Kinetics of severe dengue virus infection and development of gut pathology in mice

IMPORTANCE

Dengue virus, an arbovirus, causes an estimated 100 million symptomatic infections annually and is an increasing threat as the mosquito range expands with climate change. Dengue epidemics are a substantial strain on local economies and health infrastructure, and an understanding of what drives severe disease may enable treatments to help reduce hospitalizations. Factors exacerbating dengue disease are debated, but gut-related symptoms are much more frequent in severe than mild cases. Using mouse models of dengue infection, we have shown that inflammation and damage are earlier and more severe in the gut than in other tissues. Additionally, we observed impairment of the gut mucus layer and propose that breakdown of the barrier function exacerbates inflammation and promotes severe dengue disease. This idea is supported by recent data from human patients showing elevated bacteria-derived molecules in dengue patient serum. Therapies aiming to maintain gut integrity may help to abrogate severe dengue disease.

Effects of chloroquine or hydroxychloroquine treatment on non-SARS-CoV2 viral infections: A systematic review of clinical studies

Chloroquine (CQ) and hydroxychloroquine (HCQ) have been used as antiviral agents for the treatment of severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) infection. We performed a systematic review to examine whether prior clinical studies that compared the effects of CQ and HCQ to a control for the treatment of non-SARS-CoV2 infection supported the use of these agents in the present SARS-CoV2 outbreak. PubMed, EMBASE, Scopus and Web of Science (PROSPERO CRD42020183429) were searched from inception through 2 April 2020 without language restrictions. Of 1766 retrieved reports, 18 studies met our inclusion criteria, including 17 prospective controlled studies and one retrospective study. CQ or HCQ were compared to control for the treatment of infectious mononucleosis (EBV, n = 4), warts (human papillomavirus, n = 2), chronic HIV infection (n = 6), acute chikungunya infection (n = 1), acute dengue virus infection (n = 2), chronic HCV (n = 2), and as preventive measures for influenza infection (n = 1). Survival was not evaluated in any study. For HIV, the virus that was most investigated, while two early studies suggested HCQ reduced viral levels, four subsequent ones did not, and in two of these CQ or HCQ increased viral levels and reduced CD4 counts. Overall, three studies concluded CQ or HCQ were effective; four concluded further research was needed to assess the treatments' effectiveness; and 11 concluded that treatment was ineffective or potentially harmful. Prior controlled clinical trials with CQ and HCQ for non-SARS-CoV2 viral infections do not support these agents' use for the SARS-CoV2 outbreak.

Dengue epidemic in a non-endemic zone of Bangladesh: Clinical and laboratory profiles of patients

BACKGROUNDS

Approximately, half of the population in the world including tropical and sub-tropical climates region is at risk of dengue. Being an endemic country, Bangladesh has experienced the largest dengue epidemic in 2019. The present study aimed at evaluating the clinical and laboratory profile of dengue patients in northern Bangladesh during the epidemic.

METHODS

This cross-sectional study included 319 serologically confirmed dengue patients admitted in Shaheed Ziaur Rahman Medical College Hospital in Bogra district. It is one of the main tertiary care hospitals in northern Bangladesh. Data were collected from July to September 2019. Patients' clinical and laboratory data were extracted from clinical records. Patients were classified into two classes according to the WHO 2009 dengue classification such as (i) non-severe dengue and (ii) severe dengue. Chi-square test and independent t-test were used in this study.

RESULTS

Of the 319 patients, 94.1% had non-severe dengue and the remaining 5.9% had severe dengue (severe plasma leakage 68.4%, severe organ involvement 68.4%, and severe clinical bleeding 10.5%). Most of the patients were suffering from primary dengue infection. The most common clinical presentation was fever followed by headache and myalgia. Vomiting and abdominal pain were the most prevalent warning signs. The common hematological findings on admission were leukopenia (63.3%), thrombocytopenia (30.4%) and increased hematocrit (26.6%). Raised serum ALT or AST was observed in 14.1% cases whereas raised serum creatinine was observed in 6.6% cases. Signs of plasma leakage (pleural effusion, respiratory distress, and ascites, rise of hematocrit >20% during hospital stay) and hepatic or renal involvement (serum ALT >42UI/L or serum creatinine >1.2 mg/dL) on admission were mostly associated with severe dengue.

CONCLUSION

The study provides clinical evidence on presentation as well as hematological and biochemical profile of dengue patients in northern Bangladesh that should be implicated in effective patient management.

Comparison of dengue case classification schemes and evaluation of biological changes in different dengue clinical patterns in a longitudinal follow-up of hospitalized children in Cambodia

BACKGROUND

The World Health Organization (WHO) proposed guidelines on dengue clinical classification in 1997 and more recently in 2009 for the clinical management of patients. The WHO 1997 classification defines three categories of dengue infection according to severity: dengue fever (DF), dengue hemorrhagic fever (DHF), and dengue shock syndrome (DSS). Alternative WHO 2009 guidelines provide a cross-sectional classification aiming to discriminate dengue fever from dengue with warning signs (DWWS) and severe dengue (SD). The primary objective of this study was to perform a comparison of two dengue classifications. The secondary objective was to describe the changes of hematological and biochemical parameters occurring in patients presenting with different degrees of severity during the course of the disease, since progression to more severe clinical forms is unpredictable.

METHODOLOGY/PRINCIPAL FINDINGS

We performed a prospective, monocentric, cross-sectional study of hospitalized children in Cambodia, aged from 2 to 15 years old with severe and non-severe dengue. We enrolled 243 patients with acute dengue-like illness: 71.2% were dengue infections confirmed using quantitative reverse transcription PCR or NS1 antigen capture ELISA, of which 87.2% and 9.0% of DF cases were respectively classified DWWS and SD, and 35.9% of DHF were designated SD using an adapted WHO 2009 classification for SD case definition. Systematic use of ultrasound at patient admission was crucial for detecting plasma leakage. No difference was observed in the concentration of secreted NS1 protein between different dengue severity groups. Lipid profiles were different between DWWS and SD at admission, characterized by a decrease in total cholesterol, HDL cholesterol, and LDL cholesterol, in SD.

CONCLUSIONS/SIGNIFICANCE

Our results show discrepancies between the two classifications, including misclassification of severe dengue cases as mild cases by the WHO 1997 classification. Using an adapted WHO 2009 classification, SD more precisely defines the group of patients requiring careful clinical care at a given time during hospitalization.

Severe dengue categories as research endpoints-Results from a prospective observational study in hospitalised dengue patients

Severe dengue was perceived as one clinical disease entity until the WHO 2009 classification stratified it into severe vascular leakage, severe bleeding, and severe organ dysfunction. The objectives of this study were to investigate the potential use of severe dengue categories as endpoints for intervention research. 271 patients with severe dengue among 1734 confirmed dengue patients were followed prospectively in this hospital-based observational study in Latin America and Asia. We compared the distribution of severe dengue categories according to gender and age (below/above 15y), and determined the relative frequency and the overlap of severe dengue categories in the same patients. In a next step, we extended the analysis to candidate moderate severity categories, based on recently suggested definitions which were adapted for our purposes. Severe vascular leakage occurred in 244 (90%), severe bleeding in 39 (14%), and severe organ dysfunction in 28 (10%) of 271 severe dengue patients. A higher frequency of severe leakage was seen in children or adolescents (<15y) compared to adults. More than 80% of the severe leakage cases, and 30-50% of the cases with severe bleeding or severe organ dysfunction, were defined as severe on the basis of that feature alone. In 136 out of 213 patients with severe leakage alone, neither moderate bleeding manifestation nor hepatic involvement was recorded. On the other hand, moderate leakage manifestations were detected in 4 out of 12 cases that were classified as severe based on bleeding alone. A major proportion of severe dengue patients exhibited clinical manifestations of severe vascular leakage only, which may constitute a useful endpoint for intervention research or pathophysiology studies. Severe bleeding and severe organ manifestation were recorded less frequently and exhibited a higher degree of overlap with severe leakage. Severe bleeding without leakage may be associated with individual predisposition or the presence of comorbidities. More detailed assessments are needed to explore this hypothesis. Candidate moderate disease endpoints were investigated and need to be further validated.

Molecular Signatures of Dengue Virus-Specific IL-10/IFN-γ Co-producing CD4 T Cells and Their Association with Dengue Disease

Dengue virus (DENV) can cause diseases ranging from dengue fever (DF) to more severe dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). Whether antiviral T cells contribute to the protection against or pathogenesis of severe disease is not well defined. Here, we identified antigen-specific IL-10+IFN-γ+ double-positive (DP) CD4 T cells during acute DENV infection. While the transcriptomic signatures of DP cells partially overlapped with those of cytotoxic and type 1 regulatory CD4 T cells, the majority of them were non-cytotoxic/Tr1 and included IL21, IL22, CD109, and CCR1. Although we observed a higher frequency of DP cells in DHF, the transcriptomic profile of DP cells was similar in DF and DHF, suggesting that DHF is not associated with the altered phenotypic or functional attributes of DP cells. Overall, this study revealed a DENV-specific DP cell subset in patients with acute dengue disease and argues against altered DP cells as a determinant of DHF.

Clinical relevance of gallbladder wall thickening for dengue severity: A cross-sectional study

Dengue fever is the most important arthropod-borne viral infection worldwide. Secondary prevention to reduce mortality through improved clinical case management has substantially lowered the mortality rate for severe dengue during the past two decades. Gallbladder wall thickening (GBWT) is a nonspecific finding often associated with more severe cases of dengue infection. This study had the aim to describe the ultrasonographic findings in hospitalized patients with dengue infection from Manaus (in the Western Brazilian Amazon) and to correlate the GBWT with dengue severity, symptoms and laboratorial analysis. Patients from 13–84 years admitted to the emergency department at the Fundação de Medicina Tropical Dr. Heitor Vieira Dourado (FMT-HVD) were enrolled in this study. Patients’ selection occurred during the most recent and huge dengue outbreak within the first semester of 2011. All enrolled subjects were systematically tested in order to rule out other possible etiologies for gallbladder inflammation. Abdominal ultrasound was performed by a single physician through bedside portable equipment and all other clinical and laboratorial information were retrieved from patients’ electronic files. 54 subjects were considered for analysis, with confirmed dengue infection by NS1 and/or RT-PCR positivity. From all enrolled patients, 50 (42.4%) presented GBWT. GBWT was significantly and independently related to: age under 31 years, pregnancy, presence of bleeding, presence of any cavitary effusion, DHF classification and severe dengue classifications. During dengue outbreaks, the GBWT identification through a non-invasive and bedside procedure is a confident marker for prompt recognition of potential severe cases.

Association of tumour necrosis factor-α (TNF-α) gene polymorphisms (-308 G>A and -238 G>A) and the risk of severe dengue: A meta-analysis and trial sequential analysis

Individual studies have assessed the association between TNF-α-308G>A and TNF-α-238 G>A polymorphisms and severity of dengue infection. However, the results are inconclusive and most studies had small sample sizes. The objective of this study was to summarize the evidence of association between TNF-α-308 G>A and TNF-α-238 G>A and severity of dengue infection. This study follows the preferred reporting items for systematic reviews and meta- analyses of genetic association studies, recommended by PLOS One. We calculated pooled odds ratio and its 95% confidence interval (CI) to estimate the association between TNF-α-308 G>A or TNF-α-238 G>A and the risk of severe dengue infections. To determine the information size required for this meta-analysis study, a trial sequential analysis (TSA) was done. Eight studies (640 cases and 1275 controls), which assessed the association of TNF-α-308 G>A or TNF-α-238 G>A and the risk of DHF were included. Overall, we found no significant association between TNF-α-308 G>A and the DHF risk in the allelic model (OR, 0.91; 95% CI, 0.51-1.63), the recessive model (OR,1.32;95%CI,0.73-2.37), the dominant model (OR,0.93;95%CI:0.59-1.47) or the additive model (OR,1.43,95;95%CI:0.79-2.59). There was also no significant association between TNF-α-238 G>A and DHF risk under the allele contrast model (OR:1.51;95%CI:0.88-2.58), the recessive model (OR,1.48,95% CI:0.33-6.58), the dominant model (OR,1.48;95%CI:0.56-3.92), or the additive model (OR:1.5;95%CI:0.34-6.69). On subgroup analysis, neither the Asian population nor the non-Asian population showed significant association between TNF-α-308 G>A/TNF-α-238 G>A and the DHF risk under any genetic models. Leave-one-out meta-analysis showed stability of the results. TSA plots suggested that the sample size in this meta-analysis study was below the required information size. The findings suggest an inclusive evidence of the association between TNF-α-308/ TNF-α-238 G>A and the risk of developing severe dengue infection. Large studies with evidence of Hardy-Weinberg equilibrium, assessing gene-gene interactions are recommended.

The Sensitivity, Specificity and Accuracy of Warning Signs in Predicting Severe Dengue, the Severe Dengue Prevalence and Its Associated Factors

Objectives: To study Malaysian dengue clinical practice guideline (CPG) warning signs (WS) in predicting severe dengue (SD) and its associated factors among confirmed cases presented to a teaching hospital in north-eastern Malaysia in 2014. Methods: A cross-sectional study was performed in February 2015 using secondary data acquired from the hospital records. There were 2607 confirmed dengue cases presented to Hospital Universiti Sains Malaysia (HUSM) in 2014. Seven hundred patients were selected after proportionate stratified random sampling conducted according to the number of cases in 12 different months in 2014. Data were collected and analysed using SPSS version 22.0. Results: Severe dengue outcomes represented 4.9% of cases. The prevalence of any of WS in SD was 91.2%. The most common WSs prior to SD were persistent vomiting (55.9%), and abdominal pain/tenderness (52.9%). The most sensitive warning sign in detecting SD was abdominal pain (59%). Specificity of individual WS were generally good, especially of clinical fluid accumulation (99%), hepatomegaly (98%) and mucosal bleeding (93%). Factors associated with SD were persistent vomiting (Adjusted odds ratio (aOR)): 2.41), mucosal bleeding (aOR: 4.73) and haematocrit rise with rapid platelet drop (aOR: 2.74). Conclusion: A focus on sensitivity, specificity, predictive values and association of a number of particular WS should be emphasized in order to better predict severe dengue outcomes.

Serum metabolome changes in adult patients with severe dengue in the critical and recovery phases of dengue infection

Dengue virus (DENV) is the most prevalent arbovirus leading to an estimated 100 million symptomatic dengue infections every year. DENV can cause a spectrum of clinical manifestations, ranging from mild dengue fever (DF) to more life threatening forms such as dengue hemorrhagic fever (DHF). The clinical symptoms of DHF become evident typically at the critical phase of infection (5-7 days after onset of fever), yet the mechanisms that trigger transition from DF to DHF are not well understood. We performed a mass spectrometry-based metabolomic profiling of sera from adult DF and DHF patients at the critical and recovery phases of infection. There were 29 differentially expressed metabolites identified between DF and DHF at the critical phase. These include bile acids, purines, acylcarnitines, phospholipids, and amino acids. Bile acids were observed up to 5 fold higher levels among DHF compared to DF patients and were significantly correlated to the higher levels of aspartate transaminase (AST) and alanine transaminase (ALT), suggestive of liver injury among DHF. Uric acid, the most abundant antioxidant in the blood, was observed to be 1.5 fold lower among DHF compared to DF patients. This could result in decreased capacity of endogenous antioxidant defense and elevated oxidative stress among DHF patients. In the recovery phase, the levels of eight metabolites were still significantly higher or lower among DHF patients, including chenodeoxyglycocholic acid, one of the bile acids observed at the critical phase. This indicates potential prolonged adverse impact on the liver due to DENV infection in DHF patients. Our study identified altered metabolic pathways linked to DHF in the critical and recovery phases of dengue infection and provided insights into the different host and DENV interactions between DF and DHF. The results advance our understanding on the mechanisms of DHF pathogenesis, alluding to possible novel therapeutic targets to dengue management.

A tetravalent virus-like particle vaccine designed to display domain III of dengue envelope proteins induces multi-serotype neutralizing antibodies in mice and macaques which confer protection against antibody dependent enhancement in AG129 mice

Background

Dengue is one of the fastest spreading vector-borne diseases, caused by four antigenically distinct dengue viruses (DENVs). Antibodies against DENVs are responsible for both protection as well as pathogenesis. A vaccine that is safe for and efficacious in all people irrespective of their age and domicile is still an unmet need. It is becoming increasingly apparent that vaccine design must eliminate epitopes implicated in the induction of infection-enhancing antibodies.

Methodology/principal findings

We report a Pichia pastoris-expressed dengue immunogen, DSV4, based on DENV envelope protein domain III (EDIII), which contains well-characterized serotype-specific and cross-reactive epitopes. In natural infection, <10% of the total neutralizing antibody response is EDIII-directed. Yet, this is a functionally relevant domain which interacts with the host cell surface receptor. DSV4 was designed by in-frame fusion of EDIII of all four DENV serotypes and hepatitis B surface (S) antigen and co-expressed with unfused S antigen to form mosaic virus-like particles (VLPs). These VLPs displayed EDIIIs of all four DENV serotypes based on probing with a battery of serotype-specific anti-EDIII monoclonal antibodies. The DSV4 VLPs were highly immunogenic, inducing potent and durable neutralizing antibodies against all four DENV serotypes encompassing multiple genotypes, in mice and macaques. DSV4-induced murine antibodies suppressed viremia in AG129 mice and conferred protection against lethal DENV-4 virus challenge. Further, neither murine nor macaque anti-DSV4 antibodies promoted mortality or inflammatory cytokine production when passively transferred and tested in an in vivo dengue disease enhancement model of AG129 mice.

Conclusions/significance

Directing the immune response to a non-immunodominant but functionally relevant serotype-specific dengue epitope of the four DENV serotypes, displayed on a VLP platform, can help minimize the risk of inducing disease-enhancing antibodies while eliciting effective tetravalent seroconversion. DSV4 has a significant potential to emerge as a safe, efficacious and inexpensive subunit dengue vaccine candidate.

Dengue is mosquito-borne viral disease which is currently a global public health problem. It is caused by four different types of dengue viruses. Nearly a 100 million people a year suffer from overt sickness, which may range from mild fever to potentially fatal disease. A virus-based dengue vaccine was launched for the first time in late 2015. Unexpectedly, this vaccine mimics the dengue viruses in that it appears to elicit disease-enhancing antibodies. To reduce such risk, safer vaccines that eliminate viral proteins responsible for undesirable antibodies are needed. We focused our attention on a small domain of the dengue virus surface protein known as envelope domain III (EDIII). Humans make only a small amount of antibodies against EDIII, but these antibodies are effective in blocking dengue virus from entering cells. We used a yeast expression system to display EDIIIs of all four types of dengue viruses on the surface of non-infectious virus-like particles (VLPs). These VLPs elicited antibodies, in mice and monkeys, which blocked all four dengue virus types and their variants from entering cells in culture. Importantly, these antibodies did not enhance dengue infection in a mouse model.

The value of daily platelet counts for predicting dengue shock syndrome: Results from a prospective observational study of 2301 Vietnamese children with dengue

BACKGROUND

Dengue is the most important mosquito-borne viral infection to affect humans. Although it usually manifests as a self-limited febrile illness, complications may occur as the fever subsides. A systemic vascular leak syndrome that sometimes progresses to life-threatening hypovolaemic shock is the most serious complication seen in children, typically accompanied by haemoconcentration and thrombocytopenia. Robust evidence on risk factors, especially features present early in the illness course, for progression to dengue shock syndrome (DSS) is lacking. Moreover, the potential value of incorporating serial haematocrit and platelet measurements in prediction models has never been assessed.

METHODOLOGY/PRINCIPAL FINDINGS

We analyzed data from a prospective observational study of Vietnamese children aged 5-15 years admitted with clinically suspected dengue to the Hospital for Tropical Diseases in Ho Chi Minh City between 2001 and 2009. The analysis population comprised all children with laboratory-confirmed dengue enrolled between days 1-4 of illness. Logistic regression was the main statistical model for all univariate and multivariable analyses. The prognostic value of daily haematocrit levels and platelet counts were assessed using graphs and separate regression models fitted on each day of illness. Among the 2301 children included in the analysis, 143 (6%) progressed to DSS. Significant baseline risk factors for DSS included a history of vomiting, higher temperature, a palpable liver, and a lower platelet count. Prediction models that included serial daily platelet counts demonstrated better ability to discriminate patients who developed DSS from others, than models based on enrolment information only. However inclusion of daily haematocrit values did not improve prediction of DSS.

CONCLUSIONS/SIGNIFICANCE

Daily monitoring of platelet counts is important to help identify patients at high risk of DSS. Development of dynamic prediction models that incorporate signs, symptoms, and daily laboratory measurements, could improve DSS prediction and thereby reduce the burden on health services in endemic areas.

JNK1/2 inhibitor reduces dengue virus-induced liver injury

High viral load with liver injury is exhibited in severe dengue virus (DENV) infection. Mitogen activated protein kinases (MAPKs) including ERK1/2 and p38 MAPK were previously found to be involved in the animal models of DENV-induced liver injury. However, the role of JNK1/2 signaling in DENV-induced liver injury has never been investigated. JNK1/2 inhibitor, SP600125, was used to investigate the role of JNK1/2 signaling in the BALB/c mouse model of DENV-induced liver injury. SP600125-treated DENV-infected mice ameliorated leucopenia, thrombocytopenia, hemoconcentration, liver transaminases and liver histopathology. DENV-induced liver injury exhibited induced phosphorylation of JNK1/2, whereas SP600125 reduced this phosphorylation. An apoptotic real-time PCR array profiler was used to screen how SP600125 affects the expression of 84 cell death-associated genes to minimize DENV-induced liver injury. Modulation of caspase-3, caspase-8 and caspase-9 expressions by SP600125 in DENV-infected mice suggests its efficiency in restricting apoptosis via both extrinsic and intrinsic pathways. Reduced expressions of TNF-α and TRAIL are suggestive to modulate the extrinsic apoptotic signals, where reduced p53 phosphorylation and induced anti-apoptotic Bcl-2 expression indicate the involvement of the intrinsic apoptotic pathway. This study thus demonstrates the pivotal role of JNK1/2 signaling in DENV-induced liver injury and how SP600125 modulates this pathogenesis.

Dengue-associated hemophagocytic lymphohistiocytosis in an adult: A case report and literature review

BACKGROUND

Infection-associated hemophagocytic syndrome (IAHS) is potentially a fatal disease caused by systemic infection complicated by hemophagocyticlymphohistiocytosis (HLH). Here, we report a case of HLH associated with dengue hemorrhagic fever (DHF) after a trip to Thailand.

CASE SUMMARY

A 33-year-old healthy female patient presented with 3 days of fever, myalgia, and skin rash. Serotype 3 dengue virus was isolated. Clinical and laboratory findings fulfilled the criteria of HLH. After the initiation of corticosteroid therapy, the patient recovered and laboratory findings were normalized.

CONCLUSION

It would be important to differentially diagnose dengue-associated HLH from severe DHF. Early recognition and initiation of steroid treatment would be crucial for the successful treatment of dengue fever complicated by HLH.

Down-regulation of complement receptors on the surface of host monocyte even as in vitro complement pathway blocking interferes in dengue infection

In dengue virus (DENV) infection, complement system (CS) activation appears to have protective and pathogenic effects. In severe dengue fever (DF), the levels of DENV non-structural-1 protein and of the products of complement activation, including C3a, C5a and SC5b-9, are higher before vascular leakage occurs, supporting the hypothesis that complement activation contributes to unfavourable outcomes. The clinical manifestations of DF range from asymptomatic to severe and even fatal. Here, we aimed to characterise CS by their receptors or activation product, in vivo in DF patients and in vitro by DENV-2 stimulation on monocytes. In comparison with healthy controls, DF patients showed lower expression of CR3 (CD11b), CR4 (CD11c) and, CD59 on monocytes. The DF patients who were high producers of SC5b-9 were also those that showed more pronounced bleeding or vascular leakage. Those findings encouraged us to investigate the role of CS in vitro, using monocytes isolated from healthy subjects. Prior blocking with CR3 alone (CD11b) or CR3 (CD11b/CD18) reduced viral infection, as quantified by the levels of intracellular viral antigen expression and soluble DENV non-structural viral protein. However, we found that CR3 alone (CD11b) or CR3 (CD11b/CD18) blocking did not influence major histocompatibility complex presentation neither active caspase-1 on monocytes, thus probably ruling out inflammasome-related mechanisms. Although it did impair the secretion of tumour necrosis factor alpha and interferon alpha. Our data provide strategies of blocking CR3 (CD11b) pathways could have implications for the treatment of viral infection by antiviral-related mechanisms.

The pathology of severe dengue in multiple organs of human fatal cases: histopathology, ultrastructure and virus replication

Dengue is a public health problem, with several gaps in understanding its pathogenesis. Studies based on human fatal cases are extremely important and may clarify some of these gaps. In this work, we analyzed lesions in different organs of four dengue fatal cases, occurred in Brazil. Tissues were prepared for visualization in optical and electron microscopy, with damages quantification. As expected, we observed in all studied organ lesions characteristic of severe dengue, such as hemorrhage and edema, although other injuries were also detected. Cases presented necrotic areas in the liver and diffuse macro and microsteatosis, which were more accentuated in case 1, who also had obesity. The lung was the most affected organ, with hyaline membrane formation associated with mononuclear infiltrates in patients with pre-existing diseases such as diabetes and obesity (cases 1 and 2, respectively). These cases had also extensive acute tubular necrosis in the kidney. Infection induced destruction of cardiac fibers in most cases, with absence of nucleus and loss of striations, suggesting myocarditis. Spleens revealed significant destruction of the germinal centers and atrophy of lymphoid follicles, which may be associated to decrease of T cell number. Circulatory disturbs were reinforced by the presence of megakaryocytes in alveolar spaces, thrombus formation in glomerular capillaries and loss of endothelium in several tissues. Besides histopathological and ultrastructural observations, virus replication were investigated by detection of dengue antigens, especially the non-structural 3 protein (NS3), and confirmed by the presence of virus RNA negative strand (in situ hybridization), with second staining for identification of some cells. Results showed that dengue had broader tropism comparing to what was described before in literature, replicating in hepatocytes, type II pneumocytes and cardiac fibers, as well as in resident and circulating monocytes/macrophages and endothelial cells.

Factors associated with dengue shock syndrome: a systematic review and meta-analysis

BACKGROUND

The pathogenesis of dengue shock syndrome (DSS, grade 3 and 4) is not yet completely understood. Several factors are reportedly associated with DSS, a more severe form of dengue infection that reportedly causes 50 times higher mortality compared to that of dengue patients without DSS. However, the results from these reports remain inconclusive. To better understand the epidemiology, clinical manifestation, and pathogenesis of DSS for development of new therapy, we systematically reviewed and performed a meta-analysis of relevant studies that reported factors in both DSS and dengue hemorrhagic fever (DHF, grade 1 and 2) patients.

METHODS AND FINDINGS

PubMed, EMBASE, Scopus, Google Scholar, Dengue Bulletin, Cochrane Library, Virtual Health Library, and a manual search of reference lists of articles published before September 2010 were used to retrieve relevant studies. A meta-analysis using fixed- or random-effects models was used to calculate pooled odds ratios (OR) or event rate with corresponding 95% confidence intervals. Assessment of heterogeneity and publication bias, meta-regression analysis, subgroup analysis, sensitivity analysis, and analysis of factor-specific relationships were further performed. There were 198 studies constituting 203 data sets that met our eligibility criteria. Our meta-regression analysis showed a sustained reduction of DSS/dengue hemorrhagic fever (DHF) ratio over a period of 40 years in Southeast Asia, especially in Thailand. The meta-analysis revealed that age, female sex, neurological signs, nausea/vomiting, abdominal pain, gastrointestinal bleeding, hemoconcentration, ascites, pleural effusion, hypoalbuminemia, hypoproteinemia, hepatomegaly, levels of alanine transaminase and aspartate transaminase, thrombocytopenia, prothrombin time, activated partial thromboplastin time, fibrinogen level, primary/secondary infection, and dengue virus serotype-2 were significantly associated with DSS when pooling all original relevant studies.

CONCLUSIONS

The results improve our knowledge of the pathogenesis of DSS by identifying the association between the epidemiology, clinical signs, and biomarkers involved in DSS.

Variable selection methods for developing a biomarker panel for prediction of dengue hemorrhagic fever

BACKGROUND

The choice of selection methods to identify important variables for binary classification modeling is critical to produce stable models that are interpretable, that generate accurate predictions and have minimum bias. This work is motivated by data on clinical and laboratory features of severe dengue infections (dengue hemorrhagic fever, DHF) obtained from 51 individuals enrolled in a prospective observational study of acute human dengue infections.

RESULTS

We carry out a comprehensive performance comparison using several classification models for DHF over the dengue data set. We compared variable selection results by Multivariate Adaptive Regression Splines, Learning Ensemble, Random Forest, Bayesian Moving Averaging, Stochastic Search Variable Selection, and Generalized Regularized Logistics Regression. Model averaging methods (bagging, boosting and ensemble learners) have higher accuracy, but the generalized regularized regression model has the highest predictive power because the linearity assumptions of candidate predictors are strongly satisfied via deviance chi-square testing procedures. Bootstrapping applications for evaluating predictive regression coefficients in regularized regression model are performed.

CONCLUSIONS

Feature reduction methods introduce inherent biases and therefore are data-type dependent. We propose that these limitations can be overcome using an exhaustive approach for searching feature space. Using this approach, our results suggest that IL-10, platelet and lymphocyte counts are the major features for predicting dengue DHF on the basis of blood chemistries and cytokine measurements.

Microbial translocation is associated with extensive immune activation in dengue virus infected patients with severe disease

Background

Severe dengue virus (DENV) disease is associated with extensive immune activation, characterized by a cytokine storm. Previously, elevated lipopolysaccharide (LPS) levels in dengue were found to correlate with clinical disease severity. In the present cross-sectional study we identified markers of microbial translocation and immune activation, which are associated with severe manifestations of DENV infection.

Methods

Serum samples from DENV-infected patients were collected during the outbreak in 2010 in the State of São Paulo, Brazil. Levels of LPS, lipopolysaccharide binding protein (LBP), soluble CD14 (sCD14) and IgM and IgG endotoxin core antibodies were determined by ELISA. Thirty cytokines were quantified using a multiplex luminex system. Patients were classified according to the 2009 WHO classification and the occurrence of plasma leakage/shock and hemorrhage. Moreover, a (non-supervised) cluster analysis based on the expression of the quantified cytokines was applied to identify groups of patients with similar cytokine profiles. Markers of microbial translocation were linked to groups with similar clinical disease severity and clusters with similar cytokine profiles.

Results

Cluster analysis indicated that LPS levels were significantly increased in patients with a profound pro-inflammatory cytokine profile. LBP and sCD14 showed significantly increased levels in patients with severe disease in the clinical classification and in patients with severe inflammation in the cluster analysis. With both the clinical classification and the cluster analysis, levels of IL-6, IL-8, sIL-2R, MCP-1, RANTES, HGF, G-CSF and EGF were associated with severe disease.

Conclusions

The present study provides evidence that both microbial translocation and extensive immune activation occur during severe DENV infection and may play an important role in the pathogenesis.

The pathogenesis of severe dengue virus (DENV) infection is still not fully understood. It is hypothesized that it is caused by a cytokine storm as is described in severe sepsis. In the sepsis field, the potent immunostimulator lipopolysaccharide (LPS) is proposed to play an important role in the development of a cytokine storm. In a previous study we have found elevated levels of LPS in children with severe DENV infection. In this study we have investigated if we could confirm that microbial translocation occurs in DENV-infected patients. Moreover, we have determined the levels of thirty cytokines to get more insight in the cytokine storm during DENV infections and we have investigated whether microbial translocation is associated with immune activation. The patients in this cohort were classified according to their clinical presentation. Furthermore, a cluster analysis based on the expression of the determined cytokines was applied to identify patients with similar cytokine profiles. With these two techniques, we identified cytokines that may contribute significantly to the cytokine storm, and we could relate elevated levels of LPS to patients with a pro-inflammatory cytokine profile.

Is pregnancy associated with severe dengue? A review of data from the Rio de Janeiro surveillance information system

Background

Dengue is a reportable disease in Brazil; however, pregnancy has been included in the application form of the Brazilian notification information system only after 2006. To estimate the severity of maternal dengue infection, the available data that were compiled from January 2007 to December 2008 by the official surveillance information system of the city of Rio de Janeiro were reviewed.

Methods and Principal Findings

During the study period, 151,604 cases of suspected dengue infection were reported. Five hundred sixty-one women in their reproductive age (15–49 years) presented with dengue infection; 99 (18.1%) pregnant and 447 (81.9%) non-pregnant women were analyzed. Dengue cases were categorized using the 1997 WHO classification system, and DHF/DSS were considered severe disease. The Mann-Whitney test was used to compare maternal age, according to gestational period, and severity of disease. A chi-square test was utilized to evaluate the differences in the proportion of dengue severity between pregnant and non-pregnant women. Univariate analysis was performed to compare outcome variables (severe dengue and non-severe dengue) and explanatory variables (pregnancy, gestational age and trimester) using the Wald test. A multivariate analysis was performed to assess the independence of statistically significant variables in the univariate analysis. A p-value<0.05 was considered statistically significant.

A higher percentage of severe dengue infection among pregnant women was found, p = 0.0001. Final analysis demonstrated that pregnant women are 3.4 times more prone to developing severe dengue (OR: 3.38; CI: 2.10–5.42). Mortality among pregnant women was superior to non-pregnant women.

Conclusion

Pregnant women have an increased risk of developing severe dengue infection and dying of dengue.

Dengue represents a major worldwide public health problem. According to the WHO, up to 50 million dengue infections occur each year. The occurrence of dengue fever and dengue hemorrhagic fever has increased in Brazil, in part due to the simultaneous circulation of DENV-1, DENV-2 and DENV-3. Although a primary infection with one serotype confers a partial or transient immunity against other serotypes, any subsequent infections harbor the risk of increased morbidity/mortality. Several case reports have been published regarding maternal and fetal outcomes from dengue infection, but it is still inconclusive if pregnancy is associated with severity. To estimate the severity of maternal dengue infection, available data that were compiled from 2007 to 2008 by the official surveillance information system of the city of Rio de Janeiro were reviewed. The cases of dengue were analyzed using the 1997 WHO classification. Pregnant women were 3.4 times more prone to developing severe dengue than non-pregnant women. Mortality among pregnant women was superior to non-pregnant women. The increased risk of severe outcomes in pregnant women merits further attention to effective public health and medical interventions that will aid in avoiding morbidity/fatalities within this population.

Secondary infection as a risk factor for dengue hemorrhagic fever/dengue shock syndrome: an historical perspective and role of antibody-dependent enhancement of infection

Today, dengue viruses are the most prevalent arthropod-borne viruses in the world. Since the 1960s, numerous reports have identified a second heterologous dengue virus (DENV) infection as a principal risk factor for severe dengue disease (dengue hemorrhagic fever/dengue shock syndrome, DHF/DSS). Modifiers of dengue disease response include the specific sequence of two DENV infections, the interval between infections, and contributions from the human host, such as age, ethnicity, chronic illnesses and genetic background. Antibody-dependent enhancement (ADE) of dengue virus infection has been proposed as the early mechanism underlying DHF/DSS. Dengue cross-reactive antibodies raised following a first dengue infection combine with a second infecting virus to form infectious immune complexes that enter Fc-receptor-bearing cells. This results in an increased number of infected cells and increased viral output per cell. At the late illness stage, high levels of cytokines, possibly the result of T cell elimination of infected cells, result in vascular permeability, leading to shock and death. This review is focused on the etiological role of secondary infections (SI) and mechanisms of ADE.

Dengue virus enhances thrombomodulin and ICAM-1 expression through the macrophage migration inhibitory factor induction of the MAPK and PI3K signaling pathways

Dengue virus (DV) infections cause mild dengue fever (DF) or severe life-threatening dengue hemorrhagic fever (DHF). The mechanisms that cause hemorrhage in DV infections remain poorly understood. Thrombomodulin (TM) is a glycoprotein expressed on the surface of vascular endothelial cells that plays an important role in the thrombin-mediated activation of protein C. Prior studies have shown that the serum levels of soluble TM (sTM) and macrophage migration inhibitory factor (MIF) are significantly increased in DHF patients compared to levels in DF patients or normal controls. In this study, we investigated how MIF and sTM concentrations are enhanced in the plasma of DHF patients and the potential effect of MIF on coagulation through its influence on two factors: thrombomodulin (TM) and intercellular adhesion molecule-1 (ICAM-1) in endothelial cells and monocytes. Recombinant human macrophage migration inhibitory factor (rMIF) was used to treat monocytic THP-1 cells and endothelial HMEC-1 cells or primary HUVEC cells. The subsequent expression of TM and ICAM-1 was assessed by immunofluorescent staining and flow cytometry analysis. Additionally, the co-incubation of THP-1 cells with various cell signaling pathway inhibitors was used to determine the pathways through which MIF mediated its effect. The data provided evidence that severe DV infections induce MIF expression, which in turn stimulates monocytes or endothelial cells to express TM and ICAM-1 via the Erk, JNK MAPK and the PI3K signaling pathways, supporting the idea that MIF may play an important role as a regulator of coagulation.

Serum proteome and cytokine analysis in a longitudinal cohort of adults with primary dengue infection reveals predictive markers of DHF

Background

Infections caused by dengue virus are a major cause of morbidity and mortality in tropical and subtropical regions of the world. Factors that control transition from mild forms of disease such as dengue fever (DF) to more life-threatening forms such as dengue hemorrhagic fever (DHF) are poorly understood. Consequently, there are no reliable methods currently available for early triage of DHF patients resulting in significant over-hospitalization.

Methodology/Principal Findings

We have systematically examined the proteome, cytokines and inflammatory markers in sera from 62 adult dengue patients (44 DF; 18 DHF) with primary DENV infection, at three different times of infection representing the early febrile, defervescence and convalescent stages. Using fluorescent bioplex assays, we measured 27 cytokines in these serum samples. Additionally, we used multiple mass spectrometry methods for iTRAQ-based comparative analysis of serum proteome as well as measurements of protein adducts- 3-nitrotyrosine and 3-chlorotyrosine as surrogate measures of free radical activity. Using multiple methods such as OPLS, MRMR and MSVM-RFE for multivariate feature selection and classification, we report molecular markers that allow prediction of primary DHF with sensitivity and specificity of >80%.

Conclusions/Significance

This report constitutes a comprehensive analysis of molecular signatures of dengue disease progression and will help unravel mechanisms of dengue disease progression. Our analysis resulted in the identification of markers that may be useful for early prediction of DHF during the febrile phase. The combination of highly sensitive analytical methods and novel statistical approaches described here forms a robust platform for biomarker discovery.

While the majority of patients who exhibit febrile dengue infection recover within a week, a small proportion of the patients progress to develop severe symptoms that can be life-threatening if not managed in a hospital setting. Because there is no method to accurately identify this subgroup of patients, many dengue patients are hospitalized unnecessarily, which causes significant burden to the healthcare system. In our study, we have systematically measured a large number of molecules including cytokines and serum proteins in blood samples from a dengue patient cohort using highly sensitive mass spectrometry-based methods. We have further developed novel statistical methods that allow us to identify small panels of measureable blood markers, which can distinguish dengue patients that develop milder, self-limiting form of the disease from those that progress to develop severe symptoms. Because these markers can be applied within 48–72 hours of onset of febrile symptoms, we expect them to be useful for early classification of severe dengue disease.

Controversies in dengue pathogenesis

Research into the pathogenesis of dengue fever has exploded over the last half-century, with issues that were considered simple becoming more complex as additional data are found. This has led to the development of a number of controversies that are being studied across the globe and debated in the literature. In this paper, the following six controversies are analysed and, where possible, resolved: the 1997 World Health Organization (WHO) case definition of dengue haemorrhagic fever (DHF) is not useful; DHF is not significantly associated with secondary dengue infection; DHF results from infection with a 'virulent' dengue virus; DHF is owing to abnormal T-cell responses; DHF results from auto-immune responses; and DHF results from direct infection of endothelial cells.

Fatal dengue hemorrhagic fever in adults: emphasizing the evolutionary pre-fatal clinical and laboratory manifestations

Background

A better description of the clinical and laboratory manifestations of fatal patients with dengue hemorrhagic fever (DHF) is important in alerting clinicians of severe dengue and improving management.

Methods and Findings

Of 309 adults with DHF, 10 fatal patients and 299 survivors (controls) were retrospectively analyzed. Regarding causes of fatality, massive gastrointestinal (GI) bleeding was found in 4 patients, dengue shock syndrome (DSS) alone in 2; DSS/subarachnoid hemorrhage, Klebsiella pneumoniae meningitis/bacteremia, ventilator associated pneumonia, and massive GI bleeding/Enterococcus faecalis bacteremia each in one. Fatal patients were found to have significantly higher frequencies of early altered consciousness (≤24 h after hospitalization), hypothermia, GI bleeding/massive GI bleeding, DSS, concurrent bacteremia with/without shock, pulmonary edema, renal/hepatic failure, and subarachnoid hemorrhage. Among those experienced early altered consciousness, massive GI bleeding alone/with uremia/with E. faecalis bacteremia, and K. pneumoniae meningitis/bacteremia were each found in one patient. Significantly higher proportion of bandemia from initial (arrival) laboratory data in fatal patients as compared to controls, and higher proportion of pre-fatal leukocytosis and lower pre-fatal platelet count as compared to initial laboratory data of fatal patients were found. Massive GI bleeding (33.3%) and bacteremia (25%) were the major causes of pre-fatal leukocytosis in the deceased patients; 33.3% of the patients with pre-fatal profound thrombocytopenia (<20000/µL), and 50% of the patients with pre-fatal prothrombin time (PT) prolongation experienced massive GI bleeding.

Conclusions

Our report highlights causes of fatality other than DSS in patients with severe dengue, and suggested hypothermia, leukocytosis and bandemia may be warning signs of severe dengue. Clinicians should be alert to the potential development of massive GI bleeding, particularly in patients with early altered consciousness, profound thrombocytopenia, prolonged PT and/or leukocytosis. Antibiotic(s) should be empirically used for patients at risk for bacteremia until it is proven otherwise, especially in those with early altered consciousness and leukocytosis.

Fatality rate and causes of fatality in dengue-affected patients greatly varied from one reported series to another. A better understanding of the clinical and laboratory manifestations of fatal patients with dengue hemorrhagic fever (DHF) is important in alerting clinicians of severe dengue and improving management. In a retrospective analysis of 10 adults who died of and 299 survived (controls) DHF, dengue shock syndrome (DSS) alone was found in only 20% of dengue-related death, while intractable massive gastrointestinal (GI) bleeding was found in 40%, and DSS with concurrent subarachnoid hemorrhage, intractable massive GI bleeding with concurrent bacteremia, bacterial sepsis/meningitis, and sepsis due to ventilator associated pneumonia each were found in 10%. Early altered consciousness (developed ≤24 h after hospitalization), GI bleeding/massive GI bleeding and concurrent bacteremia were significantly found among the deceased patients. Our data suggest that hypothermia, leukocytosis and bandemia at hospital presentation may be warning signs of severe dengue. Clinicians should be alert to the potential development of massive GI bleeding, particularly in patients with early altered consciousness, profound thrombocytopenia, prothrombin time prolongation and/or leukocytosis. Antibiotic(s) should be empirically used for patients at risk for bacteremia until it is proven otherwise, especially in those with early altered consciousness and leukocytosis.

Association of mast cell-derived VEGF and proteases in Dengue shock syndrome

BACKGROUND

Recent in-vitro studies have suggested that mast cells are involved in Dengue virus infection. To clarify the role of mast cells in the development of clinical Dengue fever, we compared the plasma levels of several mast cell-derived mediators (vascular endothelial cell growth factor [VEGF], soluble VEGF receptors [sVEGFRs], tryptase, and chymase) and -related cytokines (IL-4, -9, and -17) between patients with differing severity of Dengue fever and healthy controls.

METHODOLOGY/PRINCIPAL FINDINGS

The study was performed at Children's Hospital No. 2, Ho Chi Minh City, and Vinh Long Province Hospital, Vietnam from 2002 to 2005. Study patients included 103 with Dengue fever (DF), Dengue hemorrhagic fever (DHF), and Dengue shock syndrome (DSS), as diagnosed by the World Health Organization criteria. There were 189 healthy subjects, and 19 febrile illness patients of the same Kinh ethnicity. The levels of mast cell-derived mediators and -related cytokines in plasma were measured by ELISA. VEGF and sVEGFR-1 levels were significantly increased in DHF and DSS compared with those of DF and controls, whereas sVEGFR-2 levels were significantly decreased in DHF and DSS. Significant increases in tryptase and chymase levels, which were accompanied by high IL-9 and -17 concentrations, were detected in DHF and DSS patients. By day 4 of admission, VEGF, sVEGFRs, and proteases levels had returned to similar levels as DF and controls. In-vitro VEGF production by mast cells was examined in KU812 and HMC-1 cells, and was found to be highest when the cells were inoculated with Dengue virus and human Dengue virus-immune serum in the presence of IL-9.

CONCLUSIONS

As mast cells are an important source of VEGF, tryptase, and chymase, our findings suggest that mast cell activation and mast cell-derived mediators participate in the development of DHF. The two proteases, particularly chymase, might serve as good predictive markers of Dengue disease severity.

Infection-associated hemophagocytic syndrome among patients with dengue shock syndrome and invasive aspergillosis: a case series and review of the literature

The authors report four autopsy cases of previously healthy children with dengue shock syndrome complicated with infection-associated hemophagocytosis and invasive aspergillosis. Hemophagocytosis is confirmed by histopathology of autopsied reticuloendothelial organs. All four children were identified to have invasive aspergillosis by histopathology and three cases were positive on fungal culture for Aspergillus spp. Regarding the cause of death among the four children without pre-existing underlying disease, three cases were directly ascribable to invasive aspergillosis and the remaining case was ascribed to dengue shock syndrome. The transmigration of preexisting fungi from the respiratory mucosa damaged by the dengue shock process is postulated as the pathogenesis of invasive aspergillosis. The main predisposing factor was found to be prolonged dengue shock syndrome. We reviewed the clinicopathologic features and therapeutic management of infection-associated hemophagocytic syndrome in patients with dengue shock syndrome and invasive aspergillosis.

Clinical profile of dengue haemorrhagic fever from Jan 2009 to Dec 2009 in and around Aurangabad

In present study 890 serum samples suspected of dengue fever on clinical grounds were received in department of Microbiology. Out of these 249 cases showed thrombocytopenia (platelet count < 1 lakh/cumm) and were subjected to rapid dengue serological test as well as IgM capture ELISA. 11(4%) cases were diagnosed as primary dengue infection (only IgM positive) by rapid dengue IgG/IgM bispot immunocomb test. There were 123(49%) cases with only IgG positive suggesting secondary/past dengue infection. Both IgM and IgG were seen in 24(10%) cases. Number of cases negative for both IgM and IgG were 91(37%). IgM positive cases were confirmed by IgM capture ELISA. Classical dengue fever (DF) was noted in 168 (67%) patients and dengue hemorrhagic fever (DHF) in 81(33%) cases. Common clinical presentations of DHF were fever 78 (96%), body-ache 74 (91%), arthralgia 74 (91%), retro-orbital pain 65 (80%), abdominal pain 07 (09%). Bleeding manifestation were in the form of petechiae, melena, epistaxis, hematuria, hemoptysis, hematemesis, bleeding gums and conjunctival hemorrhages. Out of 81 DHS patients 13 (16%) patients had platelet count between 50,000 and 1 lakh. 68 (84%) patients had platelet count below 50,000. Majority of these patients 47 (58%) had platelet below 20000 and were IgG positive. Thrombocytopenia correlated well with bleeding manifestations in our patients. In an epidemic setting if the patients present with fever, vomiting, musculoskeletal pain and bleeding along with low platelet count a strong possibility of DHF/DSS should be kept.

DC-SIGN (CD209) Promoter -336 A/G polymorphism is associated with dengue hemorrhagic fever and correlated to DC-SIGN expression and immune augmentation

Background

The C-type lectin DC-SIGN (CD209) is known to be the major dengue receptor on human dendritic cells, and a single nucleotide polymorphism (SNP) in the promoter region of CD209 (−336 A/G; rs4804803) is susceptible to many infectious diseases. We reason that variations in the DC-SIGN gene might have a broad influence on viral replication and host immune responses.

Methods and Findings

We studied whether the rs4804803 SNP was associated with a susceptibility to dengue fever (DF) and/or dengue hemorrhagic fever (DHF) through genotyping analysis in a Taiwanese cohort. We generated monocyte-derived dendritic cells (MDDCs) from individuals with AA or AG genotype of rs4804803 to study the viral replication and immune responses for functional validation. A total of 574 DNA samples were genotyped, including 176 DF, 135 DHF, 143 other non-dengue febrile illnesses (OFI) and 120 population controls. A strong association between GG/AG genotypes of rs4804803 and risk of DHF was found when compared among DF, OFI and controls (p = 0.004, 3×10⁻⁵ and 0.001, respectively). The AA genotype was associated with protection against dengue infection compared with OFI and controls (p = 0.002 and 0.020, respectively). Moreover, MDDCs from individuals with AG genotype with a higher cell surface DC-SIGN expression had a significantly higher TNFα, IL-12p40, and IP-10 production than those with AA genotype in response to dengue infection. However, the viral replication in MDDCs with AG genotype was significantly lower than those with AA genotype. With both genotypes, MDDCs revealed an increase in viral replication following the addition of anti-IP-10 neutralizing antibody.

Conclusions/Significance

The rs4804803 SNP in the CD209 promoter contributed to susceptibility to dengue infection and complication of DHF. This SNP with AG genotype affects the cell surface DC-SIGN expression related to immune augmentation and less viral replication.

Dengue fever (DF) is an arthropod-borne disease that is prevalent in tropical and subtropical regions of the world. DC-SIGN [dendritic cell-specific intercellular adhesion molecule 3 (ICAM-3)-grabbing non-integrin] is a major receptor for dengue infection. DC-SIGN, also called CD209, expresses on dendritic cells (DCs) that bind to ICAM-3, which is expressed on T cells to facilitate the initial interaction between DCs and T cells. Variations in the CD209 promoter (−336 A/G; rs4804803) genotype are involved in the pathogenesis of human infectious diseases. Here we found that patients with dengue hemorrhagic fever (DHF) had a higher frequency of the AG or GG genotype of rs4804803 than DF or controls. Functional studies determined that monocyte-derived DCs (MDDCs) from individuals with AG genotype had significantly higher cell surface DC-SIGN expression, associated with higher TNFα, IL-12p40, and IP-10 production, but lower viral replication than those with AA genotype. An increase in DEN-2 replication in MDDCs was observed following the addition of anti-IP-10 neutralizing antibody. These findings highlight the fact that the rs4804803 SNP in the CD209 promoter is associated with DHF and correlated to DC-SIGN expression and immune augmentation.

A non mouse-adapted dengue virus strain as a new model of severe dengue infection in AG129 mice

The spread of dengue (DEN) worldwide combined with an increased severity of the DEN-associated clinical outcomes have made this mosquito-borne virus of great global public health importance. Progress in understanding DEN pathogenesis and in developing effective treatments has been hampered by the lack of a suitable small animal model. Most of the DEN clinical isolates and cell culture-passaged DEN virus strains reported so far require either host adaptation, inoculation with a high dose and/or intravenous administration to elicit a virulent phenotype in mice which results, at best, in a productive infection with no, few, or irrelevant disease manifestations, and with mice dying within few days at the peak of viremia. Here we describe a non-mouse-adapted DEN2 virus strain (D2Y98P) that is highly infectious in AG129 mice (lacking interferon-α/β and -γ receptors) upon intraperitoneal administration. Infection with a high dose of D2Y98P induced cytokine storm, massive organ damage, and severe vascular leakage, leading to haemorrhage and rapid death of the animals at the peak of viremia. In contrast, very interestingly and uniquely, infection with a low dose of D2Y98P led to asymptomatic viral dissemination and replication in relevant organs, followed by non-paralytic death of the animals few days after virus clearance, similar to the disease kinetic in humans. Spleen damage, liver dysfunction and increased vascular permeability, but no haemorrhage, were observed in moribund animals, suggesting intact vascular integrity, a cardinal feature in DEN shock syndrome. Infection with D2Y98P thus offers the opportunity to further decipher some of the aspects of dengue pathogenesis and provides a new platform for drug and vaccine testing.

The spread of dengue (DEN) worldwide combined with an increased severity of the DEN-associated clinical outcomes have made this mosquito-borne virus of great global public health importance. Infection with DEN virus can be asymptomatic or trigger a wide spectrum of clinical manifestations, ranging from mild acute febrile illness to classical dengue fever and to severe DEN hemorrhagic fever/DEN shock syndrome (DHF/DSS). Progress in understanding DEN disease and in developing effective treatments has been hampered by the lack of a suitable animal model that can reproduce all or part of the disease's clinical manifestations and outcome. Only a few of the DEN virus strains reported so far elicit a virulent phenotype in mice, which results at best in an acute infection where mice die within few days with no, few or irrelevant disease manifestations. Here we describe a DEN virus strain which is highly virulent in mice and reproduces some of the aspects of severe DEN in humans, including the disease kinetics, organ damage/dysfunction and increased vascular permeability. This DEN virus strain thus offers the opportunity to further decipher some of the mechanisms involved in DEN pathogenesis, and provides a new platform for drug and vaccine testing in the mouse model.

Dengue virus-induced hemorrhage in a nonhuman primate model

Lack of a dengue hemorrhagic animal model recapitulating human dengue virus infection has been a significant impediment in advancing our understanding of the early events involved in the pathogenesis of dengue disease. In efforts to address this issue, a group of rhesus macaques were intravenously infected with dengue virus serotype 2 (strain 16 681) at 1 x 10(7) PFU/animal. A classic dengue hemorrhage developed 3 to 5 days after infection in 6 of 6 animals. Blood chemistry appeared to be normal with exception of creatine phosphokinase, which peaked at 7 days after infection. A modest thrombocytopenia and noticeable neutropenia concomitant with slight decrease of hemoglobin and hematocrit were registered. In addition, the concentration of D-dimer was elevated significantly. Viremia peaked at 3 to 5 days after infection followed by an inverse relationship between T and B lymphocytes and a bimodal pattern for platelet-monocytes and platelet-neutrophil aggregates. Dengue virus containing platelets engulfed by monocytes was noted at 8 or 9 days after infection. Thus, rhesus macaques inoculated intravenously with a high dose of dengue virus produced dengue hemorrhage, which may provide a unique platform to define the early events in dengue virus infection and help identify which blood components contribute to the pathogenesis of dengue disease.

Serotype-specific differences in the risk of dengue hemorrhagic fever: an analysis of data collected in Bangkok, Thailand from 1994 to 2006

Background

It is unclear whether dengue serotypes differ in their propensity to cause severe disease. We analyzed differences in serotype-specific disease severity in children presenting for medical attention in Bangkok, Thailand.

Methodology/Principal Findings

Prospective studies were conducted from 1994 to 2006. Univariate and multivariate logistic and multinomial logistic regressions were used to determine if dengue hemorrhagic fever (DHF) and signs of severe clinical disease (pleural effusion, ascites, thrombocytopenia, hemoconcentration) were associated with serotype. Crude and adjusted odds ratios were calculated. There were 162 (36%) cases with DENV-1, 102 (23%) with DENV-2, 123 (27%) with DENV-3, and 64 (14%) with DENV-4. There was no significant difference in the rates of DHF by serotype: DENV-2 (43%), DENV-3 (39%), DENV-1 (34%), DENV-4 (31%). DENV-2 was significantly associated with increased odds of DHF grade I compared to DF (OR 2.9 95% CI 1.1, 8.0), when using DENV-1 as the reference. Though not statistically significant, DENV-2 had an increased odds of total DHF and DHF grades II, III, and IV. Secondary serologic response was significantly associated with DHF (OR 6.2) and increased when considering more severe grades of DHF. DENV-2 (9%) and -4 (3%) were significantly less often associated with primary disease than DENV-1 (28%) and -3 (33%). Restricting analysis to secondary cases, we found DENV-2 and DENV-3 to be twice as likely to result in DHF as DEN-4 (p = 0.05). Comparing study years, we found the rate of DHF to be significantly less in 1999, 2000, 2004, and 2005 than in 1994, the study year with the highest percentage of DHF cases, even when controlling for other variables.

Conclusions/Significance

As in other studies, we find secondary disease to be strongly associated with DHF and with more severe grades of DHF. DENV-2 appears to be marginally associated with more severe dengue disease as evidenced by a significant association with DHF grade I when compared to DENV-1. In addition, we found non-significant trends with other grades of DHF. Restricting the analysis to secondary disease we found DENV-2 and -3 to be twice as likely to result in DHF as DEN-4. Differences in severity by study year may suggest that other factors besides serotype play a role in disease severity.

The four dengue viruses (DENV) represent the most common human arbovirus infections in the world and are currently a challenging problem, particularly in the tropical and subtropical regions of Asia and the Americas. Infection with DENV may produce symptoms of varying severity. While access to care, appropriate interventions, host genetic factors, and previous exposure to DENV are all known to affect the outcome of the infection, it is not entirely understood why some individuals develop more severe disease. It has been hypothesized that the four dengue serotypes differ in disease severity and clinical manifestations. This analysis assessed whether there were significant differences in severity of disease caused by the dengue serotypes in a pediatric population in Thailand. We found significant and non-significant correlations between dengue serotype 2 infection and more severe dengue disease. We also found that individual serotypes varied in disease severity between study years, perhaps supporting the hypothesis that the particular sequences of primary and secondary DENV infections influence disease severity.

Modification of the cytoprotective protein C pathway during Dengue virus infection of human endothelial vascular cells

Dengue fever (DF) is the most prevalent arthropod-borne viral disease of humans. No safe vaccine is available, there is no experimental animal model and no specific treatment (antiviral) for Dengue virus (DV) infection exists. The pathogenic mechanisms of the severe forms of the disease, such as Dengue shock syndrome (DSS) and Dengue haemorrhagic fever (DHF), in which endothelial damage is the pathognomonic sign, are not fully understood. Clinical observations have revealed significant abnormalities in the coagulation and inflammation systems, with increased levels of soluble thrombomodulin (sTM) in the plasma of patients with DHF/DSS (grade III or IV). Blood sTM was proposed as an early predictor of DSS during the febrile stage. However, the role of the DV in endothelial injury during DSS is unclear. Here, we present novel insights into the participation of DV in the downregulation of the thrombomodulin-thrombin-protein C complex formation at the endothelial surface, with a reduction in activated protein C (APC). APC is the most important vasoprotective protein because it downregulates thrombin generation (by the inactivation of procoagulant factors Va and VIIIa) and has anti-inflammatory, antiapoptotic, and barrier protection properties. These biological functions of APC are associated with the endothelial protein C receptor (EPCR) and protease-activated receptor 1 (PAR-1) signalling pathways, which link the coagulation-inflammation responses. We found alterations in the antithrombotic and cytoprotective protein C pathways during DV infection of human endothelial vascular cells, which may explain the vasculopathy observed during DHF/DSS. Clarification of the basic principles that underlie these processes has important implications for the design of new therapeutic strategies for DHF/DSS.

Vascular endothelium: the battlefield of dengue viruses

Increased vascular permeability without morphological damage to the capillary endothelium is the cardinal feature of dengue haemorrhagic fever (DHF)/dengue shock syndrome (DSS). Extensive plasma leakage in various tissue spaces and serous cavities of the body, including the pleural, pericardial and peritoneal cavities in patients with DHF, may result in profound shock. Among various mechanisms that have been considered include immune complex disease, T-cell-mediated, antibodies cross-reacting with vascular endothelium, enhancing antibodies, complement and its products, various soluble mediators including cytokines, selection of virulent strains and virus virulence, but the most favoured are enhancing antibodies and memory T cells in a secondary infection resulting in cytokine tsunami. Whatever the mechanism, it ultimately targets vascular endothelium (making it a battlefield) leading to severe dengue disease. Extensive recent work has been done in vitro on endothelial cell monolayer models to understand the pathophysiology of vascular endothelium during dengue virus (DV) infection that may be translated to help understand the pathogenesis of DHF/DSS. The present review provides a broad overview of the effects of DV infection and the associated host responses contributing towards alterations in vascular endothelial cell physiology and damage that may be responsible for the DHF/DSS.

Decision tree algorithms predict the diagnosis and outcome of dengue fever in the early phase of illness

Background

Dengue is re-emerging throughout the tropical world, causing frequent recurrent epidemics. The initial clinical manifestation of dengue often is confused with other febrile states confounding both clinical management and disease surveillance. Evidence-based triage strategies that identify individuals likely to be in the early stages of dengue illness can direct patient stratification for clinical investigations, management, and virological surveillance. Here we report the identification of algorithms that differentiate dengue from other febrile illnesses in the primary care setting and predict severe disease in adults.

Methods and Findings

A total of 1,200 patients presenting in the first 72 hours of acute febrile illness were recruited and followed up for up to a 4-week period prospectively; 1,012 of these were recruited from Singapore and 188 from Vietnam. Of these, 364 were dengue RT-PCR positive; 173 had dengue fever, 171 had dengue hemorrhagic fever, and 20 had dengue shock syndrome as final diagnosis. Using a C4.5 decision tree classifier for analysis of all clinical, haematological, and virological data, we obtained a diagnostic algorithm that differentiates dengue from non-dengue febrile illness with an accuracy of 84.7%. The algorithm can be used differently in different disease prevalence to yield clinically useful positive and negative predictive values. Furthermore, an algorithm using platelet count, crossover threshold value of a real-time RT-PCR for dengue viral RNA, and presence of pre-existing anti-dengue IgG antibodies in sequential order identified cases with sensitivity and specificity of 78.2% and 80.2%, respectively, that eventually developed thrombocytopenia of 50,000 platelet/mm³ or less, a level previously shown to be associated with haemorrhage and shock in adults with dengue fever.

Conclusion

This study shows a proof-of-concept that decision algorithms using simple clinical and haematological parameters can predict diagnosis and prognosis of dengue disease, a finding that could prove useful in disease management and surveillance.

Dengue illness appears similar to other febrile illness, particularly in the early stages of disease. Consequently, diagnosis is often delayed or confused with other illnesses, reducing the effectiveness of using clinical diagnosis for patient care and disease surveillance. To address this shortcoming, we have studied 1,200 patients who presented within 72 hours from onset of fever; 30.3% of these had dengue infection, while the remaining 69.7% had other causes of fever. Using body temperature and the results of simple laboratory tests on blood samples of these patients, we have constructed a decision algorithm that is able to distinguish patients with dengue illness from those with other causes of fever with an accuracy of 84.7%. Another decision algorithm is able to predict which of the dengue patients would go on to develop severe disease, as indicated by an eventual drop in the platelet count to 50,000/mm³ blood or below. Our study shows a proof-of-concept that simple decision algorithms can predict dengue diagnosis and the likelihood of developing severe disease, a finding that could prove useful in the management of dengue patients and to public health efforts in preventing virus transmission.

Predictive value of simple clinical and laboratory variables for dengue hemorrhagic fever in adults

BACKGROUND

Singapore experienced its worst dengue outbreak in 30 years in 2004, with 9459 notified cases, of which 83% were hospitalized.

OBJECTIVES

To determine predictors of dengue hemorrhagic fever (DHF) upon first presentation to hospital to aid clinicians in determining need for admission.

STUDY DESIGN

We conducted a retrospective cohort study on dengue patients in Tan Tock Seng Hospital, Singapore in 2004, with patients categorized into dengue fever (DF) and DHF. Demographic, clinical, and laboratory variables upon first presentation were compared to determine the likelihood of developing DHF.

RESULTS

There were 1973 dengue patients-118 (6.0%) were DHF, of which 82 (4.2%) developed DHF during hospitalization. From the multivariate analysis, patients with bleeding had an odds of developing DHF 237.6 times that of DF, a unit decrease in total protein (g/L) had an odds of 1.28 times, a unit increase in blood urea (mmol/L) had an odds of 1.31 times, and a unit decrease in lymphocyte proportion had an odds of 1.08 times. The model had a sensitivity of 97.6%, specificity of 60.2%, and may reduce 1118 (56.7%) dengue admissions.

CONCLUSIONS

A few easily available clinical and laboratory results may assist clinicians in determining dengue admissions.

Dengue hemorrhagic fever complicated with acute idiopathic scrotal edema and polyneuropathy

We report a case of an adult with dengue hemorrhagic fever who developed acute idiopathic scrotal edema and glove-and-stocking polyneuropathy. A 54-year-old man who had fever, chills, bone pain, and skin rash for 4 days was admitted. We diagnosed dengue hemorrhagic fever because of fever, gum bleeding, thrombocytopenia, and hemoconcentration, and confirmed the diagnosis by serology. The patient had scrotal and penile edema and distal limb numbness with a glove-and-stocking distribution. After supportive care, the scrotal edema and other symptoms subsided. Patients with dengue hemorrhagic fever may develop scrotal edema caused by plasma leakage.

Fulminant liver failure secondary to haemorrhagic dengue in an international traveller

Dengue infections are caused by a single-stranded RNA virus, which has four serotypes (DEN 1-4); mosquitoes of the genus Aedes serve as vectors of transmission. Risk factors for dengue infection are related to both the host and virus. Age, gender, immune status, and genetic background of the host all contribute to the severity of dengue infection. Recently, international travel to endemic areas has also been identified as a major risk factor for both primary and secondary dengue infection. Dengue remains a diagnostic challenge, given its protean nature, ranging from mild febrile illness to profound shock. The most severe manifestation of dengue infection is dengue shock syndrome, which has an estimated mortality rate close to 50%. Dengue shock syndrome typically presents with increased anion gap metabolic acidosis, disseminated intravascular coagulation, severe hypotension, and jaundice. Liver involvement appears to occur more frequently when infections involve DEN-3 and DEN-4 serotypes. While hepatocellular damage has been reported previously in dengue infection, acute liver failure is an extremely rare occurrence in adults. We report a patient with dengue shock syndrome who presented with acute liver failure and hepatic encephalopathy after recent travel to an endemic area.

Dengue infection: a growing global health threat

Dengue infection, one of the most devastating mosquito-borne viral diseases in humans, is now a significant problem in several tropical countries. The disease, caused by the four dengue virus serotypes, ranges from asymptomatic infection to undifferentiated fever, dengue fever (DF), and severe dengue hemorrhagic fever (DHF) with or without shock. DHF is characterized by fever, bleeding diathesis and a tendency to develop a potentially fatal shock syndrome. Consistent hematological findings include vasculopathy, coagulopathy, and thrombocytopenia. There are increasing reports of dengue infection with unusual manifestations that mainly involve cerebral and hepatic symptoms. Laboratory diagnosis includes virus isolation, serology, and detection of dengue ribonucleic acid. Successful treatment, which is mainly supportive, depends on early recognition of the disease and careful monitoring for shock. Prevention depends primarily on control of the mosquito vector. Further study of the pathogenesis of DHF is required for the development of a safe and effective dengue vaccine.

Apoptosis in tissues from fatal dengue shock syndrome

BACKGROUND

Apoptosis, or programmed cell death, has been implicated in dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) pathogenesis.

OBJECTIVES

To determine the in vivo apoptosis contribution to the pathogenesis of fatal DHF/DSS during a Cuban dengue epidemic.

STUDY DESIGN

We detected apoptosis by the TdT-mediated dUTP Nick-End Labeling (TUNEL) technique and dengue virus (DENV) antigens by an immunohistochemical assay in different tissues from six individuals who died of DHF/DSS during the Santiago de Cuba DENV-2 epidemic in 1997.

RESULTS

DENV antigens were immunolocalized mainly in hepatocytes. Apoptotic cells were found in five of the six cases studied. Apoptosis was demonstrated in liver, brain, intestinal and lung tissues. Severe brain hypoxia and ischemia in the studied subjects during DHF/DSS probably might induce apoptosis in cerebral cells. Apoptotic microvascular endothelial cells (ECs) in pulmonary and intestinal tissues, a finding only previously reported in vitro, are likely related to vascular plasma leakage manifested by the individuals.

CONCLUSIONS

Apoptosis was demonstrated in cerebral cells, white blood cells, intestinal and pulmonary microvascular ECs from Cuban fatal cases of DHF/DSS. As far as we know, these findings have not been previously reported in DHF/DSS. Our results indicate there is very likely an in vivo contribution of apoptosis to the pathophysiological mechanisms of DHF/DSS.

Environmental factors and incidence of dengue fever and dengue haemorrhagic fever in an urban area, Southern Thailand

Using the enumeration district (ED) block level this study looked at the incidence of dengue fever and dengue haemorrhagic fever (DF/DHF) within the Songkhla municipality in Thailand. Each of the 146 blocks in this area were considered as study units and surveyed for their environmental characteristics. A total of 287 cases of DH/DHF occurring in the year 1998 were selected for this study and the location of their homes mapped. Clustering analysis showed point clustering of the homes (P<0.0001) which was probably due to high density habitation, without any actual prevalence of case clustering. There was no evidence of clustering of the ED blocks with an incidence of DF/DHF (P=0.32). DF/DHF incidence for each block was strongly associated with the percentages of shop-houses, brick-made houses and houses with poor garbage disposal (all P<0.01). DF/DHF control should be emphasized for the areas which have a predominance of these housing types.

Both virus and tumor necrosis factor alpha are critical for endothelium damage in a mouse model of dengue virus-induced hemorrhage

Hemorrhage is a common clinical manifestation in dengue patients. However, the pathogenic mechanism of dengue virus (DV)-induced hemorrhage awaits clarification. We established a mouse model of DV hemorrhage using immunocompetent C57BL/6 mice by injecting DV serotype 2 strain 16681 intradermally. While inoculation of 3 x 10(9) PFU of DV induced systemic hemorrhage in all of the mice by day 3 of infection, one out of three of those injected with 4 x 10(7) to 8 x 10(7) PFU developed hemorrhage in the subcutaneous tissues. The mice that were inoculated with 4 x 10(7) to 8 x 10(7) PFU but that did not develop hemorrhage were used as a basis for comparison to explore the pathogenic mechanism of dengue hemorrhage. The results showed that mice with severe thrombocytopenia manifested signs of vascular leakage and hemorrhage. We observed that high viral titer, macrophage infiltration, and tumor necrosis factor alpha (TNF-alpha) production in the local tissues are three important events that lead to hemorrhage. Immunofluorescence staining revealed that DV targeted both endothelial cells and macrophages. In addition, the production of high levels of TNF-alpha in tissues correlated with endothelial cell apoptosis and hemorrhage. By comparing TNF-alpha(-/-) to IgH(-/-), C5(-/-), and wild-type mice, we found that TNF-alpha was important for the development of hemorrhage. In vitro studies showed that mouse primary microvascular endothelial cells were susceptible to DV but that TNF-alpha enhanced DV-induced apoptosis. Our mouse model illustrated that intradermal inoculation of high titers of DV predisposes endothelial cells to be susceptible to TNF-alpha-induced cell death, which leads to endothelium damage and hemorrhage development. This finding highlights the contribution of the innate immune response to dengue hemorrhage.

Histologic, viral, and molecular correlates of dengue fever infection of the liver using highly sensitive immunohistochemistry

The mechanism by which the virus associated with dengue fever can cause a fatal hepatitis is not well understood. The purpose of this study was to examine 9 cases of fatal dengue hemorrhagic fever-associated hepatitis, and to correlate the histologic findings with viral detection and cytokine response. The histologic changes were nonspecific and included massive hepatic necrosis and a pauci-cellular acute hepatitis. Viral cDNA detection by reverse transcriptase in situ polymerase chain reaction demonstrated that the fatal hepatitis was due to infection on average of >90% of hepatocytes and many Kupffer cells. Similar results were obtained using immunohistochemistry for viral protein using an automated highly sensitive system. Immunohistochemical analysis for tumor necrosis factor alpha, and interleukin-2, showed rare positive Kupffer cells. In comparison, fatal cases of hepatitis C associated liver failure demonstrated far fewer infected hepatocytes and a concomitant strong up-regulation of many cytokines, notably tumor necrosis factor alpha and interleukin-2. It is concluded that fatal dengue hemorrhagic fever is associated with acute, severe liver damage due primarily to massive direct infection of hepatocytes and Kupffer cells with minimal cytokine response. The infection can be readily detected in a few hours using an automated system that has a sensitivity equivalent to reverse transcriptase in situ polymerase chain reaction.

MCP-1, a highly expressed chemokine in dengue haemorrhagic fever/dengue shock syndrome patients, may cause permeability change, possibly through reduced tight junctions of vascular endothelium cells

Vascular leakage, one hallmark of dengue haemorrhagic fever (DHF) and dengue shock syndrome, has been linked to the mediators secreted from cells in the circulatory system. In this study, extremely high expression levels of monocyte chemoattractant protein-1 (MCP-1) were found in the plasma of DHF patients compared with low MCP-1 expression levels in the plasma of enterovirus 71-infected patients. It was also found that MCP-1 expression was induced in dengue virus 2 (DV2)-infected monocytes and lymphocytes, but not in liver or endothelial cells. Exposing monolayers of human umbilical vein endothelial cells (HUVECs) to recombinant human MCP-1 (rhMCP-1) or to the culture supernatant of DV2-infected human monocytes increased the vascular permeability of the cells. MCP-1-neutralizing monoclonal antibody only partially prevented monolayer permeability change. Consistently, the distribution of the tight junction protein ZO-1 on the cellular membranes of HUVECs was disrupted by rhMCP-1 or by the conditioned medium of DV2-infected monocytes. In summary, it was found that the increased permeability and disrupted tight junctions of human vascular endothelium cells were effected through a mechanism partially dependent on MCP-1, which was secreted by DV2-infected monocytes and lymphocytes.

Murine model for dengue virus-induced lethal disease with increased vascular permeability

Lack of an appropriate animal model for dengue virus (DEN), which causes dengue fever and dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS), has impeded characterization of the mechanisms underlying the disease pathogenesis. The cardinal feature of DHF/DSS, the severe form of DEN infection, is increased vascular permeability. To develop a murine model that is more relevant to DHF/DSS, a novel DEN strain, D2S10, was generated by alternately passaging a non-mouse-adapted DEN strain between mosquito cells and mice, thereby mimicking the natural transmission cycle of the virus between mosquitoes and humans. After infection with D2S10, mice lacking interferon receptors died early without manifesting signs of paralysis, carried infectious virus in both non-neuronal and neuronal tissues, and exhibited signs of increased vascular permeability. In contrast, mice infected with the parental DEN strain developed paralysis at late times after infection, contained detectable levels of virus only in the central nervous system, and displayed normal vascular permeability. In the mice infected with D2S10, but not the parental DEN strain, significant levels of serum tumor necrosis factor alpha (TNF-alpha) were produced, and the neutralization of TNF-alpha activity prevented early death of D2S10-infected mice. Sequence analysis comparing D2S10 to its parental strain implicated a conserved region of amino acid residues in the envelope protein as a possible source for the D2S10 phenotype. These results demonstrate that D2S10 causes a more relevant disease in mice and that TNF-alpha may be one of several key mediators of severe DEN-induced disease in mice. This report represents a significant advance in animal models for severe DEN disease, and it begins to provide mechanistic insights into DEN-induced disease in vivo.