Association of Microvascular Function and Endothelial Biomarkers With Clinical Outcome in Dengue: An Observational Study

Dengue Fever Accompanied by Neurological Manifestations: Challenges and Treatment

Dengue, commonly referred to as 'breakbone fever,' is a mosquito-borne arboviral infection transmitted by Aedes aegypti, featuring an average incubation period of approximately seven days. Key cytokines such as interferon-gamma (IFN-γ), tumor necrosis factor (TNF)-α, and interleukin (IL)-10 are pivotal in the pathogenesis of dengue. Travelers are particularly susceptible to contracting dengue fever, with disease severity often associated with CD8+ T cell response. Without proper hospitalization during severe cases like dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS), mortality rates can escalate to 50%. Dengue fever can lead to various complications, including neurological manifestations such as encephalopathy, encephalitis, cerebral venous thrombosis, myelitis, posterior reversible encephalopathy syndrome, strokes (both ischemic and hemorrhagic), immune-mediated neurological syndromes (such as mononeuropathy, acute transverse myelitis, Guillain-Barre syndrome, and acute disseminated encephalomyelitis), and neuromuscular complications. Treatment protocols typically involve assessing disease activity using composite indices, pursuing treatment objectives, and administering intravenous fluids according to symptomatology. Given the absence of specific antiviral treatment for dengue, supportive care, particularly hydration, remains paramount during the early stages. It is crucial to recognize that dengue viruses may contribute to the development of neurological disorders, particularly in regions where dengue is endemic. Furthermore, there is a necessity for well-defined criteria for specific neurological complications. Primary prevention strategies primarily revolve around vector control measures, which play a critical role in curtailing the spread of dengue.

Endothelial and inflammatory pathophysiology in dengue shock: New insights from a prospective cohort study in Vietnam

Dengue shock (DS) is the most severe complication of dengue infection; endothelial hyperpermeability leads to profound plasma leakage, hypovolaemia and extravascular fluid accumulation. At present, the only treatment is supportive with intravenous fluid, but targeted endothelial stabilising therapies and host immune modulators are needed. With the aim of prioritising potential therapeutics, we conducted a prospective observational study of adults (≥16 years) with DS in Vietnam from 2019-2022, comparing the pathophysiology underlying circulatory failure with patients with septic shock (SS), and investigating the association of biomarkers with clinical severity (SOFA score, ICU admission, mortality) and pulmonary vascular leak (daily lung ultrasound for interstitial and pleural fluid). Plasma was collected at enrolment, 48 hours later and hospital discharge. We measured biomarkers of inflammation (IL-6, ferritin), endothelial activation (Ang-1, Ang-2, sTie-2, VCAM-1) and endothelial glycocalyx breakdown (hyaluronan, heparan sulfate, endocan, syndecan-1). We enrolled 135 patients with DS (median age 26, median SOFA score 7, 34 required ICU admission, 5 deaths), together with 37 patients with SS and 25 healthy controls. Within the DS group, IL-6 and ferritin were associated with admission SOFA score (IL-6: βeta0.70, p<0.001 & ferritin: βeta0.45, p<0.001), ICU admission (IL-6: OR 2.6, p<0.001 & ferritin: OR 1.55, p<0.001) and mortality (IL-6: OR 4.49, p = 0.005 & ferritin: OR 13.8, p = 0.02); both biomarkers discriminated survivors and non-survivors at 48 hours and all patients who died from DS had pre-mortem ferritin ≥100,000ng/ml. IL-6 most strongly correlated with severity of pulmonary vascular leakage (R = 0.41, p<0.001). Ang-2 correlated with pulmonary vascular leak (R = 0.33, p<0.001) and associated with SOFA score (β 0.81, p<0.001) and mortality (OR 8.06, p = 0.002). Ang-1 was associated with ICU admission (OR 1.6, p = 0.005) and mortality (OR 3.62, p = 0.006). All 4 glycocalyx biomarkers were positively associated with SOFA score, but only syndecan-1 was associated with ICU admission (OR 2.02, p<0.001) and mortality (OR 6.51, p<0.001). This study highlights the central role of hyperinflammation in determining outcomes from DS; the data suggest that anti-IL-1 and anti-IL-6 immune modulators and Tie2 agonists may be considered as candidates for therapeutic trials in severe dengue.

Facing the escalating burden of dengue: Challenges and perspectives

Dengue is the most rapidly emerging mosquito-borne infection and, due to climate change and unplanned urbanization, it is predicted that the global burden of dengue will rise further as the infection spreads to new geographical locations. Dengue-endemic countries are often unable to cope with such increases, with health care facilities becoming overwhelmed during each dengue season. Furthermore, although dengue has been predominantly a childhood illness in the past, it currently mostly affects adults in many countries, with higher incidence of severe disease and mortality rates in pregnant women and in those with comorbidities. As there is currently no specific treatment for dengue and no early biomarker to identify those who will progress to develop vascular leakage, all individuals with dengue are closely monitored in case they need fluid management. Furthermore, diagnosing patients with acute dengue is challenging due to the similarity of clinical symptoms during early illness and poor sensitivity and specificity of point-of-care diagnostic tests. Novel vector control methods, such as the release of Wolbachia-infected mosquitoes, have shown promising results by reducing vector density and dengue incidence in clinical trial settings. A new dengue vaccine, TAK-003, had an efficacy of 61.2% against virologically confirmed dengue, 84.1% efficacy against hospitalizations and a 70% efficacy against development of dengue haemorrhagic fever (DHF) at 54 months. While vaccines and mosquito control methods are welcome, they alone are unlikely to fully reduce the burden of dengue, and a treatment for dengue is therefore essential. Several novel antiviral drugs are currently being evaluated along with drugs that inhibit host mediators, such as mast cell products. Although viral proteins such as NS1 contribute to the vascular leak observed in severe dengue, the host immune response to the viral infection also plays a significant role in progression to severe disease. There is an urgent need to discover safe and effective treatments for dengue to prevent disease progression.

Early biomarkers for prediction of severe manifestations of dengue fever: a systematic review and a meta-analysis

Early identification of dengue patients at risk of adverse outcomes is important to prevent hospital overcrowding in low- to middle- income countries during epidemics. We performed a systematic review to identify which biomarkers measured in first 96 h of fever could predict dengue haemorrhagic fever (DHF, World Health Organization 1997 clinical classification) or severe dengue (SD, WHO 2009, clinical classification). PubMed, Scopus, CINAHL, Web of Science, and EMBASE databases were searched for prospective cohort and nested case-control studies published from 1997 to Feb 27, 2022. The protocol for the study was registered in PROSPERO (ID: CRD42021230053). After screening 6747 publications, and analysing 37 eligible studies reporting on 5925 patients, elevated C-reactive protein, aspartate aminotransferase, interleukin-8 and decreased albumin levels were strongly associated with dengue haemorrhagic fever (by meta-analyses of multiple studies, p < 0.05), while elevated vascular cell adhesion protein 1, syndecan-1, aspartate aminotransferase and C-reactive protein levels were strongly associated with severe dengue (by meta-analyses of multiple studies, p < 0.05). Further 44 and 28 biomarkers were associated with the risk of DHF and SD respectively, but only in a single study. The meta-analyses suggest the importance of early acute inflammation with hepatic involvement in determining the subsequent course of illness in dengue.

The Role of Growth Factors in the Pathogenesis of Dengue: A Scoping Review

Growth factors (GFs) have a role in tissue repair and in the modulation of the expression of inflammatory cells in damage caused by pathogens. This study aims to systematize the evidence on the role of GFs in the pathogenesis of dengue. This scoping review considered all published peer-reviewed studies in the MEDLINE and Embase databases. Ultimately, 58 studies that analyzed GFs in dengue patients, published between 1998 and 2021, were included. DENV-2 infection and secondary infection were more frequent in the patients studied. ELISA and multiplex immunoassay (Luminex) were the most used measurement techniques. Increased levels of vascular endothelial growth factor, granulocyte–macrophage colony-stimulating factor, granulocyte colony-stimulating factor, transforming growth factor beta, and hepatocyte growth factor as well as reduced levels of platelet-derived growth factor and epidermal growth factor were observed in severe dengue in most studies. Vascular endothelial growth factor and hepatocyte growth factor were identified as biomarkers of severity. In addition, there is evidence that the dengue virus can use the growth factor pathway to facilitate its entry into the cell and promote its viral replication. The use of tyrosine kinase inhibitors is an alternative treatment for dengue that is being studied.

Assessment of sublingual microcirculation for the screening of diabetic nephropathy

OBJECTIVE

To investigate the potential of employing sublingual microcirculation as an early noninvasive screening technique for diabetic nephropathy (DN).

RESEARCH DESIGN AND METHODS

We recruited 89 patients with type 2 diabetes mellitus (T2DM) and 41 healthy subjects in this cross-sectional observational study. All participants underwent fluorescein fundus angiography, vibration perception testing, 10 g (Semmes-Weinstein) monofilament examination, nerve conduction velocity, and 24-h urine microalbumin determination. HbA1c, fasting plasma glucose, blood lipid, and estimated glomerular filtration rate(eGFR) were measured. Sublingual microcirculatory images were captured using side-stream dark-field (SDF) microcirculation microscopy, and total and perfused vascular density (TVD and PVD) were calculated.

RESULTS

The sublingual microcirculatory parameters denoting microvascular density and perfusion were negatively correlated with both fasting plasma glucose (TVD, r =  - 0.316, P < 0.001; PVD, r =  - 0.350, P < 0.001; PPV, r =  - 0.279, P = 0.001) and HbA1c (TVD, r =  - 0.367, P < 0.001; PVD, r =  - 0.423, P < 0.001; PPV, r =  - 0.399, P < 0.001). Diabetes patients already had a reduction in sublingual microcirculation compared with healthy control, and more severe reductions in TVD (7.07 ± 1.64 vs. 9.67 ± 1.94 mm/mm², P < 0.001) and PVD (5.88 ± 1.82 vs. 8.64 ± 2.46 mm/mm², P < 0.001) were found in those diabetes patients developed microvascular complications. Sublingual microcirculation impairment was accompanied with higher urinary albumin creatinine ratio (UACR). Receiver operating characteristic (ROC) analysis showed that TVD (area under the curve, AUC = 0.890 [0.836 0.944], P < 0.001) and PVD (AUC = 0.883 [0.826, 0.940], P < 0.001) could be indicators for DN screening. We derived a combined predictor index (CPI) considering both TVD and PVD for screening DN, and both the AUC (0.892, [0.838 0.945], P < 0.001) and cutoff point of 11.30 mm/mm² showed great improvement (sensitivity: 95.5%, specificity: 67.4%).

CONCLUSIONS

Diabetes patients experienced impaired sublingual microcirculation, which was closely correlated with UACR. Sublingual microcirculation monitoring could be used for the noninvasive early detection of DN.

Hyperinflammatory syndrome, natural killer cell function and genetic polymorphisms in the pathogenesis of severe dengue

BACKGROUND

Severe dengue, characterized by shock and organ dysfunction is driven by an excessive host immune response. We investigated the role of hyperinflammation in dengue pathogenesis.

METHODS

Patients recruited into an observational study were divided into three plasma leak severity grades. Hyperinflammatory biomarkers were measured at 4 time-points. Frequencies, activation and cytotoxic potential of NK cells were analysed by flow cytometry. RNA was extracted from sorted CD56+ NK cells and libraries prepared using SMART-Seq and sequenced using HiSeq3000 (Illumina).

RESULTS

69 patients were included (grade 0: 42, grade 1: 19, grade 2: 8 patients). Patients with grade 2 leakage had higher biomarkers than grade 0, including higher peak ferritin levels (83.3% vs 45.2%) and H scores (median 148.5 vs 105.5). NK cells from grade 2 patients exhibited decreased expression of perforin and granzyme B and activation markers. RNA sequencing revealed three SNPs in NK cell functional genes associated with more severe leakage; NK cell lectin-like receptor K1 gene (KLRK1) and PRF1 gene.

CONCLUSIONS

Features of hyperinflammation are associated with dengue severity, including higher biomarkers, impaired NK cell function and polymorphisms in genes NK cell cytolyitc function genes (KLRK1 and PRF-1). Trials of immunomodulatory therapy in these patients is now warranted.

Applied machine learning for the risk-stratification and clinical decision support of hospitalised patients with dengue in Vietnam

BACKGROUND

Identifying patients at risk of dengue shock syndrome (DSS) is vital for effective healthcare delivery. This can be challenging in endemic settings because of high caseloads and limited resources. Machine learning models trained using clinical data could support decision-making in this context.

METHODS

We developed supervised machine learning prediction models using pooled data from adult and paediatric patients hospitalised with dengue. Individuals from 5 prospective clinical studies in Ho Chi Minh City, Vietnam conducted between 12th April 2001 and 30th January 2018 were included. The outcome was onset of dengue shock syndrome during hospitalisation. Data underwent random stratified splitting at 80:20 ratio with the former used only for model development. Ten-fold cross-validation was used for hyperparameter optimisation and confidence intervals derived from percentile bootstrapping. Optimised models were evaluated against the hold-out set.

FINDINGS

The final dataset included 4,131 patients (477 adults and 3,654 children). DSS was experienced by 222 (5.4%) of individuals. Predictors were age, sex, weight, day of illness at hospitalisation, indices of haematocrit and platelets over first 48 hours of admission and before the onset of DSS. An artificial neural network model (ANN) model had best performance with an area under receiver operator curve (AUROC) of 0.83 (95% confidence interval [CI], 0.76-0.85) in predicting DSS. When evaluated against the independent hold-out set this calibrated model exhibited an AUROC of 0.82, specificity of 0.84, sensitivity of 0.66, positive predictive value of 0.18 and negative predictive value of 0.98.

INTERPRETATION

The study demonstrates additional insights can be obtained from basic healthcare data, when applied through a machine learning framework. The high negative predictive value could support interventions such as early discharge or ambulatory patient management in this population. Work is underway to incorporate these findings into an electronic clinical decision support system to guide individual patient management.

Plasma leakage in dengue: a systematic review of prospective observational studies

Plasma leakage is a precursor to life-threatening complications of dengue, but this group is poorly defined and not often reported in literature. Patients with Dengue haemorrhagic fever (DHF) as defined in the 1997 World Health Organization classification are often reported, and they all have plasma leakage, but some patients with plasma leakage do not meet the definition of DHF. The study aims to estimate the frequency of plasma leakage and DHF (as a surrogate of plasma leakage) in dengue and its variations based on virus serotype, geography, patient gender and pre-existing immunity to dengue. PUBMED, Scopus, EMBASE, CINAHL and Web of Science were searched for prospective observational studies reporting on plasma leakage or DHF. Quality of data was assessed using the NIH quality assessment tool for cohort studies. Forty-three studies that recruited 15,794 confirmed dengue patients were eligible. Cumulative frequency of plasma leakage was 36.8% (15 studies, 1642/4462, 95% CI 35.4-38.2%), but surprisingly the estimated cumulative frequency of DHF was higher (45.7%, 32 studies, 4758/10417, 95% CI 44.7-46.6%), indicating that current medical literature over-reports DHF or under-reports plasma leakage. Therefore, a reliable estimate for the proportion of dengue patients developing plasma leakage cannot be derived from existing medical literature even after applying rigorous inclusion criteria to select homogenous studies. Plasma leakage is an important marker of "at-risk" dengue patients and standardizing its definition, diagnosis and reporting should be a priority in research and global policy.

Platelet activation and aggregation response to dengue virus nonstructural protein 1 and domains

BACKGROUND

Platelets are now recognized as immunological sentries in the first line of defense that participate in the detection and response to pathogens. This frequently results in a decrease in the number of circulating platelets. Different mechanisms have been hypothesized to explain the thrombocytopenia in patients with severe dengue, one of them is the participation of the non-structural protein 1 (NS1) of dengue virus (DENV), which can be secreted into circulation during DENV infection and promotes a more efficient infection.

OBJECTIVE

The present study aimed to investigate the ability of platelet response to stimulation with full-length DENV NS1 protein and its domains.

METHODS

DENV NS1 plasmid was transfected into HEK-293T. Proteins were purified by Niquel Sepharose affinity chromatography. Secreted proteins were assessed by sodium dodecylsulfate polyacrylamide gel electrophoresis, Coomassie staining and western blot. Platelet-rich plasma was directly incubated with DENV NS1 proteins. Platelet activation was confirmed by expression of αIIbβIII and P-selectin by flow cytometry. Platelet aggregation was also assessed using DENV NS1 protein and its individual domains as agonists.

RESULTS

DENV NS1 protein and its domains induce P-selectin and αIIbβ3 complex expression on platelet surfaces. DENV NS1 induce a stable platelet aggregation after the addition of a minimal dose of adenosine diphosphate (ADP), epinephrine (EPI), or collagen. Interestingly, only EPI could induce the formation of platelet aggregates after incubation with the protein domains of NS1.

CONCLUSION

Our results suggest that the full DENV NS1 protein and also its domains promote platelet recognition, activation, and aggregation.

Combination of inflammatory and vascular markers in the febrile phase of dengue is associated with more severe outcomes

Background

Early identification of severe dengue patients is important regarding patient management and resource allocation. We investigated the association of 10 biomarkers (VCAM-1, SDC-1, Ang-2, IL-8, IP-10, IL-1RA, sCD163, sTREM-1, ferritin, CRP) with the development of severe/moderate dengue (S/MD).

Methods

We performed a nested case-control study from a multi-country study. A total of 281 S/MD and 556 uncomplicated dengue cases were included.

Results

On days 1-3 from symptom onset, higher levels of any biomarker increased the risk of developing S/MD. When assessing together, SDC-1 and IL-1RA were stable, while IP-10 changed the association from positive to negative; others showed weaker associations. The best combinations associated with S/MD comprised IL-1RA, Ang-2, IL-8, ferritin, IP-10, and SDC-1 for children, and SDC-1, IL-8, ferritin, sTREM-1, IL-1RA, IP-10, and sCD163 for adults.

Conclusions

Our findings assist the development of biomarker panels for clinical use and could improve triage and risk prediction in dengue patients.

Funding

This study was supported by the EU's Seventh Framework Programme (FP7-281803 IDAMS), the WHO, and the Bill and Melinda Gates Foundation.

A chimeric dengue virus vaccine candidate delivered by high density microarray patches protects against infection in mice

Dengue viruses (DENV) cause an estimated 390 million infections globally. With no dengue-specific therapeutic treatment currently available, vaccination is the most promising strategy for its control. A wide range of DENV vaccines are in development, with one having already been licensed, albeit with limited distribution. We investigated the immunogenicity and protective efficacy of a chimeric virus vaccine candidate based on the insect-specific flavivirus, Binjari virus (BinJV), displaying the structural prM/E proteins of DENV (BinJ/DENV2-prME). In this study, we immunized AG129 mice with BinJ/DENV2-prME via a needle-free, high-density microarray patch (HD-MAP) delivery system. Immunization with a single, 1 µg dose of BinJ/DENV2-prME delivered via the HD-MAPs resulted in enhanced kinetics of neutralizing antibody induction when compared to needle delivery and complete protection against mortality upon virus challenge in the AG129 DENV mouse model.

Metformin as adjunctive therapy for dengue in overweight and obese patients: a protocol for an open-label clinical trial (MeDO)

Background:  Dengue is a disease of major global importance. While most symptomatic infections are mild, a small proportion of patients progress to severe disease with risk of hypovolaemic shock, organ dysfunction and death.  In the absence of effective antiviral or disease modifying drugs, clinical management is solely reliant on supportive measures. Obesity is a growing problem among young people in Vietnam and is increasingly recognised as an important risk factor for severe dengue, likely due to alterations in host immune and inflammatory pathways. Metformin, a widely used anti-hyperglycaemic agent with excellent safety profile, has demonstrated potential as a dengue therapeutic in vitro and in a retrospective observational study of adult dengue patients with type 2 diabetes.  This study aims to assess the safety and tolerability of metformin treatment in overweight and obese dengue patients, and investigate its effects on several clinical, immunological and virological markers of disease severity. Methods: This open label trial of 120 obese/overweight dengue patients will be performed in two phases, with a metformin dose escalation if no safety concerns arise in phase one. The primary endpoint is identification of clinical and laboratory adverse events.  Sixty overweight and obese dengue patients aged 10-30 years will be enrolled at the Hospital for Tropical Diseases in Ho Chi Minh City, Vietnam. Participants will complete a 5-day course of metformin therapy and be compared to a non-treated group of 60 age-matched overweight and obese dengue patients. Discussion:  Previously observed antiviral and immunomodulatory effects of metformin make it a promising dengue therapeutic candidate in appropriately selected patients. This study will assess the safety and tolerability of adjunctive metformin in the management of overweight and obese young dengue patients, as well as its effects on markers of viral replication, endothelial dysfunction and host immune responses.  Trial registration: ClinicalTrials.gov: NCT04377451 (May 6 th 2020).

Metformin as adjunctive therapy for dengue in overweight and obese patients: a protocol for an open-label clinical trial (MeDO)

Background:  Dengue is a disease of major global importance. While most symptomatic infections are mild, a small proportion of patients progress to severe disease with risk of hypovolaemic shock, organ dysfunction and death.  In the absence of effective antiviral or disease modifying drugs, clinical management is solely reliant on supportive measures. Obesity is a growing problem among young people in Vietnam and is increasingly recognised as an important risk factor for severe dengue, likely due to alterations in host immune and inflammatory pathways. Metformin, a widely used anti-hyperglycaemic agent with excellent safety profile, has demonstrated potential as a dengue therapeutic in vitro and in a retrospective observational study of adult dengue patients with type 2 diabetes.  This study aims to assess the safety and tolerability of metformin treatment in overweight and obese dengue patients, and investigate its effects on several clinical, immunological and virological markers of disease severity.

Methods: This open label trial of 120 obese/overweight dengue patients will be performed in two phases, with a metformin dose escalation if no safety concerns arise in phase one. The primary endpoint is identification of clinical and laboratory adverse events.  Sixty overweight and obese dengue patients aged 10-30 years will be enrolled at the Hospital for Tropical Diseases in Ho Chi Minh City, Vietnam. Participants will complete a 5-day course of metformin therapy and be compared to a non-treated group of 60 age-matched overweight and obese dengue patients.

Discussion:  Previously observed antiviral and immunomodulatory effects of metformin make it a promising dengue therapeutic candidate in appropriately selected patients. This study will assess the safety and tolerability of adjunctive metformin in the management of overweight and obese young dengue patients, as well as its effects on markers of viral replication, endothelial dysfunction and host immune responses. 

Trial registration: ClinicalTrials.gov: NCT04377451 (May 6 ^th 2020).

Serum Levels of Markers of Endothelial Activation Are Not Associated with a Positive Blood Culture in Surinamese Children with Suspected Severe Infection

BACKGROUND

Systemic serum levels of markers of endothelial activation are associated with infection. We hypothesize that levels of markers of endothelial activation are associated with the presence of a positive blood culture as a manifestation of a systemic infection in children with a suspected severe infection in Suriname.

METHODS

In this prospective observational cohort study, children between 1 month and 18 years of age suspected of severe infection as assessed by the threating physician, and in whom laboratory testing and blood culturing was performed before start of intravenous antibiotic treatment, were recruited at the emergency department of the Academic Hospital Paramaribo, Suriname. Serum was collected at blood culturing and after 48-72 h of admission. Serum was stored for measurement of levels of Angiopoietin (Ang)-1, Ang-2, soluble (s)P-selectin, sE-selectin, vascular cell adhesion molecule-1, intercellular adhesion molecule-1 and platelet and endothelial cell adhesion molecule-1.

RESULTS

Fifty-one children were included of whom 10 had a positive blood culture. Baseline characteristics were similar between children with and without a positive blood culture. No significant differences in serum levels of the Angiopoietins or soluble cellular adhesion molecules between groups were observed at start of antibiotic treatment nor after 48-72 h.

CONCLUSIONS

The data from this study indicate that in children with severe infection, serum levels of markers of endothelial cell activation are not associated with a positive blood culture. Thus, having a positive bacterial blood culture may not be the only factor driving endothelial activation in this patient population.

Microvascular dysfunction in septic and dengue shock: Pathophysiology and implications for clinical management

The microcirculation comprising of arterioles, capillaries and post-capillary venules is the terminal vascular network of the systemic circulation. Microvascular homeostasis, comprising of a balance between vasoconstriction, vasodilation and endothelial permeability in healthy states, regulates tissue perfusion. In severe infections, systemic inflammation occurs irrespective of the infecting microorganism(s), resulting in microcirculatory dysregulation and dysfunction, which impairs tissue perfusion and often precedes end-organ failure. The common hallmarks of microvascular dysfunction in both septic shock and dengue shock, are endothelial cell activation, glycocalyx degradation and plasma leak through a disrupted endothelial barrier. Microvascular tone is also impaired by a reduced bioavailability of nitric oxide. In vitro and in vivo studies have however demonstrated that the nature and extent of microvascular dysfunction as well as responses to volume expansion resuscitation differ in these two clinical syndromes. This review compares and contrasts the pathophysiology of microcirculatory dysfunction in septic versus dengue shock and the attendant effects of fluid administration during resuscitation.

Visual and Biochemical Evidence of Glycocalyx Disruption in Human Dengue Infection, and Association With Plasma Leakage Severity

Background: Dengue is the most common arboviral infection globally; a minority of patients develop shock due to profound plasma leak through a disrupted endothelial barrier. Understanding of the pathophysiology underlying plasma leak is incomplete, but emerging evidence indicates a key role for degradation of the endothelial glycocalyx.

Methods: We conducted an observational study in Vietnam to evaluate the sublingual microcirculation using sidestream darkfield imaging in (1) outpatients with confirmed dengue (2) patients hospitalized with dengue and (3) outpatients with other febrile illness (OFI). We estimated the glycocalyx degradation by measuring the perfused boundary region (PBR hf) and an overall microvascular health score (MVHS) with the software application GlycoCheck^TM at enrolment, 48 h later and hospital discharge/defervescence. We measured plasma syndecan1 and endocan at the same time-points. We compared PBR hf, MVHS, syndecan1 and endocan, between (1) outpatients with confirmed dengue vs. OFI and (2) patients with dengue subdivided by clinical severity of plasma leak.

Results: We included 75 patients with dengue (41 outpatients, 15 inpatients, 19 in intensive care) and 12 outpatients with OFI. Images from 45 patients were analyzed using GlycoCheck^TM. There was no significant difference in PBR hf or MVHS between outpatients with dengue and OFI. Median plasma syndecan1 was not significantly different in outpatients with dengue vs. OFI, while median plasma endocan was significantly lower among patients with dengue vs. OFI during the critical phase. In patients with dengue, PBR hf was higher in patients with Grade 2 vs. Grade 0 plasma leakage during the critical phase (PBR hf 1.96 vs. 1.36 μm for Grade 2 vs. Grade 0 plasma leakage on days 4–6, respectively, p < 0.001). Median levels of plasma syndecan1 and endocan were higher in Grade 2 vs. Grade 0 plasma leakage, especially during the critical phase (Syndecan1 2,613.8 vs. 125.9 ng/ml for Grade 2 vs. Grade 0 plasma leakage on days 4–6, respectively, p < 0.001, and endocan 3.21 vs. 0.16 ng/ml for Grade 2 vs. Grade 0 plasma leakage on days 4–6, respectively).

Conclusions: We present the first human in vivo evidence of glycocalyx disruption in dengue, with worse visual glycocalyx damage and higher plasma degradation products associated with more severe plasma leak.

A Critical Role for Perivascular Cells in Amplifying Vascular Leakage Induced by Dengue Virus Nonstructural Protein 1

Dengue is the most prevalent arthropod-borne viral disease affecting humans, with severe dengue typified by potentially fatal microvascular leakage and hypovolemic shock. Blood vessels of the microvasculature are composed of a tubular structure of endothelial cells ensheathed by perivascular cells (pericytes). Pericytes support endothelial cell barrier formation and maintenance through paracrine and contact-mediated signaling and are critical to microvascular integrity. Pericyte dysfunction has been linked to vascular leakage in noncommunicable pathologies such as diabetic retinopathy but has never been linked to infection-related vascular leakage. Dengue vascular leakage has been shown to result in part from the direct action of the secreted dengue virus (DENV) nonstructural protein NS1 on endothelial cells. Using primary human vascular cells, we show here that NS1 also causes pericyte dysfunction and that NS1-induced endothelial hyperpermeability is more pronounced in the presence of pericytes. Notably, NS1 specifically disrupted the ability of pericytes to support endothelial cell function in a three-dimensional (3D) microvascular assay, with no effect on pericyte viability or physiology. These effects are mediated at least in part through contact-independent paracrine signals involved in endothelial barrier maintenance by pericytes. We therefore identify a role for pericytes in amplifying NS1-induced microvascular hyperpermeability in severe dengue and thus show that pericytes can play a critical role in the etiology of an infectious vascular leakage syndrome. These findings open new avenues of research for the development of drugs and diagnostic assays for combating infection-induced vascular leakage, such as severe dengue.IMPORTANCE The World Health Organization considers dengue one of the top 10 global public health problems. There is no specific antiviral therapy to treat dengue virus and no way of predicting which patients will develop potentially fatal severe dengue, typified by vascular leakage and circulatory shock. We show here that perivascular cells (pericytes) amplify the vascular leakage-inducing effects of the dengue viral protein NS1 through contact-independent signaling to endothelial cells. While pericytes are known to contribute to noncommunicable vascular leakage, this is the first time these cells have been implicated in the vascular effects of an infectious disease. Our findings could pave the way for new therapies and diagnostics to combat dengue and potentially other infectious vascular leakage syndromes.

Risk factors and biomarkers of severe dengue

Dengue virus infects several million people each year. Although usually a self-limiting disease, some patients can develop life-threatening severe complications, characterized by plasma leakage, hemorrhaging, and shock. The signs and symptoms of severe disease usually arise late in the disease course when patients are recovering and fever has subsided, making it difficult to predict. Efforts are underway to identify risk factors and biomarkers that can accurately predict disease severity in the acute febrile phase of the disease, facilitating early intervention and treatment strategies for those at greatest risk. In this review we discuss recent advancements in identifying risk factors and biomarkers for the prognosis of severe dengue.

Towards Predicting Progression to Severe Dengue

There is an urgent need for prognostic assays to predict progression to severe dengue infection, which is a major global threat. While the majority of symptomatic dengue patients experience an acute febrile illness, 5-20% progress to severe infection associated with significant morbidity and mortality. Early monitoring and administration of supportive care reduce mortality and clinically usable biomarkers to predict severe dengue are needed. Here, we review recent discoveries of gene sets, anti-dengue antibody properties, and inflammatory markers with potential utility as predictors of disease progression. Upon larger scale validation and development of affordable sample-to-answer technologies, some of these biomarkers may be utilized to develop the first prognostic assay for improving patient care and allocating healthcare resources more effectively in dengue endemic countries.

Raman spectral analysis for rapid screening of dengue infection

Infection with the dengue virus is currently clinically detected according to different biomarkers in human blood plasma, commonly measured by enzyme linked immunosorbent assays, including non-structural proteins (Ns1), immunoglobulin M (IgM) and immunoglobulin G (IgG). However, there is little or no mutual correlation between the biomarkers, as demonstrated in this study by a comparison of their levels in samples from 17 patients. As an alternative, the label free, rapid screening technique, Raman spectroscopy has been used for the characterisation/diagnosis of healthy and dengue infected human blood plasma samples. In dengue positive samples, changes in specific Raman spectral bands associated with lipidic and amino acid/protein content are observed and assigned based on literature and these features can be considered as markers associated with dengue development. Based on the spectroscopic analysis of the current, albeit limited, cohort of samples, Principal Components Analysis (PCA) coupled Factorial Discriminant Analysis, yielded values of 97.95% sensitivity and 95.40% specificity for identification of dengue infection. Furthermore, in a comparison of the normal samples to the patient samples which scored low for only one of the biomarker tests, but high or medium for either or both of the other two, PCA-FDA demonstrated a sensitivity of 97.38% and specificity of 86.18%, thus providing an unambiguous screening technology.

Rift valley fever viral load correlates with the human inflammatory response and coagulation pathway abnormalities in humans with hemorrhagic manifestations

Rift Valley fever virus is an arbovirus that affects both livestock and humans throughout Africa and in the Middle East. Despite its endemicity throughout Africa, it is a rare event to identify an infected individual during the acute phase of the disease and an even rarer event to collect serial blood samples from the affected patient. Severely affected patients can present with hemorrhagic manifestations of disease. In this study we identified three Ugandan men with RVFV disease that was accompanied by hemorrhagic manifestations. Serial blood samples from these men were analyzed for a series of biomarkers specific for various aspects of human pathophysiology including inflammation, endothelial function and coagulopathy. There were significant differences between biomarker levels in controls and cases both early during the illness and after clearance of viremia. Positive correlation of viral load with markers of inflammation (IP-10, CRP, Eotaxin, MCP-2 and Granzyme B), markers of fibrinolysis (tPA and D-dimer), and markers of endothelial function (sICAM-1) were all noted. However, and perhaps most interesting given the fact that these individuals exhibited hemorrhagic manifestations of disease, was the finding of a negative correlation between viral load and P-selectin, ADAMTS13, and fibrinogen all of which are associated with coagulation pathways occurring on the endothelial surface.

Tie2 protects the vasculature against thrombus formation in systemic inflammation

Disordered coagulation contributes to death in sepsis and lacks effective treatments. Existing markers of disseminated intravascular coagulation (DIC) reflect its sequelae rather than its causes, delaying diagnosis and treatment. Here we show that disruption of the endothelial Tie2 axis is a sentinel event in septic DIC. Proteomics in septic DIC patients revealed a network involving inflammation and coagulation with the Tie2 antagonist, angiopoietin-2 (Angpt-2), occupying a central node. Angpt-2 was strongly associated with traditional DIC markers including platelet counts, yet more accurately predicted mortality in 2 large independent cohorts (combined N = 1,077). In endotoxemic mice, reduced Tie2 signaling preceded signs of overt DIC. During this early phase, intravital imaging of microvascular injury revealed excessive fibrin accumulation, a pattern remarkably mimicked by Tie2 deficiency even without inflammation. Conversely, Tie2 activation normalized prothrombotic responses by inhibiting endothelial tissue factor and phosphatidylserine exposure. Critically, Tie2 activation had no adverse effects on bleeding. These results mechanistically implicate Tie2 signaling as a central regulator of microvascular thrombus formation in septic DIC and indicate that circulating markers of the Tie2 axis could facilitate earlier diagnosis. Finally, interventions targeting Tie2 may normalize coagulation in inflammatory states while averting the bleeding risks of current DIC therapies.

Molecular Responses of Human Retinal Cells to Infection with Dengue Virus

Recent clinical reports indicate that infection with dengue virus (DENV) commonly has ocular manifestations. The most serious threat to vision is dengue retinopathy, including retinal vasculopathy and macular edema. Mechanisms of retinopathy are unstudied, but observations in patients implicate retinal pigment epithelial cells and retinal endothelial cells. Human retinal cells were inoculated with DENV-2 and monitored for up to 72 hours. Epithelial and endothelial cells supported DENV replication and release, but epithelial cells alone demonstrated clear cytopathic effect, and infection was more productive in those cells. Infection induced type I interferon responses from both cells, but this was stronger in epithelial cells. Endothelial cells increased expression of adhesion molecules, with sustained overexpression of vascular adhesion molecule-1. Transcellular impedance decreased for epithelial monolayers, but not endothelial monolayers, coinciding with cytopathic effect. This reduction was accompanied by disorganization of intracellular filamentous-actin and decreased expression of junctional molecules, zonula occludens 1, and catenin-β1. Changes in endothelial expression of adhesion molecules are consistent with the retinal vasculopathy seen in patients infected with DENV; decreases in epithelial junctional protein expression, paralleling loss of integrity of the epithelium, provide a molecular basis for DENV-associated macular edema. These molecular processes present potential therapeutic targets for vision-threatening dengue retinopathy.

Endothelial Nitric Oxide Pathways in the Pathophysiology of Dengue: A Prospective Observational Study

BACKGROUND

Dengue can cause increased vascular permeability that may lead to hypovolemic shock. Endothelial dysfunction may underlie this; however, the association of endothelial nitric oxide (NO) pathways with disease severity is unknown.

METHODS

We performed a prospective observational study in 2 Vietnamese hospitals, assessing patients presenting early (<72 hours of fever) and patients hospitalized with warning signs or severe dengue. The reactive hyperemic index (RHI), which measures endothelium-dependent vasodilation and is a surrogate marker of endothelial function and NO bioavailability, was evaluated using peripheral artery tonometry (EndoPAT), and plasma levels of l-arginine, arginase-1, and asymmetric dimethylarginine were measured at serial time-points. The main outcome of interest was plasma leakage severity.

RESULTS

Three hundred fourteen patients were enrolled; median age of the participants was 21(interquartile range, 13-30) years. No difference was found in the endothelial parameters between dengue and other febrile illness. Considering dengue patients, the RHI was significantly lower for patients with severe plasma leakage compared to those with no leakage (1.46 vs 2.00; P < .001), over acute time-points, apparent already in the early febrile phase (1.29 vs 1.75; P = .012). RHI correlated negatively with arginase-1 and positively with l-arginine (P = .001).

CONCLUSIONS

Endothelial dysfunction/NO bioavailability is associated with worse plasma leakage, occurs early in dengue illness and correlates with hypoargininemia and high arginase-1 levels.

Increased microcirculatory heterogeneity in patients with obstructive sleep apnea

INTRODUCTION

Obstructive sleep apnea (OSA) is the most common form of sleep disordered breathing and has been associated with major cardiovascular comorbidities. We hypothesized that the microcirculation is impaired in patients with OSA and that the magnitude of impairment correlates to OSA severity.

METHODS

Subjects were consecutive patients scheduled for routine diagnostic polysomnography (PSG). OSA was defined by paradoxical rib cage movements together with abdominal excursions and by the apnea-hypopnea index (AHI) (events/hour; no apnea AHI<5; mild apnea 5≤AHI<15; moderate apnea 15≤AHI<30; severe apnea AHI ≥30). Sidestream darkfield imaging was used to assess the sublingual microcirculation. Recordings of sublingual microcirculation (5 random sites) were performed before and after overnight PSG. Data are summarized as mean (±SD); p values <0.05 were considered statistically significant.

RESULTS

Thirty-three consecutive patients were included. OSA was diagnosed in 16 subjects (4 moderate, 12 severe). There was no significant difference in microcirculation between subjects with moderate OSA and without OSA. However, compared to subjects without OSA, subjects with severe OSA (AHI≥30) showed a significant decrease of microvascular flow index (-0.07±0.17 vs. 0.08±0.14; p = 0.02) and increase of microvascular flow index heterogeneity (0.06±0.15 vs. -0.06±0.11; p = 0.02) overnight. Multiple regression analysis (adjusted for age and gender) showed both decrease of flow and increase of flow heterogeneity associated with AHI (b = -0.41; F = 1.8; p = 0.04 and b = 0.43; F = 1.9; p = 0.03, respectively).

CONCLUSION

Acute overnight microcirculatory changes are observed in subjects with severe OSA characterized by decreased flow and increased flow heterogeneity.

IL-10 and socs3 Are Predictive Biomarkers of Dengue Hemorrhagic Fever

Background

Cytokines play important roles in the physiopathology of dengue infection; therefore, the suppressors of cytokine signaling (socs) that control the type and timing of cytokine functions could be involved in the origin of immune alterations in dengue.

Objective

To explore the association of cytokine and socs levels with disease severity in dengue patients.

Methods

Blood samples of 48 patients with confirmed dengue infection were analyzed. Amounts of interleukins IL-2, IL-4, IL-6, and IL-10, interferon- (IFN-) γ, and tumor necrosis factor- (TNF-) α were quantified by flow cytometry, and the relative expression of socs1 and socs3 mRNA was quantified by real-time RT-PCR.

Results

Increased levels of IL-10 and socs3 and lower expression of socs1 were found in patients with dengue hemorrhagic fever (DHF) with respect to those with dengue fever (DF) (p < 0.05). Negative correlations were found between socs1 and both IL-10 and socs3 (p < 0.01). The cutoff values of socs3 (>199.8-fold), socs1 (<1.94-fold), and IL-10 (>134 pg/ml) have the highest sensitivity and specificity to discriminate between DF and DHF.

Conclusion

Simultaneous changes in IL-10 and socs1/socs3 could be used as prognostic biomarkers of dengue severity.

Cardio-haemodynamic assessment and venous lactate in severe dengue: Relationship with recurrent shock and respiratory distress

Background

Dengue can cause plasma leakage that may lead to dengue shock syndrome (DSS). In approximately 30% of DSS cases, recurrent episodes of shock occur. These patients have a higher risk of fluid overload, respiratory distress and poor outcomes. We investigated the association of echocardiographically-derived cardiac function and intravascular volume parameters plus lactate levels, with the outcomes of recurrent shock and respiratory distress in severe dengue.

Methods/Principle findings

We performed a prospective observational study in Paediatric and adult ICU, at the Hospital for Tropical Diseases (HTD), Ho Chi Minh City, Vietnam. Patients with dengue were enrolled within 12 hours of admission to paediatric or adult ICU. A haemodynamic assessment and portable echocardiograms were carried out daily for 5 days from enrolment and all interventions recorded.

102 patients were enrolled; 22 patients did not develop DSS, 48 had a single episode of shock and 32 had recurrent shock. Patients with recurrent shock had a higher enrolment pulse than those with 1 episode or no shock (median: 114 vs. 100 vs. 100 b/min, P = 0.002), significantly lower Stroke Volume Index (SVI), (median: 21.6 vs. 22.8 vs. 26.8mls/m², P<0.001) and higher lactate levels (4.2 vs. 2.9 vs. 2.2 mmol/l, P = 0.001). Higher SVI and worse left ventricular function (higher Left Myocardial Performance Index) on study days 3–5 was associated with the secondary endpoint of respiratory distress. There was an association between the total IV fluid administered during the ICU admission and respiratory distress (OR: 1.03, 95% CI 1.01–1.06, P = 0.001). Admission lactate levels predicted patients who subsequently developed recurrent shock (P = 0.004), and correlated positively with the total IV fluid volume received (rho: 0.323, P = 0.001) and also with admission ALT (rho: 0.764, P<0.001) and AST (rho: 0.773, P<0.001).

Conclusions/Significance

Echo-derived intravascular volume assessment and venous lactate levels can help identify dengue patients at high risk of recurrent shock and respiratory distress in ICU. These findings may serve to, not only assist in the management of DSS patients, but also these haemodynamic endpoints could be used in future dengue fluid intervention trials.

Dengue is a viral illness that can lead to severe and potentially fatal complications. The most common complication is fluid leakage from blood vessels, which can cause low blood pressure or dengue shock syndrome (DSS). The majority of patients recover with simple intravenous fluid replacement, however in approximately 30% of DSS cases, recurrent episodes of shock occur, and these patients have a higher risk of fluid overload, respiratory distress and death. We investigated whether using portable echocardiograms (Echo) in the intensive care unit (ICU) to assess cardiac function and intravascular volume parameters as well as blood lactate levels, can help identify these patients. We found patients who developed recurrent shock had higher heart rates and lower Stroke Volume Index (SVI), and higher lactate levels at enrolment than those with 1 episode or no shock. Higher SVI and worse cardiac function after 3 days in ICU was associated with respiratory distress. Admission lactate levels predicted patients who subsequently developed recurrent shock and correlated positively with the total IV fluid volume received. These results demonstrate that Echo-derived intravascular volume assessment and venous lactate levels can help identify dengue patients at high risk of poor outcomes in the ICU, and could assist in the management of severe dengue.

Pathogenesis of vascular leak in dengue virus infection

Endothelial dysfunction leading to vascular leak is the hallmark of severe dengue. Vascular leak typically becomes clinically evident 3-6 days after the onset of illness, which is known as the critical phase. This critical phase follows the period of peak viraemia, and lasts for 24-48 hr and usually shows rapid and complete reversal, suggesting that it is likely to occur as a result of inflammatory mediators, rather than infection of the endothelium. Cytokines such as tumour necrosis factor-α, which are known to be elevated in the critical phase of dengue, are likely to be contributing factors. Dengue NS1, a soluble viral protein, has also been shown to disrupt the endothelial glycocalyx and thus contribute to vascular leak, although there appears to be a discordance between the timing of NS1 antigenaemia and occurrence of vascular leak. In addition, many inflammatory lipid mediators are elevated in acute dengue viral infection such as platelet activating factor (PAF) and leukotrienes. Furthermore, many other inflammatory mediators such as vascular endothelial growth factor and angiopoietin-2 have been shown to be elevated in patients with dengue haemorrhagic fever, exerting their action in part by inducing the activity of phospholipases, which have diverse inflammatory effects including generation of PAF. Platelets have also been shown to significantly contribute to endothelial dysfunction by production of interleukin-1β through activation of the NLRP3 inflammasome and also by inducing production of inflammatory cytokines by monocytes. Drugs that block down-stream immunological mediator pathways such as PAF may also be beneficial in the treatment of severe disease.

The Angiopoietin-Tie2 Signaling Axis in Systemic Inflammation

Systemic inflammation is a hallmark of commonly encountered diseases ranging from bacterial sepsis to sterile syndromes such as major trauma. Derangements in the host vasculature contribute to the cardinal manifestations of sepsis in profound ways. Recent studies of control pathways regulating the vascular endothelium have illuminated how this single cell layer toggles between quiescence and activation to affect the development of shock and multiorgan dysfunction. This article focuses on one such control pathway, the Tie2 receptor and its ligands the angiopoietins, to describe a growing body of genetic, biochemical, mechanistic, and human studies that implicate Tie2 as a critical switch. In health, activated Tie2 maintains the endothelium in a quiescent state characterized by dynamic barrier function and antiadhesion against circulating leukocytes. In sepsis and related diseases, expression of the angiopoietins becomes markedly imbalanced and Tie2 signaling is greatly attenuated. These rapid molecular changes potentiate pathophysiologic responses throughout the body, resulting in injurious vascular leakage and organ inflammation. The Tie2 axis, therefore, may be a promising avenue for future translational studies.

Clinical and Laboratory Diagnosis of Dengue Virus Infection

Infection with any of the 4 dengue virus serotypes results in a diverse range of symptoms, from mild undifferentiated fever to life-threatening hemorrhagic fever and shock. Given that dengue virus infection elicits such a broad range of clinical symptoms, early and accurate laboratory diagnosis is essential for appropriate patient management. Virus detection and serological conversion have been the main targets of diagnostic assessment for many years, however cross-reactivity of antibody responses among the flaviviruses has been a confounding issue in providing a differential diagnosis. Furthermore, there is no single, definitive diagnostic biomarker that is present across the entire period of patient presentation, particularly in those experiencing a secondary dengue infection. Nevertheless, the development and commercialization of point-of-care combination tests capable of detecting markers of infection present during different stages of infection (viral nonstructural protein 1 and immunoglobulin M) has greatly simplified laboratory-based dengue diagnosis. Despite these advances, significant challenges remain in the clinical management of dengue-infected patients, especially in the absence of reliable biomarkers that provide an effective prognostic indicator of severe disease progression. This review briefly summarizes some of the complexities and issues surrounding clinical dengue diagnosis and the laboratory diagnostic options currently available.