The clinical and immunological characteristics in fatal severe fever with thrombocytopenia syndrome virus (SFTSV) infection

Elevated CD4- CD8- double-negative T cells in the peripheral blood of SFTS patients are associated with disease severity

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS), caused by the Dabie bandavirus, is a fatal infectious disease with no specific vaccines or antiviral treatments. Early diagnosis and severity assessment are critical for clinical management.

METHODS

This study analyzed peripheral blood samples from 81 SFTS patients and healthy controls, focusing on the distribution of CD4+, CD8+, CD4+CD8+ double-positive T (DPT) cells, and CD4-CD8- double-negative T (DNT) cells. The relationship between T cell subsets, clinical parameters, viral load, and cytokine levels was examined for diagnostic and prognostic potential.

RESULTS

DPT cells were lower and DNT cells higher in SFTS patients compared to controls. DNT cell proportions were higher in severe and fatal cases, correlating positively with viral load, APTT, TT, D-dimer, ferritin, and LDH, and negatively with platelet count, HDL, and fibrinogen. DNT cells were also positively correlated with IFN-α and IFN-γ levels, and higher in patients with complications like shock and sepsis. Furthermore, Cox regression analysis revealed that an elevated DNT cell proportion was an independent risk factor for poor prognosis in SFTS patients.

CONCLUSION

DNT cell proportion changes are linked to SFTS severity and prognosis, suggesting DNT cells as potential biomarkers for early diagnosis and prognosis assessment.

The Impact of Non-Thyroidal Illness Syndromes on The Prognosis and Immune Profile in Severe Fever with Thrombocytopenia Syndrome Patients

Background

Non-thyroidal illness syndrome (NTIS) is the most common endocrine dysfunction in critically ill patients and is often associated with poor prognosis. Thyroid dysfunction and immune cell disturbances are frequently observed in patients with severe fever with thrombocytopenia syndrome (SFTS). This study aims to evaluate the impact of NTIS on the prognosis of SFTS patients and to explore the relationship between thyroid hormones (THs) and immune cell profiles.

Methods

Adult patients admitted to Yantai Qishan Hospital for SFTS from January 2023 to December 2023 with no prior history of thyroid disease were retrospectively recruited. Multivariable regressions were used to assess the associations between NTIS and clinical outcomes. Spearman correlation analysis was conducted to evaluate the relationships between immune cells and THs. SFTS patients with NTIS were categorized into four subtypes based on different levels of FT4 and TSH, and the association between NTIS subtypes and mortality was further analyzed.

Results

Of the 84 SFTS patients included in the study, 62 (73.8%) were diagnosed with NTIS. Independent risk predictors which may affect prognosis of SFTS patients include NTIS subtype (P =0.002), viral load (P = 0.029), FT3 (P = 0.032), and FT4 (P = 0.041). SFTS patients with NTIS exhibited a higher mortality rate compared to euthyroid patients (P = 0.033). Spearman correlation analysis revealed that LYM, LYM%, MONO, MONO%, BAS, CD3+T, CD3+T%, Th, and Th% were positively correlated with FT3, FT4, or TSH levels. NTIS patients were more likely to present with coagulation abnormalities (APTT, P = 0.005; D-Dimer, P < 0.001), liver enzyme abnormalities (AST, P = 0.001), electrolyte imbalances (Sodium, P = 0.003), elevated LDH (P = 0.001), and increased ɑ-HBDH (P = 0.003).

Conclusion

NTIS is common in SFTS patients, and SFTS patients with NTIS have a lower survival rate compared to euthyroid patients. The mortality risk in NTIS type 3 patients is higher than in those with NTIS type 1.

Development and validation of a novel mortality risk stratification simplified scoring scale for severe fever with thrombocytopenia syndrome

OBJECTIVES

The global incidence of severe fever with thrombocytopenia syndrome (SFTS) has markedly increased over the past decade. There is an urgent need to establish a reliable scoring system for predicting the mortality of patients with SFTS.

METHODS

In this ambispective study, 714 patients with SFTS were recruited from 11 sites in China. Among these, 544 patients hospitalized for SFTS from May 2012 to June 2022 were included retrospectively in the training cohort, and 170 were prospectively enrolled between April 2021 and November 2023 in the validation cohort. Logistic regression analysis was performed to identify risk factors for 30-day mortality. A nomogram model (SFTS-logistic model) and a simplified scoring system (SFTS-Wuhan model) were established for predicting mortality. The performance of these models in terms of calibration, discrimination, and clinical utility was evaluated and validated.

RESULTS

The 30-day mortality rate was 12.89% (92/714). The mean age was 65 years old (interquartile range, 57-71), and 322 (45.10%) patients were male. The SFTS-logistic model and SFTS-Wuhan model were developed based on seven independent risk factors, including age (adjusted OR [AOR], 1.062; 95% CI, 1.019-1.106), temperature at admission (AOR, 1.599; 95% CI, 1.095-2.336), white blood cell count (AOR, 0.799; 95% CI, 0.653-0.978), platelet count (AOR, 0.977, 95% CI, 0.959-0.996), aspartate aminotransferase (AOR, 1.001, 95% CI, 1.000-1.003), creatinine (AOR, 1.006; 95% CI, 1.001-1.011), and vasopressors use (AOR, 6.270; 95% CI, 1.397-28.146). Both models demonstrated good discrimination with areas under the receiver operating characteristic curve above 0.84, satisfactory calibration, and comparable clinical net benefit in the training and validation cohorts.

DISCUSSION

The prognostic scoring model and its simplified surrogate can serve as robust tools for mortality risk stratification in SFTS, allowing the early identification of high-risk patients.

Circulation of tick-borne pathogens in wildlife of the Republic of Korea

Habitat loss of wildlife and increased human activities in their habitat provide more opportunities for human-wild animal contact. These artificial environments influence humans by facilitating the transmission of tick-borne pathogens. Therefore, we aimed to detect and understand circulating tick-borne pathogens in the natural environment by analyzing blood and spleen samples of wild animals admitted to wildlife rescue centers in the Republic of Korea. In total, 376 samples were collected from 355 rescued wild animals immediately after their arrival or death. After DNA deoxyribonucleic acid and RNA extractions, reverse transcription polymerase chain reaction (RT-PCR) and nested PCR were conducted to detect target tick-borne pathogens. This study detected six positive samples of severe fever with thrombocytopenia syndrome virus (SFTSV), 146 Anaplasma phagocytophilum, 55 Anaplasma bovis, 19 Rickettsia spp., 45 Borrelia theileri, and 4 Bartonella schoenbuchensis. Among the positive samples, SFTSV was detected in one spleen sample from a Korean water deer, from which SFTSV was successfully isolated. After full genome sequencing, the L, M, and S segments all belonged to genotype B-3 and indicated 99.84 % ∼ 99.94 % similarity with SFTSV isolated from human serum. In conclusion, wild animals are potential reservoirs of tick-borne pathogens. Therefore, surveillance systems to prevent transmission among ticks, animals, and humans must be developed using the One Health concept.

Current insights into human pathogenic phenuiviruses and the host immune system

Phenuiviruses are a class of segmented negative-sense single-stranded RNA viruses, typically consisting of three RNA segments that encode four distinct proteins. The emergence of pathogenic phenuivirus strains, such as Rift Valley fever phlebovirus (RVFV) in sub-Saharan Africa, Severe Fever with Thrombocytopenia Syndrome Virus (SFTSV) in East and Southeast Asia, and Heartland Virus (HRTV) in the United States has presented considerable challenges to global public health in recent years. The innate immune system plays a crucial role as the initial defense mechanism of the host against invading pathogens. In addition to continued research aimed at elucidating the epidemiological characteristics of phenuivirus, significant advancements have been made in investigating its viral virulence factors (glycoprotein, non-structural protein, and nucleoprotein) and potential host-pathogen interactions. Specifically, efforts have focused on understanding mechanisms of viral immune evasion, viral assembly and egress, and host immune networks involving immune cells, programmed cell death, inflammation, nucleic acid receptors, etc. Furthermore, a plethora of technological advancements, including metagenomics, metabolomics, single-cell transcriptomics, proteomics, gene editing, monoclonal antibodies, and vaccines, have been utilized to further our understanding of phenuivirus pathogenesis and host immune responses. Hence, this review aims to provide a comprehensive overview of the current understanding of the mechanisms of host recognition, viral immune evasion, and potential therapeutic approaches during human pathogenic phenuivirus infections focusing particularly on RVFV and SFTSV.

Comparative analysis of the color change in blue-green inclusions within neutrophils between two patients with different clinical outcomes

Blue-green neutrophilic inclusions (BGNI), also known as "death bodies," are bright green structures observed in the cytoplasm of neutrophils or monocytes and are closely associated with acute liver failure, lactic acidosis, and other serious diseases. Some studies suggested a potential association with phagocytic lipofuscin released by damaged liver cells. The presence of BGNI typically indicated a poor prognosis. We presented two cases. Case 1 was diagnosed with novel bunyavirus infection and exhibited severe hepatic impairment and coagulation dysfunction along with the presence of BGNI in neutrophils. Despite receiving comprehensive symptomatic treatment, the patient's condition rapidly deteriorated leading to eventual demise. Case 2 had severe liver injury caused by wasp stings, and BGNI was observed. Following active treatment measures, the patient eventually achieved recovery. Throughout the disease course of case 1, there was a progressive deepening in color and increase in quantity of BGNI. Conversely, case 2 demonstrated an opposite trend. Based on the comparison of clinical outcomes and variations in color and quantity of BGNI between these two patients, it was found that an increase in the number and deepening of BGNI color corresponded to worsening condition. Conversely, a decrease in quantity and lightening of color indicated improvement. Hence, these findings suggest a possible association between changes in BGNI characteristics and prognosis.

The first diagnosis of Severe Fever with Thrombocytopenia Syndrome caused by tick-borne Severe Fever with Thrombocytopenia Syndrome virus in Chongqing, China: A case report and literature review

BACKGROUND

Severe Fever with Thrombocytopenia Syndrome (SFTS) is a tick-borne disease caused by the SFTS virus (SFTSV) which has the potential to become a pandemic and is currently a major public health concern.

CASE PRESENTATION

We present the case of a 74-year-old female from an urban area of Chongqing, with leukocytopenia, thrombocytopenia, organ function, inflammatory, blood coagulation, and immune abnormalities. SFTSV infection was confirmed through molecular detection and metagenomic next-generation sequencing (mNGS) analysis, indicating a diagnosis of SFTS due to the patient's history of tick bites. The patient received symptomatic and supportive therapy, including antibiotics, antiviral treatment, and antifungal therapy, and finally discharged from the hospital on day 18.

CONCLUSIONS

This study highlights the need for increased awareness, early diagnosis, and prompt treatment for tick-borne SFTS. It also provides a comprehensive understanding of the disease's characteristics, pathogenesis, detection methods, and available treatments.

Kinetics and Prognostic Significance of Laboratory Markers in Patients With Severe Fever With Thrombocytopenia Syndrome: Insight From a Comprehensive Analysis

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with significant mortality. Identifying prognostic factors that influence patient outcomes is crucial for effective clinical management. In this study, we assessed the dynamic changes of laboratory markers and their association with outcomes in 93 SFTS patients. We found that age and hypertension were significantly associated with poor outcomes in SFTS patients. The deceased group exhibited lower platelet counts, elevated liver and kidney function markers, coagulation profiles, inflammatory markers, and cytokines compared to the survival group. Kinetic analysis showed that these markers gradually normalized in the survival group, while they remained persistently abnormal in the deceased group. Furthermore, hypertension, elevated aspartate aminotransferase, procalcitonin, and interleukin 10 were identified as independent risk factors for predicting poor prognosis of SFTS patients. These findings provide valuable insights into the prognostic significance of laboratory markers and highlight the importance of early identification of high-risk SFTS patients.

Prolonged coagulation times in severe fever with thrombocytopenia syndrome virus infection, the indicators of heparin-like effect and increased haemorrhagic risk

Prolonged coagulation times, such as activated partial thromboplastin time (APTT) and thrombin time (TT), are common in patients infected with severe fever with thrombocytopenia syndrome virus (SFTSV) and have been confirmed to be related to patient's poor outcome by previous studies. To find out the reason for prolonged coagulation time in patients with SFTSV infection, and whether it predicts haemorrhagic risk or not. Seventy-eight consecutive patients with confirmed SFTSV infection were enrolled in this prospective, single-centre, observational study. Several global and specific coagulation parameters of these patients on admission were detected, and the haemorrhagic events during hospitalization and their outcomes were recorded. Most of the enrolled patients had prolonged APTT (82.1%) and TT (80.8%), normal prothrombin time (83.3%) and intrinsic coagulation factors above haemostatic levels (97.4%). The heparin-like effect was confirmed by a protamine neutralization test and anti-Xa activity detection in most patients. Interestingly, the APTT and TT results were significantly positively correlated with the levels of endothelial markers and viral load, respectively. The APTT was independently associated with the haemorrhage of patients. The prolonged APTT and TT of SFTS patients may mainly be attributed to endogenous heparinoids and are associated with increased haemorrhagic risk.

Antiviral immunity of severe fever with thrombocytopenia syndrome: current understanding and implications for clinical treatment

Dabie Banda virus (DBV), a tick-borne pathogen, was first identified in China in 2009 and causes profound symptoms including fever, leukopenia, thrombocytopenia and multi-organ dysfunction, which is known as severe fever with thrombocytopenia syndrome (SFTS). In the last decade, global incidence and mortality of SFTS increased significantly, especially in East Asia. Though previous studies provide understandings of clinical and immunological characteristics of SFTS development, comprehensive insight of antiviral immunity response is still lacking. Here, we intensively discuss the antiviral immune response after DBV infection by integrating previous ex- and in-vivo studies, including innate and adaptive immune responses, anti-viral immune responses and long-term immune characters. A comprehensive overview of potential immune targets for clinical trials is provided as well. However, development of novel strategies for improving the prognosis of the disease remains on challenge. The current review may shed light on the establishment of immunological interventions for the critical disease SFTS.

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.

Dabie bandavirus infection induces macrophagic pyroptosis and this process is attenuated by platelets

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infection with a high mortality rate in humans, which is caused by Dabie bandavirus (DBV), formerly known as SFTS virus. Clinical manifestations of SFTS are characterized by high fever, thrombocytopenia, leukopenia, hemorrhage, gastrointestinal symptoms, myalgia and local lymph node enlargement with up to 30% case fatality rates in human. Macrophage depletion in secondary lymphoid organs have important roles in the pathogenic process of fatal SFTS, but its exact cell death mechanism remains largely unknown. Here, we showed for the first time that DBV infection induced macrophagic pyroptosis, as evidenced by swollen cells, pore-forming structures, accumulation of gasdermin D N-terminal (GSDMD-NT) as well as the release of lactate dehydrogenase (LDH) and IL-1β in human macrophages. In addition to the upregulation of pyronecrosis genes, the expressions of pyroptosis-related proteins (GSDMD, caspase-1 and IL-1β) were also elevated. To be noted, platelets were found to play a protective role in DBV-derived pyroptosis. Transcriptome analysis and in vitro studies demonstrated that platelets significantly reduced the gene expressions and protein production of pro-pyroptotic markers and inflammatory cytokines in macrophages, whereas platelets conferred a propagation advantage for DBV. Collectively, this study demonstrates a novel mechanism by which DBV invasion triggers pyroptosis as a host defense to remove replication niches in human macrophages and platelets provide an additional layer to reduce cellular death. These findings may have important implications to the pathogenesis of lethal DBV, and provide new ideas for developing novel therapeutics to combat its infection.