HLA and other gene associations with dengue disease severity

Dengue Disease Severity in Pediatric Patients With Different Blood Groups: A Study at a Tertiary Care Hospital in Jharkhand

BACKGROUND

Dengue fever (DF) is a serious public health concern, especially in tropical regions like India. Cases cluster during the monsoon season due to the proliferation of Aedes mosquitoes, significantly burdening public health and the economy. In addition to prevention and control, identifying risk factors that provide early indications of progression to severe forms of the disease can help in prognostication and improve case management. This study aims to explore the association between ABO blood groups and the severity of dengue disease in pediatric patients admitted to a tertiary care hospital in Jharkhand.

METHODOLOGY

This hospital-based observational cross-sectional study enrolled 88 patients, aged 1 to 18 years, with laboratory-confirmed dengue. Clinical features, hematological parameters, and outcomes, including DF, dengue hemorrhagic fever (DHF), and dengue shock syndrome (DSS), were analyzed across different blood groups.

RESULTS

A higher prevalence of dengue was noted in patients with blood group O (33, 37.5%) compared to other blood groups. While blood group O was associated with higher rates of severe outcomes such as DHF in 12 (46.1%) patients and DSS in 9 (56.2%) patients, statistical analysis did not establish a significant association between ABO blood groups and dengue severity (P = 0.155). Common presenting symptoms included abdominal pain in 61 (69.3%), body ache in 57 (64.8%), and fever in 50 (56.8%) patients, while complications like vascular leakage and thrombocytopenia varied across blood groups.

CONCLUSIONS

While no definitive link between blood group and disease progression was found, the result of higher prevalence of severe disease in blood group O can help us to stay vigilant. Identifying predictive markers for severe dengue can enhance handling of these patients and improve morbidity and mortality in pediatric populations. This study underscores the need for further research into the genetic and immunological factors that influence dengue severity.

Uncovering the Burden of Dengue in Africa: Considerations on Magnitude, Misdiagnosis, and Ancestry

Dengue is a re-emerging neglected disease of major public health importance. This review highlights important considerations for dengue disease in Africa, including epidemiology and underestimation of disease burden in African countries, issues with malaria misdiagnosis and co-infections, and potential evidence of genetic protection from severe dengue disease in populations of African descent. The findings indicate that dengue virus prevalence in African countries and populations may be more widespread than reported data suggests, and that the Aedes mosquito vectors appear to be increasing in dissemination and number. Changes in climate, population, and plastic pollution are expected to worsen the dengue situation in Africa. Dengue misdiagnosis is also a problem in Africa, especially due to the typical non-specific clinical presentation of dengue leading to misdiagnosis as malaria. Finally, research suggests that a protective genetic component against severe dengue exists in African descent populations, but further studies should be conducted to strengthen this association in various populations, taking into consideration socioeconomic factors that may contribute to these findings. The main takeaway is that Africa should not be overlooked when it comes to dengue, and more attention and resources should be devoted to this disease in Africa.

Mobilization and Activation of the Innate Immune Response to Dengue Virus

Dengue virus is an important human pathogen, infecting an estimated 400 million individuals per year and causing symptomatic disease in a subset of approximately 100 million. Much of the effort to date describing the host response to dengue has focused on the adaptive immune response, in part because of the well-established roles of antibody-dependent enhancement and T cell original sin as drivers of severe dengue upon heterotypic secondary infection. However, the innate immune system is a crucial factor in the host response to dengue, as it both governs the fate and vigor of the adaptive immune response, and mediates the acute inflammatory response in tissues. In this review, we discuss the innate inflammatory response to dengue infection, focusing on the role of evolutionarily conserved innate immune cells, their effector functions, and clinical course.

Major Histocompatibility Complex Class I Chain-Related A and B (MICA and MICB) Gene, Allele, and Haplotype Associations With Dengue Infections in Ethnic Thais

BACKGROUND

Major histocompatibility complex class I chain-related (MIC) A and B (MICA and MICB) are polymorphic stress molecules recognized by natural killer cells. This study was performed to analyze MIC gene profiles in hospitalized Thai children with acute dengue illness.

METHODS

MIC allele profiles were determined in a discovery cohort of patients with dengue fever or dengue hemorrhagic fever (DHF) (n = 166) and controls (n = 149). A replication cohort of patients with dengue (n = 222) was used to confirm specific MICB associations with disease.

RESULTS

MICA*045 and MICB*004 associated with susceptibility to DHF in secondary dengue virus (DENV) infections (odds ratio [OR], 3.22; [95% confidence interval (CI), 1.18-8.84] and 1.99 [1.07-2.13], respectively), and MICB*002 with protection from DHF in secondary DENV infections (OR, 0.41; 95% CI, .21-.68). The protective effect of MICB*002 against secondary DHF was confirmed in the replication cohort (OR, 0.43; 95% CI, .22-.82) and was stronger when MICB*002 is present in individuals also carrying HLA-B*18, B*40, and B*44 alleles which form the B44 supertype of functionally related alleles (0.29, 95% CI, .14-.60).

CONCLUSIONS

Given that MICB*002 is a low expresser of soluble proteins, these data indicate that surface expression of MICB*002 with B44 supertype alleles on DENV-infected cells confer a protective advantage in controlling DENV infection using natural killer cells.

Next-generation sequencing of 11 HLA loci in a large dengue vaccine cohort from the Philippines

HLA genotyping by next-generation sequencing (NGS) has evolved with significant advancements in the last decade. Here we describe full-length HLA genotyping of 11 loci in 612 individuals comprising a dengue vaccine cohort from Cebu province in the Philippines. The multi-locus individual tagging NGS (MIT-NGS) method that we developed initially for genotyping 4-6 loci in one MiSeq run was expanded to 11 loci including HLA-A, B, C, DPA1, DPB1, DQA1, DQB1, DRB1, and DRB3/4/5. This change did not affect the overall coverage or depth of the sequencing reads. HLA alleles with frequencies greater than 10% were A*11:01:01, A*24:02:01, A*24:07:01, A*34:01:01, B*38:02:01, B*15:35, B*35:05:01, C*07:02:01, C*04:01:01, DPA1*02:02:02, DPB1*05:01:01, DPB1*01:01:01, DQA1*01:02:01, DQA1*06:01:01, DQB1*05:02:01, DQB1*03:01:01, DRB1*15:02:01, DRB1*12:02:01, DRB3*03:01:03, DRB4*01:03:01, and DRB5*01:01:01. Improvements in sequencing library preparation provide uniform and even coverage across all exons and introns. This has led to a marked reduction in allele imbalance and dropout. Furthermore, including more loci, such as DRB3/4/5, decreases cross-mapping and incorrect allele assignment at the DRB1 locus. The increased number of loci sequenced for each sample does not reduce the number of samples that can be multiplexed on a single MiSeq run and is therefore more cost-efficient. We believe that such improvements will help HLA genotyping by NGS to gain momentum over other conventional methods by increasing confidence in the calls.

Genetic risk for dengue hemorrhagic fever and dengue fever in multiple ancestries

Background

Genetic risk factors for dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) and dengue fever (DF) are limited, in particular there are sparse data on genetic risk across diverse populations.

Methods

We conducted a genome-wide association study (GWAS) in a derivation and validation sample of 7, 460 participants of Latin American, South Asian, and South East Asian ancestries. We then developed a weighted polygenic risk score (PRS) for each participant in each of the validation cohorts of the three ancestries to predict the risk of DHF/DSS compared to DF, DHF/DSS compared to controls, and, DF compared to controls.

Findings

The risk of DHF/DSS was significantly increased, odds ratio [OR] 1.84 (95%CI 1.47 to 2.31) (195 SNPs), compared to DF, fourth PRS quartile versus first quartile, in the validation cohort. The risk of DHF/DSS compared to controls was increased (OR=3.94; 95% CI 2.84 to 5.45) (278 SNPs), as was the risk of DF compared to controls (OR=1.97; 95%CI 1.63 to 2.39) (251 SNPs). Risk increased in a dose-dependent manner with increase in quartiles of PRS across comparisons. Significant associations persisted for PRS built within ancestries and applied to the same or different ancestries as well as for PRS built for one outcome (DHF/DSS or DF) and applied to the other.

Interpretation

There is a strong genetic effect that predisposes to risk of DHF/DSS and DF. The genetic risk for DHF/DSS is higher than that for DF when compared to controls, and this effect persists across multiple ancestries.

Elimination of Falciparum Malaria and Emergence of Severe Dengue: An Independent or Interdependent Phenomenon?

The global malaria burden, including falciparum malaria, has been reduced by 50% since 2000, though less so in Sub-Saharan Africa. Regional malaria elimination campaigns beginning in the 1940s, up-scaled in the 1950s, succeeded in the 1970s in eliminating malaria from Europe, North America, the Caribbean (except Haiti), and parts of Asia and South- and Central America. Dengue has grown dramatically throughout the pantropical regions since the 1950s, first in Southeast Asia in the form of large-scale epidemics including severe dengue, though mostly sparing Sub-Saharan Africa. Globally, the WHO estimates 50 million dengue infections every year, while others estimate almost 400 million infections, including 100 million clinical cases. Curiously, despite wide geographic overlap between malaria and dengue-endemic areas, published reports of co-infections have been scarce until recently. Superimposed acute dengue infection might be expected to result in more severe combined disease because both pathogens can induce shock and hemorrhage. However, a recent review found no reports on more severe morbidity or higher mortality associated with co-infections. Cases of severe dual infections have almost exclusively been reported from South America, and predominantly in persons infected by Plasmodium vivax. We hypothesize that malaria infection may partially protect against dengue – in particular falciparum malaria against severe dengue – and that this inter-species cross-protection may explain the near absence of severe dengue from the Sub-Saharan region and parts of South Asia until recently. We speculate that malaria infection elicits cross-reactive antibodies or other immune responses that infer cross-protection, or at least partial cross-protection, against symptomatic and severe dengue. Plasmodia have been shown to give rise to polyclonal B-cell activation and to heterophilic antibodies, while some anti-dengue IgM tests have high degree of cross-reactivity with sera from malaria patients. In the following, the historical evolution of falciparum malaria and dengue is briefly reviewed, and we explore early evidence of subclinical dengue in high-transmission malaria areas as well as conflicting reports on severity of co-morbidity. We also discuss examples of other interspecies interactions.

Genome-Wide Analysis to Identify HLA Factors Potentially Associated With Severe Dengue

The pathogenesis of dengue hemorrhagic fever (DHF), following dengue virus (DENV) infection, is a complex and poorly understood phenomenon. In view of the clinical need of identifying patients with higher likelihood of developing this severe outcome, we undertook a comparative genome-wide association analysis of epitope variants from sequences available in the ViPR database that have been reported to be differentially related to dengue fever and DHF. Having enumerated the incriminated epitope variants, we determined the corresponding HLA alleles in the context of which DENV infection could potentially precipitate DHF. Our analysis considered the development of DHF in three different perspectives: (a) as a consequence of primary DENV infection, (b) following secondary DENV infection with a heterologous serotype, (c) as a result of DENV infection following infection with related flaviviruses like Zika virus, Japanese Encephalitis virus, West Nile virus, etc. Subject to experimental validation, these viral and host markers would be valuable in triaging DENV-infected patients for closer supervision owing to the relatively higher risk of poor prognostic outcome and also for the judicious allocation of scarce institutional resources during large outbreaks.

Hyperendemic dengue transmission and identification of a locally evolved DENV-3 lineage, Papua New Guinea 2007-2010

Background

Dengue is endemic in the Western Pacific and Oceania and the region reports more than 200,000 cases annually. Outbreaks of dengue and severe dengue occur regularly and movement of virus throughout the region has been reported. Disease surveillance systems, however, in many areas are not fully established and dengue incidence is underreported. Dengue epidemiology is likely least understood in Papua New Guinea (PNG), where the prototype DENV-2 strain New Guinea C was first isolated by Sabin in 1944 but where routine surveillance is not undertaken and little incidence and prevalence data is available.

Methodology/Principal findings

Serum samples from individuals with recent acute febrile illness or with non-febrile conditions collected between 2007–2010 were tested for anti-DENV neutralizing antibody. Responses were predominantly multitypic and seroprevalence increased with age, a pattern indicative of endemic dengue. DENV-1, DENV-2 and DENV-3 genomes were detected by RT-PCR within a nine-month period and in several instances, two serotypes were identified in individuals sampled within a period of 10 days. Phylogenetic analysis of whole genome sequences identified a DENV-3 Genotype 1 lineage which had evolved on the northern coast of PNG which was likely exported to the western Pacific five years later, in addition to a DENV-2 Cosmopolitan Genotype lineage which had previously circulated in the region.

Conclusions/Significance

We show that dengue is hyperendemic in PNG and identify an endemic, locally evolved lineage of DENV-3 that was associated with an outbreak of severe dengue in Pacific countries in subsequent years, although severe disease was not identified in PNG. Additional studies need to be undertaken to understand dengue epidemiology and burden of disease in PNG.

Dengue virus (DENV) was first identified in Papua New Guinea (PNG) in 1944. Dengue is currently assumed to be an endemic disease in PNG although there is little incidence or prevalence data, and the evidence consensus for dengue presence is low. Routine surveillance is not undertaken and dengue is not a notifiable disease. Severe dengue is rarely identified by local clinicians and the reasons for this are unclear but may be related to poor recognition of dengue and a low index of suspicion, despite high incidence and prevalence rates in neighbouring countries. For example, Indonesia shares borders with PNG and regularly reports outbreaks of severe dengue and transmission of multiple DENV serotypes. DENV infection is identified in travellers from PNG however there are no data on locally circulating strains and how they may compare to viruses associated with severe dengue epidemics in other countries in the Asia Pacific region. We identified evidence for previous infection with all four DENV serotypes among people living on the northern coast of PNG, in Madang, and on Lihir Island in the Bismarck Archipelago off the northeastern coast. We also detected DENV-1, DENV-2, and DENV-3 virus in febrile patients, and we describe the first whole genome sequences of endemically circulating DENV since the prototype 1944 DENV-2_{New Guinea C} strain was characterized. Of note, severe dengue was not diagnosed in any patient infected with these viruses in PNG although introduction of the PNG DENV-3 strain into the Solomon Islands five years later resulted in a large outbreak of severe dengue with hospitalizations and deaths in that country. Dengue epidemiology and burden of disease should be investigated in PNG.

The reintroduction of DENV-2 in 2011 in Panama and subsequent outbreak characteristic

The circulation of the South-east Asian/American (AS/AM) dengue 2 virus (DENV-2) genotype in the Americas has been associated with a high rate of severe disease. From 1993, the year DENV was reintroduced in Panama, until 2011 there were 29 dengue-associated deaths, 17 of which occurred in 2011, the most severe outbreak with a case fatality rate (CFR) of 44% (17 deaths out of 38 severe dengue cases). During this outbreak DENV-2 was reintroduced into the country, whereas over the prior five years DENV-1 and -3 were predominant. Herein, we describe the 2011 Panama outbreak and genetically characterize the Panamanian DENV-2 strains, which were associated with severe dengue disease in Panama. Our results suggest that the DENV-2 isolates from this outbreak belonged to the AS/AM genotype sub-clade 2BI and were genetically close to viruses described in the outbreaks in Nicaragua, Honduras, Guatemala and Mexico from 2006-2011. Sub-clade 2BI has previously been associated with severe disease in Nicaragua during outbreaks from 2005-2007.

Dengue Hemorrhagic Fever: A State-of-the-Art Review Focused in Pulmonary Involvement

Dengue fever is an arboviral disease transmitted to humans through the bites of infected female Aedes mosquitoes. Dengue virus is a member of the Flaviviridae family, and human infection can be caused by any of the four antigenically distinct serotypes (DENV 1–4). The infection has become recognized as the most important and prevalent arboviral disease in humans, endemic in almost 100 countries worldwide. Nearly 3 billion people live in areas with transmission risk. Autochthonous transmission of the virus in previously disease-free areas, increased incidence in endemic areas, and epidemic resurgence in controlled regions could increase the risk of contracting more severe forms of the disease, such as dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS). Symptomatic dengue virus infection can present with a wide range of clinical manifestations, from mild fever to life-threatening DSS. Thoracic complications may manifest as pleural effusion, pneumonitis, non-cardiogenic pulmonary edema, and hemorrhage/hemoptysis. No vaccine is currently available and no specific treatment for dengue fever exists, but prevention and prompt management of complications in patients with DHF can help reduce mortality. This review describes the main clinical, pathological, and imaging findings of thoracic involvement in DHF.

Blood type biochemistry and human disease

Associations between blood type and disease have been studied since the early 1900s when researchers determined that antibodies and antigens are inherited. In the 1950s, the chemical identification of the carbohydrate structure of surface antigens led to the understanding of biosynthetic pathways. The blood type is defined by oligosaccharide structures, which are specific to the antigens, thus, blood group antigens are secondary gene products, while the primary gene products are various glycosyltransferase enzymes that attach the sugar molecules to the oligosaccharide chain. Blood group antigens are found on red blood cells, platelets, leukocytes, plasma proteins, certain tissues, and various cell surface enzymes, and also exist in soluble form in body secretions such as breast milk, seminal fluid, saliva, sweat, gastric secretions, urine, and amniotic fluid. Recent advances in technology, biochemistry, and genetics have clarified the functional classifications of human blood group antigens, the structure of the A, B, H, and Lewis determinants and the enzymes that produce them, and the association of blood group antigens with disease risks. Further research to identify differences in the biochemical composition of blood group antigens, and the relationship to risks for disease, can be important for the identification of targets for the development of nutritional intervention strategies, or the identification of druggable targets. WIREs Syst Biol Med 2016, 8:517-535. doi: 10.1002/wsbm.1355 For further resources related to this article, please visit the WIREs website.

A community-based prospective cohort study of dengue viral infection in Malaysia: the study protocol

Background

Globally, dengue infections constitute a significant public health burden. In recent decades, Malaysia has become a dengue hyper-endemic country with the co-circulation of the four dengue virus serotypes. The cyclical dominance of sub-types contributes to a pattern of major outbreaks. The consequences can be observed in the rising incidence of reported dengue cases and dengue related deaths. Understanding the complex interaction of the dengue virus, its human hosts and the mosquito vectors at the community level may help develop strategies for addressing the problem.

Methods

A prospective cohort study will be conducted in Segamat district of Johor State in Peninsular Malaysia. Researchers received approval from the Malaysian Medical Research Ethics Committee and Monash University Human Research Ethics Committee. The study will be conducted at a Malaysian based health and demographic surveillance site over a 1 year period in three different settings (urban, semi-urban and rural). The study will recruit healthy adults (male and female) aged 18 years and over, from three ethnic groups (Malay, Chinese and Indian). The sample size calculated using the Fleiss method with continuity correction is 333. Sero-surveillance of participants will be undertaken to identify asymptomatic, otherwise healthy cases; cases with dengue fever who are managed as out-patients; and cases with dengue fever admitted to a hospital. A genetic analysis of the participants will be undertaken to determine whether there is a relationship between genetic predisposition and disease severity. A detailed medical history, past history of dengue infection, vaccination history against other flaviviruses such as Japanese encephalitis and Yellow fever, and the family history of dengue infection will also be collected. In addition, a mosquito surveillance will be carried out simultaneously in recruitment areas to determine the molecular taxonomy of circulating vectors.

Discussion

The research findings will estimate the burden of asymptomatic and symptomatic dengue at the community level. It will also examine the relationship between virus serotypes and host genotypes, and the association of the clinical manifestation of the early phase with the entire course of illness.

Electronic supplementary material

The online version of this article (doi:10.1186/s40249-016-0172-3) contains supplementary material, which is available to authorized users.

Leukocyte Ig-Like Receptors - A Model for MHC Class I Disease Associations

MHC class I (MHC-I) polymorphisms are associated with the outcome of some viral infections and autoimmune diseases. MHC-I proteins present antigenic peptides and are recognized by receptors on natural killer cells and cytotoxic T lymphocytes, thus enabling the immune system to detect self-antigens and eliminate targets lacking self or expressing foreign antigens. Recognition of MHC-I, however, extends beyond receptors on cytotoxic leukocytes. Members of the leukocyte Ig-like receptor (LILR) family are expressed on monocytic cells and can recognize both classical and non-classical MHC-I alleles. Despite their relatively broad specificity when compared to the T cell receptor or killer Ig-like receptors, variations in the strength of LILR binding between different MHC-I alleles have recently been shown to correlate with control of HIV infection. We suggest that LILR recognition may mediate MHC-I disease association in a manner that does not depend on a binary discrimination of self/non-self by cytotoxic cells. Instead, the effects of LILR activity following engagement by MHC-I may represent a “degrees of self” model, whereby strength of binding to different alleles determines the degree of influence exerted by these receptors on immune cell functions. LILRs are expressed by myelomonocytic cells and lymphocytes, extending their influence across antigen-presenting cell subsets including dendritic cells, macrophages, and B cells. They have been identified as important players in the response to infection, inflammatory diseases, and cancer, with recent literature to indicate that MHC-I recognition by these receptors and consequent allelic effects could extend an influence beyond the immune system.

Association of genetic polymorphisms of IL1β -511 C>T, IL1RN VNTR 86 bp, IL6 -174 G>C, IL10 -819 C>T and TNFα -308 G>A, involved in symptomatic patients with dengue in Brazil

OBJECTIVE

In this study, single nucleotide polymorphisms (SNP) of interleukin (IL) 1β -511C>T, IL1RN VNTR 86 bp, IL6 -174G>C, IL10 -819C>T and TNFα -308G>A were analyzed by PCR-RFLP with symptoms of dengue with the clinical features.

SUBJECTS

196 individuals admitted to the São José Infectious Diseases Hospital with suspected dengue infection. Dengue was confirmed in 111 of the patients. The control group consisted of 85 other individuals confirmed without dengue.

RESULTS

It was demonstrated that the presence the T allele of IL1β (P < 0.05) was associated with susceptibility to developing the disease. Other results also suggested that the polymorphism in the combinations IL6 × IL1β (C and T alleles, respectively), IL1β (T allele) × IL1RN (*2/*2 genotype), IL6 (C allele) × TNFα (A allele), IL10 (C/T genotype) × TNFα (A/A genotype) (P < 0.01, P = 0.01, P < 0.05 and P = 0.03, respectively) were associated with predisposition to developing the disease and its symptoms.

CONCLUSIONS

In summary, the findings of this study in a Brazilian population point out the importance of studies of combinations of polymorphisms in the development of dengue, which can increase the risk of dengue infection and its severity.

Interaction of a dengue virus NS1-derived peptide with the inhibitory receptor KIR3DL1 on natural killer cells

Killer immunoglobulin-like receptors (KIRs) interact with human leucocyte antigen (HLA) class I ligands and play a key role in the regulation and activation of NK cells. The functional importance of KIR-HLA interactions has been demonstrated for a number of chronic viral infections, but to date only a few studies have been performed in the context of acute self-limited viral infections. During our investigation of CD8(+) T cell responses to a conserved HLA-B57-restricted epitope derived from dengue virus (DENV) non-structural protein-1 (NS1), we observed substantial binding of the tetrameric complex to non-T/non-B lymphocytes in peripheral blood mononuclear cells (PBMC) from a long-standing clinical cohort in Thailand. We confirmed binding of the NS1 tetramer to CD56(dim) NK cells, which are known to express KIRs. Using depletion studies and KIR-transfected cell lines, we demonstrated further that the NS1 tetramer bound the inhibitory receptor KIR3DL1. Phenotypical analysis of PBMC from HLA-B57(+) subjects with acute DENV infection revealed marked activation of NS1 tetramer-binding natural killer (NK) cells around the time of defervescence in subjects with severe dengue disease. Collectively, our findings indicate that subsets of NK cells are activated relatively late in the course of acute DENV illness and reveal a possible role for specific KIR-HLA interactions in the modulation of disease outcomes.

Recent advances in understanding dengue

Dengue is an emerging threat to billions of people worldwide. In the last 20 years, the incidence has increased four-fold and this trend appears to be continuing. Caused by one of four viral serotypes, dengue can present as a wide range of clinical phenotypes with the severe end of the spectrum being defined by a syndrome of capillary leak, coagulopathy, and organ impairment. The pathogenesis of severe disease is thought to be in part immune mediated, but the exact mechanisms remain to be defined. The current treatment of dengue relies on supportive measures with no licensed therapeutics available to date. There have been recent advances in our understanding of a number of areas of dengue research, of which the following will be discussed in this review: the drivers behind the global dengue pandemic, viral structure and epitope binding, risk factors for severe disease and its pathogenesis, as well as the findings of recent clinical trials including therapeutics and vaccines. We conclude with current and future dengue control measures and key areas for future research.

Dengue vaccine: hypotheses to understand CYD-TDV-induced protection

Dengue virus (DENV) is a human pathogen with a large impact on public health. Although no vaccine against DENV is currently licensed, a recombinant vaccine - chimeric yellow fever virus-DENV tetravalent dengue vaccine (CYD-TDV) - has shown efficacy against symptomatic dengue disease in two recent Phase III clinical trials. Safety observations were also recently reported for these trials. In this Opinion article, we review the data from recent vaccine clinical trials and discuss the putative mechanisms behind the observed efficacy of the vaccine against different forms of the disease, focusing on the interactions between the infecting virus, pre-existing host immunity and vaccine-induced immune responses.

Immune correlates for dengue vaccine development

Dengue virus is the leading cause of vector-borne viral disease with four serotypes in circulation. Vaccine development has been complicated by the potential for both protection and disease enhancement during heterologous infection. Secondary infection triggers cross-reactive immune memory responses that have varying functional and epitope specificities that determine protection or risk. Strongly neutralizing antibodies to quaternary epitopes may be especially important for virus neutralization. Cell-mediated immunity dominated by Th1 functions may also play an important role. Determining an immune correlate of protection or risk would be highly beneficial for vaccine development but is hampered by mechanistic uncertainties and assay limitations. Clinical efficacy trials and human infection models along with a systems approach may provide future opportunities to elucidate such correlates.

Ancestry, admixture and fitness in Colombian genomes

The human dimension of the Columbian Exchange entailed substantial genetic admixture between ancestral source populations from Africa, the Americas and Europe, which had evolved separately for many thousands of years. We sought to address the implications of the creation of admixed American genomes, containing novel allelic combinations, for human health and fitness via analysis of an admixed Colombian population from Medellin. Colombian genomes from Medellin show a wide range of three-way admixture contributions from ancestral source populations. The primary ancestry component for the population is European (average = 74.6%, range = 45.0%–96.7%), followed by Native American (average = 18.1%, range = 2.1%–33.3%) and African (average = 7.3%, range = 0.2%–38.6%). Locus-specific patterns of ancestry were evaluated to search for genomic regions that are enriched across the population for particular ancestry contributions. Adaptive and innate immune system related genes and pathways are particularly over-represented among ancestry-enriched segments, including genes (HLA-B and MAPK10) that are involved in defense against endemic pathogens such as malaria. Genes that encode functions related to skin pigmentation (SCL4A5) and cutaneous glands (EDAR) are also found in regions with anomalous ancestry patterns. These results suggest the possibility that ancestry-specific loci were differentially retained in the modern admixed Colombian population based on their utility in the New World environment.

HLA Class I Supertype Associations With Clinical Outcome of Secondary Dengue Virus Infections in Ethnic Thais

BACKGROUND

Human leukocyte antigen (HLA) supertypes are groups of functionally related alleles that present structurally similar antigens to the immune system.

OBJECTIVES

To analyze HLA class I supertype associations with clinical outcome in hospitalized Thai children with acute dengue illness.

METHODS

Seven hundred sixty-two patients and population-matched controls recruited predominantly in Bangkok were HLA-A and -B typed. HLA supertype frequencies were compared and tested for significant dengue disease associations using logistic regression analyses. Multivariable models were built by conducting forward stepwise selection procedures.

RESULTS

In the final logistic regression model, the HLA-B44 supertype was protective against dengue hemorrhagic fever (DHF) in secondary infections (odds ratio [OR] = 0.46, 95% confidence interval [CI], .30-.72), while the HLA-A02 supertype (OR = 1.92, 95% CI, 1.30-2.83) and the HLA-A01/03 supertype (OR = 3.01, 95% CI, 1.01-8.92) were associated with susceptibility to secondary dengue fever. The B07 supertype was associated with susceptibility to secondary DHF in the univariate analysis (OR = 1.60, 95% CI, 1.05-2.46), whereas that was not retained in the final model.

CONCLUSIONS

As the HLA-B44 supertype is predicted to target conserved epitopes in dengue, our results suggest that B44 supertype-restricted immune responses to highly conserved regions of the dengue proteome may protect against secondary DHF.

HLA-A*33:01 as protective allele for severe dengue in a population of Filipino children

Dengue virus infection is a leading cause of morbidity among children in the Philippines in recent years. In order to investigate the association of HLA Class I and II alleles and dengue disease severity in a cohort of Filipino children, we performed a case control study in 2 hospitals in Metro Manila from June 2008 to December 2009. A total of 250 laboratory confirmed dengue patients and 300 healthy individuals aged 5 to 15 years old were typed for HLA-A, B and DRB1 alleles. The frequency of HLA-A*33:01 was significantly decreased in severe dengue (DHF/ DSS; Pc = 0.0016)) and DSS (Pc = 0.0032) compared to the background population. These findings support a previous study that this allele may confer protection against the severe form of dengue and provide the first evidence of HLA association with dengue in the Philippines. Future studies should be directed in investigating the possible mechanisms of protection.

Elucidating the role of T cells in protection against and pathogenesis of dengue virus infections

Dengue viruses (DENV) cause significantly more human disease than any other arbovirus, with hundreds of thousands of cases leading to severe disease in thousands annually. Antibodies and T cells induced by primary infection with DENV have the potential for both positive (protective) and negative (pathological) effects during subsequent DENV infections. In this review, we summarize studies that have examined T-cell responses in humans following natural infection and vaccination. We discuss studies that support a role for T cells in protection against and those that support a role for the involvement of T cells in the pathogenesis of severe disease. The mechanisms that lead to severe disease are complex, and T-cell responses are an important component that needs to be further evaluated for the development of safe and efficacious DENV vaccines.

Molecular classification of outcomes from dengue virus -3 infections

OBJECTIVES

Dengue virus (DENV) infection is a significant risk to over a third of the human population that causes a wide spectrum of illness, ranging from sub-clinical disease to intermediate syndrome of vascular complications called dengue fever complicated (DFC) and severe, dengue hemorrhagic fever (DHF). Methods for discriminating outcomes will impact clinical trials and understanding disease pathophysiology.

STUDY DESIGN

We integrated a proteomics discovery pipeline with a heuristics approach to develop a molecular classifier to identify an intermediate phenotype of DENV-3 infectious outcome.

RESULTS

121 differentially expressed proteins were identified in plasma from DHF vs dengue fever (DF), and informative candidates were selected using nonparametric statistics. These were combined with markers that measure complement activation, acute phase response, cellular leak, granulocyte differentiation and viral load. From this, we applied quantitative proteomics to select a 15 member panel of proteins that accurately predicted DF, DHF, and DFC using a random forest classifier. The classifier primarily relied on acute phase (A2M), complement (CFD), platelet counts and cellular leak (TPM4) to produce an 86% accuracy of prediction with an area under the receiver operating curve of >0.9 for DHF and DFC vs DF.

CONCLUSIONS

Integrating discovery and heuristic approaches to sample distinct pathophysiological processes is a powerful approach in infectious disease. Early detection of intermediate outcomes of DENV-3 will speed clinical trials evaluating vaccines or drug interventions.

DHIM supporting immunologic investigations and the identification of immune correlates of protection

Evidence suggesting that immune responses to dengue virus (DENV) have the potential for both beneficial and detrimental effects on the outcome of infection is a concern for dengue vaccine development. There is thus a great need to define measures of DENV-specific immune responses that reliably indicate when immunity is protective. The existence of 4 main DENV serotypes and the difficulty in defining which individuals have been exposed and to which viruses present challenges to defining immune correlates of protective immunity against DENV in field efficacy studies; experimental infection studies in humans offer a pathway to address these challenges.

Corticosteroids in the treatment of dengue shock syndrome

Dengue infection causes significant morbidity and mortality in over 100 countries worldwide, and its incidence is on the rise. The pathophysiological basis for the development of severe dengue, characterized by plasma leakage and the “shock syndrome” are poorly understood. No specific treatment or vaccine is available, and careful monitoring and judicious administration of fluids forms the mainstay of management at present. It is postulated that vascular endothelial dysfunction, induced by cytokine and chemical mediators, is an important mechanism of plasma leakage. Although corticosteroids are potent modulators of the immune system, their role in pharmacological doses in modulating the purported immunological effects that take place in severe dengue has been a subject of controversy. The key evidence related to the role of corticosteroids for various manifestations of dengue are reviewed here. In summary, there is currently no high-quality evidence supporting the beneficial effects of corticosteroids for treatment of shock, prevention of serious complications, or increasing platelet counts. Non-randomized trials of corticosteroids given as rescue medication for severe shock have shown possible benefit. Nonetheless, the evidence base is small, and good-quality trials are lacking. We reiterate the need for well-designed and adequately powered randomized controlled trials of corticosteroids for the treatment of dengue shock.

Clinical and immunological markers of dengue progression in a study cohort from a hyperendemic area in Malaysia

Background

With its elusive pathogenesis, dengue imposes serious healthcare, economic and social burden on endemic countries. This study describes the clinical and immunological parameters of a dengue cohort in a Malaysian city, the first according to the WHO 2009 dengue classification.

Methodology and Findings

This longitudinal descriptive study was conducted in two Malaysian hospitals where patients aged 14 and above with clinical symptoms suggestive of dengue were recruited with informed consent. Among the 504 participants, 9.3% were classified as non-dengue, 12.7% without warning signs, 77.0% with warning signs and 1.0% with severe dengue based on clinical diagnosis. Of these, 37% were misdiagnosed as non-dengue, highlighting the importance of both clinical diagnosis and laboratory findings. Thrombocytopenia, prolonged clotting time, liver enzymes, ALT and AST served as good markers for dengue progression but could not distinguish between patients with and without warning signs. HLA-A*24 and -B*57 were positively associated with Chinese and Indians patients with warning signs, respectively, whereas A*03 may be protective in the Malays. HLA-A*33 was also positively associated in patients with warning signs when compared to those without. Dengue NS1, NS2A, NS4A and NS4B were found to be important T cell epitopes; however with no apparent difference between with and without warning signs patients. Distinction between the 2 groups of patients was also not observed in any of the cytokines analyzed; nevertheless, 12 were significantly differentially expressed at the different phases of illness.

Conclusion

The new dengue classification system has allowed more specific detection of dengue patients, however, none of the clinical parameters allowed distinction of patients with and without warning signs. While the HLA-A*33 may be predictive marker for development of warning signs; larger studies will be needed to support this findings.

Vascular events in viral hemorrhagic fevers: a comparative study of dengue and hantaviruses

Viral hemorrhagic diseases are a group of systemic viral infections with worldwide distribution and are significant causes of global mortality and morbidity. The hallmarks of viral hemorrhagic fevers are plasma leakage, thrombocytopenia, coagulopathy and hemorrhagic manifestations. The molecular mechanisms leading to plasma leakage in viral hemorrhagic fevers are not well understood. A common theme has emerged in which a complex interplay between pathogens, host immune response, and endothelial cells leads to the activation of endothelial cells and perturbation of barrier integrity. In this article, two clinically distinct viral hemorrhagic fevers caused by dengue viruses and hantaviruses are discussed to highlight their similarities and differences that may provide insights into the pathogenesis and therapeutic approach.

T-cell immunity to infection with dengue virus in humans

Dengue virus (DENV) is the etiologic agent of dengue fever, the most significant mosquito-borne viral disease in humans. Up to 400 million DENV infections occur every year, and severity can range from asymptomatic to an acute self-limiting febrile illness. In a small proportion of patients, the disease can exacerbate and progress to dengue hemorrhagic fever and/or dengue shock syndrome, characterized by severe vascular leakage, thrombocytopenia, and hemorrhagic manifestations. A unique challenge in vaccine development against DENV is the high degree of sequence variation, characteristically associated with RNA viruses. This is of particular relevance in the case of DENV since infection with one DENV serotype (primary infection) presumably affords life-long serotype-specific immunity but only partial and temporary immunity to other serotypes in secondary infection settings. The role of T cells in DENV infection and subsequent disease manifestations is not fully understood. According to the original antigenic sin theory, skewing of T-cell responses induced by primary infection with one serotype causes less effective response upon secondary infection with a different serotype, predisposing to severe disease. Our recent study has suggested an HLA-linked protective role for T cells. Herein, we will discuss the role of T cells in protection and pathogenesis from severe disease as well as the implications for vaccine design.

Distinct activation phenotype of a highly conserved novel HLA-B57-restricted epitope during dengue virus infection

Variation in the sequence of T-cell epitopes between dengue virus (DENV) serotypes is believed to alter memory T-cell responses during second heterologous infections. We identified a highly conserved, novel, HLA-B57-restricted epitope on the DENV NS1 protein. We predicted higher frequencies of B57-NS1(26-34) -specific CD8(+) T cells in peripheral blood mononuclear cells from individuals undergoing secondary rather than primary DENV infection. However, high tetramer-positive T-cell frequencies during acute infection were seen in only one of nine subjects with secondary infection. B57-NS1(26-34) -specific and other DENV epitope-specific CD8(+) T cells, as well as total CD8(+) T cells, expressed an activated phenotype (CD69(+) and/or CD38(+)) during acute infection. In contrast, expression of CD71 was largely limited to DENV epitope-specific CD8(+) T cells. In vitro stimulation of cell lines indicated that CD71 expression was differentially sensitive to stimulation by homologous and heterologous variant peptides. CD71 may represent a useful marker of antigen-specific T-cell activation.

Immunopathogenesis Versus Protection in Dengue Virus Infections

Dengue viruses (DENV) are mosquito-borne viruses that cause significant morbidity. The existence of four serotypes of DENV with partial immunologic cross-reactivity creates the opportunity for individuals to experience multiple acute DENV infections over the course of their lifetimes. Research over the past several years has revealed complex interactions between DENV and the human innate and adaptive immune systems that can have either beneficial or detrimental influences on the outcome of infection. Further studies that seek to distinguish protective from pathological immune responses in the context of natural DENV infection as well as clinical trials of candidate DENV vaccines have an important place in efforts to control the global impact of this re-emerging viral disease.

Can non-human primates serve as models for investigating dengue disease pathogenesis?

Dengue Virus (DV) infects between 50 and 100 million people globally, with public health costs totaling in the billions. It is the causative agent of dengue fever (DF) and dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS), vector-borne diseases that initially predominated in the tropics. Due to the expansion of its mosquito vector, Aedes spp., DV is increasingly becoming a global problem. Infected individuals may present with a wide spectrum of symptoms, spanning from a mild febrile to a life-threatening illness, which may include thrombocytopenia, leucopenia, hepatomegaly, hemorrhaging, plasma leakage and shock. Deciphering the underlining mechanisms responsible for these symptoms has been hindered by the limited availability of animal models that can induce classic human pathology. Currently, several permissive non-human primate (NHP) species and mouse breeds susceptible to adapted DV strains are available. Though virus replication occurs in these animals, none of them recapitulate the cardinal features of human symptomatology, with disease only occasionally observed in NHPs. Recently our group established a DV serotype 2 intravenous infection model with the Indian rhesus macaque, which reliably produced cutaneous hemorrhages after primary virus exposure. Further manipulation of experimental parameters (virus strain, immune cell expansion, depletion, etc.) can refine this model and expand its relevance to human DF. Future goals include applying this model to elucidate the role of pre-existing immunity upon secondary infection and immunopathogenesis. Of note, virus titers in primates in vivo and in vitro, even with our model, have been consistently 1000-fold lower than those found in humans. We submit that an improved model, capable of demonstrating severe pathogenesis may only be achieved with higher virus loads. Nonetheless, our DV coagulopathy disease model is valuable for the study of select pathomechanisms and testing DV drug and vaccine candidates.

The role of endothelial activation in dengue hemorrhagic fever and hantavirus pulmonary syndrome

The loss of the endothelium barrier and vascular leakage play a central role in the pathogenesis of hemorrhagic fever viruses. This can be caused either directly by the viral infection and damage of the vascular endothelium, or indirectly by a dysregulated immune response resulting in an excessive activation of the endothelium. This article briefly reviews our knowledge of the importance of the disruption of the vascular endothelial barrier in two severe disease syndromes, dengue hemorrhagic fever and hantavirus pulmonary syndrome. Both viruses cause changes in vascular permeability without damaging the endothelium. Here we focus on our understanding of the virus interaction with the endothelium, the role of the endothelium in the induced pathogenesis, and the possible mechanisms by which each virus causes vascular leakage. Understanding the dynamics between viral infection and the dysregulation of the endothelial cell barrier will help us to define potential therapeutic targets for reducing disease severity.

HLA-B∗44 Is Associated with Dengue Severity Caused by DENV-3 in a Brazilian Population

Human leukocyte antigen (HLA) alleles have been correlated with susceptibility or resistance to severe dengue; however, few immunogenetic studies have been performed in Latin American (LA) populations. We have conducted immunogenetic studies of HLA class I and II alleles in a cohort of 187 patients with DENV-3 infection and confirmed clinical diagnosis of either severe dengue, known as dengue hemorrhagic fever (DHF), or the less severe form, dengue fever (DF), in Recife, Pernambuco, Brazil. An association analysis was performed using Fisher's association test, with odds ratios (ORs) calculated using conditional maximum likelihood estimates. HLA-B∗44 (P = 0.047, OR = 2.025, 95% CI = 0.97–4.24) was found to be associated with increased susceptibility to DHF in response to DENV-3 infection. In addition, HLA-B∗07 (P = 0.048, OR = 0.501, one-sided 95% CI = 0–0.99) and HLA-DR∗13 (P = 0.028, OR = 0.511, one-sided 95% CI = 0–0.91) were found to be associated with resistance to secondary dengue infection by DENV-3. These results suggest that HLA-B∗44 supertype alleles and their respective T-cell responses might be involved in susceptibility to severe dengue infections, whereas the HLA-B∗07 supertype alleles and DR∗13 might be involved in cross-dengue serotype immunity.

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.

Genetic susceptibility to West Nile virus and dengue

This article focuses on the host genetic predisposition to 2 viruses, West Nile virus and dengue virus, which belong to the genus Flavivirus. Although by definition these viruses have shared characteristics (e.g. similar size, single stranded, RNA viruses, both transmitted by the bite from an infected mosquito), they differ greatly in epidemiology and clinical manifestations. The text below not only summarizes the genetic factors that predispose to complications of these 2 important flaviviruses, but also illustrates the challenges in determining the genomic basis for complications to these viruses.

Molecular epidemiological and virological study of dengue virus infections in Guangzhou, China, during 2001-2010

Background

Dengue virus (DENV) infection is the most prevalent arthropod-borne viral infection in tropical and subtropical regions worldwide. Guangzhou has the ideal environment for DENV transmission and DENV epidemics have been reported in this region for more than 30 years.

Methods

Information for DENV infection cases in Guangzhou from 2001 to 2010 were collected and analyzed. The DENV strains were cultured and isolated from patients’ sera. Viral RNA was extracted from cell culture supernatants. cDNA was synthesized by reverse transcription PCR. Phylogenetic trees of four DENV serotypes were constructed respectively.

Results

In total, 2478 DENV infection cases were reported; 2143 of these (86.43%) occurred during 3 months of the year: August, September and October. Of these, 2398 were local cases (96.77%) and 80 were imported cases (3.23%). Among the imported cases, 69 (86.25%) were from Southeast Asian countries. From the 90 isolated strains, 66.67%, 3.33%, 14.44%, and 15.56% belonged to DENV serotypes 1, 2, 3, and 4, respectively. DENV-1 was predominant in most of the years, including during 2 outbreaks in 2002 and 2006; however, none of the strains or genotypes identified in this study were found to be predominant. Interestingly, DENV strains from different years had different origins. Moreover, the strains from each year belonged to different serotypes and/or genotypes.

Conclusions

Southeast Asia countries were found to be the possible source of DENV in Guangzhou. These findings suggest that there is increasing diversity in DENV strains in Guangzhou, which could increase the risk of DENV outbreaks in the near future.

Effects of short-course oral corticosteroid therapy in early dengue infection in Vietnamese patients: a randomized, placebo-controlled trial

BACKGROUND

Patients with dengue can experience a variety of serious complications including hypovolemic shock, thrombocytopenia, and bleeding. These problems occur as plasma viremia is resolving and are thought to be immunologically mediated. Early corticosteroid therapy may prevent the development of such complications but could also prolong viral clearance.

METHODS

We performed a randomized, placebo-controlled, blinded trial of low-dose (0.5 mg/kg) or high-dose (2 mg/kg) oral prednisolone therapy for 3 days in Vietnamese patients aged 5-20 years admitted with dengue and fever for ≤72 hours, aiming to assess potential harms from steroid use during the viremic phase. Intention-to-treat analysis was performed using linear trend tests with a range of clinical and virological endpoints specified in advance. In addition to recognized complications of dengue, we focused on the are under the curve for serial plasma viremia measurements and the number of days after enrollment to negative viremia and dengue nonstructural protein 1 status.

RESULTS

Between August 2009 and January 2011, 225 participants were randomized to 1 of the 3 treatment arms. Baseline characteristics were similar across the groups. All patients recovered fully and adverse events were infrequent. Aside from a trend toward hyperglycemia in the steroid recipients, we found no association between treatment allocation and any of the predefined clinical, hematological, or virological endpoints.

CONCLUSIONS

Use of oral prednisolone during the early acute phase of dengue infection was not associated with prolongation of viremia or other adverse effects. Although not powered to assess efficacy, we found no reduction in the development of shock or other recognized complications of dengue virus infection in this study.

High-throughput, high-fidelity HLA genotyping with deep sequencing

Human leukocyte antigen (HLA) genes are the most polymorphic in the human genome. They play a pivotal role in the immune response and have been implicated in numerous human pathologies, especially autoimmunity and infectious diseases. Despite their importance, however, they are rarely characterized comprehensively because of the prohibitive cost of standard technologies and the technical challenges of accurately discriminating between these highly related genes and their many allelles. Here we demonstrate a high-resolution, and cost-effective methodology to type HLA genes by sequencing, which combines the advantage of long-range amplification, the power of high-throughput sequencing platforms, and a unique genotyping algorithm. We calibrated our method for HLA-A, -B, -C, and -DRB1 genes with both reference cell lines and clinical samples and identified several previously undescribed alleles with mismatches, insertions, and deletions. We have further demonstrated the utility of this method in a clinical setting by typing five clinical samples in an Illumina MiSeq instrument with a 5-d turnaround. Overall, this technology has the capacity to deliver low-cost, high-throughput, and accurate HLA typing by multiplexing thousands of samples in a single sequencing run, which will enable comprehensive disease-association studies with large cohorts. Furthermore, this approach can also be extended to include other polymorphic genes.

Identification and immunogenicity of two new HLA-A*0201-restricted CD8+ T-cell epitopes on dengue NS1 protein

Immunopathogenesis of dengue virus (DEN) infection remains poorly studied. Identification and characterization of human CD8(+) T-cell epitopes on DEN are necessary for a better understanding of the immunopathogenesis of dengue infection and would facilitate the development of immunotherapy and vaccines to protect from dengue infection. Here, we identified two new HLA-A*0201-restricted CD8(+) T-cell epitopes, DEN-4 NS1(990)(-998) and DEN-4 NS1(997)(-1005) that are conserved in three or four major DEN serotypes, respectively. Unexpectedly, we found that immunization of HLA-A*0201 transgenic mice with DEN-4 NS1(990)(-998) or DEN-4 NS1(997)(-1005) epitope peptide induced de novo synthesis of tumor necrosis factor (TNF)-α and IFN-γ, two important pro-inflammatory molecules that are hard to be detected directly without in vitro antigenic re-stimulation. Importantly, we demonstrated that CD8(+) T cells specifically activated by DEN-4 NS1(990)(-998) or DEN-4 NS1(997)(-1005) epitope peptide induced de novo synthesis of perforin. Furthermore, we observed that DEN-4 NS1(990)(-998) or DEN-4 NS1(997)(-1005)-specific CD8(+) T cells capable of producing large amounts of perforin, TNF-α and IFN-γ preferentially displayed CD27(+)CD45RA(-), but not CD27(-)CD45RA(+), phenotypes. This study, therefore, suggested the importance of synergistic effects of pro-inflammatory cytokines and cytotoxic molecules which were produced by dengue-specific CD8(+) T cells in immunopathogenesis or anti-dengue immunity during dengue infection.

Simple Prognostic Criteria can Definitively Identify Patients who Develop Severe Versus Non-Severe Dengue Disease, or Have Other Febrile Illnesses

Background

Severe dengue disease (SDD) (DHF/DSS: dengue hemorrhagic fever/dengue shock syndrome) results from either primary or secondary dengue virus (DENV) infections, which occur 4 - 6 days after the onset of fever. As yet, there are no definitive clinical or hematological criteria that can specifically identify SDD patients during the early acute febrile-phase of disease (day 0 - 3: < 72 hours). This study was performed during a SDD (DHF/DSS) epidemic to: 1) identify the DENV serotypes that caused SDD during primary or secondary DENV infections; 2) identify simple clinical and hematological criteria that could significantly discriminate between patients who subsequently developed SDD versus non-SDD (N-SDD), or had a non-DENV fever of unknown origin (FUO) during day 0 - 3 of fever; 3) assess whether DENV serotype co-infections resulted in SDD.

Methods

First serum samples, with clinical and hematological criteria, were collected from 100 patients during the early acute febrile-phase (day 0 - 3: < 72 hours), assessed for DENV or FUO infections by IgM- and IgG-capture ELISAs on paired serum samples and by DENV isolations, and subsequently graded as SDD, N-SDD or FUO patients.

Results

In this study: 1) Thirty-three patients had DENV infections, predominantly secondary DENV-2 infections, including each SDD (DHF/DSS) case; 2) Secondary DENV-2/-3 and DENV-2/-4 serotype co-infections however resulted in N-SDD; 3) Each patient who subsequently developed SDD, but none of the others, displayed three clinical criteria: abdominal pain, conjunctival injection and veni-puncture bleeding, therefore each of these criteria provided definitively significant prognostic (P < 0.001) values; 4) Petechia, positive tourniquet tests and hepatomegaly, and neutrophilia or leukopenia also significantly identified those who: a) subsequently developed SDD versus N-SDD, or had a FUO; b) subsequently developed SDD versus N-SDD; c) subsequently developed N-SDD versus FUOs, respectively.

Conclusions

This is the first report of simple definitively prognostic criteria for SDD patients, including the first assessment and confirmation of conjunctival injection. The three definitive clinical criteria used alone, or supported by the other four criteria, could be essential for specifically identifying those patients needing prompt hospital-based therapies to lessen or avert SDD, without unnecessary hospitalization of the other patients.

Keywords

Dengue virus; Severe dengue; Dengue fever; Diagnostic; Criteria; Hemorrhage; Shock

Host genetic susceptibility to severe dengue infection

Epidemiological evidence indicates that host genetic factors are relevant and predispose DHF/DSS development. Here, we review the host genetic studies concerning human leucocyte antigens, antibody receptors, immune/inflammatory mediators, attachment molecules, cytokines and other factors exerting an immunoregulatory effect as well as the current genome-wide association studies. We also discuss some viewpoints on future challenges related to the design of safe and effective prevention and treatment options.

Contribution of dengue fever to the burden of acute febrile illnesses in Papua New Guinea: an age-specific prospective study

Malaria is a major contributor to the burden of febrile illnesses in Papua New Guinea (PNG). Dengue fever (DF) is likely to contribute; however, its epidemiology in PNG is poorly understood. We performed a prospective age-stratified study in outpatient clinics investigating the prevalence of DF; 578 patients were enrolled, and 317 patients with a negative rapid diagnostic test (RDT) for malaria were tested for dengue. Malaria was confirmed in 52% (301/578, 95% confidence interval [CI] = 48-56%), DF was diagnosed in 8% (46/578, 95% CI = 6-10%), and 40% (95% CI = 36-44%) had neither diagnosis. Among the 317 malaria RDT-negative patients, 14% (45/317, 95% CI = 10-18%) had DF. The seroprevalence of dengue immunoglobulin G (IgG) was 83% (204/247, 95% CI = 78-87%), and no dengue hemorrhagic fever was seen. This study provides good evidence for the first time that DF is common in PNG and is responsible for 8% of fever episodes. The common occurrence of DF in a population with presumed previous exposure to dengue is an important observation.

Contribution of dengue fever to the burden of acute febrile illnesses in Papua New Guinea: an age-specific prospective study

Malaria is a major contributor to the burden of febrile illnesses in Papua New Guinea (PNG). Dengue fever (DF) is likely to contribute; however, its epidemiology in PNG is poorly understood. We performed a prospective age-stratified study in outpatient clinics investigating the prevalence of DF; 578 patients were enrolled, and 317 patients with a negative rapid diagnostic test (RDT) for malaria were tested for dengue. Malaria was confirmed in 52% (301/578, 95% confidence interval [CI] = 48-56%), DF was diagnosed in 8% (46/578, 95% CI = 6-10%), and 40% (95% CI = 36-44%) had neither diagnosis. Among the 317 malaria RDT-negative patients, 14% (45/317, 95% CI = 10-18%) had DF. The seroprevalence of dengue immunoglobulin G (IgG) was 83% (204/247, 95% CI = 78-87%), and no dengue hemorrhagic fever was seen. This study provides good evidence for the first time that DF is common in PNG and is responsible for 8% of fever episodes. The common occurrence of DF in a population with presumed previous exposure to dengue is an important observation.

Immunity to dengue virus: a tale of original antigenic sin and tropical cytokine storms

Dengue is a mosquito-borne viral disease of expanding geographical range and incidence. The existence of four viral serotypes and the association of prior dengue virus infection with an increased risk for more severe disease have presented significant obstacles to vaccine development. An increased understanding of the adaptive immune response to natural dengue virus infection and candidate dengue vaccines has helped to define the specific antibody and T cell responses that are associated with either protective or pathological immunity during dengue infection. Further characterization of immunological correlates of disease outcome and the validation of these findings in vaccine trials will be invaluable for developing effective dengue vaccines.

Illumination of parainfluenza virus infection and transmission in living animals reveals a tissue-specific dichotomy

The parainfluenza viruses (PIVs) are highly contagious respiratory paramyxoviruses and a leading cause of lower respiratory tract (LRT) disease. Since no vaccines or antivirals exist, non-pharmaceutical interventions are the only means of control for these pathogens. Here we used bioluminescence imaging to visualize the spatial and temporal progression of murine PIV1 (Sendai virus) infection in living mice after intranasal inoculation or exposure by contact. A non-attenuated luciferase reporter virus (rSeV-luc(M-F*)) that expressed high levels of luciferase yet was phenotypically similar to wild-type Sendai virus in vitro and in vivo was generated to allow visualization. After direct intranasal inoculation, we unexpectedly observed that the upper respiratory tract (URT) and trachea supported robust infection under conditions that result in little infection or pathology in the lungs including a low inoculum of virus, an attenuated virus, and strains of mice genetically resistant to lung infection. The high permissivity of the URT and trachea to infection resulted in 100% transmission to naïve contact recipients, even after low-dose (70 PFU) inoculation of genetically resistant BALB/c donor mice. The timing of transmission was consistent with the timing of high viral titers in the URT and trachea of donor animals but was independent of the levels of infection in the lungs of donors. The data therefore reveals a disconnect between transmissibility, which is associated with infection in the URT, and pathogenesis, which arises from infection in the lungs and the immune response. Natural infection after transmission was universally robust in the URT and trachea yet limited in the lungs, inducing protective immunity without weight loss even in genetically susceptible 129/SvJ mice. Overall, these results reveal a dichotomy between PIV infection in the URT and trachea versus the lungs and define a new model for studies of pathogenesis, development of live virus vaccines, and testing of antiviral therapies.

Human parainfluenza viruses (HPIVs) are a leading cause of pediatric hospitalization for lower respiratory tract infection, yet it is unknown why primary infection typically induces immunity without causing severe pathology. To study the determinants of PIV spread within the respiratory tracts of living animals, we developed a model for non-invasive imaging of living mice infected with Sendai virus, the murine counterpart of HPIV1. This system allowed us to measure the temporal and spatial dynamics of paramyxovirus infection throughout the respiratory tracts of living animals after direct inoculation or transmission. We found that the upper respiratory tract and trachea were highly permissive to infection, even under conditions that limit lower respiratory infection and pathogenesis. The timing of transmission coincided with high virus growth in the upper respiratory tracts and trachea of donor mice independent of the extent of infection in the lungs. After transmission, infection spread preferentially in the upper respiratory tract and trachea, inducing protective immunity without weight loss. Our work reveals a disconnect between Sendai virus transmissibility and pathogenicity, and the experimental model developed here will be instrumental in studying PIV pathogenesis.

NIAID workshop on Flavivirus immunity

On September 16, 2009, the National Institute of Allergy and Infectious Diseases (NIAID), part of the U.S. National Institutes of Health, convened a workshop to discuss current knowledge of T- and B-cell immune epitopes for members of the Flavivirus genus (family Flaviviridae), and how this information could be used to increase our basic understanding of host-pathogen interactions and/or advance the development of new or improved vaccines and diagnostics for these pathogens. B-cell and T-cell responses to flaviviruses are critical components of protective immunity against these pathogens. However, they have also been linked to disease pathogenesis. A detailed understanding of the biological significance of immune epitope information may provide clues regarding the mechanisms governing the induction of protective versus pathogenic adaptive immune responses.