Li et al. Virology Journal (2018) 15:97 https://doi.org/10.1186/s12985-018-1006-7 RESEARCH Open Access Multiple organ involvement in severe fever with thrombocytopenia syndrome: an immunohistochemical finding in a fatal case 1*† 2† 3 1 4 5 6 7 Shibo Li , Yang Li , Qiujing Wang , Xuewen Yu , Miaomiao Liu , Haibo Xie , Liyong Qian , Ling Ye , 3 8 1 2 Zhejuan Yang , Jianjing Zhang , Huimin Zhu and Wenhong Zhang Abstracts Background: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by SFTS bunyavirus (SFTSV), a tick borne bunyavirus. However, Immunohistochemistry of SFTS patients are not well studied. Methods: We obtained multiple of tissues from a fatal case with SFTS, including blood, lungs, kidneys, heart, and spleen. The blood samples were used to isolate the causative agent for detection of viral RNA and further expression of recombinant viral protein as primary antibody. Immunohistochemistry of the heart, lungs, spleen and kidneys was used to characterize the viral antigen in tissue sections. Results: A 79-year-old man, together with his wife, was admitted because of fever. Both patients were diagnosed with SFTS by the positive SFTSV RNA in the blood. The gentleman died of multiple organ failure 8 days after hospitalization. However, his wife recovered and was discharged. Immunohistochemistry indicated that SFTSV antigens were present in all studied organs including the heart, kidney, lung and spleen, of which the spleen presented with the highest amount of SFTSV antigens. The kidney was next while the heart and lungs showed lower amount of SFTSV antigens. Conclusions: SFTSV can direct infect multiple organs, resulting in multiple organ failure and ultimately in an unfavorable outcome. Keywords: SFTSV, Thrombocytopenia, Immunohistochemistry, Bunyavirus, Tick-borne, Emerging infectious diseases Background with mortality mainly occurring to those above 60 years, Severe fever with thrombocytopenia syndrome (SFTS) is suggesting that the severity of SFTS is correlated to an emerging infectious disease that was first reported in compromised immunity . The mortality rate ranged China in 2011 and then in South Korea and Japan [1–3]. from 7.9 to 50% in previous studies [1, 3, 8]. The inci- SFTS bunyavirus (SFTSV), the causative agent of SFTS dence of the disease followed a trend of increasing an- [3, 4], is mainly transmitted through tick bites, but occa- nually . sionally from person to person through blood [5, 6], and The genome of SFTSV consists of three single-stranded rarely through aerosol . SFTSV infects humans of all negative sense RNA segments: S, M and L . The M and the ages, but predominantly those above 50 years old L segments encode viral envelope glycoproteins and viral RNA polymerase, respectively. The S segment is an ambi- sense RNA that encodes a nonstructural protein (NSs) * Correspondence: firstname.lastname@example.org † and a nucleoprotein (NP). The NSs protein of SFTSV has Shibo Li and Yang Li contributed equally to this work. Department of Infectious Diseases, Zhoushan Hospital, Wenzhou Medical been reported to play pivotal roles in SFTSV replication University, Zhejiang, China and host responses . Full list of author information is available at the end of the article © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Li et al. Virology Journal (2018) 15:97 Page 2 of 8 The clinical manifestations of SFTS range from an acute TTA CAG GTT CCT GTA AG, respectively. The ampli- febrile illness to multiple organ failure, encompassing fever, fication conditions and parameters were as follows: one thrombocytopenia, leukopenia, gastrointestinal symptoms, cycles at 45 °C for 45 min, 94 °C for 2 min, 40 cycles at and liver injury . However, SFTSV viral protein expres- 94 °C for 30s, 60 °C for 1 min, 68 °C for 2 min, one cy- sion in human tissues has been rarely studied. In light of cles at 68 °C for 7 min. The PCR product was cloned these uncertainties, in this study we analyzed the viral NP into pMD19 (Simple) T-Vectors (Clontech Laboratories, expression in various tissues from autopsy in a lethal SFTV CA). The cloned insert was excised from the recombin- case by immunohistochemistry assays and indirect im- ant vector by double enzyme digestion and sub-cloned munofluorescence assays with closely monitoring SFTSV into pet-32a vector to express the NP. The recombinant viral load. NP was purified with the pET Express & Purify Kit— His60 (Clontech Laboratories, CA). Methods The purified recombinant NP was mixed with equal Ethics statement volume complete or incomplete Freund’s adjuvant (Sig- The ethical committee of the Zhoushan Hospital has ap- ma-Aldrich, USA) and injected subcutaneously into six proved all human study and the study was conducted ac- 6- to 8-weekold Kunming mice (The Animal Experiment cording to the medical research regulations of China. Center of Shandong University, Jinan City, China) to Written informed consent was obtained from the patients make polyclonal antibody. Each mouse was injected with and their family members for this study. The animal ex- 100 μg recombinant protein at multiple sites at perimental research in this study was approved by the bio- one-week interval for 4 times. Mice were sacrificed ethics committee of School of Public Health, Shandong 15 days after the last immunization to obtain sera. Sera University. All experiments were performed in accordance were frozen at − 80 °C until use as the primary antibody. with relevant guidelines and regulations of China. Sample preparation SFTSV RNA load determination using quantitative real Autopsy tissues were obtained by puncture from the time PCR (qPCR) heart, lungs, spleen, liver, and kidneys of the fatal case in Patients’ blood sample in heparin anticoagulant was col- postmortem examine during the immediate 30 min fol- lected on day 7 of hospitalization and RNA was extracted lowing the death. Tissue slides were initially stained with with RNeasy Purification Kits (QIAGEN, Germany). Hematoxylin & Eosin (H&E) for morphological observa- SFTSV RNA in the patient’ blood was detected by a tions. Furthermore, tissue slides of heart, lungs, spleen, qPCR. PCR primers and a probe were designed from a and kidneys were selected for immunohistochemistry conserved region of the S segment of SFTSV, including with mouse antibody against recombinant NP of SFTSV. forward primer P3: AGT TCA CAG CAG CAT GGA Paraffin embedded tissue sections were deparaffinized as GAG GAT, reverse primer P4: ACT CTC TGT GGC described elsewhere . Briefly, the sections were AAG ATG CCT TCA, and a probe: FAM- TTG CTG placed in a 60 °C incubator for 30 min. The sections GCT CCG CGC ATC TTC ACA TT –TAMRA. The were dewaxed with xylene and gradient ethanol and qPCR was performed for one cycle at 95 °C for 15 s, 45 cy- washed with phosphate buffer (PBS) and distilled water. cles at 95 °C for 5 s and 60 °C for 31 s. The sections were heat repaired in a container con- taining citrate buffer by heating with a microwave to Genetic analysis keep the liquid temperature at about 98 °C for 10 to After extracting the viral RNA from the fatal case, the virus 15 min. The sections in the container were cooled down was sequenced with the use of the sequence-independent at room temperature for 30 min and then washed with single-primer amplification (SISPA) method. Phylogenetic PBS and dried by blotting. Hydrogen peroxide (3%) was analyses were performed with the maximum likelihood added to the sections which were then incubated in a method with the use of MEGA7 software. 37 °C water bath for 15 min to block the activity of en- dogenous peroxidase. After washing with PBS, the sec- Viral detection using the immunohistochemistry assays tions were dried by blotting. and indirect immunofluorescence assays Expression and purification of recombinant NP and Sampling labeling obtaining primary antibody One drop (30–50 μl) of the diluted mouse antibody to The NP gene of SFTSV was amplified by reverse tran- SFTSV recombinant NP as previously mentioned was scription PCR (RT-PCR) with the Access RT-PCR Sys- added. Negative controls were added with normal mouse tem Kit (Promega, Madison, WI). The sequences of the sera without the primary antibody correspondently. The forward primer and reverse primer were: GAG GTA sections were incubated at 37 °C for 1 h. The slides were CCA TGT CAG AGT GGT CC and AAT CTC GAG rinsed with PBS. For the immunohistochemistry assays, the Li et al. Virology Journal (2018) 15:97 Page 3 of 8 sections were incubated with rabbit anti-mouse horseradish resolve. On day 7 after hospitalization, the patient devel- peroxidase-labeled secondary antibody (1: 1000) (ZSGB-Bio, oped coma with sluggish pupillary light reflex and un- Beijing, China), and incubated at 37 °C for 1 h. The sections stable vital signs. Two days later, the patient died. were stained with DAB coloring liquid (ZSGB-Bio, Beijing, Case two was conscious but listless without bleeding, skin China) and observed under a light microscope by two rash, jaundice, or lymphadenopathy. The patient had scat- pathologists. For the indirect immunofluorescence assays, tered rales in the lungs. Laboratory test results showed that the sections were incubated with rabbit anti-mouse aminotransferase, LDH, CK and viral load were mildly in- peroxidase-labeled secondary antibody (Alexa Fluor creased (Fig. 1) and thrombocytopenia and leukocytopenia 488-conjugated Affinipure Goat Anti-Rabbit IgG, Protein- were further observed; serum potassium and sodium ions tech, USA) (1:100 diluted), and then placed in an incubator were decreased slightly (Table 1). Bone marrow biopsy at 37 °C for 1 h. After immunoreaction, nucleus staining showed hemophagocytic phenomenon. The patient was with DAPI (C0065, Solarbio) was performed for 10 min at treated positively and her condition gradually returned to room temperature. The slides were washed again and the normal. The patient recovered and was discharged on the slides were examined under a fluorescence microscope sixteenth day after admission. (Olympus BX3). SFTSV viral load of the patients Results SFTSV viral load was closely followed up for 7 days for Case presentations both patients. On the second day after hospitalization, A couple was admitted into a local hospital on case one was serum positive for SFTSV RNA by qPCR Zhoushan Island, Zhejiang Province, China because of amplification. On day 3 after hospitalization case two fever with nausea and vomiting. Both two patients had also turned into serum positive for SFTSV by qPCR. no significant past medical history. Case one was the hus- Case one had much higher viral load and longer period band, 79-year-old male presenting with fever (38.5 °C), fa- of SFTSV viremia than case two and the viral load of tigue, diarrhea for 6 days, complicated with one episode of case one had been continuously increasing with the ex- bright red hematemesis. On admission blood tests showed tension of the disease until death (Fig. 1). neutropenia, thrombocytopenia, with normal hemoglobin (Table 1). The patient was given hemostatic drugs, cefti- Laboratory results of the patients zoxime and ribavirin after admission. Case two was the Laboratory examination showed that PLT, WBC, and wife, 66-year-old. On admission, she reported fever (38.2 ° hemoglobin decreased in both patients. The level of aspar- C), fatigue, nausea, and anorexia. Blood test showed tate transaminase (AST), LDH, and CK was dramatically slightly low white blood cells (WBC), thrombocytopenia, elevated in the fatal patient (case one). Unremarkable and slightly anemia (Table 1). She was given lansoprazole, change (LDH) or no change (AST, CK) was observed in levofloxacin, rehydration and symptomatic treatment. Fur- mild patient (case two) (Fig. 1). The level of D -dimer was ther questioning revealed that both patients had tick bites significantly high in the fatal case during the entire course on the face and legs about 1 week before onset of illness. of illness, but only slightly increased in the mild patient Therefore, SFTS was highly suspected for this couple. The for 2 days. Prolonged APTT was only presented in the decision was made to determine the SFTSV viral load and fatal case. These results suggested multiple organ failure samples from the couple tested positive for SFTFV. and presence of DIC in the fatal case. After admission, Case one experienced continuous pro- gressive increase of aminotransferase, lactate dehydrogen- Microscopic morphological findings ase (LDH), creatine phosphokinase (CK), and serum Findings of H&E staining sections showed congestion SFTSV viral load (Fig. 1) and decrease of platelet and and focal hemorrhage in the spleen. Ischemic lesions serum albumin, prolonged activated partial thromboplas- were also observed (Fig. 2a). The kidney was microscop- tin clotting time (APTT) (Table 1). On day 5 after ically eroded with dilated tubules where swollen renal hospitalization, the patient became delirium and uncon- tubular epithelial cells were seen (Fig. 2b). The alveolar sciousness and had oral mucosal bleeding, crackles in the spaces were flooded with edema fluid and interstitial fi- lungs, right lower extremity ecchymosis, and respiratory brous proliferated (Fig. 2c). A small amount of expan- failure. An APACHE II (Acute Physiology and Chronic sion of capillary could be observed in several organs Health Evaluation II) score was seven points and a SOFA including kidneys and lungs. Myocardium cells revealed (sequential organ failure assessment) score was four structural disorders with vacuolar degeneration, with points. The patient was given tracheal intubated on mech- lipofuscin dispersed (Fig. 2d). Liver histological changes anic ventilation, plasma exchange, blood filtration, red could be found as well, such as expansion of portal area, blood cell transfusion, anti-viral and antibacterial drugs, congestion in hepatic sinusoid, and acidophilic degener- albumin, and fibrinogen. His symptoms still did not ation (Fig. 2e). Li et al. Virology Journal (2018) 15:97 Page 4 of 8 Table 1 Laboratory test results of patients Day after admission 1 2 3456 789 Days after onset P1 67 8 9 1011 121314 P2 2 3 4567 8910 PLT (× 10 /L) P1 89 58 35 20 11 10 14 62 69 P2 83 ND 44 39 28 28 38 44 67 WBC (×10 /L) P1 1.3 1.1 0.7 3 4.4 3.9 6.5 11 15.4 P2 4.1 ND 2 2 1.5 1.9 2.1 2.2 2.3 HB (g/L) P1 138 135 134 126 114 81 77 50 41 P2 130 ND 124 127 119 116 120 117 111 AST (U/L) P1 93 131 650 650 862 852 703 719 922 P2 ND ND 45 48 49 39 38 31 40 ALT (U/L) P1 38 40 171 164 223 168 102 83 166 P2 ND ND 17 24 27 25 24 23 26 ALB (g/L) P1 33.8 32.4 27.6 25.9 26.3 26.3 23.5 21.7 17.4 P2 ND ND 37.1 37.7 35.8 37.4 39.3 43.9 40 LDH (U/L) P1 240 337 965 1134 1418 1649 2511 – 4840 P2 ND ND 218 295 286 282 267 241 246 CK (U/L) P1 499 665 1151 1261 1451 1126 2337 – 3783 P2 ND ND 217 255 207 149 97 62 52 CKMBU/L) P1 17 19 42 50 51 74 92 – 125 P2 ND ND 8 11 8 11 8 6 5 CR (umol/L) P1 83.2 101.7 87 85 84 107 153.6 152 232 P2 ND ND 75.2 65.7 57.7 52.9 68.2 54.1 55.7 BUN (mmol/L) P1 6.9 7.33 5.2 7.8 6.41 7.8 10.33 9.6 12.6 P2 ND ND 4.43 3.23 2.68 2.12 2.51 3.17 3.89 APTT (s) P1 ND 41.6 49.3 54.7 90.5 97.9 116.2 78.1 76.4 P2 ND ND 34.1 31.2 31.7 30.5 29.5 28.9 27.2 PT (s) P1 ND 12.3 13.3 11.8 11.4 10.4 10.8 11.7 14.2 P2 ND ND 12.1 11.2 11.1 10.8 11.2 11.2 11.4 D-D (ng/ml) P1 ND 983 3110 4522 2581 1210 392 389 409 P2 ND ND 608 572 412 401 418 415 390 Potassium (mmol/l) P1 3.88 3.71 3.28 3.4 3.36 3.48 3.62 3.9 4.13 P2 ND ND 3.02 3.6 3.37 3.45 3.52 3.74 4.3 Sodium (mmol/l) P1 127 129.9 132.6 129.9 134.0 130.1 138.4 139.0 138 P2 ND ND 132.6 140.6 139.4 142.4 142.1 137.4 143 a b c P1 patient 1, P2 patient 2, ND not done Immunohistochemistry assays and indirect especially in the white pulp. The sections from the kidneys immunofluorescence assay results also revealed the viral antigens expressing in the glomeruli. Immunohistochemistry studies showed a positive staining Compared to the spleen and the kidneys, the virus antigens for SFTSV NP in sections from all organs tested including in the heart and lungs was detectable despite much lower the spleen, kidneys, lungs, and heart (Fig. 3a, c, e, g)while abundance. Meanwhile, the immunofluorescence assays negative staining corresponded to the controls specimen showed the spleen, kidneys, lungs, and heart tissue were (Fig. 3b, d, f, h). Furthermore, the SFTSV antigens predom- positive in SFTSV antigens (Fig. 4). The discrepancies in inantlyexhibits acytoplasmicpattern. TheSFTSV antigens antigens between different organs were comparable with were the most widespread and abundant in the spleen, that appeared in the immunohistochemistry assays. Li et al. Virology Journal (2018) 15:97 Page 5 of 8 Fig. 1 The clinical course of two SFTS patients. The condition of Patient 1 deteriorated rapidly and he died at day 9 of hospitalization while Patient 2 was in a relatively stable condition. Patient 1 revealed a higher SFTSV viral load, higher levels of AST, LDH and CK than his wife (Patient 2). AST: Aspartate transaminase; LDH: lactate dehydrogenase; CK: creatine kinase Fig. 2 The microscopic morphological observation using Hematoxylin & Eosin stained slides of a decreased SFTSV patient. SFTSV infections involved multiple organs including the spleen (Panel a), kidneys (Panel b), lungs (Panel c), heart (Panel d) and liver (Panel e) Li et al. Virology Journal (2018) 15:97 Page 6 of 8 Fig. 4 Immunofluorescence assays results of a deceased SFTSV patient. The high immunofluorescence staining of SFTSV antigens Fig. 3 Immunohistochemistry results of a deceased SFTSV patient. within the spleen was shown (Panel a) while the median The spleen tissues had the most amounts of SFTSV antigens (Panel immunofluorescence staining of SFTSV antigens within the kidneys a); the kidney had moderate amount of SFTSV antigens (Panel c), (Panel c), lungs (Panel e), and the low immunofluorescence staining and the lung (Panel e) and the heart (Panel g) had least amount of SFTSV antigens within the heart (Panel g). Corresponding SFTSV antigens. Negative controls were stained by omitting the negative controls showed no immunofluorescence staining (Panel b, primary antibody incubation using the spleen (Panel b), kidneys spleen; Panel d, kidney; Panel f, lungs, Panel h, heart) (original (Panel d), lungs (Panel f), heart (Panel h) tissue sections respectively. magnification × 400) (original magnification × 400) immunofluorescence assays of multiple tissues were ex- Molecular characterization amined in the deceased patient. Tick bites were rarely re- The whole genome of the fatal patient’s SFTSV isolates ported in SFTS patients usually with an unknown was completely sequenced. We are able to yield the full incubation time. These two patients had a clear date of sequence of three viral segments, including L segment of their tick bites and onset of illness, consisting with the in- 6368 nucleotides, M segment of 3378 nucleotides and S cubation time around 5 to 8 days since the contact. segment of 1744 nucleotides respectively (see Additional The fatal case suffered from severe coagulopathy with file 1). Phylogenetic trees based on complete viral diffused bleeding of GI tract and skin, ended up with de- genome sequence of L segment showed the SFTSV lirium, and coma. The fatal patient had higher liver en- isolate clustered well with other known SFTSV isolates zymes, LDH, and CK than the mild patient who (Fig. 5). And the sequence date also suggested that case recovered from the disease. The fatal patient also had one was infected by genotype D SFTSV. coagulation dysfunction with prolonged activated partial thromboplastin time and elevated D-dimer levels than Discussion the mild patient. Previous study indicated that elevated We reported the clinical manifestations and laboratory AST, LDH, CK and CK-MB were risk factors associated tests of a fatal SFTS patient and a mild SFTS patient in a with severity among SFTS patients and fatality among cluster. Viral immunohistochemistry assays and indirect severe SFTS patients . Li et al. Virology Journal (2018) 15:97 Page 7 of 8 Fig. 5 Phylogenetic analysis of the isolate from the fatal patient and other SFTSV. The phylogenetic tree was generated from complete nucleotide sequence of L segment High serum viral load has been considered to be a Conclusions high-risk factor that resulted in the death of SFTS pa- SFTSV virus was found in multiple organs, with the tients . Our study further confirmed that the highest viral load in the spleen, moderate load in kid- serum viral load was correlated with the severity of neys, and the least in the lung and heart. In addition, the disease. Therefore, monitoring viral load might SFTS patients with higher viral load and higher liver en- assist in evaluating the prognosis of the disease. Al- zymes, LDH, and CK indicated severity of the disease though the pathogenesis of SFTS remains elusive. The and even fatal outcome; the incubation time of SFTS host immune system is essentially indispensable for was about 5 to 8 days after tick bite. the pathogenesis of SFTSV infection, in addition to the high level of virus replication. Some studies sug- Additional file gested that cytokine mediated inflammatory response is characterized by the imbalance of cytokines and Additional file 1: The DNA sequence information from the SFTSV isolated from the fatal diseases. (DOCX 17 kb) chemokines, and plays an important role in the pro- gression of SFTSV infection [12, 14]. Previous reports Abbreviations have showed SFTSV antigens in lymph nodes, liver, APTT: Activated partial thromboplastin clotting time; AST: Aspartate spleen, bone marrow and adrenals, but not in the transaminase; CK: Creatine phosphokinase; LDH: Lactate dehydrogenase; heart, lungs, kidneys, gastrointestinal tract, aorta, or NP: Nucleoprotein; NSs: Nonstructural protein; PBS: Phosphate buffer; qPCR: Quantitative real time PCR; RT-PCR: Reverse transcription PCR; iliopsoas muscle [1, 15, 16]. Although we failed to SFTS: Severe fever with thrombocytopenia syndrome; SFTSV: Severe fever perform the IHC assay for the liver tissue due to with thrombocytopenia syndrome bunyavirus; SISPA: Sequence-independent overmuch liver tissues loss when trimmed and liver single-primer amplification; WBC: White blood cells tissue sections falling coming off slide, the initial im- Acknowledgements munohistochemistry and immunofluorescence findings We acknowledge the outstanding contributions from the staff at Zhoushan still broadened the knowledge of the extent of SFTS Hospital, Huashan Hospital, Jining medical University, Maternal and Child that SFTSV infection is not only limited in the Health Hospital, Daishan Centers for Disease Control and Prevention, The First people’s hospital of Daishan. We also express our greatest thanks to the spleen, but also extensively involves the kidneys, the couple and their family for their great contributions to extend our lungs, and the heart. Our study is consistent with a knowledge of this disease. mouse model of SFTSV infection, which indicated that SFTSV primarily infects the spleen and lymph Funding This study was funded by grants from the municipal science and technology nodes . These studies suggested that SFTSV could plan projects of Zhoushan Municipal Science and Technology infect most organs of the patients, with heaviest in- Bureau(Nos.2016C11001), Public welfare project of Zhoushan Municipal fection in the spleen. Science and Technology Bureau, Zhejiang Province (Nos.2016C31038, Li et al. Virology Journal (2018) 15:97 Page 8 of 8 2014C31069); Youth Fund Project of Zhoushan Municipal Health Planning 8. Ding S, Niu G, Xu X, Li J, Zhang X, Yin H, Zhang N, Jiang X, Wang S, Liang Bureau, Zhejiang Province (Nos.2013Q01). M. Age is a critical risk factor for severe fever with thrombocytopenia syndrome. PLoS One. 2014;9(11):e111736. 9. Jiang F, Wang L, Wang S, Zhu L, Dong L, Zhang Z, Hao B, Yang F, Liu W, Availability of data and materials Deng Y, et al. Meteorological factors affect the epidemiology of All data generated or analyzed during this study are included in this hemorrhagic fever with renal syndrome via altering the breeding and published article and its supplementary information files. hantavirus-carrying states of rodents and mites: a 9 years’ longitudinal study. Emerg Microbes Infect. 2017;6(11):e104. Authors’ contributions 10. Chen X, Ye H, Li S, Jiao B, Wu J, Zeng P, Chen L. Severe fever with SBL, WHZ conceived, designed and supervised the study. HMZ, JJZ performed thrombocytopenia syndrome virus inhibits exogenous type I IFN signaling the experiments and analyzed the data. QJW, XWY, HBX, LY acquired the data pathway through its NSs in vitro. PLoS One. 2017;12(2):e0172744. and performed laboratory tests. MML performed the pathological examination 11. Ramos-Vara J, Miller M. When tissue antigens and antibodies get along: and analyzed the data. ZJY, YL analyzed and interpreted the data. SBL, QJW, YL revisiting the technical aspects of immunohistochemistry—the red, brown, wrote the draft and WHZ, SBL revised it critically and gave final approval. All of and blue technique. Vet Pathol. 2014;51(1):42–87. authors agreed on the content of this manuscript. 12. M-m L, Lei X-Y, Yu X-j. Meta-analysis of the clinical and laboratory parameters of SFTS patients in China. Virol J. 2016;13(1):198. Ethics approval and consent to participate 13. Gai ZT, Zhang Y, Liang MF, Jin C, Zhang S, Zhu CB, Li C, Li XY, Zhang QF, All applicable international, national, and/or institutional guidelines for the care Bian PF, et al. Clinical progress and risk factors for death in severe fever with and use of animals were followed. All procedures performed in studies involving thrombocytopenia syndrome patients. J Infect Dis. 2012;206(7):1095–102. human participants were in accordance with the ethical standards of the 14. Sun Y, Jin C, Zhan F, Wang X, Liang M, Zhang Q, Ding S, Guan X, Huo X, Li institutional and/or national research committee and with the 1964 Helsinki C, et al. Host cytokine storm is associated with disease severity of severe declaration and its later amendments or comparable ethical standards. Informed fever with thrombocytopenia syndrome. J Infect Dis. 2012;206(7):1085–94. consent was obtained from all individual participants included in the study. 15. Hiraki T, Yoshimitsu M, Suzuki T, Goto Y, Higashi M, Yokoyama S, Tabuchi T, Futatsuki T, Nakamura K, Hasegawa H, et al. Two autopsy cases of severe fever with thrombocytopenia syndrome (SFTS) in Japan: a pathognomonic Competing interests histological feature and unique complication of SFTS. Pathol Int. 2014; The authors declare that they have no competing interest. 64(11):569–75. 16. Uehara N, Yano T, Ishihara A, Saijou M, Suzuki T. Fatal severe fever with thrombocytopenia syndrome: an autopsy case report. Intern Med. 2016; Publisher’sNote 55(7):831–8. Springer Nature remains neutral with regard to jurisdictional claims in 17. Liu Y, Wu B, Paessler S, Walker DH, Tesh RB, Yu XJ. The pathogenesis of published maps and institutional affiliations. severe fever with thrombocytopenia syndrome virus infection in alpha/beta interferon knockout mice: insights into the pathologic mechanisms of a Author details 1 new viral hemorrhagic fever. J Virol. 2014;88(3):1781–6. Department of Infectious Diseases, Zhoushan Hospital, Wenzhou Medical University, Zhejiang, China. Department of Infectious Diseases, Huashan Hospital, Fudan University, Shanghai, China. Department of Infectious Diseases, Zhoushan Hospital, Zhejiang, China. School of Public Health, Jining medical University, Jining, Shandong, China. 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Published: May 30, 2018