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The World Health Organization (WHO) estimates that there are over 50 million cases of dengue fever reported annually and approximately 2.5 billion people are at risk. Mild dengue fever presents with headache, fever, rash, myalgia, osteogenic pain, and lethargy. Severe disease can manifest as dengue shock syndrome (DSS) or dengue hemorrhagic fever (DHF). Symptoms of DSS/DHF are leukopenia, low blood volume and pressure encephalitis, cold and sweaty skin, gastrointestinal bleeding, and spontaneous bleeding from gums and nose. Currently, there are no therapeutics available beyond supportive care and untreated complicated dengue fever can have a 50% mortality rate. According to WHO DSS/DHF is the leading cause of childhood mortality in some Asian countries. Dendritic cells are professional antigen presenting cells that are primary targets in a dengue infection. Dengue binds to Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin (DC-SIGN). DC-SIGN has a high affinity for ICAM3 which is expressed in activating T-cells. Previous studies have demonstrated an altered T-cell phenotype expressed in dengue infected patients that could be potentially mediated by dengue-infected DCs.

Dengue is enhanced by three interacting components of the immune system. Dengue begins by infecting dendritic cells which in immature dendritic cells is mediated by DC-SIGN. In mature dendritic cells, antibodies can enhance dengue infection via Fc receptors. Downstream of dendritic cells T-cells become activated and generate the very cytokines implicated in vascular leak and shock in addition to activating effector cells. Both the virus and the antibodies are involved in release of complement and anaphylatoxins which can cause or exacerbate DHF/DSS. These systems are inextricable and strongly associated with dengue pathogenesis.

Dengue is a major public health problem worldwide and continues to increase in incidence. Dengue virus (DENV) infection leads to a range of outcomes, including subclinical infection, undifferentiated febrile illness, Dengue Fever (DF), life-threatening syndromes with fluid loss and hypotensive shock, or other severe manifestations such as bleeding and organ failure. The long-standing World Health Organization (WHO) dengue classification and management scheme was recently revised, replacing DF, Dengue Hemorrhagic Fever (DHF), and Dengue Shock Syndrome (DSS) with Dengue without Warning Signs, Dengue with Warning Signs (abdominal pain, persistent vomiting, fluid accumulation, mucosal bleeding, lethargy, liver enlargement, increasing hematocrit with decreasing platelets) and Severe Dengue (SD; dengue with severe plasma leakage, severe bleeding, or organ failure). We evaluated the traditional and revised classification schemes against clinical intervention levels to determine how each captures disease severity using data from five years (2005–2010) of a hospital-based study of pediatric dengue in Managua, Nicaragua. Laboratory-confirmed dengue cases (n = 544) were categorized using both classification schemes and by level of care (I–III). Category I was out-patient care, Category II was in-patient care that did not meet criteria for Category III, which included ICU admission, ventilation, administration of inotropic drugs, or organ failure. Sensitivity and specificity to capture Category III care for DHF/DSS were 39.0% and 75.5%, respectively; sensitivity and specificity for SD were 92.1% and 78.5%, respectively. In this data set, DENV-2 was found to be significantly associated with DHF/DSS; however, this association was not observed with the revised classification. Among dengue-confirmed cases, the revised WHO classification for severe dengue appears to have higher sensitivity and specificity to identify cases in need of heightened care, although it is no longer as specific for a particular pathogenic entity as was the traditional schema.

Author Summary

Dengue is a mosquito-transmitted viral disease that is a major public health problem worldwide. Dengue virus (DENV) infection leads to Dengue Fever (DF) and a spectrum of life-threatening syndromes with fluid loss and hypotensive shock or other severe manifestations. Recently, the traditional World Health Organization (WHO) dengue classification scheme (classic DF, Dengue Hemorrhagic Fever (DHF), and Dengue Shock Syndrome (DSS)) was replaced with Dengue without Warning Signs, Dengue with Warning Signs and Severe Dengue (SD). Using data from 544 laboratory-confirmed dengue cases recruited over five years of a hospital-based study of pediatric dengue in Managua, Nicaragua, we evaluated the traditional and revised classification schemes against clinical intervention levels (I–III) to determine how each captures disease severity. The sensitivity and specificity to capture Category III care for DHF/DSS were 39.0% and 75.5%, respectively, and for SD were 92.1% and 78.5%, respectively. Interestingly, DENV-2 was significantly associated with DHF/DSS; however, this association was not observed with the revised classification. This study indicates that among dengue-confirmed cases, the revised WHO classification appears to have higher sensitivity and specificity for identifying cases in need of heightened care, although it is no longer as specific for a particular pathogenic entity as was the traditional schema.

To assess the incidence of and risk factors for clinical and subclinical dengue virus (DENV) infection, we prospectively studied 1,207 adult short-term travelers from the Netherlands to dengue-endemic areas. Participants donated blood samples for serologic testing before and after travel. Blood samples were tested for antibodies against DENV. Seroconversion occurred in 14 (1.2%) travelers at risk. The incidence rate was 14.6 per 1,000 person-months. The incidence rate was significantly higher for travel during the rainy months. Dengue-like illness occurred in 5 of the 14 travelers who seroconverted. Seroconversion was significantly related to fever, retro-orbital pain, myalgia, arthralgia, and skin rash. The risk for DENV infection for short-term travelers to dengue-endemic areas is substantial. The incidence rate for this study is comparable with that in 2 other serology-based prospective studies conducted in the 1990s.

Autochthonous dengue infections were last reported in Hawaii in 1944. In September 2001, the Hawaii Department of Health was notified of an unusual febrile illness in a resident with no travel history; dengue fever was confirmed. During the investigation, 1,644 persons with locally acquired denguelike illness were evaluated, and 122 (7%) laboratory-positive dengue infections were identified; dengue virus serotype 1 was isolated from 15 patients. No cases of dengue hemorrhagic fever or shock syndrome were reported. In 3 instances autochthonous infections were linked to a person who reported denguelike illness after travel to French Polynesia. Phylogenetic analyses showed the Hawaiian isolates were closely associated with contemporaneous isolates from Tahiti. Aedes albopictus was present in all communities surveyed on Oahu, Maui, Molokai, and Kauai; no Ae. aegypti were found. This outbreak underscores the importance of maintaining surveillance and control of potential disease vectors even in the absence of an imminent disease threat.

Dengue is the most important mosquito-borne, arboviral infection found in tropical and sub-tropical climates. Clinical presentation varies from a severe flu-like illness to a potentially lethal dengue hemorrhagic fever. Dengue has been regarded as a nonneurotropic virus. However, there are reports describing neurological involvements in dengue virus infection. The neurological involvement in dengue virus infection includes encephalitis, acute disseminated encephalomyelitis, transverse myelitis, and Guillain-Barre syndrome. The neurological spectrum of dengue patients has been limited because of small number of case reports, paucity of imaging, and neurophysiologic studies. There are only a few isolated case reports and case series documenting acute pure motor quadriparesis in dengue fever. We report acute pure motor reversible quadriparesis due to hypokalemia. Clinicians in the endemic area should be aware of such association of acute pure motor reversible quadriparesis with dengue fever

Introduction

Dengue virus (DENV) affects over half the world’s population in 112 countries, and dengue fever (DF) is the second largest arthropod borne infectious global hazard after malaria with complications like Dengue Hemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS), accounting for significant morbidity and mortality world-over. Pakistan is significantly affected with DENV infection and to-date no study identifying risk factors associated with development of severe complications of DF has been done.

Methods

997 confirmed cases of DF were collected from a tertiary care hospital in Lahore, Pakistan and their clinical and biochemical data were collected. Univariate, multivariate and logistics regression analysis was performed to identify risk factors associated with development of DHF and DSS.

Results

Bleeding OR 70.7 (CI 38.4–129.9), deranged liver function test OR 1.9 (CI 0.97–0.99), presence of urinary red blood cells OR 1.4 (95%CI 0.179–0.900) and presence of urinary protein OR 1.1 (95%CI 0.191–0.974) were related to development of DHF and DSS.

Discussion

Severe Dengue, like DHF and DSS can be predicted by the presence of clinical and biochemical factors like signs of bleeding, deranged liver function test, presence of urinary red blood cells and urinary protein; so that the patients at high risk for complication be identified early and started on treatment timely.

Conclusion

Predictors of severe dengue are identified in this study but further large scale multi-centered studies are needed for better interpretation.

Dengue infection is a leading cause of illness and death in tropical and subtropical regions of the world. Forty percent of the world's population currently lives in these areas. The clinical picture resulting from dengue infection can range from relatively minor to catastrophic hemorrhagic fever. Recently, reports have increased of neurological manifestations. Neuropathogenesis seems to be related to direct nervous system viral invasion, autoimmune reaction, metabolic and hemorrhagic disturbance. Neurological manifestations include encephalitis, encephalopathy, meningitis, Guillain-Barré syndrome, myelitis, acute disseminated encephalomyelitis, polyneuropathy, mononeuropathy, and cerebromeningeal hemorrhage. The development of neurological symptoms in patients with positive Immunoglobulin M (IgM) dengue serology suggests a means of diagnosing the neurological complications associated with dengue. Viral antigens, specific IgM antibodies, and the intrathecal synthesis of dengue antibodies have been successfully detected in cerebrospinal fluid. However, despite diagnostic advancements, the treatment of neurological dengue is problematic. The launch of a dengue vaccine is expected to be beneficial.

Background

Since the first reported outbreak of dengue hemorrhagic fever in Pakistan, several mini outbreaks have erupted in the region. Dengue virus serotype 3 (DEN-3) was first documented in 2005 outbreak in Karachi. Reports show that serotype 3 is prevalent in Lahore since 2008. Serotype 2 (DEN-2) is the major circulating serotype in Pakistan as it is documented since 1994. We have conducted a detailed study of three outbreaks of dengue virus infection that occurred in years 2007, 2008 and 2009 in Lahore by using molecular techniques such as PCR and nucleotide sequencing of the C-prM gene junction of Dengue virus.

Results

Through the analysis of 114 serum samples collected over the period of three years (2007-2009), total 20 patients were found to be infected with dengue virus. In year 2007, four were positive for serotype 2 and one sample was positive for serotype DEN-3. In 2008, five samples had concurrent infection with serotypes DEN-2 and DEN-3 while three samples were infected only with serotype DEN-2. In year 2009, one sample had concurrent infection with serotypes DEN-2 and DEN-3 while six were positive for serotype DEN-2 only.

Conclusions

Our study showed that serotype DEN-2 was dominant in positive samples of dengue virus infection collected during the period of three years (2007-2009). The other serotype present was serotype DEN-3. Genotypes of serotype DEN-2 and serotype DEN-3 were subtype IV and subtype III, respectively.

There has been considerable debate regarding the value of both the 1997 and 2009 World Health Organization (WHO) dengue case classification criteria for its diagnosis and management. Differentiation between classic dengue fever (DF) and dengue haemorrhagic fever (DHF) or severe dengue is a key aspect of dengue case classification. The geographic expansion of dengue and its increased incidence in older age groups have contributed to the limited applicability of the 1997 case definitions. Clinical experience of dengue suggests that the illness presents as a spectrum of disease instead of distinct phases. However, despite the rigid grouping of dengue into DF, DHF and dengue shock syndrome (DSS), overlap between the different manifestations has often been observed, which has affected clinical management and triage of patients. The findings of the DENCO study evaluating the 1997 case definitions formed the basis of the revised 2009 WHO case definitions, which classified the illness into dengue with and without warning signs and severe dengue. Although the revised scheme is more sensitive to the diagnosis of severe dengue, and beneficial to triage and case management, there remain issues with its applicability. It is considered by many to be too broad, requiring more specific definition of warning signs. Quantitative research into the predictive value of these warning signs on patient outcomes and the cost-effectiveness of the new classification system is required to ascertain whether the new classification system requires further modification, or whether elements of both classification systems can be combined.

Background

Dengue fever is an endemic illness in the tropics with early and post infectious complications affecting multiple systems. Though neurological sequelae including mononeuropathy, encephalopathy, transverse myelitis, polyradiculopathy, Guillain-Barre syndrome , optic neuropathy and oculomotor neuropathy have been reported in medical literature, the abducens nerve despite its notoriety in cranial neuropathies in a multitude of condition due to its long intracranial course had not been to date reported to manifest with lateral rectus paralysis following dengue.

Case presentation

A previously well 29 year old male with serologically confirmed dengue hemorrhagic fever developed symptomatic right lateral rectus palsy during the critical phase of the illness, which persisted into convalescence and post convalescence with proven deficit on Hess screen. Alternate etiologies were excluded by imaging, serology and electrophysiology.

Conclusions

The authors detail the first reported case of abducens nerve palsy complicating dengue fever in a previously healthy male from Sri Lanka. In a tropical country with endemic dengue infections, dengue related abducens neuropathy may be considered as a differential diagnosis in cases of acquired lateral rectus palsy after dengue fever.

Dengue virus infection causes diseases in people, ranging from the acute febrile illness Dengue fever, to life-threatening Dengue Hemorrhagic Fever/Dengue Shock Syndrome. We previously reported that a host cellular α-glucosidases I and II inhibitor, imino sugar CM-10-18, potently inhibited dengue virus replication in cultured cells, and significantly reduced viremia in dengue virus infected AG129 mice. In this report we show that CM-10-18 also significantly protects mice from death and/or disease progress in two mouse models of lethal dengue virus infection. Our results thus provide a strong support for the development of CM-10-18 or its derivatives as antiviral agents to treat server dengue virus infections.

Dengue viral infections are one of the most important mosquito-borne diseases in the world. Presently dengue is endemic in 112 countries in the world. It has been estimated that almost 100 million cases of dengue fever and half a million cases of dengue hemorrhagic fever (DHF) occur worldwide. An increasing proportion of DHF is in children less than 15 years of age, especially in South East and South Asia. The unique structure of the dengue virus and the pathophysiologic responses of the host, different serotypes, and favorable conditions for vector breeding have led to the virulence and spread of the infections. The manifestations of dengue infections are protean from being asymptomatic to undifferentiated fever, severe dengue infections, and unusual complications. Early recognition and prompt initiation of appropriate supportive treatment are often delayed resulting in unnecessarily high morbidity and mortality. Attempts are underway for the development of a vaccine for preventing the burden of this neglected disease. This review outlines the epidemiology, clinical features, pathophysiologic mechanisms, management, and control of dengue infections.

Summary

Background

Dengue virus infection causes a spectrum of clinical manifestations, usually classified according to the World Health Organization (WHO) guidelines into dengue fever (DF) and dengue hemorrhagic fever (DHF). Its ability to categorize severe dengue illness has recently been questioned.

Methods

We evaluated dengue case definitions in a prospective study at a pediatric hospital in Bangkok from 1994-2005. One thousand and thirteen children were enrolled within the first three days of fever and followed with standardized data collection. Cases were classified based on application of the strict WHO criteria. All dengue virus infections were laboratory confirmed. We retrospectively grouped patients based on whether they received significant intervention based on the fluid replacement and/or requirements for blood transfusion.

Results

Fifty eight percent (85/150), 15% (40/264), and 12% (73/599) of DHF, DF and other febrile illnesses (OFI) cases, respectively, received significant intervention. Sixty-eight percent of dengue cases requiring intervention met strict WHO criteria for DHF. In contrast, only 1% of OFI cases met WHO criteria for DHF. Plasma leakage and thrombocytopenia were the two components contributing to the specificity of the WHO case definition and identified dengue cases that required intervention. Hemorrhagic tendency did not reliably differentiate DF and DHF. In DF cases, thrombocytopenia and bleeding were associated with severity.

Conclusions

Dengue illness is heterogeneous in severity, and severe clinical features occurred in patients that were not characterized as DHF. The WHO case definition of DHF demonstrates 62% sensitivity and 92% specificity in identifying dengue illness requiring intervention without the need for laboratory confirmation of dengue virus infection in endemic areas.

Background

Dengue re-emerges in Singapore despite decades of effective vector control; the infection predominantly afflicts adults. Severe dengue not fulfilling dengue hemorrhagic fever (DHF) criteria according to World Health Organization (WHO) 1997 guideline was increasingly reported. A new WHO 2009 guideline emphasized warning signs and a wider range of severe dengue manifestations. We aim to evaluate the utility of these two guidelines in confirmed adult dengue fatalities.

Methods

We conducted a multi-center retrospective chart review of all confirmed adult dengue deaths in Singapore from 1 January 2004 to 31 December 2008.

Results

Of 28 adult dengue deaths, median age was 59 years. Male gender comprised 67.9% and co-morbidities existed in 75%. From illness onset, patients presented for admission at a median of 4 days and death occurred at a median of 12 days. Intensive care admission was required in 71.4%. Probable dengue was diagnosed in 32.1% by WHO 1997 criteria and 78.6% by WHO 2009. The earliest warning sign was persistent vomiting at a median of 1.5 days. Hematocrit change ≥20% concurrent with platelet count <20 × 10^9/L was associated with the shortest interval to death at a median of 3 days. Only 35.7% of death cases fulfilled DHF criteria by WHO 1997 versus severe dengue in 100.0% by WHO 2009 criteria. Deaths were due to shock and organ failure. Acute renal impairment occurred in 71.4%, impaired consciousness 57.1% and severe hepatitis 53.6%.

Conclusions

In our adult fatal dengue cohort, WHO 2009 criteria had higher sensitivity in diagnosing probable dengue and severe dengue compared with WHO 1997. As warning signs, persistent vomiting occurred early and hematocrit change ≥20% concurrent with platelet count <20 × 10^9/L preceded death most closely.

Objective

Hepatic dysfunction is common in dengue infection and the degree of liver dysfunction in children varies from mild injury with elevation of transaminases to severe injury with jaundice. This study was undertaken to assess the spectrum of hepatic involvement in dengue infection.

Methods

110 children with serologically positive dengue fever aged between 2 months - 14 years were studied for their hepatic functions both clinically and biochemically after excluding malaria, enteric fever, Hepatitis A and Hepatitis B with relevant investigations.

Findings

All cases were grouped into DF (Dengue fever), DHF (Dengue hemorrhagic fever) and DSS (Dengue shock syndrome) according to WHO criteria. The spectrum of hepatic manifestations included hepatomegaly (79%), hepatic tenderness (56%), jaundice (4.5%), raised levels of aspartate transaminase (AST)(93%), alanine transaminase (ALT)(78%), alkaline phosphatase (AP) (57%), prolonged prothrombin time (PT) (20%), reduced levels of serum albumin (66%) and abnormal abdomen ultrasound (65%).

Conclusion

Hepatic dysfunction was observed more in DHF and DSS group compared to DF group. About 17.27% of children had >10 fold increase in the liver enzymes. There was no correlation between the degree of hepatic enlargement or hepatic tenderness with the abnormalities of liver functions. Any child with fever, jaundice and tender hepatomegaly in geographical areas where dengue is endemic, the diagnosis of dengue infection should be strongly considered.

Background

Despite the seriousness of dengue-related disease, with an estimated 50–100 million cases of dengue fever and 250,000–500,000 cases of dengue hemorrhagic fever/dengue shock syndrome each year, a clear understanding of dengue pathogenesis remains elusive. Because of the lack of a disease model in animals and the complex immune interaction in dengue infection, the study of host response and immunopathogenesis is difficult. The development of genomics technology, microarray and high throughput quantitative PCR have allowed researchers to study gene expression changes on a much broader scale. We therefore used this approach to investigate the host response in dengue virus-infected cell lines and in patients developing dengue fever.

Methodology/Principal Findings

Using microarray and high throughput quantitative PCR method to monitor the host response to dengue viral replication in cell line infection models and in dengue patient blood samples, we identified differentially expressed genes along three major pathways; NF-κB initiated immune responses, type I interferon (IFN) and the ubiquitin proteasome pathway. Among the most highly upregulated genes were the chemokines IP-10 and I-TAC, both ligands of the CXCR3 receptor. Increased expression of IP-10 and I-TAC in the peripheral blood of ten patients at the early onset of fever was confirmed by ELISA. A highly upregulated gene in the IFN pathway, viperin, was overexpressed in A549 cells resulting in a significant reduction in viral replication. The upregulation of genes in the ubiquitin-proteasome pathway prompted the testing of proteasome inhibitors MG-132 and ALLN, both of which reduced viral replication.

Conclusion/Significance

Unbiased gene expression analysis has identified new host genes associated with dengue infection, which we have validated in functional studies. We showed that some parts of the host response can be used as potential biomarkers for the disease while others can be used to control dengue viral replication, thus representing viable targets for drug therapy.

Author Summary

Dengue is the most prevalent mosquito-born viral disease affecting humans, yet there is, at present, no drug treatment for the disease nor are there any validated host targets for therapeutic intervention. Using microarray technology to monitor the response of virtually every human gene, we aimed to identify the ways in which humans interact with dengue virus during infection in order to discover new therapeutic targets that could be exploited to control viral replication. From the activated genes, we identified three pathways common to in vitro and in vivo infection; the NF-κB initiated immune pathway, the type I interferon pathway, and the ubiquitin proteasome pathway. We next found that inhibiting the ubiquitin proteasome pathway, or activating the type I interferon pathway, resulted in significant inhibition of viral replication. However, inhibiting the NF-κB initiated immune pathway had no effect on viral replication. We suggest that drugs that target the ubiquitin proteasome pathway may prove effective at killing the dengue virus, and, if used therapeutically, improve clinical outcome in dengue disease.

Dengue fever, a very old disease, has reemerged in the past 20 years with an expanded geographic distribution of both the viruses and the mosquito vectors, increased epidemic activity, the development of hyperendemicity (the cocirculation of multiple serotypes), and the emergence of dengue hemorrhagic fever in new geographic regions. In 1998 this mosquito-borne disease is the most important tropical infectious disease after malaria, with an estimated 100 million cases of dengue fever, 500,000 cases of dengue hemorrhagic fever, and 25,000 deaths annually. The reasons for this resurgence and emergence of dengue hemorrhagic fever in the waning years of the 20th century are complex and not fully understood, but demographic, societal, and public health infrastructure changes in the past 30 years have contributed greatly. This paper reviews the changing epidemiology of dengue and dengue hemorrhagic fever by geographic region, the natural history and transmission cycles, clinical diagnosis of both dengue fever and dengue hemorrhagic fever, serologic and virologic laboratory diagnoses, pathogenesis, surveillance, prevention, and control. A major challenge for public health officials in all tropical areas of the world is to devleop and implement sustainable prevention and control programs that will reverse the trend of emergent dengue hemorrhagic fever.

The severe complications of dengue virus infections, hemorrhagic manifestation and shock, are much more commonly observed during secondary infections caused by a different serotype of dengue virus than that which caused the primary infections. It has been speculated, therefore, that dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) are caused by serotype crossreactive immunopathological mechanisms. We analyzed clones of dengue serotype crossreactive T lymphocytes derived from the PBMC of a donor who had been infected with dengue 3 virus. These PBMC responded best to dengue 3 antigen, but also responded to dengue 1, 2, and 4 antigens, in bulk culture proliferation assays. 12 dengue antigen-specific clones were established using a limiting dilution technique. All of the clones had CD3+ CD4+ CD8 phenotypes. Eight clones responded to dengue 1, 2, 3, and 4 antigens and are crossreactive, while four other clones responded predominantly to dengue 3 antigen. These results indicate that the serotype crossreactive dengue-specific T lymphocyte proliferation observed in bulk cultures reflects the crossreactive responses detected at the clonal level. Serotype crossreactive clones produced high titers of IFN- gamma after stimulation with dengue 3 antigens, and also produced IFN- gamma to lower levels after stimulation with dengue 1, 2, and 4 antigens. The crossreactive clones lysed autologous lymphoblastoid cell line (LCL) pulsed with dengue antigens, and the crossreactivity of CTL lysis by T cell clones was consistent with the crossreactivity observed in proliferation assays. Epidemiological studies have shown that secondary infections with dengue 2 virus cause DHF/DSS at a higher rate than the other serotypes. We hypothesized that the lysis of dengue virus-infected cells by CTL may lead to DHF/DSS; therefore, the clones were examined for cytotoxic activity against dengue 2 virus-infected LCL. All but one of the serotype crossreactive clones lysed dengue 2 virus-infected autologous LCL, and they did not lyse uninfected autologous LCL. The lysis of dengue antigen-pulsed or virus-infected LCL by the crossreactive CTL clones that we have examined is restricted by HLA DP or DQ antigens. These results indicate that primary dengue virus infections induce predominantly crossreactive memory CD4+ T lymphocytes. These crossreactive T lymphocytes proliferate and produce IFN-gamma after stimulation with a virus strain of another serotype, and demonstrate crossreactive cyotoxic activity against autologous cells infected with heterologous dengue viruses.(ABSTRACT TRUNCATED AT 400 WORDS)

Analyses of a prospective case-control study of infant dengue by Daniel Libraty and colleagues casts doubt on the antibody-dependent enhancement model for dengue hemorrhagic fever.

Background

Dengue hemorrhagic fever (DHF) is the severe and life-threatening syndrome that can develop after infection with any one of the four dengue virus (DENV) serotypes. DHF occurs almost exclusively in individuals with secondary heterologous DENV infections and infants with primary DENV infections born to dengue immune mothers. The widely accepted explanation for the pathogenesis of DHF in these settings, particularly during infancy, is antibody-dependent enhancement (ADE) of DENV infection.

Methods and Findings

We conducted a prospective nested case-control study of DENV infections during infancy. Clinical data and blood samples were collected from 4,441 mothers and infants in up to two pre-illness study visits, and surveillance was performed for symptomatic and inapparent DENV infections. Pre-illness plasma samples were used to measure the associations between maternally derived anti-DENV3 antibody-neutralizing and -enhancing capacities at the time of DENV3 infection and development of infant DHF.

The study captured 60 infants with DENV infections across a wide spectrum of disease severity. DENV3 was the predominant serotype among the infants with symptomatic (35/40) and inapparent (15/20) DENV infections, and 59/60 infants had a primary DENV infection. The estimated in vitro anti-DENV3 neutralizing capacity at birth positively correlated with the age of symptomatic primary DENV3 illness in infants. At the time of symptomatic DENV3 infection, essentially all infants had low anti-DENV3 neutralizing activity (50% plaque reduction neutralizing titers [PRNT50] ≤50) and measurable DENV3 ADE activity. The infants who developed DHF did not have significantly higher frequencies or levels of DENV3 ADE activity compared to symptomatic infants without DHF. A higher weight-for-age in the first 3 mo of life and at illness presentation was associated with a greater risk for DHF from a primary DENV infection during infancy.

Conclusions

This prospective nested case-control study of primarily DENV3 infections during infancy has shown that infants exhibit a full range of disease severity after primary DENV infections. The results support an initial in vivo protective role for maternally derived antibody, and suggest that a DENV3 PRNT50 >50 is associated with protection from symptomatic DENV3 illness. We did not find a significant association between DENV3 ADE activity at illness onset and the development of DHF compared with less severe symptomatic illness. The results of this study should encourage rethinking or refinement of the current ADE pathogenesis model for infant DHF and stimulate new directions of research into mechanisms responsible for the development of DHF during infancy.

Trial registration

ClinicalTrials.gov NCT00377754

Please see later in the article for the Editors' Summary

Editors' Summary

Background

Every year, dengue infects 50–100 million people living in tropical and subtropical areas. The four closely related viruses that cause dengue (DENV1–4) are transmitted to people through the bites of female Aedes aegypti mosquitoes, which acquire the viruses by feeding on the blood of an infected person. Many people who become infected with DENV have no symptoms but some develop dengue fever, a severe, flu-like illness that lasts a few days. Other people—about half a million a year—develop a potentially fatal condition called dengue hemorrhagic fever (DHF). In DHF, which can be caused by any of the DENVs, small blood vessels become leaky and friable. This leakiness causes nose and gum bleeds, bruising and, in the worst cases, failure of the circulatory system and death. There is no vaccine to prevent dengue and no specific treatment for dengue fever or DHF. However, with standard medical care—in particular, replacement of lost fluids—most people can survive DHF.

Why Was This Study Done?

DHF is increasingly common, but why do only some people develop DHF after infection with DENV? The widely accepted explanation for the development of DHF is “antibody-dependent enhancement” (ADE) of DENV infection. DHF occurs almost exclusively in two settings; (i) children and adults who become infected with a second DENV serotype after an initial “primary” DENV infection with a different serotype, and (ii) infants with primary DENV infections whose mothers have some DENV immunity. The ADE model suggests that in individuals who develop DHF, although there are some antibodies (proteins made by the immune system to fight infections) against DENV in their blood (in secondary heterologous infections, antibodies left over from the primary infection; in infants with primary infections, antibodies acquired from their mothers before birth), these antibodies cannot “neutralize” the virus. Instead, they bind to it and enhance its uptake by certain immune system cells, thus increasing viral infectivity and triggering an immunological cascade that results in DHF. In this prospective, nested case-control study, the researchers directly test the ADE model for infant DHF. In a prospective study, a group of people is selected and followed to see if they develop a disease; in a nested case-control study, each case is compared with people in the group who do not develop the disease.

What Did the Researchers Do and Find?

The researchers collected clinical data and blood samples from 4,441 mothers and their babies at up to two pre-illness study visits. They then followed the infants for a year to see which of them developed symptomatic and symptom-free DENV infections. Finally, they used the pre-illness blood samples to estimate the maternally derived anti-DENV antibody-neutralizing and -enhancing capacities in the infants at the time of DENV infection. 60 infants were infected with DENV—mainly DENV3—during the study. All but one infection was a primary infection. The infected infants showed a wide range of disease severity. Infants who had a high DENV3 neutralizing capacity at birth tended to develop symptomatic DENV3 infections later than infants who had a low DENV3 neutralizing capacity at birth. All the infants who developed a symptomatic DENV3 infection had a low estimated DENV3 neutralizing activity at the time of infection, and nearly all had measurable levels of DENV3 ADE activity. Infants who developed DHF did not have significantly higher frequencies or levels of DENV3 ADE activity than DENV3-infected infants with less severe symptoms.

What Do These Findings Mean?

These findings indicate that maternally derived anti-DENV3 antibody initially provides protection against dengue infections. That is, babies born to DENV immune mothers are protected against dengue infections by maternally derived antibodies. Over time, the level of these antibodies declines until eventually the infant becomes susceptible to DENV infections. However, the lack of a significant association between the estimated level of DENV3 ADE activity at illness onset and the development of DHF rather than a less severe illness throws doubt onto (but does not completely rule out) the current ADE pathogenesis model for infant DHF, at least for DENV3 infections. The results of this study, the researchers conclude, should encourage rethinking or refinement of the ADE model for infant DHF and should promote further prospective studies into the development of DHF during infancy.

Additional Information

Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1000171.

TropIKA.net provides review articles, news, opinions, research articles, and reports on dengue (in English)

The US Centers for Disease Control and Prevention provide detailed information about dengue fever and dengue hemorrhagic fever (in English and Spanish)

The World Health Organization provides information on dengue fever and dengue hemorrhagic fever around the world (in several languages)

Links to additional resources about dengue are provided by MedlinePlus (in English and Spanish)

Wikipedia has a page on antibody-dependent enhancement of viral infections (note that Wikipedia is a free online encyclopedia that anyone can edit; available in several languages)

Background

Periodic outbreaks of dengue fever occur in the United States Virgin Islands. In June 2005, an outbreak of dengue virus (DENV) serotype-2 with cases of dengue hemorrhagic fever (DHF) was detected in St. Croix, US Virgin Islands. The objective of this report is to describe this outbreak of DENV-2 and the findings of a case-control study examining risk factors for DHF.

Methodology/Principal Findings

This is the largest dengue outbreak ever recorded in St. Croix, with 331 suspected dengue cases reported island-wide during 2005 (62.2 cases/10,000 population); 54% were hospitalized, 21% had at least one hemorrhagic manifestation, 28% had thrombocytopenia, 5% had DHF and 1 patient died. Eighty-nine laboratory-positive hospitalized patients were identified. Of these, there were 15 (17%) who met the WHO criteria for DHF (cases) and 74 (83%) who did not (controls). The only variable significantly associated with DHF on bivariate or multivariable analysis was age, with an adjusted odds ratio (95% confidence interval) of 1.033 (1.003,1.064).

Conclusions/Significance

During this outbreak of DENV-2, a high proportion of cases developed DHF and increasing age was significantly associated with DHF.

Dengue is endemic in Sri Lanka and the physician should be aware of different and unusual presentation of the illness. Rhabdomyolysis is a well-known complication following many viral and bacterial infections; however, only a few cases have been reported with dengue viral infections. Further occurrence of coinfection by dengue and bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) has been underestimated, and few reports have been published so far. This case describes a 17-year-old boy who presented with prolonged severe myalgia, dark red urine, and a febrile illness that was diagnosed as having dengue viral myositis, dark red urine, and a febrile illness that was diagnosed as having dengue viral myositis complicated with rhabdomyolysis and superinfection of MRSA. Despite intensive care management, he died due to multiorgan failure. Autopsy and serological studies confirmed the diagnosis. This case stresses that red-coloured urine in dengue patients is not always due to haematuria, and if a patient's vital signs do not respond to appropriate fluid management in DHF, sepsis from a secondary pathogen including MRSA should be suspected.

Dengue has been recognized as one of the most important vector-borne emerging infectious diseases globally. Though dengue normally causes a self-limiting infection, some patients may develop a life-threatening illness, dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS). The reason why DHF/DSS occurs in certain individuals is unclear. Studies in the endemic regions suggest that the preexisting antibodies are a risk factor for DHF/DSS. Viremia and thrombocytopenia are the key clinical features of dengue virus infection in patients. The amounts of virus circulating in patients are highly correlated with severe dengue disease, DHF/DSS. Also, the disturbance, mainly a transient depression, of hematological cells is a critical clinical finding in acute dengue patients. However, the cells responsible for the dengue viremia are unresolved in spite of the intensive efforts been made. Dengue virus appears to replicate and proliferate in many adapted cell lines, but these in vitro properties are extremely difficult to be reproduced in primary cells or in vivo. This paper summarizes reports on the permissive cells in vitro and in vivo and suggests a hematological cell lineage for dengue virus infection in vivo, with the hope that a new focus will shed light on further understanding of the complexities of dengue disease.

Background

Chikungunya virus (CHIKV) has caused multiple outbreaks in tropical and temperate areas worldwide, but the clinical and biological features of this disease are poorly described, particularly in Africa. We report a prospective study of clinical and biological features during an outbreak that occurred in Franceville, Gabon in 2010.

Methodology/Principal Findings

We collected, in suspect cases (individuals presenting with at least one of the following symptoms or signs: fever, arthralgias, myalgias, headaches, rash, fatigue, nausea, vomiting, diarrhea, bleeding, or jaundice), blood samples, demographic and clinical characteristics and outcome. Hematological and biochemical tests, blood smears for malaria parasites and quantitative PCR for CHIKV then dengue virus were performed. CHIKV+ patients with concomitant malaria and/or dengue were excluded from the study. From May to July 2010, data on 270 laboratory-confirmed CHIK patients were recorded. Fever and arthralgias were reported by respectively 85% and 90% of patients, while myalgias, rash and hemorrhage were noted in 73%, 42% and 2% of patients. The patients were grouped into 4 clinical categories depending on the existence of fever and/or joint pain. On this basis, mixed forms accounted for 78.5% of cases, arthralgic forms 12.6%, febrile forms 6.7% and unusual forms (without fever and arthralgias) 2.2%. No cases of organ failure or death were reported. Elevated liver enzyme and creatinine levels, anemia and lymphocytopenia were the predominant biological abnormalities, and lymphocytopenia was more severe in patients with high viral loads (p = 0.01).

Conclusions/Significance

During CHIK epidemics, some patients may not have classical symptoms. The existence of unusual forms and the absence of severe forms of CHIK call for surveillance to detect any change in pathogenicity.

Author Summary

Chikungunya fever (CHIK) is a disease caused by a virus transmitted to humans by infected mosquitos. The virus is responsible for multiple outbreaks in tropical and temperate areas worldwide, and is now a global concern. Clinical and biological features of the disease are poorly described, especially in Africa, where the disease is neglected because it is considered benign. During a recent CHIK outbreak that occurred in southeast Gabon, we prospectively studied clinical and biological features of 270 virologically confirmed cases. Fever and arthralgias were the predominant symptoms. Furthermore, variable and distinct clinical pictures including pure febrile, pure arthralgic and unusual forms (neither fever nor arthralgias) were detected. No severe forms or deaths were reported. These findings suggest that, during CHIK epidemics, some patients may not have classical symptoms (fever and arthralgias). Local surveillance is needed to detect any changes in the pathogenicity of this virus.

Summary

Dengue virus (DENV) is a mosquito-borne flavivirus that has strained global healthcare systems throughout tropical and subtropical regions of the world. In addition to plaguing developing nations, it has re-emerged in several developed countries with recent outbreaks in the USA (CDC, 2010), Australia (Hanna et al., 2009), Taiwan (Kuan et al., 2010) and France (La Ruche et al., 2010). DENV infection can cause significant disease, including dengue fever, dengue hemorrhagic fever, dengue shock syndrome, and death. There are no approved vaccines or antiviral therapies to prevent or treat dengue-related illnesses. However, the viral NS2B-NS3 protease complex provides a strategic target for antiviral drug development since NS3 protease activity is required for virus replication. Recently, we reported two compounds with inhibitory activity against the DENV protease in vitro and antiviral activity against dengue 2 (DEN2V) in cell culture (Tomlinson et al., 2009a). Analogs of one of the lead compounds were purchased, tested in protease inhibition assays, and the data evaluated with detailed kinetic analyses. A structure activity relationship (SAR) identified key atomic determinants (i.e. functional groups) important for inhibitory activity. Four “second series” analogs were selected and tested to validate our SAR and structural models. Here, we report improvements to inhibitory activity ranging between ~2- and 60-fold, resulting in selective low micromolar dengue protease inhibitors.

Secondary dengue infections are frequently associated with increased risk for dengue hemorrhagic fever and dengue shock syndrome. Surprisingly, we observed no dengue hemorrhagic fever cases among 353 hospitalized dengue-infected patients including 212 with primary, and 141 with secondary dengue 1 infection in China. To explore virological and immunological mechanisms which may account for this unexpected clinical observation, we assessed dengue viremia, type I interferon and inflammatory cytokine levels in these patients. While the levels of viremia and inflammatory cytokines are indistinguishable between primary and secondary infections, IFNα levels are significantly higher in primary than that in secondary infection. However, IFNα levels are positively correlated with dengue viremia levels (p<0.0001), but negatively correlated with the platelet counts (p<0.0001) and serum ALT levels (p = 0.0003). These results provide direct in vivo evidence that clinical dengue disease severity is affected by both viral and human immune factors.