu Province, with 66 occurrence locations. The reported number of SFTS cases increased year by year and SFTS cases occurred from April to October with a peak between May and August each year. Three clusters detected by space-time scan statistical analysis were connected together and shared the similar ecological environmental characteristic of hilly landscape. Fifteen environmental variables with different percent contribution can influence the ecological niche model in different degrees, whereas slope (suitable range: 0.1-4) and maximum temperature of warmest month (suitable range: 32.8-34.2°C) as the key environmental factors contributed 46.1% and 23.2%, respectively. The model had high accuracy on prediction with the averaged training AUC of 0.926. Within a predicted risk map, potential areas at high risk and 10 previously unidentified endemic regions were recognized. The distribution of SFTS natural foci was under the influence of multidimensional environmental factors. Slope and maximum temperature of warmest month were the key environmental risk factors. These results provide a valuable basis for the selection of prevention and control strategies, and the identification of potential risk areas.

M Segment-Based Minigenomes and Virus-Like Particle Assays as an Approach To Assess the Potential of Tick-Borne Phlebovirus Genome Reassortment

Bunyaviruses have a tripartite negative-sense RNA genome. Due to the segmented nature of these viruses, if two closely related viruses coinfect the same host or vector cell, it is possible that RNA segments from either of the two parental viruses will be incorporated into progeny virions to give reassortant viruses. Little is known about the ability of tick-borne phleboviruses to reassort. The present study describes the development of minigenome assays for the tick-borne viruses Uukuniemi phlebovirus (UUKV) and Heartland phlebovirus (HRTV). We used these minigenome assays in conjunction with the existing minigenome system of severe fever with thrombocytopenia syndrome (SFTS) phlebovirus (SFTSV) to assess the abilities of viral N and L proteins to recognize, transcribe, and replicate the M segment-based minigenome of a heterologous virus. The highest minigenome activity was detected with the M segment-based minigenomes of cognate viruses. However, our findings indicate that several combinations utilizing N and L proteins of heterologous viruses resulted in M segment minigenome activity. This suggests that the M segment untranslated regions (UTRs) are recognized as functional promoters of transcription and replication by the N and L proteins of related viruses. Further, virus-like particle assays demonstrated that HRTV glycoproteins can package UUKV and SFTSV S and L segment-based minigenomes. Taken together, these results suggest that coinfection with these viruses could lead to the generation of viable reassortant progeny. Thus, the tools developed in this study could aid in understanding the role of genome reassortment in the evolution of these emerging pathogens in an experimental setting.IMPORTANCE In recent years, there has been a large expansion in the number of emerging tick-borne viruses that are assigned to the Phlebovirus genus. Bunyaviruses have a tripartite segmented genome, and infection of the same host cell by two closely related bunyaviruses can, in theory, result in eight progeny viruses with different genome segment combinations. We used genome analogues expressing reporter genes to assess the abilities of Phlebovirus nucleocapsid protein and RNA-dependent RNA polymerase to recognize the untranslated region of a genome segment of a related phlebovirus, and we used virus-like particle assays to assess whether viral glycoproteins can package genome analogues of related phleboviruses. Our results provide strong evidence that these emerging pathogens could reassort their genomes if they were to meet in nature in an infected host or vector. This reassortment process could result in viruses with new pathogenic properties.

Seroprevalence of Severe Fever with Thrombocytopenia Syndrome Virus Antibodies in Rural Areas, South Korea

We investigated 1,228 residents of 3 rural areas in South Korea and determined that 50 (4.1%) were positive for severe fever with thrombocytopenia syndrome virus antibodies. Fever and gastrointestinal symptoms in the previous 3 years and career duration were associated with virus seropositivity.

Seroprevalence of severe fever with thrombocytopenia syndrome (SFTS) virus antibodies in humans and animals in Ehime prefecture, Japan, an endemic region of SFTS

Severe fever with thrombocytopenia syndrome (SFTS) was first identified as an emerging tick-borne infectious disease caused by the SFTS virus (SFTSV) in China and has also been found to be endemic to Japan and South Korea, indicating that SFTS is of great concern in East Asia. The aim of the present study was to determine the seroprevalence of SFTSV antibodies in humans and animals in SFTS-endemic regions of Japan. One of 694 (0.14%) healthy persons over 50 years of age and 20 of 107 (18.7%) wild and domestic animals in Ehime prefecture of western Japan were determined to be seropositive for SFTSV antibodies by virus neutralization test and ELISA, respectively. The seropositive person, a healthy 74-year-old woman, was a resident of the southwest part of Ehime prefecture engaged in citriculture and field work. This woman's sample exhibited neutralizing activity against SFTSV although she had neither a clear experience with tick bites nor SFTS-like clinical illness. These findings indicate that most people living in the endemic regions are not infected with SFTSV and suggest that most of the SFTS patients reported so far do not reflect the tip of an iceberg of people infected with SFTSV, but at the same time, that SFTSV infection does not always induce severe SFTS-associated symptoms. These findings also suggested that SFTSV has been maintained in nature within animal species and ticks.

A cluster of cases of severe fever with thrombocytopenia syndrome bunyavirus infection in China, 1996: A retrospective serological study

BACKGROUND

A cluster of eleven patients, including eight family members and three healthcare workers with fever and thrombocytopenia occurred in Yixing County, Jiangsu Province, China, from October to November 1996. However, the initial investigation failed to identify its etiology. Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by SFTS bunyavirus (SFTSV), which was first discovered in 2009. The discovery of novel SFTSV resulted in our consideration to test SFTSV on the remaining samples of this cluster in September 2010.

METHODOLOGY/PRINCIPAL FINDINGS

We retrospectively analyzed the epidemiological and clinical data of this cluster. The first case, one 55-year-old man with fulminant hemorrhagic diseases, died on October 14, 1996. His younger brother (the second case) developed similar hemorrhagic diseases after nursing him and then died on November 3. From November 4 to November 15, nine other patients, including six family members and three medical staffs, developed fever and thrombocytopenia after exposure to the second case. The sera of six patients were collected on November 24, 1996. IgM antibodies against SFTSV were detected in all of the six patients' sera using enzyme-linked immunosorbent assay (ELISA), while IgG antibodies were detected in one patient's serum using an indirect immunofluorescence assay (IFA). We also found that IgG antibodies against SFTSV were still detected in four surviving patients' sera 14 years after illness onset.

CONCLUSIONS AND SIGNIFICANCE

The mysterious pathogen of the cluster in 1996 was proved to be SFTSV on the basis of its epidemiological data, clinical data and serological results. It suggests that SFTSV has been circulating in China for more than 10 years before being identified in 2009, and SFTSV IgG antibodies can persist for up to 14 years.

The Unique Phylogenetic Position of a Novel Tick-Borne Phlebovirus Ensures an Ixodid Origin of the Genus Phlebovirus

The emergence of novel tick-borne RNA viruses causing severe illness in humans has complicated the epidemiological landscape of tick-borne diseases, requiring further investigation to safeguard public health. In the present study, we discovered a novel tick-borne phlebovirus from Ixodes persulcatus ticks in Japan. While its viral RNA genome sequences were similar to those of mosquito/sandfly-borne viruses, molecular and biological footprints confirmed that this is a tick-borne virus. The unique evolutionary position of the virus allowed us to estimate the ancestral phlebovirus vector, which was likely a hard tick. Our findings may provide a better understanding of the evolution and emergence of phleboviruses associated with emerging infectious diseases, such as severe fever with thrombocytopenia syndrome (SFTS) and Heartland virus disease.

The recent emergence of novel tick-borne RNA viruses has complicated the epidemiological landscape of tick-borne infectious diseases, posing a significant challenge to public health systems that seek to counteract tick-borne diseases. The identification of two novel tick-borne phleboviruses (TBPVs), severe fever with thrombocytopenia syndrome virus (SFTSV) and Heartland virus (HRTV), as causative agents of severe illness in humans has accelerated the investigation and discoveries of novel TBPVs. In the present study, we isolated a novel TBPV designated Mukawa virus (MKWV) from host-questing Ixodes persulcatus females captured in Japan. Genetic characterization revealed that MKWV is a member of the genus Phlebovirus in the family Phenuiviridae. Interestingly, MKWV is genetically distinct from other known TBPVs and shares a most recent common ancestor with mosquito/sandfly-borne (insect-borne) phleboviruses. Despite its genetic similarity to insect-borne phleboviruses, the molecular footprints of its viral proteins and its biological characteristics define MKWV as a tick-borne virus that can be transmitted to mammals. A phylogenetic ancestral-state reconstruction for arthropod vectors of phleboviruses including MKWV based on viral L segment sequences indicated that ticks likely harbored ancestral phleboviruses that evolved into both the tick-borne and MKWV/insect-borne phlebovirus lineages. Overall, our findings suggest that most of the phlebovirus evolution has occurred in hard ticks to generate divergent viruses, which may provide a seminal foundation for understanding the mechanisms underlying the evolution and emergence of pathogenic phleboviruses, such as Rift Valley fever virus and SFTSV/HRTV.

IMPORTANCE The emergence of novel tick-borne RNA viruses causing severe illness in humans has complicated the epidemiological landscape of tick-borne diseases, requiring further investigation to safeguard public health. In the present study, we discovered a novel tick-borne phlebovirus from Ixodes persulcatus ticks in Japan. While its viral RNA genome sequences were similar to those of mosquito/sandfly-borne viruses, molecular and biological footprints confirmed that this is a tick-borne virus. The unique evolutionary position of the virus allowed us to estimate the ancestral phlebovirus vector, which was likely a hard tick. Our findings may provide a better understanding of the evolution and emergence of phleboviruses associated with emerging infectious diseases, such as severe fever with thrombocytopenia syndrome (SFTS) and Heartland virus disease.

Molecular Detection of Severe Fever with Thrombocytopenia Syndrome Virus in Korean Domesticated Pigs

BACKGROUND

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne virus in China, Japan, and Korea. Although the incidence of SFTS has been increasing annually since the first SFTSV case was reported in Korea, the prevalence of SFTSV in Korean livestock has not conducted. The purpose of this study was to investigate the prevalence of SFTSV in domesticated pigs (Sus scrofa domesticus) throughout Korea.

METHODS

A total of 240 sera were collected from 30 domesticated pigs in eight provinces. To detect SFTSV, one-step reverse transcription RT nested PCR was conducted using SFTSV genome-specific primer sets. The amplified PCR products were cloned and then sequenced.

RESULTS

Four of 240 (1.7%) pig sera tested positive for SFTSV through one-step RT nested PCR. Two of the four obtained sequences were included in the Japanese clade, whereas the other two sequences were related to the Chinese clade based on phylogenetic analysis. Moreover, the obtained SFTSV sequences from this study were distinct from human SFTSV strains.

CONCLUSIONS

This study is the first to attempt the identification of SFTSV sequences from domesticated pigs and the first molecular detection of SFTSV in Korean livestock. Our findings indicate that a new subclade of SFTSV-different from that in humans-may be present in domesticated pigs; the surveillance of SFTSV in livestock is required to better understand the life cycle of SFTSV.

Seroprevalence and genetic characterization of severe fever with thrombocytopenia syndrome virus in domestic goats in South Korea

Severe fever with thrombocytopenia syndrome (SFTS) is a newly emerging tick-borne infectious disease caused by the SFTS virus (SFTSV). To investigate the prevalence of SFTSV in domestic goats in South Korea, we collected blood samples in commercial slaughterhouses in Chungbuk Province in 2017. Of the 207 samples tested, 4 (2%) were found to be positive for viral RNA by RT-PCR and 30 (14.4%) were positive for SFTSV antibody as detected by a nucleocapsid (NP) protein-based ELISA. Phylogenetic analysis of the non-structural protein (NS) sequences showed that all viruses belonged to the genotype B, although they were clustered into two different sublineages that showed the highest homology with the KR612076-JP01 and KY789441-CB3 human isolate from South Korea. Further, we confirmed the specificity of seropositive goat sera by FRNT₅₀ and western blotting analysis and found differential cross-reactivity of the sera with genotype A and B SFTSV strains. Collectively, this study suggests that relatively high numbers of goats are infected by antigenically different SFTSV strains, which might have a potential for zoonotic infection.