Close correlation between development of MODS during the initial 72 h of hospitalization and hospital mortality in severe fever with thrombocytopenia syndrome

Mast Cell-Derived Proteases Induce Endothelial Permeability and Vascular Damage in Severe Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever acquired by tick bites. Whether mast cells (MCs), the body's first line of defense against pathogens, might influence immunity or pathogenesis during SFTS virus (SFTSV) infection remained unknown. Here, we found that SFTSV can cause MC infection and degranulation, resulting in the release of the vasoactive mediators, chymase, and tryptase, which can directly act on endothelial cells, break the tight junctions of endothelial cells and threaten the integrity of the microvascular barrier, leading to microvascular hyperpermeability in human microvascular endothelial cells. Local activation of MCs (degranulation) and MC-specific proteases-facilitated endothelial damage were observed in mouse models. When MC-specific proteases were injected subcutaneously into the back skin of mice, signs of capillary leakage were observed in a dose-dependent manner. MC-specific proteases, chymase, and tryptase were tested in the serum collected at the acute phase of SFTS patients, with the higher level significantly correlated with fatal outcomes. By performing receiver operator characteristic curve (ROC) analysis, chymase was determined as a biomarker with the area under the curve value of 0.830 (95% CI = 0.745 to 0.915) for predicting fatal outcomes in SFTS. Our findings highlight the importance of MCs in SFTSV-induced disease progression and outcome. An emerging role for MCs in the clinical prognosis and blocking MC activation as a potential drug target during SFTSV infection was proposed. IMPORTANCE We revealed a pathogenic role for MCs in response to SFTSV infection. The study also identifies potential biomarkers that could differentiate patients at risk of a fatal outcome for SFTS, as well as novel therapeutic targets for the clinical management of SFTS. These findings might shed light on an emerging role for MCs as a potential drug target during infection of other viral hemorrhagic fever diseases with similar host pathology as SFTS.

Acute pancreatitis in patients with severe fever with thrombocytopenia syndrome virus infection

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS), a novel tick-borne disease caused by SFTS virus (SFTSV), has been reported in China, Japan, South Korea, and Vietnam since 2009. SFTSV infection can cause multiple organ damage, including acute pancreatitis (AP). We summarize the clinical features, treatment and outcome of AP associated with SFTSV.

METHODS

We retrospectively review the clinical manifestations, laboratory tests, treatment, and outcome of AP associated with SFTSV infection from January 2009 to December 2018 in Liaoning Province, China.

RESULTS

A total of 418 SFTS patients were reviewed. Fifteen (3.6%) of 418 met the criteria for AP associated with SFTSV infection. The first reported symptom for all SFTS-AP patients was fever. All the SFTS-AP patients presented with thrombocytopenia, and 13 (86.7%) of them presented with leukopenia on admission. Thirteen (86.7%) of 15 SFTS-AP patients were severe SFTS patients, and 9 (60.0%) patients were diagnosed with multiple organ dysfunction syndrome. One SFTS-AP patient died of multiple organ failure. Six (40%) of 15 SFTS-AP patients were not confirmed with SFTSV infection when AP was diagnosed, and the median delay between SFTSV infection and AP diagnosis was 5 days (range, 2-7 days).

CONCLUSIONS

AP is not a frequent complication of SFTS, and is more frequently seen in severe SFTS patients. Most patients with SFTS-AP have mild or moderate disease, and can recover with conservative management; however, severe SFTS-AP can be fatal. In SFTS endemic areas, clinicians should be alert to the possibility of SFTS when AP patients with tick exposure, thrombocytopenia, and leukopenia have a fever before abdominal pain.

The proportion, origin and pro-inflammation roles of low density neutrophils in SFTS disease

Background

Severe fever with thrombocytopenia syndrome (SFTS) is a novel emerging viral infectious disease. We explored the percentage, origins and functional roles of low density neutrophils (LDNs), one of the neutrophils subsets, in SFTS.

Methods

The LDNs and normal density neutrophils (NDNs) from blood of SFTS and normal volunteers which were collected separately. The percentage, origins and the phagocytic capability of SFTS viral (SFTSV) of LDNs were investigated by flow cytometry and real time PCR. The capacity of LDNs to secrete cytokines and to damage endothelial cells was assessed by ELISA and flow cytometry.

Results

We observed that the proportion of LDNs increased dramatically compared with the healthy donors and became the dominant circulating neutrophil population in SFTS patients. Interestingly, the NDNs from the normal donors could switch to LDNs under the SFTS environment. Moreover, SFTSV load in LDNs was significantly higher than that of NDNs in the severe SFTS patients. In addition, the LDNs secreted much higher levels of pro-inflammatory cytokines than NDNs in SFTS and could induce endothelial cell injury.

Conclusion

The NDNs can be converted to LDNs. This conversion mechanism could become the source of LDNs. The LDNs in severe SFTS patient could engulf more SFTSV and exhibit pro-inflammation functions.

Trial registration

The Ethics Committee of Tongji Medical College, Huazhong University of Science and Technology (IORG No: IORG0003571) gave a final APPROVAL for the study.

A simple and practical score model for predicting the mortality of severe fever with thrombocytopenia syndrome patients

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging disease with a high fatality rate. The risk factors for death are not clearly identified, and there is no clinical score model to predict the prognosis. We retrospectively collected the clinical information of clinical symptoms and laboratory parameters of SFTS patients on admission. After analyzing the clinical characteristics of 179 SFTS patients, we found that an elevated level of neurologic symptoms, respiratory symptoms, viral load, and a lower level of monocyte percentage were the critical risk factors for mortality. We used the 4 variables to assemble a score formula named the SFTS index [SFTSI = 5 × Neurologic symptoms-level + 4 × Respiratory symptoms-level + 3 × LG10 Viral load - 2 × LN Monocyte% - 7]. The AURC of this model was 0.964, which was higher than the AURC 0.913 of the viral load especially among the patients with higher viral loads (0.936 vs 0.821). We identified that the neurologic symptoms, respiratory symptoms, viral load, and monocyte percentage were the critical risk factors for SFTS mortality. The clinical score model of SFTSI provides a practical method for clinicians to stratify patients with SFTS and to adopt prompt effective treatment strategies.

Circulating regulatory T cells in patients with severe fever with thrombocytopenia syndrome

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is a newly emerging infectious disease caused by SFTS virus (SFTSV). Immunologic factors have been proved to be related to the occurrence and development of SFTS; however, their role still remains to be further elucidated.

METHODS

Samples from 30 patients with laboratory-confirmed SFTS and 15 healthy controls were subjected to flow cytometry to detect the proportion of CD4+/total lymphocytes, CD4 + CD25+/CD4 + cells and CD4 + CD25+ Foxp3+/CD4 + CD25+ cells in circulating blood and to evaluate their potential function in the development of SFTS.

RESULTS

The data showed that a reduced proportion of CD4+/total lymphocytes and CD4 + CD25+/CD4 + cells was observed in patients with SFTS compared with healthy controls. In contrast, the percentage of CD4 + CD25+ Foxp3+/CD4 + CD25+ cells in the patients in the SFTS group was significantly elevated. Furthermore, we investigated the dynamic changes of the circulating regulatory T cells (Tregs) in patients with SFTS at different stages. The results showed that the proportion of CD4+/total lymphocytes and CD4 + CD25+/CD4 + cells in the non-severe group was prominently higher than that in patients with severe SFTS. Conversely, the proportion of CD4 + CD25+ Foxp3+/CD4 + CD25+ cells was lower in the non-severe group than in the severe group. Additionally, the circulating Tregs reverted to normal ranges during the convalescent phase of SFTSV infection. Moreover, the Tregs level correlated with various clinical parameters.

CONCLUSION

We demonstrated that SFTSV infection resulted in a robust circulating Treg response in patients with SFTS. Our investigation suggested that the proportions of CD4+/total lymphocytes and CD4 + CD25+ Foxp3+/CD4 + CD25+ cells in circulating blood could serve as sensitive indices to evaluate the changes in Tregs in SFTS and predict the progression of SFTS.

Detection and evaluation of immunofunction of patients with severe fever with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by SFTS virus (SFTSV) with a high fatality rate. But the immunofunction was still unclear. The objective of our study was to assess the immunofunction in SFTS patients. Immunofunction test with flow cytometry which contains CD3+, CD4+ and CD8+ T lymphocytes, B cells and NK cells would be used for detecting serum samples collected from 34 SFTS cases and 20 healthy donors. We found that CD3+ and CD4+ T lymphocytes were significantly diminished in SFTS compared to normal control. In contrast, the percentage of NK cells was elevated. Further analysis revealed that the number of CD3+ and CD4+ T lymphocytes showed that there was a more robust pattern of depression in acute phase and severe SFTS infection compared to the patients in recovery phase and mild SFTS infection. But NK cells were significantly increased in acute phase and severe SFTS. They reverted to the near normal levels in convalescent phase. Additionally, the levels of CD3+ and CD4+ T lymphocytes progressively decreased in death group when compared with the survival group, but the level of B cells was higher. The damages of immune system were obvious, and the immune dysfunction might be partly responsible for disease progression of patients with SFTSV infection.

An emerging hemorrhagic fever in China caused by a novel bunyavirus SFTSV

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever in rural areas of China and is caused by a new bunyavirus, SFTSV, named after the disease. The transmission vectors and animal hosts of SFTSV are unclear. Ticks are the most likely transmission vectors and domestic animals, including goats, dogs, and cattle, are potential amplifying hosts of SFTSV. The clinical symptoms of SFTS are nonspecific, but major symptoms include fever, gastrointestinal symptoms, myalgia, dizziness, joint pain, chills, and regional lymphadenopathy. The most common abnormalities in laboratory test results are thrombocytopenia (95%), leukocytopenia (86%), and elevated levels of serum alanine aminotransferase, aspartate aminotransferase, creatine kinase, and lactate dehydrogenase. The fatality rate for SFTS is 12% on average, and the annual incidence of the disease is approximately five per 100000 of the rural population.