Virus evolution during a severe dengue epidemic in Cuba, 1997

Secreted dengue virus NS1 from infection is predominantly dimeric and in complex with high-density lipoprotein

Severe dengue infections are characterized by endothelial dysfunction shown to be associated with the secreted nonstructural protein 1 (sNS1), making it an attractive vaccine antigen and biotherapeutic target. To uncover the biologically relevant structure of sNS1, we obtained infection-derived sNS1 (isNS1) from dengue virus (DENV)-infected Vero cells through immunoaffinity purification instead of recombinant sNS1 (rsNS1) overexpressed in insect or mammalian cell lines. We found that isNS1 appeared as an approximately 250 kDa complex of NS1 and ApoA1 and further determined the cryoEM structures of isNS1 and its complex with a monoclonal antibody/Fab. Indeed, we found that the major species of isNS1 is a complex of the NS1 dimer partially embedded in a high-density lipoprotein (HDL) particle. Crosslinking mass spectrometry studies confirmed that the isNS1 interacts with the major HDL component ApoA1 through interactions that map to the NS1 wing and hydrophobic domains. Furthermore, our studies demonstrated that the sNS1 in sera from DENV-infected mice and a human patient form a similar complex as isNS1. Our results report the molecular architecture of a biological form of sNS1, which may have implications for the molecular pathogenesis of dengue.

A fatal case of dengue hemorrhagic fever associated with dengue virus 4 (DENV-4) in Brazil: genomic and histopathological findings

Dengue infection is the most prevalent arthropod-borne viral disease in subtropical and tropical regions, whose primary vector is Aedes aegypti mosquitoes. The mechanisms of dengue virus (DENV) pathogenesis are little understood because we have no good disease models. Only humans develop symptoms (dengue fever, DF, or dengue hemorrhagic fever, DHF) and research has been limited to studies involving patients. Samples from serum, brain, cerebellum, heart, lungs, liver, and kidneys from a 13-year-old male patient that died with hemorrhagic manifestations were sent for differential diagnosis at Adolfo Lutz, using both classical virological methods (RT-qPCR, virus isolation, ELISA, and hemagglutination inhibition test) and immunohistochemistry (IHQ). A DENV serotype 4 was detected by a DENV multiplex RT-qPCR, and the C6/36 cell supernatant was used for NGS using Minion. Lesions were described in the heart, liver, lung, and kidney with positive IHQ in endothelial cells of the brain, cerebellum, heart, and kidney, and also in hepatocytes and Kuppfer cells. A whole genome was obtained, revealing a DENV-4 genotype II, with no evidence of secondary dengue infection.

A Zika virus mutation enhances transmission potential and confers escape from protective dengue virus immunity

Zika virus (ZIKV) and dengue virus (DENV) are arthropod-borne pathogenic flaviviruses that co-circulate in many countries. To understand some of the pressures that influence ZIKV evolution, we mimic the natural transmission cycle by repeating serial passaging of ZIKV through cultured mosquito cells and either DENV-naive or DENV-immune mice. Compared with wild-type ZIKV, the strains passaged under both conditions exhibit increased pathogenesis in DENV-immune mice. Application of reverse genetics identifies an isoleucine-to-valine mutation (I39V) in the NS2B proteins of both passaged strains that confers enhanced fitness and escape from pre-existing DENV immunity. Introduction of I39V or I39T, a naturally occurring homologous mutation detected in recent ZIKV isolates, increases the replication of wild-type ZIKV in human neuronal precursor cells and laboratory-raised mosquitoes. Our data indicate that ZIKV strains with enhanced transmissibility and pathogenicity can emerge in DENV-naive or -immune settings, and that NS2B-I39 mutants may represent ZIKV variants of interest.

Emergence of Dengue 4 as Dominant Serotype During 2017 Outbreak in South India and Associated Cytokine Expression Profile

Dengue virus (DENV) infection is prevalent in tropical and subtropical regions of the world, which is fatal if untreated symptomatically. Emergence of new genotype within serotypes led to enhanced severity. The objective of the study is to identify the molecular characteristics of the DENV circulated during 2017 outbreak in Tamil Nadu, India, and to investigate the role of inflammatory cytokines in different “serotypes” and in “dengue severity”. A total of 135 suspected samples were tested for DENV infection using IgM, IgG, and qPCR assay; where 76 samples were positive for DENV and analyzed for 12 inflammatory cytokines using ELISA. Serotyping shows 14 DENV-1, 22 DENV-2, 7 DENV-3, and 33 DENV-4, where DENV-4 was predominant. Among 76, 42 isolates were successfully sequenced for C-prM region and grouped. A lineage shift was observed in DENV-4 genotype. Irrespective of serotypes, IFNγ was significantly elevated in all serotypes than control as well as in primary infection than secondary, indicating its role in immune response. GM-CSF and IP-10 were significantly elevated in secondary infection and could be used as prognostic biomarkers for secondary infection. Our observation shows differential cytokine expression profile varied with each serotype, indicating serotype/genotype-specific viral proteins might play a major role in dengue severity. DENV-4 as dominant serotype was reported in Tamil Nadu for the first time during an outbreak with a mixed Th1/Th17 cytokine expression profile that correlated with disease severity. We conclude it is essential to identify circulating viral genotype and their fitness by mutational analysis to correlate with disease severity and immune status, as this correlation will be helpful in diagnostics and therapeutics applications.

Relative contribution of nonstructural protein 1 in dengue pathogenesis

Dengue is a major public health concern in the tropical and subtropical world, with no effective treatment. The controversial live attenuated virus vaccine Dengvaxia has boosted the pursuit of subunit vaccine approaches, and nonstructural protein 1 (NS1) has recently emerged as a promising candidate. However, we found that NS1 immunization or passive transfer of NS1 antibodies failed to confer protection in symptomatic dengue mouse models using two non–mouse-adapted DENV2 strains that are highly virulent. Exogenous administration of purified NS1 also failed to worsen in vivo vascular leakage in sublethally infected mice. Neither method of NS1 immune neutralization changed the disease outcome of a chimeric strain expressing a vascular leak-potent NS1. Instead, virus chimerization involving the prME structural region indicated that these proteins play a critical role in driving in vivo fitness and virulence of the virus, through induction of key proinflammatory cytokines. This work highlights that the pathogenic role of NS1 is DENV strain dependent, which warrants reevaluation of NS1 as a universal dengue vaccine candidate.

A T164S mutation in the dengue virus NS1 protein is associated with greater disease severity in mice

Dengue viruses cause severe and sudden human epidemics worldwide. The secreted form of the nonstructural protein 1 (sNS1) of dengue virus causes vascular leakage, a hallmark of severe dengue disease. Here, we reverse engineered the T164S mutation of NS1, associated with the severity of dengue epidemics in the Americas, into a dengue virus serotype 2 mildly infectious strain. The T164S mutant virus decreased infectious virus production and increased sNS1 production in mammalian cell lines and human peripheral blood mononuclear cells (PBMCs) without affecting viral RNA replication. Gene expression profiling of 268 inflammation-associated human genes revealed up-regulation of genes induced in response to vascular leakage. Infection of the mosquito vector Aedes aegypti with the T164S mutant virus resulted in increased viral load in the mosquito midgut and higher sNS1 production compared to wild-type virus infection. Infection of type 1 and 2 interferon receptor-deficient AG129 mice with the T164S mutant virus resulted in severe disease coupled with increased complement activation, tissue inflammation, and more rapid mortality compared to AG129 mice infected with wild-type virus. Molecular dynamics simulations predicted that mutant sNS1 formed stable dimers similar to the wild-type protein, whereas the hexameric mutant sNS1 was predicted to be unstable. Immunoaffinity-purified sNS1 from T164S mutant virus-infected mammalian cells was associated with different lipid classes compared to wild-type sNS1. Treatment of human PBMCs with sNS1 purified from T164S mutant virus resulted in a twofold higher production of proinflammatory cytokines, suggesting a mechanism for how mutant sNS1 may cause more severe dengue disease.

Increasing Clinical Severity during a Dengue Virus Type 3 Cuban Epidemic: Deep Sequencing of Evolving Viral Populations

During the dengue virus type 3 (DENV-3) epidemic that occurred in Havana in 2001 to 2002, severe disease was associated with the infection sequence DENV-1 followed by DENV-3 (DENV-1/DENV-3), while the sequence DENV-2/DENV-3 was associated with mild/asymptomatic infections. To determine the role of the virus in the increasing severity demonstrated during the epidemic, serum samples collected at different time points were studied. A total of 22 full-length sequences were obtained using a deep-sequencing approach. Bayesian phylogenetic analysis of consensus sequences revealed that two DENV-3 lineages were circulating in Havana at that time, both grouped within genotype III. The predominant lineage is closely related to Peruvian and Ecuadorian strains, while the minor lineage is related to Venezuelan strains. According to consensus sequences, relatively few nonsynonymous mutations were observed; only one was fixed during the epidemic at position 4380 in the NS2B gene. Intrahost genetic analysis indicated that a significant minor population was selected and became predominant toward the end of the epidemic. In conclusion, greater variability was detected during the epidemic's progression in terms of significant minority variants, particularly in the nonstructural genes. An increasing trend of genetic diversity toward the end of the epidemic was observed only for synonymous variant allele rates, with higher variability in secondary cases. Remarkably, significant intrahost genetic variation was demonstrated within the same patient during the course of secondary infection with DENV-1/DENV-3, including changes in the structural proteins premembrane (PrM) and envelope (E). Therefore, the dynamic of evolving viral populations in the context of heterotypic antibodies could be related to the increasing clinical severity observed during the epidemic.

IMPORTANCE

Based on the evidence that DENV fitness is context dependent, our research has focused on the study of viral factors associated with intraepidemic increasing severity in a unique epidemiological setting. Here, we investigated the intrahost genetic diversity in acute human samples collected at different time points during the DENV-3 epidemic that occurred in Cuba in 2001 to 2002 using a deep-sequencing approach. We concluded that greater variability in significant minor populations occurred as the epidemic progressed, particularly in the nonstructural genes, with higher variability observed in secondary infection cases. Remarkably, for the first time significant intrahost genetic variation was demonstrated within the same patient during the course of secondary infection with DENV-1/DENV-3, including changes in structural proteins. These findings indicate that high-resolution approaches are needed to unravel molecular mechanisms involved in dengue pathogenesis.

Dengue Antibody-Dependent Enhancement: Knowns and Unknowns

Dengue provides the most abundant example in human medicine and the greatest human illness burden caused by the phenomenon of intrinsic antibody-dependent infection enhancement (iADE). In this immunopathological phenomenon infection of monocytes or macrophages using infectious immune complexes suppresses innate antiviral systems, permitting logarithmic intracellular growth of dengue virus. The four dengue viruses evolved from a common ancestor yet retain similar ecology and pathogenicity, but although infection with one virus provides short-term cross-protection against infection with a different type, millions of secondary dengue infections occur worldwide each year. When individuals are infected in the virtual absence of cross-protective dengue antibodies, the dengue vascular permeability syndrome (DVPS) may ensue. This occurs in around 2 to 4% of second heterotypic dengue infections. A complete understanding of the biologic mechanism of iADE, dengue biology, and the mechanism of host responses to dengue infection should lead to a comprehensive and complete understanding of the pathogenesis of DVPS. A crucial emphasis must be placed on understanding ADE. Clinical and epidemiological observations of DVPS define the research questions and provide research parameters. This article will review knowledge related to dengue ADE and point to areas where there has been little research progress. These observations relate to the two stages of dengue illnesses: afferent phenomena are those that promote the success of the microorganism to infect and survive; efferent phenomena are those mounted by the host to inhibit infection and replication and to eliminate the infectious agent and infected tissues. Data will be discussed as "knowns" and "unknowns."

First dengue haemorrhagic fever epidemic in the Americas, 1981: insights into the causative agent

Historical records describe a disease in North America that clinically resembled dengue haemorrhagic fever during the latter part of the slave-trading period. However, the dengue epidemic that occurred in Cuba in 1981 was the first laboratory-confirmed and clinically diagnosed outbreak of dengue haemorrhagic fever in the Americas. At that time, the presumed source of the dengue type 2 strain isolated during this epidemic was considered controversial, partly because of the limited sequence data and partly because the origin of the virus appeared to be southern Asia. Here, we present a molecular characterisation at the whole-genome level of the original strains isolated at different time points during the epidemic. Phylogenetic trees constructed using Bayesian methods indicated that 1981 Cuban strains group within the Asian 2 genotype. In addition, the study revealed that viral evolution occurred during the epidemic - a fact that could be related to the increasing severity from month to month. Moreover, the Cuban strains exhibited particular amino acid substitutions that differentiate them from the New Guinea C prototype strain as well as from dengue type 2 strains isolated globally.

Epidemiological risk factors associated with high global frequency of inapparent dengue virus infections

Dengue is a major international public health concern, and the number of outbreaks has escalated greatly. Human migration and international trade and travel are constantly introducing new vectors and pathogens into novel geographic areas. Of particular interest is the extent to which dengue virus (DENV) infections are subclinical or inapparent. Not only may such infections contribute to the global spread of DENV by human migration, but also seroprevalence rates in naïve populations may be initially high despite minimal numbers of detectable clinical cases. As the probability of severe disease is increased in secondary infections, populations may thus be primed, with serious public health consequences following introduction of a new serotype. In addition, pre-existing immunity from inapparent infections may affect vaccine uptake, and the ratio of clinically apparent to inapparent infection could affect the interpretation of vaccine trials. We performed a literature search for inapparent DENV infections and provide an analytical review of their frequency and associated risk factors. Inapparent rates were highly variable, but “inapparent” was the major outcome of infection in all prospective studies. Differences in the epidemiological context and type of surveillance account for much of the variability in inapparent infection rates. However, one particular epidemiological pattern was shared by four longitudinal cohort studies: the rate of inapparent DENV infections was positively correlated with the incidence of disease the previous year, strongly supporting an important role for short-term heterotypic immunity in determining the outcome of infection. Primary and secondary infections were equally likely to be inapparent. Knowledge of the extent to which viruses from inapparent infections are transmissible to mosquitoes is urgently needed. Inapparent infections need to be considered for their impact on disease severity, transmission dynamics, and vaccine efficacy and uptake.

Origin and distribution of divergent dengue virus: novel database construction and phylogenetic analyses

Dengue virus (DENV), a mosquito-borne agent that exists as four serotypes (DENV-1–4), induces dengue illness. DENV has a positive-sense, ssRNA genome of approximately 11 kb that encodes a capsid protein, a premembrane protein and an envelope glycoprotein, in addition to seven nonstructural proteins. These individual genes show sequence variations that can be analyzed phylogenetically to yield several genotypes within each serotype. Here, the sequences of individual DENV genes were collected and used to construct a novel DENV database. This database was then used to characterize the evolution of individual genotypes in several countries. Interestingly, the database provided evidence for recombination between two or three different genotypes to yield new genotypes. This novel database will be available on the internet and is expected to be highly useful for dengue genetic studies, including phylogenetic analyses.

Understanding the dengue viruses and progress towards their control

Traditionally, the four dengue virus serotypes have been associated with fever, rash, and the more severe forms, haemorrhagic fever and shock syndrome. As our knowledge as well as understanding of these viruses increases, we now recognise not only that they are causing increasing numbers of human infections but also that they may cause neurological and other clinical complications, with sequelae or fatal consequences. In this review we attempt to highlight some of these features in the context of dengue virus pathogenesis. We also examine some of the efforts currently underway to control this "scourge" of the tropical and subtropical world.

Perspectives of public health laboratories in emerging infectious diseases

The world has experienced an increased incidence and transboundary spread of emerging infectious diseases over the last four decades. We divided emerging infectious diseases into four categories, with subcategories in categories 1 and 4. The categorization was based on the nature and characteristics of pathogens or infectious agents causing the emerging infections, which are directly related to the mechanisms and patterns of infectious disease emergence. The factors or combinations of factors contributing to the emergence of these pathogens vary within each category. We also classified public health laboratories into three types based on function, namely, research, reference and analytical diagnostic laboratories, with the last category being subclassified into primary (community-based) public health and clinical (medical) analytical diagnostic laboratories. The frontline/leading and/or supportive roles to be adopted by each type of public health laboratory for optimal performance to establish the correct etiological agents causing the diseases or outbreaks vary with respect to each category of emerging infectious diseases. We emphasize the need, especially for an outbreak investigation, to establish a harmonized and coordinated national public health laboratory system that integrates different categories of public health laboratories within a country and that is closely linked to the national public health delivery system and regional and international high-end laboratories.

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

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

Population structure of the dengue viruses, Aragua, Venezuela, 2006-2007. Insights into dengue evolution under hyperendemic transmission

During the past three decades there has been a notable increase in dengue disease severity in Venezuela. Nevertheless, the population structure of the viruses being transmitted in this country is not well understood. Here, we present a molecular epidemiological study on dengue viruses (DENV) circulating in Aragua State, Venezuela during 2006-2007. Twenty-one DENV full-length genomes representing all of the four serotypes were amplified and sequenced directly from the serum samples. Notably, only DENV-2 was associated with severe disease. Phylogenetic trees constructed using Bayesian methods indicated that only one genotype was circulating for each serotype. However, extensive viral genetic diversity was found in DENV isolated from the same area during the same period, indicating significant in situ evolution since the introduction of these genotypes. Collectively, the results suggest that the non-structural (NS) proteins may play an important role in DENV evolution, particularly NS1, NS2A and NS4B proteins. The phylogenetic data provide evidence to suggest that multiple introductions of DENV have occurred from the Latin American region into Venezuela and vice versa. The implications of the significant viral genetic diversity generated during hyperendemic transmission, particularly in NS protein are discussed and considered in the context of future development and use of human monoclonal antibodies as antivirals and tetravalent vaccines.

Dengue: a continuing global threat

Dengue fever and dengue haemorrhagic fever are important arthropod-borne viral diseases. Each year, there are ∼50 million dengue infections and ∼500,000 individuals are hospitalized with dengue haemorrhagic fever, mainly in Southeast Asia, the Pacific and the Americas. Illness is produced by any of the four dengue virus serotypes. A global strategy aimed at increasing the capacity for surveillance and outbreak response, changing behaviours and reducing the disease burden using integrated vector management in conjunction with early and accurate diagnosis has been advocated. Antiviral drugs and vaccines that are currently under development could also make an important contribution to dengue control in the future.

Dengue virus pathogenesis: an integrated view

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

Emergence of the severe syndrome and mortality associated with dengue and dengue-like illness: historical records (1890 to 1950) and their compatibility with current hypotheses on the shift of disease manifestation

Outbreaks of the severe dengue syndrome, dengue hemorrhagic fever (DHF), emerged beginning in the 1950s, marking a dramatic change in the dengue syndrome. While intense investigations in multiple directions have been conducted for many years to elucidate the intrinsic mechanisms conducive to the development of DHF, no consensus has yet emerged. Meanwhile, relatively little attention has been paid to the occurrence of severe dengue and death prior to the 1950s. This comprehensive review was designed to evaluate outbreak records in the early dengue history to better understand the epidemiologic background and other factors that existed before the emergence of DHF outbreaks. By applying a set of stringent criteria to remove unreliable data as much as possible and by interpreting the results conservatively, a short list of etiologically more reliable outbreaks with high mortality was obtained. The results show that severe dengue syndrome, clinically very much compatible with DHF, occurred far more frequently in multiple locations than it had been assumed before; that the magnitudes of mortality in several outbreaks were not negligible; and that the epidemiologic background features shared among these outbreaks in the early period were, with the exceptions of more limited demographic changes, generally similar to the post-1950 conditions.

Neutralizing antibody response variation against dengue 3 strains

To evaluate the neutralizing antibody activity of a human sera panel against seven strains of the homotypic virus. Sera were collected from DENV-3 immune individuals. Two DENV-3 genotypes and strains isolated at different time-points during the 2000 and 2001-2002 Havana epidemics were included. A panel of 20 late convalescent sera collected 16-18 months after acute illness from DF and DHF patients are studied. These individuals were infected during the 2001-2002 Havana DENV-3 epidemic. All but four sera collected from DF cases had a secondary DENV-1/DENV-3 infection. Sera neutralizing antibody titer against the seven DENV-3 strains were determined by plaque reduction neutralization technique. Sera samples were tested simultaneously. Studied sera showed higher levels of neutralizing antibodies to DENV-3 strains of genotype III compared to genotype V. Interesting, higher levels of neutralizing antibodies were detected to DENV-3 strain isolated at the end of the epidemic 2001-2002. An increased tendency of GMT of neutralizing antibodies according to epidemic evolution was observed for the 2001-2002 outbreak. In general, antibody levels in sera collected from DF cases were higher. Differences in the neutralization capacity of immune DENV-3 sera tested against two homologous genotypes including strains of the same genotype are demonstrated. Observed results suggest that virus changed in the course of the epidemic. The implications of this finding in terms of dengue pathogenesis and vaccine development need to be considered.

Specific genetic markers for detecting subtypes of dengue virus serotype-2 in isolates from the states of Oaxaca and Veracruz, Mexico

BACKGROUND

Dengue (DEN) is an infectious disease caused by the DEN virus (DENV), which belongs to the Flavivirus genus in the family Flaviviridae. It has a (+) sense RNA genome and is mainly transmitted to humans by the vector mosquito Aedes aegypti. Dengue fever (DF) and dengue hemorrhagic fever (DHF) are caused by one of four closely related virus serotypes (DENV-1, DENV-2, DENV-3 and DENV-4). Epidemiological and evolutionary studies have indicated that host and viral factors are involved in determining disease outcome and have proved the importance of viral genotype in causing severe epidemics. Host immune status and mosquito vectorial capacity are also important influences on the severity of infection. Therefore, an understanding of the relationship between virus variants with altered amino acids and high pathogenicity will provide more information on the molecular epidemiology of DEN. Accordingly, knowledge of the DENV serotypes and genotypes circulating in the latest DEN outbreaks around the world, including Mexico, will contribute to understanding DEN infections.

RESULTS

1. We obtained 88 isolates of DENV, 27 from Oaxaca and 61 from Veracruz. 2. Of these 88 isolates, 16 were serotype 1; 62 serotype 2; 7 serotype 3; and 2 serotype 4. One isolate had 2 serotypes (DENV-2 and -1). 3. Partial nucleotide sequences of the genes encoding C- prM (14 sequences), the NS3 helicase domain (7 sequences), the NS5 S-adenosyl methionine transferase domain (7 sequences) and the RNA-dependent RNA polymerase (RdRp) domain (18 sequences) were obtained. Phylogenetic analysis showed that DENV-2 isolates belonged to the Asian/American genotype. In addition, the Asian/American genotype was divided into two clusters, one containing the isolates from 2001 and the other the isolates from 2005-2006 with high bootstrap support of 94%.

CONCLUSION

DENV-2 was the predominant serotype in the DF and DHF outbreak from 2005 to 2006 in Oaxaca State as well as in the 2006 outbreak in Veracruz State, with the Asian/American genotype prevalent in both states. Interestingly, DENV-1 and DENV-2 were the only serotypes related to DHF cases. In contrast, DENV-3 and DENV-4 were poorly represented according to epidemiological data reported in Mexico. We found that isoleucine was replaced by valine at residue 106 of protein C in the isolates from these 2005-2006 outbreaks and in those from the 1997, 1998 and 2001 outbreaks in the Caribbean islands. We suggested that this amino acid change may be used as a signature for isolates arising in the Caribbean islands and pertaining to the Asian/American genotype. Other amino acid changes are specific for the Asian/American, Asian and American strains.

Clinical isolates of dengue virus with distinctive susceptibility to nitric oxide radical induce differential gene responses in THP-1 cells

In the present study, 10 clinical isolates of dengue virus were selected according to their susceptibility to the inhibitory effect of nitric oxide radical, NO. Five of them are nitric oxide-susceptible viruses while the other five are nitric oxide-resistant viruses. These isolates were investigated to identify genetic factors that are responsible for the different phenotypes. Due to the evidence showing that NO suppresses DENV RNA polymerase activity, we, therefore, hypothesized that the RdRp domain of NS5 may responsible for NO inhibition. To answer this question, sequences of NS5 gene of NO-susceptible viruses and NO-resistant viruses were compared. We found that these two groups of viruses contain different amino acid sequence at position 621 to 646 in the active site of NS5. These data suggested that response to the inhibitory effect of nitric oxide radical may, at least in part, be regulated by NS5. The effect of these two different phenotypes of viruses on host cells was studied using cDNA array screening. The cDNA array analysis demonstrated that the nitric oxide-resistant group had a stronger influence on host cells since it induced changes in the expression of a greater number of genes than did the nitric oxide-susceptible group, 97 genes versus 71 genes, respectively. The NO-resistant virus also stimulated cytokines known to be virulent factors, such as IL 6, IL 8, RANTES, and the inflammatory factors. In conclusion, our data demonstrated that dengue viruses isolated from patients show genotypic and phenotypic differences which may correlate with virulence.

Dengue haemorrhagic fever integral hypothesis: confirming observations, 1987-2007

In 1987, Kouri et al. published in Transactions their integral hypothesis to explain the development of dengue haemorrhagic fever (DHF) epidemics (Kouri, G.P., Guzmán, M.G., Bravo, J.R., 1987. Why dengue haemorrhagic fever in Cuba? 2. An integral analysis. Trans. R. Soc. Trop. Med. Hyg. 81, 821-823). Based on observations carried out during the 1981 Cuban DHF epidemic, the authors integrated in one model the most advanced knowledge at that time. Observations in the last 20 years confirm the importance of this multifactorial and unifying view of the problem, where the interaction between the host, the virus and the vector in an epidemiological and ecosystem setting might determine DHF as a final outcome. Investigations on the interaction among host, virus and mosquito with an ecosystemic view are needed.

Dengue virus-mosquito interactions

The mosquito Aedes aegypti is more widely dispersed now than at any time in the past, placing billions of humans at risk of infection with one or more of the four dengue viruses. This review presents and discusses information on mosquito-dengue infection dynamics and describes the prominent role that temperature and rainfall play in controlling dengue viral transmission including discussions of the effect of interannual climate variations and the predicted effect of global warming. Complementary human determinants of dengue epidemiology include viremia titer, variation in viremic period, enhanced viremias, and threshold viremia. Topics covered include epidemiological phenomena such as traveling waves, the generation of genetic diversity of dengue viruses following virgin soil introductions and in hyperendemic settings, and evidence for and against viral virulence as a determinant of the severity of dengue infections. Also described is the crucial role of monotypic and heterotypic herd immunity in shaping dengue epidemic behavior.

Phylogenetic analysis of dengue viruses isolated from imported dengue patients: possible aid for determining the countries where infections occurred

BACKGROUND

Molecular epidemiology of dengue viruses in endemic countries have been reported, but few were reported on the imported dengue cases among travelers. We analyzed dengue viruses isolated from imported dengue cases in Japan who were infected while traveling in endemic regions of the world.

METHOD

We sequenced the complete envelope (E) gene of 33 dengue virus strains isolated from patients returning from Asia, Oceania, South Pacific islands, and South America to Japan where no domestic dengue virus infection occurs. We then performed phylogenetic analysis to define the geographic origin of isolated viruses. Moreover, we compared the genomes of isolated dengue viruses with those of the strains already deposited in the GenBank database.

RESULT

The isolates are clustered into expected genotypes, confirming that the viruses originated from the visited countries. When patients visited more than one country during a single trip, the countries where the infection occurred were also determined for four of the six patients. There were three isolates, which were different genotypes from those previously isolated in visited countries.

CONCLUSIONS

The study demonstrates that many dengue virus strains are introduced into Japan and that phylogenic analysis of isolated dengue viruses is a unique technique to determine the countries where infection occurred. Travelers carry viruses and provide important and unique information for clarifying dengue virus trait and its dissemination.

HLA-A, -B, -C, and -DRB1 allele frequencies in Cuban individuals with antecedents of dengue 2 disease: Advantages of the Cuban population for HLA studies of dengue virus infection

Dengue virus infection has emerged as one of the most important arthropod-borne diseases. In some dengue-infected individual, the disease progresses to its severe, life-threatening form, dengue hemorrhagic fever (DHF). Host genetic factors may be relevant and predispose some individuals to the severe dengue disease. The unique history of dengue outbreaks in Cuba is extremely advantageous for genetic studies of dengue disease resistance or susceptibility. Consequently, samples collected from 120 healthy individuals that developed dengue fever (DF) and DHF during the 1997 dengue 2 outbreak in the Santiago de Cuba municipality were HLA genotyped using polymerase chain reaction-sequence-specific primers. Polymorphism at the human leukocyte antigen (HLA) class I loci was significantly associated with DHF disease susceptibility, but polymorphism in the HLA-DRB1 was associated with protection. Amino acid peptides present in the poly-protein of the dengue 2 Jamaica strain, which are able to bind to the HLA class I and class II allotypes associated with susceptibility to or protection against the dengue clinical disease, respectively, were predicted using the BIMAS and SYFPEITHI predictive algorithms of peptide/MHC interaction.

Comparative analysis reveals no consistent association between the secondary structure of the 3'-untranslated region of dengue viruses and disease syndrome

A comparative analysis was performed of the 3'-untranslated region (UTR) of Dengue virus (DENV) sampled from Bangkok, Thailand, over a 30 year period and representing all four serotypes. Considerable genetic variation was observed both within and among serotypes. Notably, a full-length version of the critical 3'-long stable hairpin structure was absent from some isolates, suggesting the occurrence of complex structural interactions within the 3'-UTR, including the influence of upstream mutations. The Thai sequences were then combined with 61 globally sampled isolates of DENV taken from patients with either dengue fever or severe dengue disease. No consistent association was found between 3'-UTR secondary structure and the clinical outcome of DENV infection, although some evidence for a trend in this direction was observed in DENV-2. It was concluded that the 3'-UTR is not the sole determinant of DENV virulence in nature, although variation in secondary structure may greatly influence viral fitness.