Epidemiological characteristics of tick-borne infectious diseases in Hubei Province, 2016-2021 / 中华流行病学杂志

Objective: To understand the epidemiological characteristics of tick-borne infectious diseases (TBID) and the risk factors of severe illness and death in Hubei Province from 2016 to 2021. Methods: Based on the incidence data of fever with thrombocytopenia syndrome (SFTS), tsutsugamushi disease, typhus and other TBID reported during 2016-2021, the epidemiological analysis was conducted. Field investigation results of TBID in areas with high incidence in 2021, logistic regression analysis of population characteristics, epidemiological history and other factors were used to explore the risk factors of severe and fatal cases. In the field vector investigation, free ticks and surface ticks of the host animals in the cases' home and surrounding grassland were monitored and detected. Results: A total of 3 826 TBID cases were reported in Hubei from 2016 to 2021, of which 71.30% (2 728/3 826) were SFTS, 13.04% (499/3 826) were tsutsugamushi disease and 15.66% (599/3 826) were typhus. A total of 44 cases died in 6 years; the fatality rate was 1.15% (44/3 826). In the peak seasons of incidence from May to July, the cases in people engaged in agriculture related work accounted for 84.61% (3 237/3 826). The incidence rate in women was higher than that in men, and the cases aged ≥50 years accounted for 81.02% of the total (3 100/3 826), and the incidence rate increased with age (P<0.001). The TBID cases were distributed in 86 counties and districts in 16 prefectures (municipality). The incidence rates of different areas had significant differences (P<0.05), and there was a certain spatial-temporal clustering and expasion. Bovis microplus and Haemaphysalis longicornis were captured in the field, and the positive rates in host animals and grassland ticks were 10.94% (7/64) and 40.00% (2/5), respectively. Univariate logistic regression analysis results showed that age ≥50 years and leukocyte <2.0×109/L were risk factors for severe illness and death. Conclusions: The TBID reported in Hubei were mainly SFTS, tsutsugamushi disease and typhus. In order to reduce the incidence of TBID, it is necessary to strengthen the prevention and control in women aged ≥50 years and reduce field exposure and tick bites during the epidemic period.

Severe Fever with Thrombocytopenia Syndrome Patients with Hemophagocytic Lymphohistiocytosis Retrospectively Identified in Korea, 2008–2013

The incidence of severe fever with thrombocytopenia syndrome (SFTS) has increased in Korea since a first report in 2013. We investigated whether SFTS existed before 2013 using real-time reverse transcription polymerase chain reaction and stored blood samples from febrile patients with thrombocytopenia. Four cases of SFTS were identified, with the earliest occurring in 2008.

Strategies Against Severe Fever with Thrombocytopenia Syndrome Increasing in Korea / 대한수혈학회지

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease that is caused by the genus phlebovirus in the family Bunyaviridae. The syndrome is characterized by fever, gastrointestinal symptoms, neutropenia, and thrombocytopenia. The number of reported cases and deaths in endemic areas, such as China and Japan, has increased each year. Since the first SFTS patient was identified in 2013, the number of cases have also been increasing every year in South Korea and the disease is posing a great public health concern. The number of patients is increasing and there is a high mortality rate, but there is no established treatment that has proven to be effective. The purpose of this review was to elucidate the various treatment modalities, such as plasma exchange, antiviral agents, e.g. ribavirin, high-dose steroids, and interferon.

The Most Common Mite- and Tick-borne Infectious Diseases in Korea: Scrub Typhus and Severe Fever Thrombocytopenia Syndrome / 대한내과학회지

The incidence of mite- and tick-borne infectious disease is increasing with climate change and the development of diagnostic tools. Tick-borne infectious diseases include Lyme disease, anaplasmosis, ehrlichiosis, severe fever with thrombocytopenia syndrome (SFTS), and Japanese spotted fever. Rickettsial pox and scrub typhus are mite-borne infectious diseases. Scrub typhus and SFTS are the most common mite- and tick-borne infectious diseases in Korea, respectively. They are often difficult to diagnose at an early stage of disease. To make a definite diagnosis of mite- and tick-borne infectious disease, polymerase chain reaction (PCR) tests or serologic testing for antibodies during the acute and convalescent periods are necessary. If patients with nonspecific symptoms, such as fever, headache, nausea, and vomiting, have a history of outdoor activity or a tick bite, it is reasonable to consider the possibility of mite- or tick-borne infectious diseases clinically. There are no vaccinations against mite- and tick-borne infectious diseases. Therefore, preventing mite or tick bites is the best way to prevent the diseases.

Effect of Early Plasma Exchange on Survival in Patients with Severe Fever with Thrombocytopenia Syndrome: A Multicenter Study

Despite a high mortality rate, no specific treatment for severe fever with thrombocytopenia syndrome (SFTS) has been established. This study compared the clinical outcomes of SFTS patients treated with plasma exchange (PE group) with those who were not treated (non-PE group) at nine Korean hospitals between May 2013 and August 2015. A total of 53 SFTS patients were included: 24 (45.3%) PE cases and 29 (54.7%) non-PE cases. The overall in-hospital mortality rate was 32.1% (17/53). The in-hospital mortality rate of the PE group did not differ from that of the non-PE group (29.3% vs. 34.5%, p=0.680). Of the 24 PE cases, 16 (66.7%) were treated with PE within 7 days of symptom onset (early PE group). The early PE group survived longer than the non-PE group (mean 28.4 days vs. 22.6 days, p=0.044). Multivariate analysis showed an inverse association between early PE implementation and 30-day mortality (adjusted hazard ratio 0.052, 95% confidence interval 0.004–0.678, p=0.024). The results of this study suggest that early PE implementation may have a beneficial effect on the clinical outcome of SFTS patients.

In vitro antiviral activity of ribavirin against severe fever with thrombocytopenia syndrome virus

BACKGROUND/AIMS: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by severe fever with thrombocytopenia syndrome virus (SFTSV), a novel bunyavirus. As yet, there is no effective antiviral therapy for SFTS. Ribavirin is a broad-spectrum antiviral agent, which has been tried for treatment of SFTS. In this study, antiviral activity of ribavirin against SFTSV has been investigated. METHODS: Vero cell-grown SFTSV strain Gangwon/Korea/2012 was treated with ribavirin at various concentrations. Antiviral activity of ribavirin was evaluated by inhibition of the SFTSV cytopathic effect in Vero cells and quantification of viral RNA load in culture supernatant using one-step real-time reverse transcription polymerase chain reaction. Cytotoxicity of ribavirin was determined by a tetrazolium-based colorimetric method. RESULTS: Ribavirin reduced SFTSV titers in a dose-dependent manner, with a half-maximal inhibitory concentration ranged from 3.69 to 8.72 μg/mL. Cytopathic effects were reduced as ribavirin concentration increased. No significant cytotoxicity was detected at ribavirin concentrations of ≤ 31.3 μg/mL. CONCLUSIONS: Ribavirin exhibited inhibitory activity against SFTSV replication in vitro, which suggests that ribavirin can be used as a potential antiviral agent for SFTS.

Development and evaluation of a competitive enzyme-linked immunosorbent assay using a monoclonal antibody for diagnosis of severe fever with thrombocytopenia syndrome virus in bovine sera

Severe fever with thrombocytopenia syndrome (SFTS) caused by the SFTS virus (SFTSV), a phlebovirus in the family Bunyaviridae, is an emerging tick-borne infectious disease that impacts humans. This disease manifests as a decreased blood cell count and multi-organ failure, with a case-fatality rate of more than 12% in China. Because vaccines or antiviral drugs for the treatment of this disease are not available, monitoring the SFTS circulation in animals and controlling the tick-mammal cycle are important for preventing SFTS. Monoclonal antibodies against the recombinant nucleoprotein of SFTSV were generated to develop a competitive enzyme-linked immunosorbent assay (cELISA) for the detection of antibodies against SFTSV infection in cattle. The specificity and sensitivity of cELISA was assessed by comparing the results of this assay to those of an immunofluorescence assay (IFA). The results of the cELISA using 416 field bovine serum samples and laboratory-immunized positive sera showed 98.1% consistency with those of the IFA. The cELISA used in this study did not show cross-reactivity with antisera against other viral cattle diseases. The cELISA presented in this study can be applied to detect antibodies against SFTSV in cattle.

Severe Fever with Thrombocytopenia Syndrome Presenting with Hemophagocytic Lymphohistiocytosis / 감염과화학요법

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne disease caused by the newly discovered SFTS Bunyavirus, and there have been no case reports of SFTS patients presenting with hemophagocytic lymphohistiocytosis (HLH) in the English literature. We report a case of SFTS presenting with HLH in a 73-year-old immunocompetent male farmer. Although the patient had poor prognostic factors for SFTS, such as old age and central nervous system symptoms, he recovered fully with supportive care.

Inclusion Bodies are Formed in SFTSV-infected Human Macrophages / 病毒学报

The severe fever with thrombocytopenia syndrome virus (SFTSV) is a new member in the genus Phlebovirus of the family Bunyaviridae identified in China. The SFTSV is also the causative pathogen of an emerging infectious disease: severe fever with thrombocytopenia syndrome. Using immunofluorescent staining and confocal microscopy, the intracellular distribution of nucleocapsid protein (NP) in SFTSV-infected THP-1 cells was investigated with serial doses of SFTSV at different times after infection. Transmission electron microscopy was used to observe the ultrafine intracellular structure of SFTSV-infected THP-1 cells at different times after infection. SFTSV NP could form intracellular inclusion bodies in infected THP-1 cells. The association between NP-formed inclusion bodies and virus production was analyzed: the size of the inclusion body formed 3 days after infection was correlated with the viral load in supernatants collected 7 days after infection. These findings suggest that the inclusion bodies formed in SFTSV-infected THP-1 cells could be where the SFTSV uses host-cell proteins and intracellular organelles to produce new viral particles.

Epidemiological investigation of predominance tick and the infectious status of severe fever thrombocytopenia syndrome virus in Penglai and Laizhou counties, Shandong province / 中华预防医学杂志

<p><b>OBJECTIVE</b>To investigate the predominance ticks and the infectious status of severe fever with thrombocytopenia (SFTSV) in Penglai and Laizhou counties, Shandong province.</p><p><b>METHODS</b>Two towns with high incidence rate were selected in Penglai and Laizhou, respectively, then three villages were selected in each towns. Parasitic ticks were collected from the host skin by hand manually and free ticks manually with white cloth from the grassland, monthly, during April to December in 2011. Samples were classified by original, varieties, developmental stages, then extracted RNA, using Realtime RT-PCR to test severe fever thrombocytopenia syndrome virus, S fragments were amplified with nested PCR, then isolated virus. By neighbor joining method in the phylogenetic tree, the minimum infection rate (MIR) was used to represent the infection status of ticks in novel bunyavirus.</p><p><b>RESULTS</b>A total of 3 145 ticks were collected totally from 5 categories, there were 3 048(96.92%) of Haemaphysalis longicornis, 73(2.32%) of Rhinpicephalus sanguineus, 10(0.32%) of microplus Boophilus, 9(0.29%) of Haemaphysalis campanulata, 5(0.16%) of Dermacentor sinicus, respectively. The positive rate of nucleic acid of 2 044 samples was 6.16% (126/2 044), minimum infection rate (MIR) was 4.01%, there were 122(96.83%) of Haemaphysalis longicornis, 3(2.38%) of Rhinpicephalus sanguineus, and 1(0.79%) of microplus Boophilus, MIR was 4.00%, 4.11%, and 10.00%, respectively. There were no nucleic acid positive samples in Haemaphysalis campanulata and Dermacentor sinicus. The 11 S segments were amplified in 126 positive samples, the homology of S fragment was 95.6%-99.9% with 11 strains isolated from the identified SFTS cases in local area, 3 strains isolated from animals, and 11 strains isolated from other areas. There was no significant difference among original, varieties and developmental stages.</p><p><b>CONCLUSION</b>Haemaphysalis longicornis was the predominant species in Penglai and Laizhou counties, it could be propagation medium with Rhipicephalus sanguineus and microplus Boophilus, S sequence in ticks was higher homology with virus isolated from local SFTS cases.</p>

Infection of the Severe Fever with Thrombocytopenia Syndrome Virus in Balb/C Mice and Hamsters / 病毒学报

The severe fever with thrombocytopenia syndrome virus (SFTSV) is the causative pathogen of an emerging infectious disease severe fever with thrombocytopenia syndrome and a new member in the genus Phlebovirus of family Bunyaviridae. Immune responses and pathological lesions in SFTSV-infected Balb/C mice and hamsters were evaluated by inoculation of SFTSV at 105 TCID50 or 103 TCID50 per animal through four different routes of infection, including intravenous, intramuscular, intraperitoneal, and intracerebral injections. The vehicle control groups were also included. At different time points after the inoculation blood and plasma samples were collected. Blood cell counts, blood viral RNA copies, and plasma antibodies were detected by automatic blood cell counters, real-time PCR, and luminex assays, respectively. At two weeks post inoculation, the animals were sacrificed. Tissues including heart, liver, spleen, lung, kidney, intestine, muscle, and brain, were collected for pathological analyses. Results showed that the SFTSV could infect Balb/C mice and hamsters with SFTSV-specific immunoglobulin (Ig) M and IgG antibodies detected in plasma samples on day 7 post inoculation. The SFTSV-specific IgM levels peaked on day 7 post inoculation and then decreased, whereas the SFTSV-specific IgG levels started to increase on day 7 and then peaked on day 14 post inoculation. Pathological analyses indicated significant pathological lesions in liver and kidney tissues. In conclusion, SFTSV could can infect different strains of rodent animals and cause similar immunological and pathological responses.

Preparation and functional analysis of the monoclonal antibodies against severe fever with thrombocytopenia syndrome bunyavirus structural proteins / 病毒学报

To prepare monoclonal antibodies (mAbs) against structural proteins of severe fever with thrombocytopenia syndrome bunyavirus (SFTSV), BALB/c mice were immunized using purified inactivated SFTSV virions as the antigens. Subsequently, hybridoma cell lines that secreted monoclonal antibodies against nucleoprotein (NP) and glycoproteins (GP) were obtained using a hybridoma technique. The antigen specificities of prepared mAbs were examined by indirect immunofluorescence and immunoprecipitation assays. Functional analyses were then performed,including the detection of IFA antibody titers,the levels of neutralizing activity and antibody affinities. After cell fusion and cloning,13 hybridoma cell lines secreted mAbs specifically against SFTSV-GP and 7 hybridoma cell lines secreted mAbs specifically against SFTSV-NP. Immunofluorescence and immunoprecipitation assays showed that the mAbs had high levels of antigen specificity. Among the 13 anti-SFTSV-GP mAbs,6 recognized Gn,whereas the others reacted with Gc. IFA titers of most anti-SFTSV-GP mAbs were between 1,280 and 20,480, and four anti-SFTSV-Gn mAbs showed neutralizing activity. Seven of the obtained anti-SFTSV-NP mAbs reacted specifically with NP,of which the IFA titers ranged from 5,120 to 20,480 with no observed neutralizing activity. Furthermore, two anti-SFTSV-GP mAbs, 1C8 and 1G8, showed high levels of affinity via a non-competitive ELISA. Our study lays the foundation for the development of further diagnostic assays and basic research into SFTSV.

Development of human antibodies against the Gn protein of severe fever with thrombocytopenia syndrome virus / 病毒学报

To obtain human antibodies against the Gn protein of Severe fever with thrombocytopenia syndrome virus (SFTSV) with phage display technology, this study aimed to screen anti-Gn protein antibodies from an anti-SFTSV Fab human phage display library. Antibody genes were identified by sequence analysis and the specificity of antibodies was confirmed by ELISA. The Fab antibody genes were cloned into the HL51-14 vector and expressed in a mammalian cell expression system. IgG antibodies were then purified by protein A affinity chromatography,and the results were further confirmed by ELISA,IFA,western blotting assays and micro-neutralization tests. The results showed that, after three rounds of panning, there were 390 human Fab antibodies against SFTSV particles, of which 364 were specific for nucleoprotein. Coated with the Gn protein, eight different Fab antibodies specific for Gn protein were obtained after the determination of the subtype and subclass of antibodies by gene sequencing; five of these antibodies were from the Lambda library and three were from the Kappa library. The eight IgG antibodies could specifically bind to Gn protein according to the ELISA, IFA and Western blotting assays. The micro-neutralization test showed that these eight antibodies had no neutralizing activity,but they could still provide a reference for research in human monoclonal antibodies against SFTSV.

Purification and Preliminary Research on the Immunogenicity of Inactivated Severe Fever with Thrombocytopenia Syndrome Bunyavirus / 病毒学报

To understand the immunogenicity of purified inactivated severe fever with thrombocytopenia syndrome bunyavirus (SFTSV), concentration by ultrafiltration as well as molecular-sieve chromatography (MSC) were used for purification of inactivated SFTSVs. Inactivated viruses in purified samples were analyzed and identified by western blotting and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the glycoprotein (GP) and nucleoprotein (NP) antigen titers of which were detected using a double-sandwich enzyme-linked immunosorbent assay (ELISA). Purified inactivated SFTSVs were enriched and observed by electron microscopy, and the total protein concentration detected using the bicinchoninic acid assay. Purified inactivated SFTSVs were applied to New Zealand rabbits via two immunization programs to evaluate immunogenicity and to compare the immune effect. After SFTSVs were inactivated and concentrated by ultrafiltration, MSC revealed two typical elution peaks. The sample of one peak was identified as inactivated virions, in which GP and NP were detected by SDS-PAGE, western blotting and ELISA. Main corponent of the other peak was NP. After concentration by ultrafiltration, purified inactivated SFTSVs with purity >90% and total protein concentration of 1. 1 mg/mL were obtained, and the typical electron microscopy of bunyavirus was observed. In the sera of animals immunized with purified inactivated SFTSVs, SFTSV-specific IgG antibody and neutralizing antibody were detected at high titers. However, antibody titers were affected by the immunization program. Effect of immunization on days 0, 14 and 28 was significantly better than that on days 0, 7 and 28. Our work revealed that cultivation of SFTSVs contained intact virus particles and large amounts of free NP. Using MSC, purified inactivated SFTSVs of high purity could be obtained. Purified inactivated SFTSVs induced high titers of neutralizing antibody and virus-specific IgG antibody showing satisfactory immunogenicity, which provides important clues for further study on a vaccine for the inactivated virus.

New Method for Stable Expression of SFTS Virus-like Particles in CHO-K1 Cells / 病毒学报

To explore a new method for stable expression of virus-like particles (VLPs) of the severe fever with thrombocytopenia syndrome (SFTS) virus, an expression plasmid for the membrane glycoprotein (GP) and nucleocapsid protein (NP) of the SFTS virus was constructed by fusion of the two proteins via a serine residue, and a yellow fluorescence protein (YFP) gene was introduced into the plasmid as a reporter. CHO-K1 cells were transfected with this plasmid, and stable cell lines constructed using the limited dilution method. Cellular colonies were hand-picked based on YFP with the help of fluorescence microscopy and expanded without selection pressure. Stability of cell lines was evaluated by monitoring of fluctuation of the intensity of YFP for 40 passages. VLP production was characterized using an indirect fluorescence assay, immunoblotting, and electronic microscopy. We showed that GP and NP fusion proteins could be assembled into VLPs in vivo, and that VLPs had similar morphologies to virus particles. Selected cell lines were stable for YFP expression: no significant fluctuation was detected in 40 passages. These data demonstrated the effectiveness of this new method for expression of structural proteins of the SFTS virus and screening for stable cell lines. Our results could provide new concepts for the production of biopharmaceuticals.

Severe Fever with Thrombocytopenia Syndrome / 대한구급학회지

Severe fever with thrombocytopenia syndrome (SFTS) is a newly emerging infectious disease, caused by a novel species of Phlebovirus of Bunyaviridae family, in China, South Korea, and Japan. SFTS is primarily known as a tick-borne disease, and human-to-human transmission is also possible in contact with infectious blood. Common clinical manifestations include fever, thrombocytopenia, and leukopenia as initial symptoms, and multiple organ dysfunction and failure manifest with disease progression. Whereas disease mortality is reported to be 12% to 30% in China, a recent report of cumulative SFTS cases indicated 47% in Korea. Risk factors associated with SFTS were age, presence of neurologic disturbance, serum enzyme levels, and elevated concentrations of certain cytokines. Diagnosis of SFTS is based on viral isolation, viral identification by polymerase chain reaction, and serologic identification of specific immunoglobulin G. Therapeutic guideline has not been formulated, but conservative management is the mainstream of treatment to prevent disease progression and fatal complications.

No Detection of Severe Fever with Thrombocytopenia Syndrome Virus from Ixodid Ticks Collected in Seoul

Larvae, nymphs, and adult stages of 3 species of ixodid ticks were collected by tick drag methods in Seoul during June-October 2013, and their infection status with severe fever with thrombocytopenia syndrome (SFTS) virus was examined using RT-PCR. During the period, 732 Haemaphysalis longicornis, 62 Haemaphysalis flava, and 2 Ixodes nipponensis specimens were collected. Among the specimens of H. longicornis, the number of female adults, male adults, nymphs, and larvae were 53, 11, 240, and 446, respectively. Ticks were grouped into 63 pools according to the collection site, species, and developmental stage, and assayed for SFTS virus. None of the pools of ticks were found to be positive for SFTS virus gene.

Experience of Therapeutic Plasma Exchange in Patients with Severe Fever with Thrombocytopenia Syndrome / 대한수혈학회지

BACKGROUND: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease recently issued in northeast Asia and China. The disease is caused by a new phlebovirus in the family Bunyaviridae, severe fever with thrombocytopenia syndrome virus (SFTSV); the transmission vector is believed to be a tick. The number of infections and resulting deaths has been increasing, but there is no effective treatment. METHODS: Clinical and laboratory features of SFTSV-positive patients during the period from May 2013 to October 2014 were reviewed retrospectively using medical records. In cases of patients who underwent therapeutic plasma exchange (TPE), the performance records were also investigated. RESULTS: During the study period, 14 patients were SFTSV-positive. The patients, who ranged in age from 47 to 82, had mostly outdoor activities before admission. The major symptoms included high fever, myalgia, and gastrointestinal symptoms. Laboratory findings showed decreased white blood cell (WBC), neutrophils and platelets and elevated activated partial thromboplastin time (aPTT), aspartate aminotransferase (AST), lactate dehydrogenase (LD), and creatine phosphokinase (CK). Two patients died during the study period, however, nine patients who received TPE showed improvement. CONCLUSION: We suppose that TPE can be used for treatment of serious SFTS and gives the effect of reducing the fatality rate.

Severe fever with thrombocytopenia syndrome virus nucleoprotein specifically binds to 60kD SSA/Ro protein in host cells / 病毒学报

This study aims to investigate whether the nucleoprotein (NP) of severe fever with thrombocytopenia syndrome virus (SFTSV) can impact the cellular immunity of host cells. Gene segments that encode the NP and non-structural protein (NSs) of SFTSV were inserted into eukaryotic expression vector VR1012. Host proteins that interact with NP and affect immunity were identified with co-immunoprecipitation (IP), SDS-PAGE, mass spectrometry (MS), and Western blot. Co-localization of NP and the identified host proteins was confirmed by confocal microscopy. A 60kD SSA/Ro, a protein related to immunity, interacted with NP, as found by IP and MS. Confocal microscopy showed that NP and SSA/Ro were co-localized in cytoplasm. These results indicated that SFTSV NP may specifically bind to 60kD SSA/Ro and cause a series of immune responses and clinical symptoms.

Severe Fever with Thrombocytopenia Syndrome / 대한내과학회지

Severe fever with thrombocytopenia syndrome (SFTS) is firstly reported in China in 2011. It is an emerging infectious disease in China, Japan and South Korea. It is caused by novel bunyavirus, called SFTS virus. The vector of SFTS is Haemaphysalis longicornis tick and domesticated animals may serve as intermediate hosts. The clinical manifestations of SFTS are fever, vomiting, diarrhea, thrombocytopenia and leukopenia. In severe cases, multiple organ failure, disseminated intravascular coagulopathy, and central nervous systems manifestation are present. The case-fatality rate is 6-30%. There is no effective antiviral therapy and supportive care is the main treatment.