Severe Severe Fever With Thrombocytopenia Syndrome Research Articles

Effect of fasting plasma glucose level in severe fever and thrombocytopenia syndrome patients without diabetes.

Hyperglycemia is correlated with worse in-hospital outcomes in acute infectious diseases such as coronavirus disease 2019 (COVID-19) and severe fever with thrombocytopenia syndrome (SFTS). This study assessed the relationship between fasting plasma glucose (FPG) levels and in-hospital mortality, disease type, and secondary infections among individuals with SFTS without preexisting diabetes. The clinical data and laboratory results upon admission of 560 patients with SFTS without preexisting diabetes meeting the inclusion criteria at Wuhan Union Hospital were collected. FPG levels in surviving patients with SFTS subjects were significantly lower than those in patients with SFTS who had died (P<0.0001). In multivariate Cox regression, high FPG level (≥11.1 mmol/L) was a risk factor independently associated with the in-hospital death of patients with SFTS without preexisting diabetes. Similarly, the FPG levels in general patients with SFTS were significantly lower than those in patients with severe SFTS (P<0.0001). Multivariate logistic regression identified high FPG level (7.0-11.1 mmol/L) as a risk factor independently associated with SFTS severity. While FPG levels were comparable between patients with SFTS with and without secondary infection (P = 0.5521), logistic regression analysis revealed that high FPG levels were not a risk factor for secondary infection in patients with SFTS without preexisting diabetes. High FPG level on admission was an independent predictor of in-hospital death and severe disease in individuals with SFTS without preexisting diabetes. FPG screening upon admission and glycemic control are effective methods for improving the prognosis of patients with SFTS.

High CRP/PNI levels predict an unfavorable prognosis in severe fever with thrombocytopenia syndrome: A propensity score matching study.

This study aimed to identify a novel inflammatory index and construct a nomogram for predicting in-hospital mortality due to severe fever with thrombocytopenia syndrome (SFTS). This cohort included 610 patients with SFTS hospitalized in Wuhan Union Hospital between March 2017 and November 2022. The ratio of C-reactive protein (CRP) to the prognostic nutritional index (PNI) was calculated and used to reflect patients' inflammatory status. Propensity score matching (PSM) was utilized to balance confounding factors between the low- and high-CRP/PNI groups. SFTS individuals from Jinyinhu Hospital were used as the validation cohort. Patients with SFTS and high CRP/PNI were significantly correlated with a higher percentage of severe and critical SFTS types and higher in-hospital mortality rates than those with low CRP/PNI. CRP/PNI was the potent risk indicator for in-hospital mortality in individuals with SFTS. The CRP/PNI nomogram showed a good predictive value for in-hospital mortality in patients with SFTS. After PSM, the predictive performance of CRP/PNI for 28-day mortality was excellent. Finally, the CRP/PNI could still assess patients with SFTS at different risks based on SFTS data from another medical center. The CPR/PNI ratio exhibited a strong positive correlation with the SFTS disease type and could predict in-hospital mortality in the early stages of SFTS. The CPR/PNI ratio could substantially help clinicians facilitate the early identification of patients with high-risk SFTS and the timely initiation of intensive therapy.

Lethal severe fever with thrombocytopenia syndrome virus infection causes systemic germinal centre failure and massive T cell apoptosis in cats.

Severe fever with thrombocytopenia syndrome (SFTS) is a fatal viral disease characterized by high fever, thrombocytopenia, leukopenia, and multi-organ haemorrhage. Disruption of the humoral immune response and decreased lymphocyte numbers are thought to contribute to the disease severity. These findings have been obtained through the analysis of peripheral blood leukocytes in human patients, whereas analysis of lymph nodes has been limited. Thus, in this study, we characterized the germinal centre response and apoptosis in the lymph nodes of cats with fatal SFTS, because SFTS in cats well mimics the pathology of human SFTS. Lymph node tissue sections collected during necropsy from seven fatal SFTS patients and five non-SFTS cases were used for histopathological analysis. Additionally, lymph node tissue sections collected from cats with experimental infection of SFTS virus (SFTSV) were also analysed. In the lymphoid follicles of cats with SFTS, a drastic decrease in Bcl6- and Ki67-positive germinal centre B cells was observed. Together, the number of T cells in the follicles was also decreased in SFTS cases. In the paracortex, a marked increase in cleaved-caspase3 positivity was observed in T cells. These changes were independent of the number of local SFTS virus-positive cell. Furthermore, the analysis of cats with experimental SFTSV infection revealed that the intrafollicular Bcl6- and CD3-positive cell numbers in cats with low anti-SFTSV antibody production were significantly lower than those in cats with high anti-SFTSV antibody production. These results suggest that dysfunction of the humoral response in severe SFTS was caused by the loss of germinal centre formation and massive apoptosis of T cells in the lymph nodes due to systemically circulating viruses.

Application of blood purification technology in severe fever with thrombocytopenia syndrome

ABSTRACT Objective: The purpose of this paper is to summarize the blood purification technology applied in patients with severe fever with thrombocytopenia syndrome (SFTS) in the clinical treatment effect. Methods: The medical records of 96 patients with severe SFTS admitted to Weihai Municipal Hospital affiliated to Shandong University from May 2014 to November 2019 were retrospectively analyzed, and they were divided into survival group and death group. The differences in basic data test indexes and treatment method selection during intensive care unit (ICU) admission between the two groups were significantly analyzed, and the indexes with statistically significant differences were included in the multivariate logistic regression analysis related to prognosis. Results: There were no statistically significant differences in age, sex composition, white blood cell count, platelet count, creatine kinase (CK), activated partial thromboplastin time (APTT), serum creatinine and hemofiltration renal replacement therapy between the survival group and the death group. There were statistically significant differences between the two groups in viral load bilirubin and the treatment methods of plasma exchange (PE) or hemoperfusion (HP). Plasma exchange group (78 cases), hemofiltration group (12 cases), hemoperfusion group (6 cases), plasma exchange and hemoperfusion and other blood purification treatment of the prognosis were statistically different. Conclusions: Compared with the three blood purification methods, plasmapheresis has a significant effect on virus removal, improvement of coagulation function and survival rate in patients with severe SFTS. Hemofiltration plays a role in removing inflammatory mediators, replacing renal function, maintaining electrolytes and acid-base balance, but not in removing viruses.

Clinical efficacy of low-dose glucocorticoid therapy for critically ill patients with severe fever with thrombocytopenia syndrome: A retrospective cohort study

ObjectivesTo determine whether glucocorticoids can improve clinical outcomes of severe fever with thrombocytopenia syndrome (SFTS) patients, and how to identify patients who may benefit from the treatment. MethodsA retrospective study was performed to include patients with confirmed SFTS from designated hospitals. The effect of glucocorticoids in reducing case fatality rate (CFR) and improving clinical recovery was evaluated by multivariate logistic regression models. ResultsA total of 2478 eligible patients were analyzed, of whom 331 received glucocorticoids. An integrated parameter (L-index) based on Log10(lactate dehydrogenase*blood urea nitrogen/lymphocyte count) was constructed to discriminate disease severity. In patients with L-index >3.823 indicating severe SFTS, significantly reduced CFR was observed in patients receiving low-moderate glucocorticoid doses with ≤60 mg daily methylprednisolone or equivalent (odds ratio [OR] 0.46, 95% confidence interval [CI], 0.23-0.88), but not in patients receiving high doses. In patients with L-index ≤3.823 indicating mild SFTS, glucocorticoid treatment was significantly associated with increased CFR (OR 3.34, 95% CI, 1.35-9.51), and mainly attributable to high-dose glucocorticoids (OR 2.83, 95% CI, 1.72-4.96). Disaggregated data analysis revealed a significant effect only in patients ≤65 years old, male, and early admission within 7 days after onset, but not in their counterparts. ConclusionGlucocorticoids are not recommended for mild patients defined by L-index <3.823; however, patients with severe SFTS may benefit from low-moderate doses of glucocorticoids.

Severe fever with thrombocytopenia syndrome virus replicates in brain tissues and damages neurons in newborn mice

Severe fever with thrombocytopenia syndrome (SFTS) virus (SFTSV) is an emerging tick-borne phlebovirus with a high fatality rate of 12–30%, which has an expanding endemic and caused thousands of infections every year. Central nervous system (CNS) manifestations are an important risk factor of SFTS outcome death. Further understanding of the process of how SFTSV invades the brain is critical for developing effective anti-SFTS encephalitis therapeutics. We obeserved changes of viral load in the brain at different time points after intraperitoneal infection of SFTSV in newborn C57/BL6 mice. The virus invaded the brain at 3 h post-infection (hpi). Notably, the viral load increased exponentially after 24 hpi. In addition, it was found that in addition to macrophages, SFTSV infected neurons and replicated in the brain. These findings provide insights into the CNS manifestations of severe SFTS, which may lead to drug development and encephalitis therapeutics.

Scoring Model for Predicting the Occurrence of Severe Illness in Hospitalized Patients with Severe Fever with Thrombocytopenia Syndrome.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever with high mortality. Severe cases progressed rapidly, with deaths occurring within 2 weeks. Therefore, constructing a model to predict disease progression among hospitalized patients plays an important role in clinical practice. The development cohort included 121 patients with SFTS, 25 with severe SFTS, and 96 with mild SFTS. Two of the 64 variables were independent risk factors, including neurological symptoms (odds ratio [OR], 12.915; 95% confidence interval [CI], 3.342-49.916; P < 0.001) and aspartate aminotransferase/alanine aminotransferase levels (OR, 1.891; 95% CI, 1.272-2.813; P = 0.002). The model's area under the curve (AUC) was 0.882 (95% CI: 0.808-0.956). The mean AUC value obtained from the internal validation was 0.883 (95% CI: 0.809-0.957). The AUC in the external validation cohort was 0.873 (95% CI: 0.775-0.972). This model can be used to identify severely ill patients as early as possible with high predictive value, stability, and repeatability. This model can help clinicians with their treatment plans.

[Clinical features and significance of coagulation dysfunction in severe fever with thrombocytopenia syndrome].

To analyze the changes of coagulation function in severe fever with thrombocytopenia syndrome (SFTS) and its relationship with thrombocytopenia, and to explore its value as an early predictor of the severity of SFTS. The clinical data of 428 SFTS patients (70 deaths and 358 survivors) admitted to the Department of Infectious Disease at Wuhan Union Hospital from January 2014 to July 2020 were retrospectively analyzed. The differences of coagulation parameters and disseminated intravascular coagulation (DIC) scores between the two groups were compared. The results showed that abnormal coagulation function was commonly presented in SFTS patients. Bleeding was more frequent in mortality group (41.4% vs. 26.5%). The D-dimer levels in mortality patients were significantly higher above normal range. Activated partial thrombin time (APTT) and thrombin time (TT) were significantly prolonged. The levels of prothrombin time (PT), TT, APTT, international standardized ratio (INR) and D-dimer between mortality group and survival group started to separate from day 5-6. The difference of fibrinogen (FIB) level developed on day 7-8, while platelet counts between the two groups were significant different from day 9-10. The mortality rate increased according to the increase of baseline DIC score. When DIC score reached 6, the mortality rate surged to 66.67%. Excessive platelet consumption is mediated by significant coagulation abnormalities during disease course, and coagulation parameters are more sensitive than platelet count as an early predictor of severe SFTS.

The role of selenium in severe fever with thrombocytopenia syndrome: an integrative analysis of surveillance data and clinical data

ObjectivesSelenium deficiency can be associated with increased susceptibility to some viral infections and even more severe diseases. In this study, we aimed to examine whether this association applies to severe fever with thrombocytopenia syndrome (SFTS). MethodAn observational study was conducted based on the data of 13,305 human SFTS cases reported in mainland China from 2010 to 2020. The associations among incidence, case fatality rate of SFTS, and crop selenium concentration at the county level were explored. The selenium level in a cohort of patients with SFTS was tested, and its relationship with clinical outcomes was evaluated. ResultsThe association between selenium-deficient crops and the incidence rate of SFTS was confirmed by multivariate Poisson analysis, with an estimated incidence rate ratio (IRR, 95% confidence interval [CI]) of 4.549 (4.215−4.916) for moderate selenium-deficient counties and 16.002 (14.706−17.431) for severe selenium-deficient counties. In addition, a higher mortality rate was also observed in severe selenium-deficient counties with an IRR of 1.409 (95% CI: 1.061−1.909). A clinical study on 120 patients with SFTS showed an association between serum selenium deficiency and severe SFTS (odds ratio, OR: 2.94; 95% CI: 1.00–8.67) or fatal SFTS (OR: 7.55; 95% CI: 1.14–50.16). ConclusionSelenium deficiency is associated with increased susceptibility to SFTS and poor clinical outcomes.

Exploration of immunological responses underpinning severe fever with thrombocytopenia syndrome virus infection reveals IL-6 as a therapeutic target in an immunocompromised mouse model.

Dabie bandavirus (previously severe fever with thrombocytopenia syndrome virus; SFTSV), is an emerging tick-borne bunyavirus responsible for severe fever with thrombocytopenia syndrome (SFTS), a disease with high case fatality that is characterized by high fever, thrombocytopenia, and potentially lethal hemorrhagic manifestations. Currently, neither effective therapeutic strategies nor approved vaccines exist for SFTS. Therefore, there remains a pressing need to better understand the pathogenesis of the disease and to identify therapeutic strategies to ameliorate SFTS outcomes. Using a type I interferon (IFN)-deficient mouse model, we investigated the viral tropism, disease kinetics, and the role of the virulence factor nonstructural protein (NSs) in SFTS. Ly6C+ MHCII+ cells in the lymphatic tissues were identified as an important target cell for SFTSV. Advanced SFTS was characterized by significant migration of inflammatory leukocytes, notably neutrophils, into the lymph node and spleen, however, these cells were not required to orchestrate the disease phenotype. The development of SFTS was associated with significant upregulation of proinflammatory cytokines, including high levels of IFN-γ and IL-6 in the serum, lymph node, and spleen. Humoral immunity generated by inoculation with delNSs SFTSV was 100% protective. Importantly, NSs was critical to the inhibition of the host IFNɣ response or downstream IFN-stimulated gene production and allowed for the establishment of severe disease. Finally, therapeutic but not prophylactic use of anti-IL-6 antibodies significantly increased the survival of mice following SFTSV infection and, therefore, this treatment modality presents a novel therapeutic strategy for treating severe SFTS.

Early-Warning Immune Predictors for Invasive Pulmonary Aspergillosis in Severe Patients With Severe Fever With Thrombocytopenia Syndrome.

Aspergillus-related disease was confirmed to be associated with immune disorders in patients, severe patients with severe fever with thrombocytopenia syndrome (SFTS) infected by novel phlebovirus were confirmed to have severe immune damage including cellular immunosuppression and cytokine storms. Secondary invasive pulmonary aspergillosis (IPA) in severe SFTS patients can increase fatality rate. This study investigated early-warning predictive factors of secondary IPA in severe SFTS patients. Receiver operating characteristic analysis was used to assess the value of immune parameters to predict IPA in SFTS patients. The cut-off values of CD4+ and CD8+ T-cell counts to predict IPA were 68 and 111 cells/mm3, with sensitivities of 82.6% and 72%, and specificities of 56.7% and 83.3%, respectively. Cut-off values of IL-6, TNF-α, IL-8, and IL-10 to predict IPA incidence in critically ill SFTS patients were 99 pg/mL, 63 pg/mL, 120 pg/mL, and 111 pg/mL, with sensitivities of 90.0%, 86.7%, 83.3% and 90.0% and specificities of 80.4%, 71.7%, 82.6% and 65.2%, respectively. Lower CD4+ and CD8+ T-cells counts, higher levels of IL-6, TNF-α, IL-8 and IL-10, higher incidence of pancreatic and renal damage, early antibacterial therapy of carbapenems, and intensive care unit admission were risk factors of IPA in SFTS patients. Multivariate logistic regression analysis indicated counts of CD4+ T-cells <68 cells/mm3 combined with CD8+ T-cells <111 cells/mm3 (odds ratio [OR] 0.218, 95% confidence interval [CI] 0.059–0.803, p=0.022), IL-6 >99 pg/ml combined with IL-10 >111 pg/ml (OR 17.614, 95% CI 2.319–133.769, p=0.006), and brain natriuretic peptide level >500 pg/ml (OR 13.681, 95% CI 1.994–93.871, p=0.008) were independent risk factors for IPA in SFTS patients. The mortality in the IPA group was significantly higher than in the non-IPA group (p=0.001). Early antifungal treatment of IPA patients was significantly associated with improved survival (log-rank, p=0.022). Early diagnosis of IPA and antifungal treatment can improve the prognosis of SFTS patients. Besides, we speculate SFTS may be as a host factor for IPA.

Clinical Progress and Risk Factors for Death from Severe Fever with Thrombocytopenia Syndrome: A Multihospital Retrospective Investigation in Anhui, China

Knowledge of the clinical progress of severe fever with thrombocytopenia syndrome (SFTS) and the associated predictors of mortality is important for providing appropriate treatment in severe cases. A multihospital retrospective study was conducted in three SFTS-endemic cities, in 2018. Of the 208 SFTS-confirmed cases, there were 189 survivors and 19 deaths. The median age was 64 years; 104 (50.0%) patients were men, and 188 (90.4%) were farmers. Furthermore, 203 (97.6%) patients reported fever and 70 (33.7%) reported fatigue. Most fatal cases had complications including multiple-organ failure, central nervous syndrome (CNS) abnormalities, and disseminated intravascular coagulation. During the fever phase, alanine transaminase, aspartate aminotransferase (AST), blood urea nitrogen (BUN), creatinine, D-dimer, glucose, hydroxybutyrate dehydrogenase, lactate dehydrogenase (LDH), procalcitonin, prothrombin time, and uric acid levels were higher in fatal than in nonfatal cases (P < 0.05). Creatine kinase (CK), CK-MB (CKMB), AST, and LDH levels were significantly lower in nonfatal than in fatal cases (P < 0.05). Central nervous syndrome abnormalities (odds ratio [OR] = 20.9, 95% CI: 4.3, 100), body temperature ≥ 38.5°C (OR = 23.2, 95% CI: 3.4, 158), BUN levels ≥ 6.4 mmol/L (OR = 9.9, 95% CI: 2.2, 44), CKMB levels ≥ 100 U/L (OR = 33.2, 95% CI: 5.8, 192), and LDH levels ≥ 1,000 U/L (OR = 8.3, 95% CI: 1.9, 37) were predictors of mortality. Our findings reveal that the presence of specific complications and laboratory parameters may serve as predictors of mortality and aid in early identification of severe SFTS cases in clinical practice.

Risk Factors and Clinical Characteristics of Severe Fever with Thrombocytopenia Syndrome.

PurposeThis study was to investigate the clinical characteristics and laboratory parameters of severe fever with thrombocytopenia syndrome (SFTS).Patients and MethodsA detailed retrospective analysis of clinical records for SFTS patients was conducted. Fifty-one cases confirmed SFTS virus infected were enrolled. The clinical characteristics and laboratory parameters between survivors and non-survivors were analyzed.ResultsAll patients aged between 30 and 80 years were farmers or residing in wooded and hilly areas. All patients occurred between April and October. The major clinical manifestations were fever, fatigue, diarrhea, myalgia, nausea and vomiting. Conscious disturbance, lymph node enlargement and hemorrhage were common. Fatal outcome occurred in 31.4% (16/51) of patients. Compared with survivors group, in non-survivors group, the proportion of consciousness disturbance, age, the levels of AST, LDH, Bun, Cr, PT and APTT were significantly increased, and PLT was significantly decreased. The age, PLT, AST, LDH, Cr, PT and APTT were the risk factors for fatal outcomes. Moreover, the age (OR, 1.245; 95% CI, 1.052–1.474) and APTT (OR, 1.095; 95% CI, 1.005–1.192) were the independent risk factors for fatal outcomes. Heteromorphic lymphocyte and hemophagocytosis could be found in SFTS patients, especially the proportion of finding hemophagocytosis was significantly higher in non-survivors group compared with survivors group.ConclusionThese results suggest SFTS is a systemic infection, the age and APTT can be used as potential predictors referring to severe SFTS cases.

[Differences in immune damage between patients with severe fever with thrombocytopenia syndrome and patients with tsutsugamushi disease].

To analyze the difference of immune damage between patients with severe fever with thrombocytopenia syndrome (SFTS) and patients with tsutsugamushi disease. A prospective case-control study was conducted. Thirty-one patients with SFTS and 16 patients with tsutsugamushi disease admitted to the First Affiliated Hospital of Anhui Medical University from October 2014 to June 2017 were enrolled, and another 10 healthy people were enrolled as control. The counts of CD4+ and CD8+ T lymphocytes, and the proportion of CD3+ T lymphocytes, natural kill cells (NK cells), B lymphocytes and plasma cells were detected by flow cytometry. Thirty-four inflammatory mediators were determined by a multiplex Luminex® system synchronously. The differences of lymphocytes and cytokines between the two groups were compared. The proportion of CD3+ T lymphocytes, the counts of CD4+ and CD8+ T lymphocytes in SFTS patients were significantly lower than those in patients with tsutsugamushi disease (t values were 4.860, 9.411 and 5.030, respectively, all P < 0.01), and the proportion of NK cells and B lymphocytes were significantly higher than those in patients with tsutsugamushi disease (t values were 2.344 and 5.896, respectively, both P < 0.05). The proportion of plasma cells in peripheral blood of SFTS patients was (7.7±1.2)%, the highest proportion of plasma cells in severe SFTS patients was up to 30%, and all patients showed λ monoclonal cell group in plasma cells. No plasma cells were detected in tsutsugamushi disease patients. The abnormal expressions of interleukin-1 receptor antibody (IL-1RA), interleukin (IL-6, IL-15, IL-10, IL-8), tumor necrosis factor-α (TNF-α), γ-interferon (IFN-γ), granulocyte colony-stimulating factor (G-CSF), eosinophil chemotactic factor (Eotaxin), IFN-γ-inducible protein-10 (IP-10), monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory protein (MIP-1α, MIP-1β), platelet-derived growth factor (PDGF-AA, PDGF-AB/BB), activated regulatory normal T cells and secretion factors (RANTES) were found in patients with SFTS and tsutsugamushi disease. The levels of IL-1RA, IL-6, IL-15, IL-10, TNF-α, IFN-γ, G-CSF, Eotaxin, IL-8, IP-10, MCP-1 and MIP-1α in SFTS patients were significantly higher than those in patients with tsutsugamushi disease (Z values were 2.312, 2.447, 3.660, 5.444, 1.965, 2.402, 2.402, 2.997, 3.525, 2.481, 3.817, and 2.211, respectively, all P < 0.05), while PDGF-AA, PDGF-AB/BB and RANTES were significantly lower than those in patients with tsutsugamushi disease (Z values were 3.728, 2.514, 2.649, respectively, all P < 0.05). Correlation analysis showed that RANTES, PDGF-AA and PDGF-AB/BB levels were significantly positively correlated with the level of platelet in patients with SFTS and tsutsugamushi disease (SFTS: r values were 0.223, 0.365, 0.330; tsutsugamushi disease: r values were 0.263, 0.632, 0.407, respectively, all P < 0.05). In SFTS patients, compared with the survival group (n = 21), the CD3+ and CD4+ T lymphocytes in the death group (n = 10) significantly decreased, while the plasma cells significantly increased (t values were 3.980, 3.314 and 26.692, respectively, all P < 0.01); IL-1RA, IL-6, IL-15, IL-10, TNF-α, IFN-γ, G-CSF, Eotaxin, IL-8, IP-10, MCP-1, MIP-1α and MIP-1β significantly increased, while PDGF-AA, PDGF-AB/BB and RANTES significantly decreased (Z values were 3.930, 4.014, 2.832, 3.592, 2.958, 3.508, 2.578, 3.254, 4.270, 3.465, 2.663, 3.085, 3.107, 3.639, 3.043 and 3.825, respectively, all P < 0.05). The immune function was impaired more seriously in SFTS patients than that in tsutsugamushi disease patients. Excessive humoral immunity and apoptosis of T lymphocytes are closely related to the death in SFTS patients. The detection of CD4 cells, plasma cells and proinflammatory and anti-inflammatory cytokines (e.g. IL-6, IL-10) had great clinical significance for the differentiation and illness evaluation in disease with SFTS or tsutsugamushi disease.

Depletion but Activation of CD56dimCD16+ NK Cells in Acute Infection with Severe Fever with Thrombocytopenia Syndrome Virus.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with high mortality (12%-30%). The mechanism by which the SFTS bunyavirus (SFTSV) causes severe illness remains unclear. To evaluate the phenotypic and functional characteristics of the NK cell subsets in SFTS patients, twenty-nine SFTS patients were sequentially sampled from admission until recovery. Phenotypic and functional characteristics of NK cell subsets in circulating blood were analysed via flow cytometry. Then, correlations between NK cell subset frequencies and the SFTS index (SFTSI) were evaluated in all SFTS patients (15 mild, 14 severe) upon admission. The frequencies of CD56dimCD16+ NK cells were greatly decreased in early SFTSV infection and were negatively correlated with disease severity. Additionally, higher Ki-67 and granzyme B expression and relatively lower NKG2A expression in CD56dimCD16+ NK cells were observed in acute infection. Moreover, the effector function of CD56dim NK cells was increased in the acute phase compared with the recovery phase in nine severe SFTS patients. Additionally, interleukin (IL)-15, interferon (IFN)-α, IL-18 and IFN-γ secretion was markedly increased during early infection. Collectively, despite depletion of CD56dimCD16+ NK cells, activation and functional enhancement of CD56dimCD16+ NK cells were still observed, suggesting their involvement in defence against early SFTSV infection.

SFTSV Infection Induces BAK/BAX-Dependent Mitochondrial DNA Release to Trigger NLRP3 Inflammasome Activation

Severe fever with thrombocytopenia syndrome (SFTS) virus (SFTSV) is an emerging tick-borne virus that carries a high fatality rate of 12%-50%. In-depth understanding of the SFTSV-induced pathogenesis mechanism is critical for developing effective anti-SFTS therapeutics. Here, we report transcriptomic analysis of blood samples from SFTS patients. We observe a strong correlation between inflammatory responses and disease progression and fatal outcome. Quantitative proteomic analysis of SFTSV infection confirms the induction of inflammation and further reveals virus-induced mitochondrial dysfunction. Mechanistically, SFTSV infection triggers BCL2 antagonist/killer 1 (BAK) upregulation and BAK/BCL2-associated X (BAX) activation, leading to mitochondrial DNA (mtDNA) oxidization and subsequent cytosolic release. The cytosolic mtDNA binds and triggers NLRP3 inflammasome activation. Notably, the BAK expression level correlates with SFTS disease progression and fatal outcome. These findings provide insights into the clinical features andmolecular underpinnings of severe SFTS, which may aid in patient care and therapeutic design, and may also be conserved during infection by other highly pathogenic viruses.

Identifying target cells for a tick-borne virus that causes fatal hemorrhagic fever.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging disease in China, South Korea, and Japan caused by the tick-borne SFTS virus (SFTSV). Severe and fatal SFTS presents as a hemorrhagic fever characterized by high viral load, uncontrolled inflammatory response, dysregulated adaptive immunity, coagulation abnormalities, hemorrhage, and multiorgan failure with up to 33% case fatality rates (CFRs). Despite its public health significance in Asia, vaccines and specific therapeutics against SFTS are still unavailable. A better understanding of the pathogenesis of SFTS is crucial to improving medical countermeasures against this devastating disease. In this issue of the JCI, Suzuki and colleagues analyzed histopathological samples from 22 individuals who succumbed to SFTS, and identified antibody-producing B cell-lineage plasmablasts and macrophages as principal target cells for SFTSV infection in fatal SFTS. Their results suggest that SFTSV-infected post-germinal center B cells, plasmablasts, and macrophages affect systemic immunopathology and dysregulation, which likely leads to fatal outcomes.

The Importance of Myeloid-Derived Suppressor Cells in the Regulation of Immunosuppressive Mechanisms by Severe Fever with Thrombocytopenia Syndrome

Objective: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by SFTS virus (SFTSV) with a high fatality rate. The objective of our study was to assess the mechanisms of immunofunction through detecting the presence of myeloid-derived suppressor cells (MDSC), granulocyte-colony stimulating factor (G-CFS) and T cells in SFTS patients. Methods: Serum samples from 30 SFTS cases and 20 healthy donors were collected for the test with flow cytometry and sandwich ELISA which contains CD3+, CD4+ T lymphocytes, subsets of MDSC and G-CSF. Results: Granulocytic MDSC (G-MDSC) and monocytic MDSC (M-MDSC) were significantly elevated in SFTS compared to normal control, and G-CSF was expressed at increased frequency. In contrast, CD3+ and CD4+ T lymphocytes were significantly diminished. Further analysis revealed that G-MDSC and G-CSF were higher in severe SFTS infection compared to the patients in mild SFTS infection, and the numbers of CD3+ and CD4+ T lymphocytes showed a more robust pattern of depression. Conclution: In summary, we have characterized an immunosuppressive mechanism in SFTSV infection dependent on G-CSF induction on MDSC and MDSC suppressing T cells.

Effects of Plasma Exchange (PE) Therapy in a Severe Fever with Thrombocytopenia Syndrome (SFTS) Patient with High Virus Quantities

Background: Severe fever with thrombocytopenia syndrome (SFTS) is an infectious disease caused by the SFTS bunyavirus, which is carried by ticks, and presents various symptoms such as fever, fatigue, digestive symptoms, and hemophagocytic lymphhistiocytosis (HLH). Since the first case was reported from China in 2011, there has been a rapid increase of newly diagnosed patients in Japan. Because the mortality rate has remained high (10-30%), there is an urgent need to establish a management strategy for SFTS.Method: We retrospectively reviewed two newly-diagnosed cases of severe SFTS in our hospital from April 2015 to July 2015. Diagnosis of SFTS was confirmed rapidly using a conventional one-step RT-PCR (cvPCR) method, and the quantity of SFTS virus in each serum was determined with a quantitative one-step RT-PCR (qPCR) method described by Yoshikawa et al. (JCM2014, 52, 3325-33). Virus titer is indicated in units of log10 copies/ml.Results: Case 1 was an 87-year-old female and Case 2 was an 81-year-old male. They showed similar severe clinical symptoms including disturbance of consciousness and a variety of abnormal laboratory findings. Both cases were quickly confirmed as SFTS using cvPCR on the next day after blood sampling. Bone marrow (BM) aspiration was performed at diagnosis, and confirmed HLH in both cases.[Case 1]Although methylprednisolone (mPSL) 250 mg was administrated to control HLH on day 3, the data indicated that HLH had become worse on day 4. To control HLH, mPSL pulse therapy (1000 mg/day) was administrated from day four to day six. However, multiple organ failure proceeded rapidly, and she expired on day eight. Serum virus quantities increased markedly from 6.99 (day 3) to 9.05 (day 6). In this case, the virus level at diagnosis was extremely high compared to previously reported cases and it was possible that the high-dose mPSL therapy suppressed anti-virus immunity.[Case 2]Although mPSL 500 mg was administrated from day two, organ damage progressed on day three. In this case, instead of increasing the dosage of mPSL, plasma exchange (PE) was performed from day four to day six, and organ damage was relieved and the patient recovered in good condition. The serum virus quantities decreased slowly from 6.62 (day 4) to 6.48 (day 7) after PE.Discussion: Yoshikawa et al. reported that virus level at diagnosis correlated to the outcomes of SFTS patients and that in most fatal cases virus quantities at diagnosis were over 5.0. In our cases, the patients had higher virus quantities at diagnosis and presented with severe symptoms. In the first case of fatality, the virus quantities remarkably increased shortly after mPSL therapy. As most SFTS patients are over the age of 50 and the mortality rate is higher in the elderly, lowered immunity in elderly patients might be the cause of SFTS progression. Moreover, immunosuppression therapy, including high dose mPSL therapy for HLH, might enhance the accelerated proliferation of SFTS virus. Although mPSL therapy is effective in some cases, immunosuppressive therapy for a SFTS patient is still controversial. In the second case, after PE therapy the virus level didn't increase and symptoms were improved. PE therapy does not suppress humoral and cellular immunity, which is different from mPSL therapy. As such, PE therapy might be effective in serious cases of SFTS with high virus quantities. In these cases, treatment plans were developed without information on virus quantities, and we obtained qPCR results afterwards. In the future, if qPCR can be performed as quickly as cvPCR, then data on the virus level at diagnosis may be the most important information for planning treatment. DisclosuresNo relevant conflicts of interest to declare.

Research Advances on Epidemiology of Severe Fever with Thrombocytopenia Syndrome: A Systematic Review of the Literature

Severe Fever with Thrombocytopenia Syndrome (SFTS) is an emerging infection disease caused by SFTSV, a newly discovered bunyavirus. Suspected SFTS cases were first reported in 2006 in Anhui province, China and SFTSV was first isolated in 2009 in Henan province, China. The disease has been reported in more than 23 provinces in central and eastern China and it was also reported in South Korea and Japan. SFTS is a hemorrhagic fever with major clinical manifestations of fever, thrombocytopenia, gastrointestinal symptoms and leucopenia. In severe SFTS patients, the clinical conditions may proceed quickly and result in multi-organ failure. The average case fatality rate was approximately 10% in humans. The incidence rate of SFTS was significantly higher in old age people and fatal cases mainly occurred in elderly people. SFTS is most likely to be transmitted by tickbite and it also can be transmitted from person to person. The potential reservoir hosts of SFTSV including goats, dogs, cattle, chicken and even birds. This article reviews the latest advances on SFTS epidemiology characteristics including risk factors, sources of infection, distribution of SFTS cases, transmission route and aetiological characteristics, laboratory testing, clinical symptoms, susceptible population, relationship between the meteorological factors and SFTS.