Noninvasive measurement of microvascular leakage in patients with dengue hemorrhagic fever

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.

Angiotensin II and dengue

Dengue is a disease caused by a flavivirus that is transmitted principally by the bite of an Aedes aegypti mosquito and represents a major public-health problem. Many studies have been carried out to identify soluble factors that are involved in the pathogenesis of this infection. Cytokines, soluble factors, and oxidative stress have been reported to be involved in the development of severe disease. Angiotensin II (Ang II) is a hormone with the ability to induce the production of cytokines and soluble factors related to the inflammatory processes and coagulation disorders observed in dengue. However, a direct involvement of Ang II in this disease has not been demonstrated. This review primarily summarizes the pathophysiology of dengue, the role of Ang II in various diseases, and reports that are highly suggestive of the involvement of this hormone in dengue.

Nine year trends of dengue virus infection in Mumbai, Western India

INTRODUCTION:

Dengue virus (DENV) causes a wide range of diseases in humans, from acute febrile illness Dengue fever (DF) to life-threatening Dengue hemorrhagic fever (DHF) or Dengue shock syndrome (DSS). Factors believed to be responsible for spread of Dengue virus infection include explosive population growth, unplanned urban overpopulation with inadequate public health systems, poor standing water and vector control, climate changes and increased international recreational, business, military travel to endemic areas. All of these factors must be addressed to control the spread of Dengue and other mosquito-borne infections. The detection of Dengue virus RNA by reverse transcriptase PCR (RT-PCR) in human serum or plasma samples is highly indicative of acute Dengue fever. Moreover, the method is able to identify the Dengue virus serotype by demonstrating defined sequence homologies in the viral genomic RNA.

METHODS AND RESULTS:

During the nine year period of this study analysis, 6767 strongly suspected cases were tested by RT-PCR. 1685 (24.9%) were Dengue PCR positive and confirmed as Dengue cases. Observations on the seasonality were based on the nine year's data as the intensity of sampling was at its maximum during monsoon season. Dengue typing was done on 100 positive samples after storage of Dengue RNA at – 80°C. Dengue serotypes were detected in 69 samples of which Dengue 2 was most predominant. 576 samples were processed for NS1 antigen and PCR simultaneously. 19/576 were positive (3.3 %) for NS1 as well as by PCR. 23/576 samples were negative for NS1 antigen, but were positive by RT-PCR. The remaining 534 samples which were negative for NS1 antigen were also negative by Dengue RT-PCR.

CONCLUSION:

In this study we sought to standardize rapid, sensitive, and specific fluorogenic probe-based RT-PCR assay to screen and serotype a representative range of Dengue viruses that are found in and around Mumbai. Qualitative Dengue virus TaqMan assays could have tremendous utility for the epidemiological investigation of Dengue illness and especially for the study of the viremic response with candidate live-attenuated dengue virus vaccines.

A review of Dengvaxia®: development to deployment

Dengue is the world's most prevalent and important arboviral disease. More than 50% of the world's population lives at daily risk of infection and it is estimated more than 95 million people a year seek medical care following infection. Severe disease can manifest as plasma leakage and potential for clinically significant hemorrhage, shock, and death. Treatment is supportive and there is currently no licensed anti-dengue virus prophylactic or therapeutic compound. A single dengue vaccine, Sanofi Pasteur's Dengvaxia®, has been licensed in 20 countries but uptake has been poor. A safety signal in dengue seronegative vaccine recipients stimulated an international re-look at the vaccine performance profile, new World Health Organization recommendations for use, and controversy in the Philippines involving the government, regulatory agencies, Sanofi Pasteur, clinicians responsible for testing and administering the vaccine, and the parents of vaccinated children. In this review, we provide an overview of Dengvaxia's® development and discuss what has been learned about product performance since its licensure.

Mathematical modeling of septic shock based on clinical data

Background

Mathematical models of diseases may provide a unified approach for establishing effective treatment strategies based on fundamental pathophysiology. However, models that are useful for clinical practice must overcome the massive complexity of human physiology and the diversity of patients’ environmental conditions. With the aim of modeling a complex disease, we choose sepsis, which is highly complex, life-threatening systemic disease with high mortality. In particular, we focused on septic shock, a subset of sepsis in which underlying circulatory and cellular/metabolic abnormalities are profound enough to substantially increase mortality. Our model includes cardiovascular, immune, nervous system models and a pharmacological model as submodels and integrates them to create a sepsis model based on pathological facts.

Results

Model validation was done in two steps. First, we established a model for a standard patient in order to confirm the validity of our approach in general aspects. For this, we checked the correspondence between the severity of infection defined in terms of pathogen growth rate and the ease of recovery defined in terms of the intensity of treatment required for recovery. The simulations for a standard patient showed good correspondence. We then applied the same simulations to a patient with heart failure as an underlying disease. The model showed that spontaneous recovery would not occur without treatment, even for a very mild infection. This is consistent with clinical experience.

We next validated the model using clinical data of three sepsis patients. The model parameters were tuned for these patients based on the model for the standard patient used in the first part of the validation. In these cases, the simulations agreed well with clinical data. In fact, only a handful parameters need to be tuned for the simulations to match with the data.

Conclusions

We have constructed a model of septic shock and have shown that it can reproduce well the time courses of treatment and disease progression. Tuning of model parameters for each patient could be easily done. This study demonstrates the feasibility of disease models, suggesting the possibility of clinical use in the prediction of disease progression, decisions on the timing of drug dosages, and the estimation of time of infection.

Endothelial Glycocalyx as Biomarker for Cardiovascular Diseases: Mechanistic and Clinical Implications

INTRODUCTION

The endothelial surface layer is covered with abundant proteoglycans, of which syndecans and glycosaminoglycans are major constituents.

RECENT FINDINGS

Among the endothelial glycocalyx (eGC) constituents, syndecan-1 (sdc1) is a main component, and an elevated serum level of sdc1 may indicate the degradation of eGC. In patients with ischemic heart disease or heart failure, elevation of serum sdc1 has been associated with worsening cardiac and renal function; however, the causal relationship between degradation of eGC and clinical outcomes is unclear. Herein, we review the previous literature on eGC in cardiovascular and noncardiovascular diseases and their clinical implications.

Skin dendritic cell and T cell activation associated with dengue shock syndrome

The pathogenesis of severe dengue remains unclear, particularly the mechanisms underlying the plasma leakage that results in hypovolaemic shock in a small proportion of individuals. Maximal leakage occurs several days after peak viraemia implicating immunological pathways. Skin is a highly vascular organ and also an important site of immune reactions with a high density of dendritic cells (DCs), macrophages and T cells. We obtained skin biopsies and contemporaneous blood samples from patients within 24 hours of onset of dengue shock syndrome (DSS), and from healthy controls. We analyzed cell subsets by flow cytometry, and soluble mediators and antibodies by ELISA; the percentage of migratory CD1a⁺ dermal DCs was significantly decreased in the DSS patients, and skin CD8⁺ T cells were activated, but there was no accumulation of dengue-specific antibodies. Inflammatory monocytic cells were not observed infiltrating the skin of DSS cases on whole-mount histology, although CD14^dim cells disappeared from blood.

Increased Serum Hyaluronic Acid and Heparan Sulfate in Dengue Fever: Association with Plasma Leakage and Disease Severity

Plasma leakage is a major pathogenic mechanism of severe dengue, but the etiology remains unclear. The association between endothelial glycocalyx integrity and vascular permeability in older adults with dengue has not been evaluated. A prospective cohort study of adults with undifferentiated fever screened for dengue by RT-PCR or NS1 antigen testing was performed. Patients were assessed daily while symptomatic and at convalescence. Serum hyaluronic acid (HA), heparan sulfate (HS) and selected cytokines (TNF-α, IL-6, IL-10) were measured on enrollment and convalescence. Patients were diagnosed as dengue fever (DF, n = 30), dengue hemorrhagic fever (DHF, n = 20) and non-dengue (ND) febrile illness (n = 11). Acute HA and HS levels were significantly higher in all dengue patients compared to ND (p = 0.0033 and p = 0.0441 respectively), but not different between DF and DHF (p = 0.3426 and p = 0.9180 respectively). Enrolment HA inversely correlated with serum albumin, protein and platelets in all dengue and DHF (p < 0.05). HA and HS in all dengue patients decreased significantly at convalescence. Serum IL-10 was significantly associated with HA in all dengue patients (p = 0.002). Serum HA and HS levels were increased in adult dengue and HA was associated with markers of disease severity. Endothelial glycocalyx damage may have a role in vascular leakage in dengue.

Mortality Predictors in Patients with Severe Dengue in the State of Amazonas, Brazil

Dengue is a major public health problem in tropical and subtropical areas worldwide. There is a lack of information on the risk factors for death due to severe dengue fever in developing countries, including Brazil where the state of Amazonas is located. This knowledge is important for decision making and the implementation of effective measures for patient care. This study aimed to identify factors associated with death among patients with severe dengue, in Amazonas from 2001 to 2013. We conducted a retrospective cohort study based on secondary data from the epidemiological surveillance of dengue provided by the Fundação de Vigilância em Saúde do Amazonas, FVS (Health Surveillance Foundation) of the Secretaria de Saúde do Amazonas, SUSAM (Health Secretariat of the State of Amazonas). Data on dengue cases were obtained from the SINAN (Notifiable Diseases Information System) and SIM (Mortality Information System) databases. We selected cases of severe dengue with laboratory confirmation, including dengue-related deaths of residents in the state of Amazonas from January 1, 2001, to December 31, 2013. The explanatory variables analyzed were sex, age, level of education, spontaneous hemorrhagic manifestations, plasma extravasation and platelet count. Patients who died due to severe dengue had more hematuria, gastrointestinal bleeding, and thrombocytopenia than the survivors. Considering the simultaneous effects of demographic and clinical characteristics with a multiple logistic regression model, it was observed that the factors associated with death were age >55 years (odds ratio [OR] 4.98), gastrointestinal bleeding (OR 10.26), hematuria (OR 5.07), and thrombocytopenia (OR 2.55). Gastrointestinal bleeding was the clinical sign most strongly associated with death, followed by hematuria and age >55 years. The study results showed that the best predictor of death from severe dengue is based on the characteristic of age >55 years, together with the clinical signs of gastrointestinal bleeding, hematuria, and low platelet count.

Dengue infection

Dengue is widespread throughout the tropics and local spatial variation in dengue virus transmission is strongly influenced by rainfall, temperature, urbanization and distribution of the principal mosquito vector Aedes aegypti. Currently, endemic dengue virus transmission is reported in the Eastern Mediterranean, American, South-East Asian, Western Pacific and African regions, whereas sporadic local transmission has been reported in Europe and the United States as the result of virus introduction to areas where Ae. aegypti and Aedes albopictus, a secondary vector, occur. The global burden of the disease is not well known, but its epidemiological patterns are alarming for both human health and the global economy. Dengue has been identified as a disease of the future owing to trends toward increased urbanization, scarce water supplies and, possibly, environmental change. According to the WHO, dengue control is technically feasible with coordinated international technical and financial support for national programmes. This Primer provides a general overview on dengue, covering epidemiology, control, disease mechanisms, diagnosis, treatment and research priorities.

Diagnostic accuracy of peripheral venous lactate and the 2009 WHO warning signs for identifying severe dengue in Thai adults: a prospective observational study

Background

Dengue is the most common mosquito-borne viral disease in humans. However, the sensitivities of warning signs (WSs) for identifying severe dengue in adults are low, and the utility of lactate levels for identifying severe dengue in adults has not been verified. Therefore, we aimed to evaluate the diagnostic accuracy of using peripheral venous lactate levels (PVL), as well as WSs established by the World Health Organization, for identifying severe dengue.

Methods

We prospectively evaluated individuals hospitalized for dengue who were admitted to the Hospital for Tropical Diseases in Thailand between May 2013 and January 2015. Blood samples to evaluate PVL levels were collected at admission and every 24 h until the patient exhibited a body temperature of <37.8 °C for at least 24 h. Data were recorded on a pre-defined case report form, including baseline characteristics, clinical parameters, and laboratory findings.

Results

Among 125 patients with confirmed dengue, 105 (84.0 %) patients had non-severe dengue, and 20 (16.0 %) patients had severe dengue. The presence of clinical fluid accumulation as a WS provided high sensitivity (75.0 %, 95 % confidence interval [CI]: 50.9–91.3 %) and specificity (90.5 %, 95 % CI: 83.2–95.3 %). The PVL level at admission was used to evaluate its diagnostic value, and receiver operating characteristic curve analysis revealed an area under the curve of 0.84 for identifying severe dengue. At the optimal cutoff value (PVL: 2.5 mmol/L), the sensitivity and specificity were 65.0 % (95 % CI: 40.8–84.6 %) and 96.2 % (95 % CI: 90.5–99.0 %), respectively. A combined biomarker comprising clinical fluid accumulation and/or PVL of ≥2.5 mmol/L provided the maximum diagnostic accuracy for identifying severe dengue, with a sensitivity of 90.0 % (95 % CI: 68.3–98.8 %) and a specificity of 87.6 % (95 % CI: 79.8–93.2 %).

Conclusions

Clinical fluid accumulation and/or PVL may be used as a diagnostic biomarker of severe dengue among adults. This biomarker may facilitate early recognition and timely treatment of patients with severe dengue, which may reduce dengue-related mortality and hospital burden.

Identification of clinical factors associated with severe dengue among Thai adults: a prospective study

BACKGROUND

Dengue is the most common mosquito-borne viral disease in humans. Recently, there has been an epidemic shift of dengue from mainly affecting children to affecting more adults with increased severity. However, clinical factors associated with severe dengue in adults have varied widely between studies. We aimed to identify the clinical factors associated with the development of severe dengue according to the World Health Organization (WHO)'s 2009 definition.

METHODS

We conducted a prospective study of adults with dengue admitted to the Hospital for Tropical Diseases in Bangkok, Thailand, from October 2012 to December 2014. Univariate and stepwise multivariate logistic regression analyses were performed.

RESULTS

Of the 153 hospitalized patients with confirmed dengue viral infections, 132 (86.3 %) patients had non-severe dengue including dengue without warning signs (7 patients, 5.3 %) and dengue with warning signs (125, 94.7 %). The rest (21, 13.7 %) had severe dengue including severe plasma leakage (16, 76.2 %), severe organ involvement (16, 76.2 %), and severe clinical bleeding (8, 38.1 %). Using stepwise multivariate logistic regression, clinical factors identified as independently associated with the development of severe dengue were: (1) being >40 years old (odds ratio [OR]: 5.215, 95 % confidence interval [CI]: 1.538-17.689), (2) having persistent vomiting (OR: 4.817, CI: 1.375-16.873), (3) having >300 cells per μL of absolute atypical lymphocytes (OR: 3.163, CI: 1.017-9.834), and (4) having lactate levels ≥2.0 mmol/L (OR: 7.340, CI: 2.334-23.087). In addition, increases in lactate and absolute atypical lymphocyte levels corresponded with severe dengue (p < 0.05).

CONCLUSIONS

Our study identified several clinical factors independently associated with the development of severe dengue among hospitalized adults with dengue. This can aid in the early recognition and prompt management of at-risk patients to reduce morbidity and mortality.

The application of biomedical engineering techniques to the diagnosis and management of tropical diseases: a review

This paper reviews a number of biomedical engineering approaches to help aid in the detection and treatment of tropical diseases such as dengue, malaria, cholera, schistosomiasis, lymphatic filariasis, ebola, leprosy, leishmaniasis, and American trypanosomiasis (Chagas). Many different forms of non-invasive approaches such as ultrasound, echocardiography and electrocardiography, bioelectrical impedance, optical detection, simplified and rapid serological tests such as lab-on-chip and micro-/nano-fluidic platforms and medical support systems such as artificial intelligence clinical support systems are discussed. The paper also reviewed the novel clinical diagnosis and management systems using artificial intelligence and bioelectrical impedance techniques for dengue clinical applications.

Association Between Increased Vascular Nitric Oxide Bioavailability and Progression to Dengue Hemorrhagic Fever in Adults

In a prospective longitudinal adult study, vascular nitric oxide bioavailability measured as reactive hyperemia index was significantly higher at enrollment in patients who developed dengue hemorrhagic fever (DHF) (n = 11), compared with the non-DHF group (n = 63) and those with other febrile illnesses (n = 25) (P = .01). After adjustment for age, fever day, and body mass index, enrollment reactive hyperemia index was associated with a 4-fold increased risk for DHF, and predicted DHF with an area under the receiver operating curve of 0.86. Increased vascular nitric oxide in dengue is associated with increased vascular permeability and impaired homeostasis and may have utility as a predictor of DHF.

Early resuscitation of dengue shock syndrome in children with hyperosmolar sodium-lactate: a randomized single-blind clinical trial of efficacy and safety

INTRODUCTION

Dengue shock syndrome (DSS) fluid resuscitation by following the World Health Organization (WHO) guideline usually required large volumes of Ringer lactate (RL) that might induce secondary fluid overload. Our objective was to compare the effectiveness of the recommended volume of RL versus a smaller volume of a hypertonic sodium lactate solution (HSL) in children with DSS. The primary end point was to evaluate the effect of HSL on endothelial cell inflammation, assessed by soluble vascular cell adhesion molecule-1 (sVCAM-1) measurements. Secondarily, we considered the effectiveness of HSL in restoring hemodynamic fluid balance, acid-base status, and sodium and chloride balances, as well as in-hospital survival.

METHODS

A prospective randomized single-blind clinical trial including 50 DSS children was conducted in the Pediatrics Department of Hasan Sadikin Hospital, Bandung, Indonesia. Only pediatric patients (2 to 14 years old) fulfilling the WHO criteria for DSS and new to resuscitation treatments were eligible. Patients were resuscitated with either HSL (5 ml/kg/BW in 15 minutes followed by 1 ml/kg/BW/h for 12 hours), or RL (20 ml/kg/BW in 15 minutes followed by decreasing doses of 10, 7, 5, and 3 ml/kg BW/h for 12 hours).

RESULTS

In total, 50 patients were randomized and included in outcome and adverse-event analysis; 46 patients (8.2 ± 0.5 years; 24.9 ± 1.9 kg; mean ± SEM) completed the protocol and were fully analyzed (24 and 22 subjects in the HSL and RL groups, respectively). Baseline (prebolus) data were similar in both groups. Hemodynamic recovery, plasma expansion, clinical outcome, and survival rate were not significantly different in the two groups, whereas fluid accumulation was one third lower in the HSL than in the RL group. Moreover, HSL was responsible for a partial recovery from endothelial dysfunction, as indicated by the significant decrease in sVCAM-1.

CONCLUSION

Similar hemodynamic shock recovery and plasma expansion were achieved in both groups despite much lower fluid intake and fluid accumulation in the HSL group.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00966628. Registered 26 August 2009.

Preliminary evaluation of near infrared spectroscopy as a method to detect plasma leakage in children with dengue hemorrhagic fever

Background

Dengue viral infections are prevalent in the tropical and sub-tropical regions of the world, resulting in substantial morbidity and mortality. Clinical manifestations range from a self-limited fever to a potential life-threatening plasma leakage syndrome (dengue hemorrhagic fever). The objective of this study was to assess the utility of near infrared spectroscopy (NIRS) measurements of muscle oxygen saturation (SmO₂) as a possible continuous measure to detect plasma leakage in children with dengue.

Methods

Children ages 6 months to 15 years of age admitted with suspected dengue were enrolled from the dengue ward at Queen Sirikit National Institute for Child Health. Children were monitored daily until discharge. NIRS data were collected continuously using a prototype CareGuide Oximeter 1100 with sensors placed on the deltoid or thigh. Daily ultrasound of the chest and a right lateral decubitus chest x-ray the day after defervescence were performed to detect and quantitate plasma leakage in the pleural cavity.

Results

NIRS data were obtained from 19 children with laboratory-confirmed dengue. Average minimum SmO₂ decreased for all subjects prior to defervescence. Average minimum SmO₂ subsequently increased in children with no ultrasound evidence of pleural effusion but remained low in children with pleural effusion following defervescence. Average minimum SmO₂ was inversely correlated with pleural space fluid volume. ROC analysis revealed a cut-off value for SmO₂ which yielded high specificity and sensitivity.

Conclusions

SmO₂ measured using NIRS may be a useful guide for real-time and non-invasive identification of plasma leakage in children with dengue. Further investigation of the utility of NIRS measurements for prediction and management of severe dengue syndromes is warranted.

Endothelial cells in dengue hemorrhagic fever

Therapies to prevent or reverse endothelial dysfunction and vascular leak found in dengue hemorrhagic fever (DHF) have not been identified. In this review we summarize dengue viruses and the spectrum of human disease and highlight evidence of endothelial cell dysfunction in DHF based on studies in patients and mouse and tissue culture models. Evidence suggests that both virus antigen and host immune response, can cause endothelial cell dysfunction and weaken endothelial barrier integrity. We suggest possible therapeutic interventions and highlight how therapies targeting altered endothelial function might be evaluated in animal models and in patients with DHF.

Cardiovascular manifestations of the emerging dengue pandemic

Dengue is one of the most important emerging viral diseases globally. The majority of symptomatic infections result in a relatively benign disease course. However, a small proportion of patients develop severe clinical manifestations, including bleeding, organ impairment, and endothelial dysfunction with increased capillary permeability causing hypovolaemic shock that can lead to cardiovascular collapse. Evidence is increasing that dengue can also cause myocardial impairment, arrhythmias and, occasionally, fulminant myocarditis. No antiviral agents or vaccines are licensed for dengue, and treatment remains supportive with judicious fluid replacement for patients with severe disease. Defining the role of cardiac dysfunction in the haemodynamic compromise of severe dengue has potentially important management implications. In this Review, we will outline the current understanding of the cardiovascular manifestations of dengue, including myocardial and vascular involvement, and conclude with a discussion of the available therapeutic options and potential future research directions.

Serum angiopoietin-2 and soluble VEGF receptor 2 are surrogate markers for plasma leakage in patients with acute dengue virus infection

BACKGROUND

Endothelial cell dysfunction is believed to play an important role in the pathogenesis of plasma leakage in patients with acute dengue virus (DENV) infection. Several factors, produced by activated endothelial cells, have been associated with plasma leakage or severe disease in patients with infectious diseases.

OBJECTIVES

The aim of this study was to investigate which of these markers could serve as a surrogate marker for the occurrence of plasma leakage in patients with acute DENV infection.

STUDY DESIGN

A case-control study was performed in patients with acute DENV infection in Santos, Brazil. Plasma leakage was detected with X-ray and/or ultrasound examination at admission. Serum levels of soluble endoglin, endothelin-1, angiopoietin-2, VEGF, soluble VEGFR-2, MMP-2, MMP-9, TIMP-1 and TIMP-2 were determined using commercially available ELISAs.

RESULTS

Increased levels of angiopoietin-2, endothelin-1 and MMP-2 and decreased levels of soluble VEGFR-2 were significantly associated with the occurrence of plasma leakage. An unsupervised cluster analysis confirmed that angiopoietin-2 and soluble VEGFR-2 were strongly associated with clinical apparent vascular leakage.

CONCLUSION

Angiopoietin-2 and soluble VEGFR-2 can serve as surrogate markers for the occurrence of plasma leakage in patients with acute DENV infection.

Dengue: Moving from Current Standard of Care to State-of-the-Art Treatment

Treatment of dengue remains supportive in the absence of targeted antiviral therapy or approved vaccines. Responsive fluid management is key to preventing progression to shock or other severe manifestations. The dynamic natural history of dengue infection and its influence on hemodynamic homeostasis needs to be carefully considered in the planning of individualized therapy. Though largely self-limiting, the sheer burden of dengue disease on the global population will result in atypical manifestations especially in children, older adults, and comorbid patients. Management of these has not yet been systematized. The failure of recent randomized controlled trials to show utility for antiviral and immunomodulatory agents in dengue is disappointing. Vaccine candidates hold promise, but growing outbreaks require more robust, evidence-based management guidelines to inform clinicians, especially in novel epidemic situations.

Performance of the tourniquet test for diagnosing dengue in Peru

The tourniquet test (TT) is a physical examination maneuver often performed on patients suspected of having dengue. It has been incorporated into dengue diagnostic guidelines and is used in clinical studies. However, little is known about TT performance characteristics in different patient types or epidemiologic conditions. In the dengue-endemic city of Iquitos, Peru, we performed TTs and dengue laboratory assays on 13,548 persons with febrile disease, recruited through either active (n = 1,095) or passive (n = 12,453) surveillance. The sensitivity was 52% and 56%, the specificity was 58% and 68%, the positive predictive value was 45% and 55%, and the negative predictive value was 64% and 69% for persons enrolled in active and passive surveillance, respectively. We demonstrated that the TT was more sensitive identifying dengue disease in women and those of younger age and that sensitivity increased the later a person came to a medical clinic for care.

The importance of hematopoietic progenitor cells in dengue

Scientific investigations designed to better understand and assess the distinguishing clinical characteristics pave the way to a successful treatment for a disease. Since the peripheral blood is obtained easily, the most frequent type of investigation performed on infectious agents focuses on the hematological components of blood drawn from patients. Bone marrow aspirates, although somewhat more difficult to obtain, should be evaluated more frequently because they provide additional information, giving us a glimpse into the development of the disease. Understanding the distinct and unique changes in hematological components of the bone marrow induced by a particular pathogen or corresponding to a specific illness may be a valuable asset for the diagnosis and prognosis of disease. A good example of a pathogen that could be better evaluated with greater knowledge of the bone marrow is dengue, one of the most important public vector-borne human diseases. Owing to the multitude of clinical manifestations and the dynamic alterations of various blood components over time, this disease is one of the most difficult to prevent and treat in humans. Although large amounts of data have been generated in the literature, there remains a large gap between this information and its relevance for the purpose of patient care. While evaluating the cellular components in the circulated blood from ill patients provides us with valuable information about the pathogenesis of various pathogens, there are other players participating in the progression to disease. The goal of this review is to emphasize the importance of bone marrow hematopoietic progenitor cells in disease and to inspire other researchers to incorporate them into their investigations on dengue pathogenesis. It is anticipated that the knowledge derived from these investigations not only elicit original concepts on the pathogenesis of dengue but also foster a new way of thinking in terms of vaccine or therapeutic development to prevent and treat dengue.

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.

Human arboviral encephalitis

Worldwide, arboviral illnesses constitute the most important international infectious threat to human neurological health and welfare. Before the availability of effective immunizations, approximately 50,000 cases of Japanese encephalitis occurred in the world each year, one-fifth of which cases proved lethal and a much larger number were left with severe neurological handicaps. With global climate change and perhaps other factors, the prevalences of some arboviral illnesses appear to be increasing. Arboviral illnesses, including Japanese encephalitis, tick-borne encephalitis, Yellow fever, and others, are emerging as possible global health care threats because of biological warfare. This chapter will review ecology, pathophysiology, diagnosis, management, and outcome of the forms of arboviral encephalitis that are of greatest importance in North America, together with some of the most important arboviral encephalitides prevalent in other parts of the world.

The early whole-blood transcriptional signature of dengue virus and features associated with progression to dengue shock syndrome in Vietnamese children and young adults

Dengue is a pantropic public health problem. In children, dengue shock syndrome (DSS) is the most common life-threatening complication. The ability to predict which patients may develop DSS may improve triage and treatment. To this end, we conducted a nested case-control comparison of the early host transcriptional features in 24 DSS patients and 56 sex-, age-, and virus serotype-matched uncomplicated (UC) dengue patients. In the first instance, we defined the "early dengue" profile. The transcriptional signature in acute rather than convalescent samples (≤72 h post-illness onset) was defined by an overabundance of interferon-inducible transcripts (31% of the 551 overabundant transcripts) and canonical gene ontology terms that included the following: response to virus, immune response, innate immune response, and inflammatory response. Pathway and network analyses identified STAT1, STAT2, STAT3, IRF7, IRF9, IRF1, CEBPB, and SP1 as key transcriptional factors mediating the early response. Strikingly, the only difference in the transcriptional signatures of early DSS and UC dengue cases was the greater abundance of several neutrophil-associated transcripts in patients who progressed to DSS, a finding supported by higher plasma concentrations of several canonical proteins associated with neutrophil degranulation (bactericidal/permeability-increasing protein [BPI], elastase 2 [ELA2], and defensin 1 alpha [DEF1A]). Elevated levels of neutrophil-associated transcripts were independent of the neutrophil count and also of the genotype of the infecting virus, as genome-length sequences of dengue virus serotype 1 (DENV-1) (n = 15) and DENV-2 (n = 3) sampled from DSS patients were phylogenetically indistinguishable from those sampled from uncomplicated dengue patients (32 DENV-1 and 9 DENV-2 sequences). Collectively, these data suggest a hitherto unrecognized association between neutrophil activation, pathogenesis, and the development of DSS and point to future strategies for guiding prognosis.

Timing of CD8+ T cell responses in relation to commencement of capillary leakage in children with dengue

Immune activation is a feature of dengue hemorrhagic fever (DHF) and CD8+ T cell responses in particular have been suggested as having a role in the vasculopathy that characterizes this disease. By phenotyping CD8+ T cells (CD38+/HLA-DR+, CD38+/Ki-67+, or HLA-DR+/Ki-67+) in serial blood samples from children with dengue, we found no evidence of increased CD8+ T cell activation prior to the commencement of resolution of viremia or hemoconcentration. Investigations with MHC class I tetramers to detect NS3(133-142)-specific CD8+ T cells in two independent cohorts of children suggested the commencement of hemoconcentration and thrombocytopenia in DHF patients generally begins before the appearance of measurable frequencies of NS3(133-142)-specific CD8+ T cells. The temporal mismatch between the appearance of measurable surface activated or NS3(133-142)-specific CD8+ T cells suggests that these cells are sequestered at sites of infection, have phenotypes not detected by our approach, or that other mechanisms independent of CD8+ T cells are responsible for early triggering of capillary leakage in children with DHF.

Dengue virus pathogenesis: an integrated view. Clin Microbiol Rev. 2009;22:564-581. [PMID: 19822889 DOI: 10.1128/cmr.00035-09]

Much remains to be learned about the pathogenesis of the different manifestations of dengue virus (DENV) infections in humans. They may range from subclinical infection to dengue fever, dengue hemorrhagic fever (DHF), and eventually dengue shock syndrome (DSS). As both cell tropism and tissue tropism of DENV are considered major determinants in the pathogenesis of dengue, there is a critical need for adequate tropism assays, animal models, and human autopsy data. More than 50 years of research on dengue has resulted in a host of literature, which strongly suggests that the pathogenesis of DHF and DSS involves viral virulence factors and detrimental host responses, collectively resulting in abnormal hemostasis and increased vascular permeability. Differential targeting of specific vascular beds is likely to trigger the localized vascular hyperpermeability underlying DSS. A personalized approach to the study of pathogenesis will elucidate the basis of individual risk for development of DHF and DSS as well as identify the genetic and environmental bases for differences in risk for development of severe disease.

Systemic vascular leakage associated with dengue infections - the clinical perspective

Vascular leakage is the most serious complication of dengue infection. However, despite considerable progress in understanding the immunological derangements associated with dengue, the pathogenic mechanisms underlying the change in vascular permeability remain unclear. Lack of suitable model systems that manifest permeability characteristics similar to human vascular endothelium has seriously impeded research in this area. Similarly, limited knowledge of the factors regulating intrinsic microvascular permeability in health, together with limited understanding of the alterations seen in disease states in general, has also hampered progress. Fortunately considerable advances have been made in the field of endothelial biology in recent years, especially following appreciation of the crucial role played by the endothelial surface glycocalyx, acting in concert with underlying cellular structures, in regulating fluid flow across the microvasculature. We review what is known about vascular leakage during dengue infections, particularly in relation to current knowledge of vascular physiology, and discuss potential areas of research that may help to elucidate the complex nature of this singular phenomenon in the future.

Assessing the prognosis of dengue-infected patients

Dengue infections pose a huge burden to health care providers in most tropical countries. Careful clinical examination and history-taking supplemented by newer rapid diagnostic tests may lead to early etiological diagnosis. For severe dengue, early recognition of vascular permeability followed by rapid physiological replacement of fluids is life-saving. Prognosis of patients depends upon optimum management, an outcome that requires preparation via organization, training, and use of evidence-based practice guidelines.

Hemoconcentration during a prolonged stress task: associations with hemodynamic reactivity and microvascular permeability

This study explored the association between stress-induced hemoconcentration and plasma colloid osmotic pressure, hemodynamic reactivity, and microvascular permeability during a protracted stress task in 26 healthy, young participants. Microvascular permeability was measured during rest using venous congestion plethysmography in a subsample of 13 participants. The task increased hematocrit, colloid osmotic pressure, blood pressure, and heart rate and decreased R-wave to pulse interval. Resting microvascular permeability was not correlated with hemoconcentration. Colloid osmotic pressure and diastolic blood pressure were associated with stress-induced hemoconcentration throughout the task. The association with systolic blood pressure as well as heart rate, however, was more evident during the initial 8min of the task than throughout the total task duration. These findings suggest that factors associated with hemoconcentration vary with task duration.

Dengue

The four dengue viruses are transmitted in tropical countries that circle the globe. All can cause syndromes that are self-limited or severe. The common severe syndrome--dengue haemorrhagic fever/dengue shock syndrome (DHF/DSS)--is characterised by sudden vascular permeability generated by cytokines released when T cells attack dengue-infected cells. Dengue 1 virus became prevalent in Hawaii where it was transmitted by Aedes albopictus, producing a classic virgin soil epidemic, with clinical disease seen largely in adults. In Cuba and Singapore, sequential dengue infections at long intervals produced unusually severe disease in adults. Evidence suggests that enhancing and cross-reactive neutralising antibodies regulate dengue epidemics and disease severity. Classic DHF/DSS arises during initial dengue infections in infants with low circulating amounts of maternal dengue antibodies, an observation that precludes an exclusive causal role for secondary T-cell responses. Here, I review and discuss data on clinical diagnosis and pathophysiology of vascular permeability and coagulopathy, parenteral treatment of DHF/DSS, and new laboratory tests.

Myocardial depression in dengue hemorrhagic fever: prevalence and clinical description

OBJECTIVES

To determine the prevalence of myocardial depression and its effect on the clinical severity in patients with dengue hemorrhagic fever.

DESIGN

Clinical study.

SETTING

King Chulalongkorn Memorial Hospital, Bangkok, Thailand.

PATIENTS

Ninety-one children (age 10.5 +/- 2.9 yrs, male/female = 52/39) with serologically or polymerase chain reaction-proven dengue virus infection.

INTERVENTIONS

Left ventricular ejection fraction (EF) was measured. The proportions of patients with EF <50% were identified in patients with dengue fever (DF, n = 30), dengue hemorrhagic fever without shock (DHF, n = 36), and dengue shock syndrome (DSS, n = 25). Comparisons of clinical findings were made among DSS patients with depressed ventricular function (EF <50%), fair ventricular function (EF > or =50% and <60%), and good ventricular function (EF > or = 60%). Serum troponin T was analyzed in nine patients.

MEASUREMENTS AND MAIN RESULTS

EF during toxic stage was significantly lower in patients with DSS than DHF, and lower in DHF than DF (p = .05) with rapid recovery within 24-48 hrs. EF <50% was found in 6.7%, 13.8%, and 36% of patients with DF, DHF, and DSS during the toxic stage, respectively (p = .01). DSS patients with poor ventricular function had significantly more tachycardia and hepatomegaly. While end-diastolic volumes were similarly reduced, patients with lower EF tended to have lower cardiac output, required more aggressive intravenous fluid resuscitation, developed larger pleural effusion, and had higher incidence of respiratory embarrassment. No patient had elevated troponin T level.

CONCLUSIONS

Transient myocardial depression is not uncommon in patients with DSS. Cardiac dysfunction in children with DSS may contribute to the clinical severity and the degree of fluid overload in these patients.

Early differentiation between dengue and septic shock by comparison of admission hemodynamic, clinical, and laboratory variables: a pilot study

OBJECTIVE

To compare the clinical, hemodynamic, and laboratory variables, treatment, and outcome in dengue shock syndrome (DSS) and septic shock (SS), with an aim to permit early differentiation at presentation to the emergency department.

DESIGN

Retrospective chart review.

SETTING

A tertiary care pediatric emergency and critical care unit.

PATIENTS

Thirty-two patients (16 DSS and 16 SS) between June 2004 and December 2005 who were treated in the emergency department and intensive care using protocols.

INTERVENTIONS

None.

RESULTS

There were no differences between groups in terms of age, number with decompensated shock, and Pediatric Risk of Mortality III scores. Differences between DSS and SS were found in heart rate, 120 +/- 39 beats per minute versus 158 +/- 35 beats per minute (P < 0.01); pulse pressures, 25 +/- 8 mm Hg versus 43 +/- 8 mm Hg (P < 0.01); presence of systemic inflammatory response syndrome, 9/16 versus 15/16 (P < 0.05); Glasgow Coma Score, 13 +/- 3 versus 10 +/- 4 (P < 0.05); hematocrit, 42 +/- 6 versus 29 +/- 7 (P < 0.01); and median platelet count, 29,000/mm3 (interquartile range, 20,500-57,500/mm3) versus 115,500/mm3 (interquartile range, 91,750-182,250/mm3 in SS) (P < 0.01). Patients with SS were more likely to require greater than 40 mL/kg of fluid for initial resuscitation, ventilation, and vasoactive support for shock compared with those with dengue. In the fluid and catecholamine refractory patients, 6 of 16 SS versus 0 of 16 DSS patients were treated with steroids (P < 0.05). The outcome was similar in both groups, with 2 of 16 deaths among children with SS and 1 of 16 in those with DSS.

CONCLUSIONS

Dengue shock syndrome is likely a distinct entity from SS with some overlapping features. The DSS patients are significantly less likely to have systemic inflammatory response syndrome, be tachycardic, and have a narrower pulse pressure at admission when compared with SS patients. Mental status is better preserved, and spontaneous clinical bleeding is more common in children with DSS compared with those in SS. These likely results from the predominantly vasodilatory state in SS versus vasoconstrictory state that is the initial response in DSS.

[Early indicators of severity in dengue virus infection]

OBJECTIVE

To identify clinical markers of severity in dengue, different from those of major hemorrhage.

DESIGN

Cross-sectional study.

POPULATION AND METHODS

Patients with a diagnosis of dengue infection admitted to hospitals in Santander (Colombia) during the years 1993 to 1998 were studied. On admittance or during hospitalization, patients were classified as cases of dengue hemorrhagic fever (DHF) or dengue fever (DF). Clinical findings differing from those of major hemorrhage were recorded in the emergency room and during the first assessment at hospitalization. The association between these findings and the outcome of DHF were evaluated using univariate and multivariate analyses.

RESULTS

891 patients (DF: 420; DHF: 471) were included in the study. Associations were found between DHF and the following signs and symptoms: vomiting (OR: 1.89; 95% CI: 1.37-2.6; p = 0.0001); gingival hemorrhage (OR: 1.55; 95% CI: 1.11-2.18; p = 0.01); epistaxis (OR: 1.78; 95% CI: 1.28-2.48; p = 0.001); hepatomegaly (OR: 2.56; 95% CI: 1.61-4.07; p < 0.0001); microscopic hematuria (OR: 2.33; 95% CI: 1.36-4; p = 0.002); and rash (OR: 1.36; 95% CI: 1.04-1.77; p = 0.02). The hematocrit in the emergency room and on the first day of hospitalization was significantly higher in the group with DHF (p < 0.001, in both observations). On multivariate analysis, the hematocrit from DHF patients obtained in the emergency room was higher than that from DF, independently of the other relevant variables (difference: 3.65; 95% CI: 2.81-4.49).

CONCLUSION

Under the study conditions, there was an association between early clinical findings and DHF. These results must be evaluated in a cohort study.

Hepatosplanchnic circulatory dysfunction in acute hepatic infection: the case of dengue hemorrhagic fever

The mechanism of shock in patients with dengue hemorrhagic fever (DHF) has not yet been fully understood. In this study, we investigated the possibility of splanchnic venous pooling as a contributor for circulatory dysfunction in these patients. Ultrasonographic studies of portal vein and inferior vena cava were done in 45 patients with serologically or PCR-confirmed diagnosis of dengue virus infection. The size of portal vein and inferior vena cava, mean blood flow velocity in the right portal vein, and modified portal vein congestion index were compared between patients with dengue fever (DF, n = 20), DHF without shock (n = 14), and dengue shock syndrome (DSS, n = 11) during the toxic stage, convalescent stage, and at follow-up. The portal vein was significantly more dilated in patients with shock (DSS) than DHF without shock and than DF during the toxic and convalescent stages (P < 0.05), but not at follow-up. The change in the size of inferior vena cava followed the opposite trend (not statistically significant). Portal vein blood flow velocity was lower and congestion index was higher in shock cases (DSS) than DHF without shock and than DF at toxic and convalescent stages (P < 0.01). The differences disappeared at follow-up. Hepatosplanchnic venous pooling and/or dysfunction occur and correlate with the severity of circulatory derangement and shock in patients with DHF. The cause(s) and significance of hepatosplanchnic circulatory dysfunction in DHF and possibly other viral hepatic diseases deserve further study.

Early T-cell responses to dengue virus epitopes in Vietnamese adults with secondary dengue virus infections

T-cell responses to dengue viruses may be important in both protective immunity and pathogenesis. This study of 48 Vietnamese adults with secondary dengue virus infections defined the breadth and magnitude of peripheral T-cell responses to 260 overlapping peptide antigens derived from a dengue virus serotype 2 (DV2) isolate. Forty-seven different peptides evoked significant gamma interferon enzyme-linked immunospot (ELISPOT) assay responses in 39 patients; of these, 34 peptides contained potentially novel T-cell epitopes. NS3 and particularly NS3200-324 were important T-cell targets. The breadth and magnitude of ELISPOT responses to DV2 peptides were independent of the infecting dengue virus serotype, suggesting that cross-reactive T cells dominate the acute response during secondary infection. Acute ELISPOT responses were weakly correlated with the extent of hemoconcentration in individual patients but not with the nadir of thrombocytopenia or overall clinical disease grade. NS3556-564 and Env414-422 were identified as novel HLA-A*24 and B*07-restricted CD8+ T-cell epitopes, respectively. Acute T-cell responses to natural variants of Env414-422 and NS3556-564 were largely cross-reactive and peaked during disease convalescence. The results highlight the importance of NS3 and cross-reactive T cells during acute secondary infection but suggest that the overall breadth and magnitude of the T-cell response is not significantly related to clinical disease grade.

An outbreak of primary dengue infection among migrant Chinese workers in Singapore characterized by prominent gastrointestinal symptoms and a high proportion of symptomatic cases

BACKGROUND

An outbreak of dengue occurred among Chinese migrant workers at a construction site in Singapore that was characterized by a number of unusual features.

METHODS

Clinical and laboratory data were prospectively collected from workers who were hospitalized with fever. We compared the frequency of disease manifestations in these patients with historical data from other cases of dengue admitted to the same centre. A serological survey was performed at the construction site one month after the onset of the outbreak.

RESULTS

Thirty-nine patients were admitted from the affected construction site with confirmed acute dengue infection in March and April 2002. Fever, headache and rash were common and occurred at similar frequency in outbreak patients and historical controls. Gastrointestinal manifestations were significantly more common in the outbreak patients compared with controls (nausea 68%, diarrhea 41%, hyponatremia 47% and elevated urea 20%). Of the 274 studied in the serological survey, 27 had serological evidence of acute dengue, of whom 24 (89%) had experienced a febrile illness in the previous month. The virus was cultured and identified as Dengue-2. Few patients had a positive IgG for dengue indicating that this was likely a primary infection.

CONCLUSION

This outbreak of primary dengue infection was characterized by unusually prominent gastrointestinal symptoms and a high proportion of symptomatic transmission. Manifestations of dengue may be altered when outbreaks involve immunologically naïve adults who have migrated to dengue endemic areas.

Microvascular permeability during experimental human endotoxemia: an open intervention study

INTRODUCTION

Septic shock is associated with increased microvascular permeability. As a model for study of the pathophysiology of sepsis, endotoxin administration to humans has facilitated research into inflammation, coagulation and cardiovascular effects. The present study was undertaken to determine whether endotoxin administration to human volunteers can be used as a model to study the sepsis-associated increase in microvascular permeability.

METHODS

In an open intervention study conducted in a university medical centre, 16 healthy volunteers were evaluated in the research unit of the intensive care unit. Eight were administered endotoxin intravenously (2 ng/kg Escherichia coli O113) and eight served as control individuals. Microvascular permeability was assessed before and 5 hours after the administration of endotoxin (n = 8) or placebo (n = 8) by three different methods: transcapillary escape rate of I(125)-albumin; venous occlusion strain-gauge plethysmography to determine the filtration capacity; and bioelectrical impedance analysis to determine the extracellular and total body water.

RESULTS

Administration of endotoxin resulted in the expected increases in proinflammatory cytokines, temperature, flu-like symptoms and cardiovascular changes. All changes were significantly different from those in the control group. In the endotoxin group all microvascular permeability parameters remained unchanged from baseline: transcapillary escape rate of I(125)-albumin changed from 7.2 +/- 0.6 to 7.7 +/- 0.9%/hour; filtration capacity changed from 5.0 +/- 0.3 to 4.2 +/- 0.4 ml/min per 100 ml mmHg x 10(-3); and extracellular/total body water changed from 0.42 +/- 0.01 to 0.40 +/- 0.01 l/l (all differences not significant).

CONCLUSION

Although experimental human endotoxaemia is frequently used as a model to study sepsis-associated pathophysiology, an endotoxin-induced increase in microvascular permeability in vivo could not be detected using three different methods. Endotoxin administration to human volunteers is not suitable as a model in which to study changes in microvascular permeability.

Modeling of hemoglobin in dengue fever and dengue hemorrhagic fever using bioelectrical impedance

This paper describes a model for predicting hemoglobin (Hb) by using bioelectrical impedance analysis (BIA) in dengue patients in the Hospital Universiti Kebangsaan Malaysia (HUKM). Bioelectrical impedance measurements were conducted on 83 (47 males and 36 females) serologically confirmed dengue fever (DF) and dengue hemorrhagic fever (DHF) patients during their hospitalization. The predictive equation for Hb was derived using multivariate analysis. We investigated all the parameters in BIA, patients' symptom and demographic data. In this developed model, four predictors (reactance (XC), sex, weight and vomiting) were found to be the best predictive factors for modeling Hb in dengue patients. However, the model can only explain approximately 42% of the variation in Hb status, thus single frequency bio-impedance stand-alone technique is insufficient to monitor Hb for the DF and DHF patients. Further investigation using multi-frequency BIA is recommended in modeling Hb to achieve the most parsimonious model.

Immunology and Immunopathogenesis of Dengue Disease

The pathophysiological basis of severe dengue disease (i.e., dengue hemorrhagic fever [DHF]), appears to be multifactorial, involving complex interactions among viral factors, host genetics, and the immunologic background of the host, principally prior exposure to dengue virus. Analysis of these processes has been limited to observational studies of naturally infected humans because there have not been useful animal models of dengue disease. Substantial evidence points to dengue virus-reactive T cells as a critical effector in the development of DHF. We are beginning to define the critical elements of T-cell epitope specificity and functional responses that contribute to DHF. Additional studies in well-characterized patient cohorts from different geographic regions will be needed to advance this research and guide new approaches to prevention and treatment of DHF.

Dengue

PURPOSE OF REVIEW

Because efforts to control dengue are flagging, this review focuses on the mechanisms underlying severe disease and on treatment options, good and bad.

RECENT FINDINGS

The year 2001 witnessed unprecedented global dengue epidemic activity in the American hemisphere, the Pacific islands and continental Asia. Early diagnosis of dengue is important but what is the value and appropriate use of the tourniquet test? A negative test does not rule out dengue infection, a positive test should be followed by close surveillance for early signs of dengue hemorrhagic fever. Low platelet counts do not predict clinically significant bleeding in dengue. It follows that platelet or blood transfusions should not be administered based upon platelet count alone. Dengue hemorrhagic fever or dengue shock syndrome cases frequently have compensated consumptive coagulopathy that seldom requires treatment. Bleeding is most likely caused by activated platelets resulting from damaged capillary endothelium. Dengue hemorrhagic fever and dengue shock syndrome can be safely treated with just normal saline. Colloids should be immediately given to children presenting with a pulse pressure at or below 10 mmHg. Human leukocyte antigen alleles correlate with both protection and susceptibility to dengue hemorrhagic fever and dengue shock syndrome; studies in Haiti suggest that blacks have a gene providing nearly complete protection against severe dengue illness.

SUMMARY

The role that antibodies play in protecting and enhancing dengue infections has been largely ignored. Such studies require definitive knowledge of what cells are infected in human dengue and an understanding of all the early antibody-accessible steps of infection of these target cells.

Chemical and biological weapons. Implications for anaesthesia and intensive care

In the wake of recent atrocities there has been renewed apprehension regarding the possibility of chemical and biological weapon (CBW) deployment by terrorists. Despite various international agreements that proscribe their use, certain states continue to develop chemical and biological weapons of mass destruction. Of greater concern, recent historical examples support the prospect that state-independent organizations have the capability to produce such weapons. Indeed, the deliberate deployment of anthrax has claimed several lives in the USA since September 11, 2001. In the event of a significant CBW attack, medical services would be stretched. However, victim survival may be improved by the prompt, coordinated response of military and civil authorities, in conjunction with appropriate medical care. In comparison with most other specialties, anaesthetists have the professional academic background in physiology and pharmacology to be able to understand the nature of the injuries caused by CBWs. Anaesthetists, therefore, play a vital role both in the initial resuscitation of casualties and in their continued treatment in an intensive care setting. This article assesses the current risk of CBW deployment by terrorists, considers factors which would affect the severity of an attack, and discusses the pathophysiology of those CBWs most likely to be used. The specific roles of the anaesthetist and intensivist in treatment are highlighted.

Assessment of body fluid compartment volumes by multifrequency bioelectrical impedance spectroscopy in children with dengue

Dengue haemorrhagic fever (DHF), the most severe form of illness following infection with a dengue virus, is characterized by plasma leakage and a period of increased microvascular permeability. Monitoring of plasma volume and body fluid compartment shifts is an integral part of the clinical management of DHF, and is crucial to the performance of clinical research studies on DHF pathogenesis. Multifrequency bioelectrical impedance spectroscopy (BIS) was assessed as a non-invasive method to monitor body fluid compartment shifts in children participating in a prospective, hospital-based, study of dengue virus infections in Thailand. Over the 48 h surrounding defervescence, the extracellular water/intracellular water ratio (ECW/ICW) rose in children with dengue virus infections and correlated with increasing disease severity [DHF > intermediate dengue fever (DF)/DHF > DF]. Plasma leakage remained within the ECW compartment and was not directly measured by multifrequency BIS. Expansion of the ECW space in DHF appeared to be primarily due to diminished renal water clearance. During the course of dengue illness, multifrequency BIS did not improve on serial haematocrit and bodyweight determinations for monitoring plasma volume contraction and ECW expansion, respectively.