The magnitude of dengue virus NS1 protein secretion is strain dependent and does not correlate with severe pathologies in the mouse infection model

Dengue NS1 interaction with lipids alters its pathogenic effects on monocyte derived macrophages

BACKGROUND

While dengue NS1 antigen has been shown to be associated with disease pathogenesis in some studies, it has not been linked in other studies, with the reasons remaining unclear. NS1 antigen levels in acute dengue are often associated with increased disease severity, but there has been a wide variation in results based on past dengue infection and infecting dengue virus (DENV) serotype. As NS1 engages with many host lipids, we hypothesize that the type of NS1-lipid interactions alters its pathogenicity.

METHODS

Primary human monocyte derived macrophages (MDMs) were co-cultured with NS1 alone or with HDL, LDL, LPS and/or platelet activating factor (PAF) from individuals with a history of past dengue fever (DF = 8) or dengue haemorrhagic fever (DHF = 8). IL-1β levels were measured in culture supernatants, and gene expression analysis carried out in MDMs. Monocyte subpopulations were assessed by flow cytometry. Hierarchical cluster analysis with Euclidean distance calculations were used to differentiate clusters. Differentially expressed variables were extracted and a classifier model was developed to differentiate between past DF and DHF.

RESULTS

Significantly higher levels of IL-1β were seen in culture supernatants when NS1 was co-cultured with LDL (p = 0.01, median = 45.69 pg/ml), but lower levels when NS1 was co-cultured with HDL (p = 0.05, median = 4.617 pg/ml). MDMs of those with past DHF produced higher levels of IL-1β when NS1 was co-cultured with PAF (p = 0.02). MDMs of individuals with past DHF, were significantly more likely to down-regulate RPLP2 gene expression when macrophages were co-cultured with either PAF alone, or NS1 combined with PAF, or NS1 combined with LDL. When NS1 was co-cultured with PAF, HDL or LDL two clusters were detected based on IL10 expression, but these did not differentiate those with past DF or DHF.

CONCLUSIONS

As RPLP2 is important in DENV replication, regulating cellular stress responses and immune responses and IL-10 is associated with severe disease, it would be important to further explore how differential expression of RPLP2 and IL-10 could lead to disease pathogenesis based on NS1 and lipid interactions.

Structural biology of flavivirus NS1 protein and its antibody complexes

The genus of flavivirus includes many mosquito-borne human pathogens, such as Zika (ZIKV) and the four serotypes of dengue (DENV1-4) viruses, that affect billions of people as evidenced by epidemics and endemicity in many countries and regions in the world. Among the 10 viral proteins encoded by the viral genome, the nonstructural protein 1 (NS1) is the only secreted protein and has been used as a diagnostic biomarker. NS1 has also been an attractive target for its biotherapeutic potential as a vaccine antigen. This review focuses on the recent advances in the structural landscape of the secreted NS1 (sNS1) and its complex with monoclonal antibodies (mAbs). NS1 forms an obligatory dimer, and upon secretion, it has been reported to be hexametric (trimeric dimers) that could dissociate and bind to the epithelial cell membrane. However, high-resolution structural information has been missing about the high-order oligomeric states of sNS1. Several cryoEM studies have since shown that DENV and ZIKV recombinant sNS1 (rsNS1) are in dynamic equilibrium of dimer-tetramer-hexamer states, with tetramer being the predominant form. It was recently revealed that infection-derived sNS1 (isNS1) forms a complex of the NS1 dimer partially embedded in a High-Density Lipoprotein (HDL) particle. Structures of NS1 in complexes with mAbs have also been reported which shed light on their protective roles during infection. The biological significance of the diversity of NS1 oligomeric states remains to be further studied, to inform future research on flaviviral pathogenesis and the development of therapeutics and vaccines. Given the polymorphism of flavivirus NS1 across sample types with variations in antigenicity, we propose a nomenclature to accurately define NS1 based on the localization and origin.

Molecular mechanisms in the pathogenesis of dengue infections

Dengue is the most rapidly emerging climate-sensitive infection, and morbidity/mortality and disease incidence are rising markedly, leading to healthcare systems being overwhelmed. There are currently no specific treatments for dengue or prognostic markers to identify those who will progress to severe disease. Owing to an increase in the burden of illness and a change in epidemiology, many patients experience severe disease. Our limited understanding of the complex mechanisms of disease pathogenesis has significantly hampered the development of safe and effective treatments, vaccines, and biomarkers. We discuss the molecular mechanisms of dengue pathogenesis, the gaps in our knowledge, and recent advances, as well as the most crucial questions to be answered to enable the development of therapeutics, biomarkers, and vaccines.

Higher-temperature-adapted dengue virus serotype 2 strain exhibits enhanced virulence in AG129 mouse model

The factors that drive dengue virus (DENV) evolution, and selection of virulent variants are yet not clear. Higher environmental temperature shortens DENV extrinsic incubation period in mosquitoes, increases human transmission, and plays a critical role in outbreak dynamics. In the present study, we looked at the effect of temperature in altering the virus virulence. We found that DENV cultured at a higher temperature in C6/36 mosquito cells was significantly more virulent than the virus grown at a lower temperature. In a mouse model, the virulent strain induced enhanced viremia and aggressive disease with a short course, hemorrhage, severe vascular permeability, and death. Higher inflammatory cytokine response, thrombocytopenia, and severe histopathological changes in vital organs such as heart, liver, and kidney were hallmarks of the disease. Importantly, it required only a few passages for the virus to acquire a quasi-species population harboring virulence-imparting mutations. Whole genome comparison with a lower temperature passaged strain identified key genomic changes in the structural protein-coding regions as well as in the 3'UTR of the viral genome. Our results point out that virulence-enhancing genetic changes could occur in the dengue virus genome under enhanced growth temperature conditions in mosquito cells.

Flavivirus nonstructural proteins and replication complexes as antiviral drug targets

Many flaviviruses are well-known pathogens, such as dengue, Zika, Japanese encephalitis, and yellow fever viruses. Among them, dengue viruses cause global epidemics and threaten billions of people. Effective vaccines and antivirals are in desperate need. In this review, we focus on the recent advances in understanding viral nonstructural (NS) proteins as antiviral drug targets. We briefly summarize the experimental structures and predicted models of flaviviral NS proteins and their functions. We highlight a few well-characterized inhibitors targeting these NS proteins and provide an update about the latest development. NS4B emerges as one of the most promising drug targets as novel inhibitors targeting NS4B and its interaction network are entering clinical studies. Studies aiming to elucidate the architecture and molecular basis of viral replication will offer new opportunities for novel antiviral discovery. Direct-acting agents against dengue and other pathogenic flaviviruses may be available very soon.

The Influence of Preforming Protein Coronas on the Performance of Dengue NS1 Immunoassays

The effect of preformed protein coronas on immunoassays for Dengue nonstructural protein 1 (NS1) immunoassays was investigated. The composition of the protein corona that forms around nanoparticle-antibody conjugates in human serum was characterized, and selected proteins from the corona were used for preformed coronas (human serum albumin and apolipoprotein A1). Coronas were formed and characterized by dynamic light scattering (DLS), and the nanoparticle-conjugate was probed by optical absorption spectroscopy. Immunoassays were run, and performance was quantified by analyzing the strip intensity as a function of NS1 concentration. The preformed coronas influenced the limit of detection (LOD) of the assay and the affinity for the NS1 target (KD). The resulting KD and LODs for the NP-Ab-ApoA1 immunoprobes were 0.83 nM and 1.24 nM, respectively. For the NP-Ab -HSA coronas, the test line intensity was lower by 33% at a given NS1 concentration than for the NP-Ab immunoprobes, and KD was 0.14 nM, a slightly higher affinity. Due to the relatively large error of the negative control, a meaningful LOD for the NP-Ab with HSA coronas could not be determined.

Association of dengue virus non-structural-1 protein with disease severity: a brief review

Dengue virus (DENV) was discovered by P. M. Ashburn and Charles F. Craig in 1907. Evidence of dengue-like illness was observed before 1907 and DENV epidemics have been reported from different parts of the world since then, with increased morbidity rates every year. DENV typically causes a febrile illness that ranges from mild asymptomatic infection to fatal dengue haemorrhagic fever (DHF) and/or dengue shock syndrome (DSS). Host mechanisms through which mild infection progresses to the fatal forms are still unknown. Few factors have been associated to aid severe disease acquisition, DENV non-structural 1 (NS1) protein being one of them. NS1 is a highly conserved glycoprotein among the Flavivirus and is often used as a biomarker for dengue diagnosis. This review focuses on assessing the role of NS1 in severe dengue. In this review, hospital-based studies on the association of dengue NS1 with severe dengue from all over the world have been assessed and analysed and the majority of the studies positively correlate high NS1 levels with DHF/DSS acquisition. The review also discusses a few experimental studies on NS1 that have shown it contributes to dengue pathogenesis. This review assesses the role of NS1 and disease severity from hospital-based studies and aims to provide better insights on the kinetics and dynamics of DENV infection with respect to NS1 for a better understanding of the role of NS1 in dengue.

Performance of the onstructural 1 Antigen Rapid Test for detecting all four DENV serotypes in clinical specimens from Bangkok, Thailand

BACKGROUND

Dengue is an arboviral disease that has a large effect on public health in subtropical and tropical countries. Rapid and accurate detection of dengue infection is necessary for diagnosis and disease management. We previously developed highly sensitive immunochromatographic devices, the TKK 1st and TKK 2nd kits, based on dengue virus (DENV) nonstructural protein 1 detection. However, these TKK kits were evaluated mainly using DENV type 2 clinical specimens collected in Bangladesh, and further validation using clinical specimens of other serotypes was needed.

METHODS

In the present study, one of the TKK kits, TKK 2nd, was evaluated using 10 DENV-1, 10 DENV-2, 4 DENV-3, 16 DENV-4, and 10 zika virus-infected clinical specimens collected in Bangkok, Thailand.

RESULTS

The TKK 2nd kit successfully detected all four DENV serotypes in patient serum specimens and did not show any cross-reactivities against zika virus serum specimens. The IgM and/or IgG anti-DENV antibodies were detected in seven serum specimens, but did not seem to affect the results of antigen detection in the TKK 2nd kit.

CONCLUSION

The results showed that the TKK 2nd kit successfully detected all four DENV serotypes in clinical specimens and confirmed the potential of the kit for dengue diagnosis in endemic countries.

Combination of the Focus-Forming Assay and Digital Automated Imaging Analysis for the Detection of Dengue and Zika Viral Loads in Cultures and Acute Disease

Optimized methods for the detection of flavivirus infections in hyperendemic areas are still needed, especially for working with patient serum as a starting material. The focus-forming assay (FFA) reveals critical aspects of virus-host interactions, as it is a quantitative assay to determine viral loads. Automated image analysis provides evaluations of relative amounts of intracellular viral protein at the single-cell level. Here, we developed an optimized FFA for the detection of infectious Zika virus (ZIKV) and dengue virus (DENV) viral particles in cell cultures and clinical serum samples, respectively. Vero-76 cells were infected with DENV-2 (16681) or ZIKV (PRVA BC59). Using a panel of anti-DENV and anti-ZIKV NS1-specific monoclonal antibodies (mAbs), the primary mAbs, concentration, and the optimal time of infection were determined. To determine whether intracellular accumulation of NS1 improved the efficiency of the FFA, brefeldin A was added to the cultures. Focus formation was identified by conventional optical microscopy combined with CellProfiler™ automated image analysis software. The FFA was used with spike assays for ZIKV and clinical specimens from natural infection by DENV-1 and DENV-2. mAb 7744-644 for ZIKV and mAb 724-323 for DENV used at a concentration of 1 μg/ml and a time of 24 hours postinfection produced the best detection of foci when combining conventional counting and automated digital analysis. Brefeldin A did not improve the assessment of FFUs or their digitally assessed intensity at single-cell level. The FFA showed 95% ZIKV recovery and achieved the detection of circulating DENV-1 and DENV-2 in the plasma of acutely ill patients. The combination of the two techniques optimized the FFA, allowing the study of DENV and ZIKV in culture supernatants and clinical specimens from natural infection in hyperendemic areas.

Dengue Infection - Recent Advances in Disease Pathogenesis in the Era of COVID-19

The dynamics of host-virus interactions, and impairment of the host’s immune surveillance by dengue virus (DENV) serotypes largely remain ambiguous. Several experimental and preclinical studies have demonstrated how the virus brings about severe disease by activating immune cells and other key elements of the inflammatory cascade. Plasmablasts are activated during primary and secondary infections, and play a determinative role in severe dengue. The cross-reactivity of DENV immune responses with other flaviviruses can have implications both for cross-protection and severity of disease. The consequences of a cross-reactivity between DENV and anti-SARS-CoV-2 responses are highly relevant in endemic areas. Here, we review the latest progress in the understanding of dengue immunopathogenesis and provide suggestions to the development of target strategies against dengue.

High viral load positively correlates with thrombocytopenia and elevated haematocrit in dengue infected paediatric patients

BACKGROUND

Dengue fever is one of the major viral diseases worldwide transmitted by mosquitoes. Depending on the severity of disease it can range from mild fever to severe fatal cases. Rapid decline of platelet levels is one of indicators of clinical worsening. The role of viral factors in dengue pathogenesis and correlation with clinical and laboratory parameters remain unclear.

METHODS

Between September 2017 to December 2018, 102 dengue confirmed paediatric cases were analysed for various viral and host parameters. Based on symptoms, they were classified into dengue without warning signs (DOS), dengue with warning signs (DWS) and severe dengue (SD) as per 2009 WHO classification. Quantitative analysis of NS1, IgM and IgG in were done by ELISA. IgM/IgG ratio revealed primary or secondary dengue infection. Serotyping of virus in serum was done by nested multiplex RT-PCR. Viral load (VL) was determined by quantitative real time polymerase chain reaction. Association between VL and NS1 in patient sera with clinical and laboratory parameters was statistically analysed.

RESULTS

It was found that disease severity (as per 2009 WHO classification) significantly associated with secondary dengue infection. DENV3 was found to be the only serotype detected. The present study reports neither NS1 nor VL significantly associated with disease severity or type of infection (primary or secondary). However, VL positively correlated with haematocrit (p < 0.05). Viral load above 10⁶ copies/mL was found in 61% of patients. Further, high viral load (>10⁶ copies/mL) negatively correlated with platelet levels (p < 0.05).

CONCLUSION

Thus, viral load could be an important predictive parameter in dengue related severe symptoms like thrombocytopenia and elevated hematocrit when it goes above a certain threshold (>10⁶ copies/ mL).

A Non-structural 1 Protein G53D Substitution Attenuates a Clinically Tested Live Dengue Vaccine

The molecular basis of dengue virus (DENV) attenuation remains ambiguous and hampers a targeted approach to derive safe but nonetheless immunogenic live vaccine candidates. Here, we take advantage of DENV serotype 2 PDK53 vaccine strain, which recently and successfully completed a phase-3 clinical trial, to identify how this virus is attenuated compared to its wild-type parent, DENV2 16681. Site-directed mutagenesis on a 16681 infectious clone identifies a single G53D substitution in the non-structural 1 (NS1) protein that reduces 16681 infection and dissemination in both Aedes aegypti, as well as in mammalian cells to produce the characteristic phenotypes of PDK53. Mechanistically, NS1 G53D impairs the function of a known host factor, the endoplasmic reticulum (ER)-resident ribophorin 1 protein, to properly glycosylate NS1 and thus induce a host antiviral gene through ER stress responses. Our findings provide molecular insights on DENV attenuation on a clinically tested strain.

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.

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.

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.

Risk factors and biomarkers of severe dengue

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

Serum chymase levels correlate with severe dengue warning signs and clinical fluid accumulation in hospitalized pediatric patients

Dengue induces a spectrum of severity in humans from the milder dengue fever to severe disease, or dengue hemorrhagic fever (DHF). Chymase is a candidate biomarker that may aid dengue prognosis. This prospective study aimed to identify whether warning signs of severe dengue, including hypovolemia and fluid accumulation, were associated with elevated chymase. Serum chymase levels were quantified prospectively and longitudinally in hospitalized pediatric dengue patients in Sri Lanka. Warning signs were determined based on daily clinical assessments, laboratory tests and ultrasound findings. Chymase was significantly elevated during the acute phase of disease in DHF or Severe dengue, defined by either the 1997 or 2009 WHO diagnosis guidelines, and persisted longer in the most severe patients. Chymase levels were higher in patients with narrow pulse pressure and clinical warning signs such as severe leakage, fluid accumulation, pleural effusion, gall-bladder wall thickening and rapid haematocrit rise concurrent with thrombocytopenia. No association between chymase and liver enlargement was observed. This study confirms that serum chymase levels are associated with DHF/Severe dengue disease in hospitalized pediatric patients. Chymase levels correlate with warning signs of vascular dysfunction highlighting the possible functional role of chymase in vascular leakage during dengue.

Repurposing Old Antibodies for New Diseases by Exploiting Cross-Reactivity and Multicolored Nanoparticles

We exploit the cross-reactivity of dengue (DENV) and Zika (ZIKV) virus polyclonal antibodies for nonstructural protein 1 (NS1) to construct a selective sensor that can detect yellow fever virus (YFV) NS1 in a manner similar to chemical olfaction. DENV and ZIKV antibodies were screened for their ability to bind to DENV, ZIKV, and YFV NS1 by enzyme linked immunosorbent assay (ELISA) and in pairs in paper immunoassays. A strategic arrangement of antibodies immobilized on paper and conjugated to different colored gold NPs was used to distinguish the three biomarkers. Machine learning of test area RGB values showed that with two spots, readout accuracies of 100% and 87% were obtained for both pure NS1 and DENV/YFV mixtures, respectively. Additional image preprocessing allowed differentiation between all four DENV serotypes with 92% accuracy. The technique was extended to hack a commercial DENV test to detect YFV and ZIKV by augmentation with DENV and ZIKV polyclonal antibodies.

Flavivirus Infection Associated with Cerebrovascular Events

Arthropod-borne viruses (arboviruses) of the genus Flavivirus are distributed globally and cause significant human disease and mortality annually. Flavivirus infections present a spectrum of clinical manifestations, ranging from asymptomatic to severe manifestations, including hemorrhage, encephalitis and death. Herein, we describe 3 case reports of cerebrovascular involvement in patients infected by dengue and Zika viruses in Sao Jose do Rio Preto, São Paulo State, Brazil, a hyperendemic area for arbovirus circulation, including dengue, yellow fever, chikungunya and Saint Louis encephalitis viruses. Our findings highlight the potential threat that unusual clinical manifestations may pose to arbovirus disease management and recovery.

Non-structural protein 1 (NS1) of dengue virus detection correlates with severity in primary but not in secondary dengue infection

BACKGROUND

Non-structural protein 1 (NS1) of dengue virus circulates in the serum of patients during the acute phase of the disease.

OBJECTIVES

To determine whether NS1 screening can serve in diagnosing primary and secondary infection and to evaluate its utility as a marker for predicting the severity of dengue in children.

STUDY DESIGN

Patients ≤15 years of age hospitalized for dengue between 2012-2018, with NS1 determination (Panbio, Australia) were included. Clinical y laboratorial characteristics were collected in a standardized data table for analysis of correlation between serotypes, primary or secondary condition of infection, severity, and presence of NS1.

RESULTS

Of 709 children hospitalized for dengue with NS1 determination, 479 (67.5 %) had the positive test. Of the 378 primary cases, 320 (85 %) were NS1 (+). while among the 242 secondary cases only 103 (42.5 %) were NS1 (+) (p < 0001). Of the 479 patients with NS1 (+), 344 (72 %) were warnig-signed cases (WSC) and 94 (19 %) were severe cases (SC), being these figures 62 % and 34 %, in the NS1 negative patients respectively (p < 0.001). There was no difference in the frequency of WSC or SC between patients with NS1 positive or negative test in secondary dengue; however, in primary dengue, the figures were 68 % vs 32 % (p < 0.001), and 87 % vs 12 % (p < 0.001), respectively.

CONCLUSIONS

The presence of NS1 positive test is associated with the condition of infection (primary or secondary) and exhibited an increased risk of developing forms with warning signs or severe dengue in primary cases, but not in secondary cases.

SERS Platform for Dengue Diagnosis from Clinical Samples Employing a Hand Held Raman Spectrometer

Dengue is a serious global health concern especially in tropical and subtropical countries. About 2.5 billion of the world's population is at risk for dengue infection. Early diagnosis is the key to prevent the deterioration of health of the patient to severe illness. Laboratory diagnosis of dengue is essential for providing appropriate supportive treatment to dengue patients with febrile illness, which is difficult to diagnose clinically. Here, we demonstrate surface enhanced Raman scattering (SERS) based diagnosis of dengue virus in clinical blood samples collected from total of 102 subjects. All of the samples were well characterized by conventional NS1 antigen and IgM antibody ELISA kits. The silver nanorods array fabricated by glancing angle deposition technique were employed as SERS substrates. A small amount of patient blood serum (5 μL) was taken for analysis and the report was prepared within a minute. SERS spectra of pure NS1 protein as well as spiked in serum was also recorded separately. Principal component analysis (PCA) was employed as the statistical tool to differentiate dengue positive, dengue negative, and healthy subjects on the basis of their respective SERS spectra. This method provides a sensitive, rapid, and field deployable diagnosis of dengue at the early stage (within 5 days of the onset of symptoms).

Differential replicative fitness of the four dengue virus serotypes circulating in Colombia in human liver Huh7 cells

Dengue has been a significant public health problem in Colombia since the simultaneous circulation of the four dengue virus serotypes. The replicative fitness of dengue is a biological feature important for virus evolution and contributes to elucidating the behavior of virus populations and viral pathogenesis. However, it has not yet been studied in Colombian isolates. This study aimed to compare the replicative fitness of the four dengue virus serotypes and understand the association between the serotypes, their in vitro infection ability, and their replication in target cells. We used three isolates of each DENV serotype to infect Huh-7 cells at an MOI of 0.5. The percentage of infected cells was evaluated by flow cytometry, cell viability was evaluated by MTT assay, and the pathogenicity index was calculated as a ratio of both parameters. The replicative fitness was measured by the number of viral genome copies produced using quantitative PCR and the production of infectious viral progeny was measured by plaque assay. We showed that Huh-7 cells were susceptible to infection with all the different strain isolates. Nevertheless, the biological characteristics, such as infectious ability and cell viability, were strain-dependent. We also found different degrees of pathogenicity between strains of the four serotypes, representative of the heterogeneity displayed in the circulating population. When we analyzed the replicative fitness using the mean values obtained from RT-qPCR and plaque assay for the different strains, we found serotype-dependent behavior. The highest mean values of replicative fitness were obtained for DENV-1 (log 4.9 PFU/ml) and DENV-4 (log 5.28 PFU/ml), followed by DENV-2 (log 3.9 PFU/ml) and DENV-3 (log 4.31 PFU/ml). The internal heterogeneity of the replicative fitness within each serotype could explain the simultaneous circulation of the four DENV serotypes in Colombia.

Identification of inhibitors of dengue viral replication using replicon cells expressing secretory luciferase

Dengue virus (DENV) is the causative agent of dengue fever (DF), dengue haemorrhagic fever (DHF), and dengue shock syndrome (DSS) and continues to be a public health problem in the tropical and subtropical areas. However, there is currently no antiviral treatment for DENV infection. In this study, our aim was to develop a stable reporter replicon cell system that supports constant viral RNA replication in cultured cells. The isolated replicon cells exhibited high levels of luciferase activity in the culture supernatant concomitant with expression of virus-encoded NS1, NS3 and NS5 proteins in the cells. The NS1, NS3 proteins and dsRNA were detected in the replicon cells by immunofluorescence analysis. Furthermore, the anti-DENV inhibitors ribavirin and bromocriptine significantly reduced the luciferase activity in a dose-dependent manner. High-throughput screening with a compound library using the stably-transfected replicon cells showed a Z' factor value of 0.57. Our screening yielded several candidates including one compound that has already shown anti-DENV activity. Taken together, our results demonstrate that this DENV subgenomic replicon cell system expressing a secretory luciferase gene can be useful for the high-throughput screening of anti-DENV compounds and the analysis of the replication mechanism of the DENV RNA.

An Attenuated Zika Virus Encoding Non-Glycosylated Envelope (E) and Non-Structural Protein 1 (NS1) Confers Complete Protection against Lethal Challenge in a Mouse Model

Zika virus (ZIKV), a mosquito-transmitted flavivirus, emerged in the last decade causing serious human diseases, including congenital microcephaly in newborns and Guillain-Barré syndrome in adults. Although many vaccine platforms are at various stages of development, no licensed vaccines are currently available. Previously, we described a mutant MR766 ZIKV (m2MR) bearing an E protein mutation (N154A) that prevented its glycosylation, resulting in attenuation and defective neuroinvasion. To further attenuate m2MR for its potential use as a live viral vaccine, we incorporated additional mutations into m2MR by substituting the asparagine residues in the glycosylation sites (N130 and N207) of NS1 with alanine residues. Examination of pathogenic properties revealed that the virus (m5MR) carrying mutations in E (N154A) and NS1 (N130A and N207A) was fully attenuated with no disease signs in infected mice, inducing high levels of humoral and cell-mediated immune responses, and protecting mice from subsequent lethal virus challenge. Furthermore, passive transfer of sera from m5MR-infected mice into naïve animals resulted in complete protection from lethal challenge. The immune sera from m5MR-infected animals neutralized both African and Asian lineage viruses equally well, suggesting that m5MR virus could be developed as a potentially broad live virus vaccine candidate.

Dengue virus-elicited tryptase induces endothelial permeability and shock

Dengue virus (DENV) infection causes a characteristic pathology in humans involving dysregulation of the vascular system. In some patients with dengue hemorrhagic fever (DHF), vascular pathology can become severe, resulting in extensive microvascular permeability and plasma leakage into tissues and organs. Mast cells (MCs), which line blood vessels and regulate vascular function, are able to detect DENV in vivo and promote vascular leakage. Here, we identified that a MC-derived protease, tryptase, is consequential for promoting vascular permeability during DENV infection, through inducing breakdown of endothelial cell tight junctions. Injected tryptase alone was sufficient to induce plasma loss from the circulation and hypovolemic shock in animals. A potent tryptase inhibitor, nafamostat mesylate, blocked DENV-induced vascular leakage in vivo. Importantly, in two independent human dengue cohorts, tryptase levels correlated with the grade of DHF severity. This study defines an immune mechanism by which DENV can induce vascular pathology and shock.

The effect of freeze-dried Carica papaya leaf juice treatment on NS1 and viremia levels in dengue fever mice model

Background

Carica papaya leaf juice (CPLJ) was well known for its thrombocytosis activity in rodents and dengue patients. However, the effect of CPLJ treatment on other parameters that could contribute to dengue pathogenesis such as nonstructural protein 1 (NS1) production and viremia level have never been highlighted in any clinical and in vivo studies. The aim of this study is to investigate the effect of freeze-dried CPLJ treatment on NS1 and viremia levels of dengue fever mouse model.

Methods

The dengue infection in mouse model was established by inoculation of non-mouse adapted New Guinea C strain dengue virus (DEN-2) in AG129 mice. The freeze-dried CPLJ compounds were identified by Ultra-High Performance Liquid Chromatography High Resolution Accurate Mass Spectrometry analysis. The infected AG129 mice were orally treated with 500 mg/kg/day and 1000 mg/kg/day of freeze-dried CPLJ, starting on day 1 post infection for 3 consecutive days. The blood samples were collected from submandibular vein for plasma NS1 assay and quantitation of viral RNA level by quantitative reverse transcription PCR.

Results

The AG129 mice infected with dengue virus showed marked increase in the production of plasma NS1, which was detectable on day 1 post infection, peaked on day 3 post-infection and started to decline from day 5 post infection. The infection also caused splenomegaly. Twenty-four compounds were identified in the freeze-dried CPLJ. Oral treatment with 500 mg/kg/day and 1000 mg/kg/day of freeze-dried CPLJ did not affect the plasma NS1 and dengue viral RNA levels. However, the morbidity level of infected AG129 mice were slightly decreased when treated with freeze-dried CPLJ.

Conclusion

Oral treatment of 500 mg/kg/day and 1000 mg/kg/day of freeze-dried CPLJ at the onset of viremia did not affect the plasma NS1 and viral RNA levels in AG129 mice infected with non-mouse adapted New Guinea C strain dengue virus.

Electronic supplementary material

The online version of this article (10.1186/s12906-018-2390-7) contains supplementary material, which is available to authorized users.

Secretion of Nonstructural Protein 1 of Dengue Virus from Infected Mosquito Cells: Facts and Speculations

Dengue virus nonstructural protein 1 (NS1) is a multifunctional glycoprotein. For decades, the notion in the field was that NS1 is secreted exclusively from vertebrate cells and not from mosquito cells. However, recent evidence shows that mosquito cells also secrete NS1 efficiently. In this review, we discuss the evidence for secretion of NS1 of dengue virus, and of other flaviviruses, from mosquito cells, differences between NS1 secreted from mosquito and NS1 secreted from vertebrate cells, and possible roles of soluble NS1 in the insect flavivirus vector.

Tapered lateral flow immunoassay based point-of-care diagnostic device for ultrasensitive colorimetric detection of dengue NS1

Dengue virus, a Flaviviridae family member, has emerged as a major worldwide health concern, making its early diagnosis imperative. Lateral flow immunoassays have been widely employed for point-of-care diagnosis of dengue because of their rapid naked eye readouts, ease of use, and cost-effectiveness. However, they entail a drawback of low sensitivity, limiting their usage in clinical applications. Herein, we report a novel lateral flow immunoassay for detection of dengue leveraging on the benefits of gold decorated graphene oxide sheets as detection labels and a tapered nitrocellulose membrane. The developed assay allows for rapid (10 min) and sensitive detection of dengue NS1 with a detection limit of 4.9 ng mL^-1, ∼11-fold improvement over the previously reported values. Additionally, the clinical application of the developed assay has been demonstrated by testing it for dengue virus spiked in human serum. The reported lateral flow immunoassay shows significant promise for early and rapid detection of several target diseases.

Establishment of a mouse model for the complete mosquito-mediated transmission cycle of Zika virus

Zika virus (ZIKV) is primarily transmitted by Aedes mosquitoes in the subgenus Stegomyia but can also be transmitted sexually and vertically in humans. STAT1 is an important downstream factor that mediates type I and II interferon signaling. In the current study, we showed that mice with STAT1 knockout (Stat1^-/-) were highly susceptible to ZIKV infection. As low as 5 plaque-forming units of ZIKV could cause viremia and death in Stat1^-/- mice. ZIKV replication was initially detected in the spleen but subsequently spread to the brain with concomitant reduction of the virus in the spleen in the infected mice. Furthermore, ZIKV could be transmitted from mosquitoes to Stat1^-/- mice back to mosquitoes and then to naïve Stat1^-/- mice. The 50% mosquito infectious dose of viremic Stat1^-/- mouse blood was close to 810 focus-forming units (ffu)/ml. Our further studies indicated that the activation of macrophages and conventional dendritic cells were likely critical for the resolution of ZIKV infection. The newly developed mouse and mosquito transmission models for ZIKV infection will be useful for the evaluation of antiviral drugs targeting the virus, vector, and host.

Zika virus (ZIKV) is transmitted mainly by mosquito bites and can also be transmitted between humans by sex or from pregnant women to their babies. ZIKV infection causes damage in many tissues including the brain in adults and newborns, making ZIKV infection an important health issue globally. To develop new tools for ZIKV research, we determined that a genetically modified mouse strain, Stat1^-/-, was highly sensitive to ZIKV infection. We also demonstrated that ZIKV could be delivered to mice by mosquito bites and transmitted back to Stat1^-/- mice. The newly developed mouse model will be useful for developing new strategies to treat ZIKV infection and for studying mechanisms to reduce mosquito-mediated transmission.

Dengue Antiviral Development: A Continuing Journey

Dengue fever is a leading cause of illness and mortality in the tropics and subtropics. There are no therapeutics currently available and a recently approved vaccine is not very efficacious demanding an urgent need to develop an effective antiviral. The path to successful dengue drug development depends on availability of relevant preclinical testing models and better understanding of dengue pathogenesis. In recent years, efforts to develop dengue therapeutics have focused on both repurposing approved drugs as well as discovery of new chemical entities that act via virus or host targeted mechanisms. Here, we discuss the various innovative approaches, their outcome, and the lessons gleaned from the development efforts.

Assessing Zika virus replication and the development of Zika-specific antibodies after a mid-gestation viral challenge in guinea pigs

Primary Zika virus (ZIKV) infections that occur during pregnancy can cause spontaneous abortion and profoundly disrupt fetal development. While the full range of developmental abnormalities associated with congenital Zika syndrome is not yet known, severe cases of the syndrome can present with microcephaly, extensive neurologic and ocular damage, and pronounced joint malformations. Animal models that accurately recapitulate congenital Zika syndrome are urgently needed for vaccine development and for the study of ZIKV pathogenesis. As guinea pigs have successfully been used to model transplacental infections by cytomegalovirus, syphilis, and Listeria monocytogenes, we sought to test whether ZIKV could productively infect guinea pigs and whether viral transmission with attendant fetal pathology would occur after a mid-gestation viral challenge. We found that guinea pig cells supported ZIKV replication in vitro. Experimental infection of non-pregnant animals did not result in overt disease but low-level, detectable viremia was observed. When pregnant guinea pigs were challenged with ZIKV at between 18 and 21 days gestational age, ZIKV was not detected in maternal or pup blood, plasma, or tissues and no significant differences in maternal weight gain or pup size were observed following challenge. Nonetheless, a robust antibody response against ZIKV was detected in both the pups and dams. These results suggest that, while guinea pigs can model aspects of the immune response to ZIKV infection during pregnancy, naturally circulating ZIKV strains are not pathogenic during the pregnancy of immunocompetent guinea pigs and do not interfere with normal pup development.

Surface-Enhanced Raman Spectroscopy-Based Sandwich Immunoassays for Multiplexed Detection of Zika and Dengue Viral Biomarkers

Zika and dengue are mosquito-borne diseases that present similar nonspecific symptoms but possess dramatically different outcomes. The first line of defense in epidemic outbreaks are rapid point-of-care diagnostics. Because many outbreaks occur in areas that are resource poor, assays that are easy to use, inexpensive, and require no power have become invaluable in patient treatment, quarantining, and surveillance. Paper-based sandwich immunoassays such as lateral flow assays (LFAs) are attractive as point-of-care solutions as they have the potential for wider deployability than lab-based assays such as PCR. However, their low sensitivity imposes limitations on their ability to detect low biomarker levels and early diagnosis. Here, we exploit the high sensitivity of surface-enhanced Raman spectroscopy (SERS) in a multiplexed assay that can distinguish between Zika and dengue nonstructural protein 1 (NS1) biomarkers. SERS-encoded gold nanostars were conjugated to specific antibodies for both diseases and used in a dipstick immunoassay, which exhibited 15-fold and 7-fold lower detection limits for Zika NS1 and dengue NS1, respectively. This platform combines the simplicity of a LFA with the high sensitivity of SERS and could not only improve Zika diagnosis but also detect diseases sooner after infection when biomarker levels are low.

Comparative whole genome analysis of dengue virus serotype-2 strains differing in trans-endothelial cell leakage induction in vitro

The role of genetic differences among dengue virus (DENV) in causing increased microvascular permeability is less explored. In the present study, we compared two closely related DENV serotype-2 strains of Cosmopolitan genotype for their in vitro infectivity phenotype and ability to induce trans-endothelial leakage. We found that these laboratory strains differed significantly in infecting human microvascular endothelial cells (HMEC-1) and hepatocytes (Huh7), two major target cells of DENV in in vivo infections. There was a reciprocal correlation in infectivity and vascular leakage induced by these strains, with the less infective strain inducing more trans-endothelial cell leakage in HMEC-1 monolayer upon infection. The cells infected with the strain capable of inducing more permeability were found to secrete more Non-Structural protein (sNS1) into the culture supernatant. A whole genome analysis revealed 37 predicted amino acid changes and changes in the secondary structure of 3' non-translated region between the strains. But none of these changes involved the signal sequence coded by the C-terminal of the Envelope protein and the two glycosylation sites within the NS1 protein critical for its secretion, and the N-terminal NS2A sequence important for surface targeting of NS1. The strain that secreted lower levels of NS1 and caused less leakage had two mutations within the NS1 protein coding region, F103S and T146I that significantly changed amino acid properties. A comparison of the sequences of the two strains with published sequences of various DENV strains known to cause clinically severe dengue identified a number of amino acid changes which could be implicated as possible key genetic differences. Our data supports the earlier observations that the vascular leakage induction potential of DENV strains is linked to the sNS1 levels. The results also indicate that viral genetic determinants, especially the mutations within the NS1 coding region, could affect this critical phenotype of DENV strains.

Current Status of Dengue Therapeutics Research and Development

Dengue is a significant global health problem. Even though a vaccine against dengue is now available, which is a notable achievement, its long-term protective efficacy against each of the 4 dengue virus serotypes remains to be definitively determined. Consequently, drugs directed at the viral targets or critical host mechanisms that can be used safely as prophylaxis or treatment to effectively ameliorate disease or reduce disease severity and fatalities are still needed to reduce the burden of dengue. This review will provide a brief account of the status of therapeutics research and development for dengue.

Dengue virus NS1 triggers endothelial permeability and vascular leak that is prevented by NS1 vaccination

The four dengue virus serotypes (DENV1 to DENV4) are mosquito-borne flaviviruses that cause up to ~100 million cases of dengue annually worldwide. Severe disease is thought to result from immunopathogenic processes involving serotype cross-reactive antibodies and T cells that together induce vasoactive cytokines, causing vascular leakage that leads to shock. However, no viral proteins have been directly implicated in triggering endothelial permeability, which results in vascular leakage. DENV nonstructural protein 1 (NS1) is secreted and circulates in patients' blood during acute infection; high levels of NS1 are associated with severe disease. We show that inoculation of mice with DENV NS1 alone induces both vascular leakage and production of key inflammatory cytokines. Furthermore, simultaneous administration of NS1 with a sublethal dose of DENV2 results in a lethal vascular leak syndrome. We also demonstrate that NS1 from DENV1, DENV2, DENV3, and DENV4 triggers endothelial barrier dysfunction, causing increased permeability of human endothelial cell monolayers in vitro. These pathogenic effects of physiologically relevant amounts of NS1 in vivo and in vitro were blocked by NS1-immune polyclonal mouse serum or monoclonal antibodies to NS1, and immunization of mice with NS1 from DENV1 to DENV4 protected against lethal DENV2 challenge. These findings add an important and previously overlooked component to the causes of dengue vascular leak, identify a new potential target for dengue therapeutics, and support inclusion of NS1 in dengue vaccines.

Optimizing celgosivir therapy in mouse models of dengue virus infection of serotypes 1 and 2: The search for a window for potential therapeutic efficacy

Although the antiviral drug celgosivir, an α-glucosidase I inhibitor, is highly protective when given twice daily to AG129 mice infected with dengue virus, a similar regimen of twice daily dosing did not significantly reduce serum viral loads in patients in a recent clinical trial. This failure presumably might reflect the initiation of treatment when patients were already viremic. To better mimic the clinical setting, we used viruses isolated from patients to develop new mouse models of DENV1 and DENV2 infection and employed the models to test the twice daily treatment, begun either on the day of infection or on the third day post-infection, when the mice had peak of viremia. We found that, although the treatment started on day 0 was effective on viral load reduction, it provided no benefit when begun on day 3, indicating that in vivo antiviral efficacy becomes less prominent once viremia reaches the peak level. To determine if the therapeutic regimen in humans could be improved, we tested regimen of four-times daily treatment and found that the treatment significantly reduced viremia, suggesting that a similar regimen may be effective in a human clinical trial. A new clinical trial to investigate an altered dosing regimen has been approved (NCT02569827).

Animal models for studying dengue pathogenesis and therapy

Development of a suitable animal model for dengue virus disease is critical for understanding pathogenesis and for preclinical testing of antiviral drugs and vaccines. Many laboratory animal models of dengue virus infection have been investigated, but the challenges of recapitulating the complete disease still remain. In this review, we provide a comprehensive coverage of existing models, from man to mouse, with a specific focus on recent advances in mouse models for addressing the mechanistic aspects of severe dengue in humans. This article forms part of a symposium in Antiviral Research on flavivirus drug discovery.

Dengue Virus Infection with Highly Neutralizing Levels of Cross-Reactive Antibodies Causes Acute Lethal Small Intestinal Pathology without a High Level of Viremia in Mice

Severe dengue virus (DENV)-associated diseases can occur in patients who have preexisting DENV antibodies (Abs) through antibody-dependent enhancement (ADE) of infection. It is well established that during ADE, DENV-antibody immune complexes (ICs) infect Fcγ receptor-bearing cells and increase the systemic viral burden that can be measured in the blood. For protection against infection with DENV serotypes 1 to 4, strongly neutralizing Abs must be elicited to overcome the effect of ADE. Clinical observations in infants who have maternal DENV Abs or recent phase II/III clinical trials with a leading tetravalent dengue vaccine suggested a lack of correlation between Ab neutralization and in vivo disease prevention. In addressing this gap in knowledge, we found that inoculation of ICs formed with serotype cross-reactive Abs that are more than 98% neutralized in vitro promotes high mortality in AG129 mice even though peak viremia was lower than that in direct virus infection. This suggests that the serum viremia level is not always correlated with disease severity. We further demonstrated that infection with the ICs resulted in increased vascular permeability, specifically in the small intestine, accompanied with increased tissue viral load and cytokine production, which can be suppressed by anti-tumor necrosis factor alpha (anti-TNF-α) Abs. Flow cytometric analysis identified increased infection in CD11b(int) CD11c(int/hi) CD103(-) antigen-presenting cells by IC inoculation, suggesting that these infected cells may be responsible for the increase in TNF-α production and vascular permeability in the small intestine that lead to mortality in mice. Our findings may have important implications for the development of dengue therapeutics.

IMPORTANCE

We examined the relationship between the neutralizing level of Abs at the time of infection and subsequent disease progression in a mouse model in order to understand why patients who are shown to have a neutralizing quantity of Abs still allow sufficient DENV replication to induce severe dengue manifestations, which sometimes do not correlate with viremia level. Strikingly, we found that high mortality was induced in AG129 mice by the increase in TNF-α-induced vascular permeability accompanied by an increased viral load, specifically in the small intestine, even when the initial infection level is suppressed to less than 5% and the peak viremia level is not enhanced. This suggests that ADE overcomes the protective efficacy of Abs in a tissue-dependent manner that leads to severe small intestinal pathology. Our findings may serve to address the pathogenic role of Abs on severe dengue disease and also help to develop safe Ab-based therapeutic strategies.

Assessing positivity and circulating levels of NS1 in samples from a 2012 dengue outbreak in Rio de Janeiro, Brazil

Dengue virus (DENV) represents a major threat to public health worldwide. Early DENV diagnosis should not only detect the infection but also identify patients with a higher likelihood to develop severe cases. Previous studies have suggested the potential for NS1 to serve as a viral marker for dengue severity. However, further studies using different sera panels are required to confirm this hypothesis. In this context, we developed a lab-based ELISA to detect and quantitate NS1 protein from the four DENV serotypes and from primary and secondary cases. This approach was used to calculate the circulating NS1 concentration in positive samples. We also tested the NS1 positivity of DENV-positive samples according to the Platelia Dengue NS1 Ag assay. A total of 128 samples were positive for DENV infection and were classified according to the WHO guidelines. The overall NS1 positivity was 68% according to the Platelia assay, whereas all samples were NS1-positive when analyzed with our lab-based ELISA. Fifty-four samples were positive by PCR, revealing a co-circulation of DENV1 and DENV4, and the NS1 positivity for DENV4 samples was lower than that for DENV1. The circulating NS1 concentration ranged from 7 to 284 ng/mL. Our results support previous data indicating the low efficiency of the Platelia assay to detect DENV4 infection. Moreover, this work is the first to analyze NS1 antigenemia using retrospective samples from a Brazilian outbreak.

A meta-analysis of the diagnostic accuracy of two commercial NS1 antigen ELISA tests for early dengue virus detection

Background

Dengue virus (DENV) NS1 antigen detection is regarded as an early diagnostic marker. Accordingly, several studies have evaluated the performance of tests that utilize NS1 capture, but the results of individual studies may be limited due to the restricted sample size of the patients recruited. Therefore, our objective was to perform a meta-analysis of the diagnostic accuracy of two commercial NS1 ELISAs (Panbio and Platelia).

Methods and Results

Studies of interest were found in PubMed, Embase and Google Scholar databases using defined inclusion/exclusion criteria. A total of 30 studies containing 12,105 total enrolled patients were included. The results were as follows: 1) Panbio assays showed low overall performance, sensitivity 66% (95% confidence interval (CI) 61–71), specificity 99% (95% CI 96–100), positive likelihood ratio (LR+) 98 (95% CI 20–464), negative likelihood ratio (LR-) 0.3 (95% CI 0.2–0.4), diagnostic odds ratio (DOR) 289 (95% CI 59–1412); 2) Platelia assays showed high overall performance, sensitivity 74% (95% CI 63–82), specificity 99% (95% CI 97–100), LR+ 175 (95% CI 28–1099), LR- 0.3 (95% CI 0.2–0.4), DOR 663 (95% CI 98–4478). The lowest sensitivity values were for secondary infections (57% [95% CI 47–67] and 66% [95% CI 53–77] for Panbio and Platelia, respectively) and for the detection of DENV4. Regarding clinical manifestations, the sensitivity of Platelia was 69% (95% CI 43–86) and 60% (95% CI 48–70) for fever and dengue hemorrhagic fever, respectively. In addition, the sensitivity of both tests was slightly lower for samples from Southeast Asia and Oceania.

Conclusion

DENV1 samples gave higher sensitivity results for both tests. We observed that factors negatively influencing the tests, such as the type of infection, geographical origins of samples and viral serotypes, require further investigation to optimize the diagnostic accuracy.

Lovastatin delays infection and increases survival rates in AG129 mice infected with dengue virus serotype 2

BACKGROUND

It has been reported that treatment of DENV-infected cultures with Lovastatin (LOV), can affect viral assembly. The objective of this study was to evaluate the effect of LOV on the survival rate and viremia levels of DENV-2-infected AG129 mice.

METHODOLOGY/PRINCIPAL FINDINGS

Mice were inoculated with 1 × 10(6) plaque-forming units (PFU/ml) of DENV-2 and treated with LOV (200 mg/kg/day). Pre-treatment with one or three doses of LOV increased the survival rate compared to untreated mice (7.3 and 7.1 days, respectively, compared to 4.8 days). Viremia levels also decreased by 21.8% compared to untreated mice, but only in the group administered three doses prior to inoculation. When LOV was administered after viral inoculation, the survival rate increased (7.3 days in the group treated at 24 hpi, 6.8 days in the group treated at 48 hpi and 6.5 days in the group treated with two doses) compared to the untreated group (4.8 days). Interestingly, the serum viral titer increased by 24.6% in mice treated at 48 hpi with a single dose of LOV and by 21.7% in mice treated with two doses (at 24 and 48 hpi) of LOV compared to untreated mice. Finally histopathological changes in the liver and spleen in infected and untreated mice included massive extramedullary erythropoiesis foci and inflammatory filtration, and these characteristics were decreased or absent in LOV-treated mice.

CONCLUSIONS/SIGNIFICANCE

Our results suggest that the effect of LOV on viremia depends on the timing of treatment and on the number of doses administered. We observed a significant increase in the survival rate in both schemes due to a delay in the progression of the disease. However, the results obtained in the post-treatment scheme must be handled carefully because this treatment scheme increases viremia and we do not know how this increase could affect disease progression in humans.

Performance of commercial dengue NS1 ELISA and molecular analysis of NS1 gene of dengue viruses obtained during surveillance in Indonesia

Background

Early diagnosis of dengue infection is crucial for better management of the disease. Diagnostic tests based on the detection of dengue virus (DENV) Non Structural Protein 1 (NS1) antigen are commercially available with different sensitivities and specificities observed in various settings. Dengue is endemic in Indonesia and clinicians are increasingly using the NS1 detection for dengue confirmation. This study described the performance of Panbio Dengue Early NS1 and IgM Capture ELISA assays for dengue detection during our surveillance in eight cities in Indonesia as well as the genetic diversity of DENV NS1 genes and its relationship with the NS1 detection.

Methods

The NS1 and IgM/IgG ELISA assays were used for screening and confirmation of dengue infection during surveillance in 2010–2012. Collected serum samples (n = 440) were subjected to RT-PCR and virus isolation, in which 188 samples were confirmed for dengue infection. The positivity of the ELISA assays were correlated with the RT-PCR results to obtain the sensitivity of the assays. The NS1 genes of 48 Indonesian virus isolates were sequenced and their genetic characteristics were studied.

Results

Using molecular data as gold standard, the sensitivity of NS1 ELISA assay for samples from Indonesia was 56.4% while IgM ELISA was 73.7%. When both NS1 and IgM results were combined, the sensitivity increased to 89.4%. The NS1 sensitivity varied when correlated with city/geographical origins and DENV serotype, in which the lowest sensitivity was observed for DENV-4 (19.0%). NS1 sensitivity was higher in primary (67.6%) compared to secondary infection (48.2%). The specificity of NS1 assay for non-dengue samples were 100%. The NS1 gene sequence analysis of 48 isolates revealed the presence of polymorphisms of the NS1 genes which apparently did not influence the NS1 sensitivity.

Conclusions

We observed a relatively low sensitivity of NS1 ELISA for dengue detection on RT-PCR-positive dengue samples. The detection rate increased significantly when NS1 data was combined with IgM. In our study, the low sensitivity of NS1 antigen detection did not relate to NS1 genetic diversity. Rather, the performance of the NS1 antigen test was affected by the infection status of patients and geographical origin of samples.

Re-evaluation of the pathogenic roles of nonstructural protein 1 and its antibodies during dengue virus infection

Dengue virus (DENV) infection can cause life-threatening dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). Vascular leakage and abnormal hemorrhage are the two major pathogenic changes found in these patients. From previous studies, it is known that both antibodies and cytokines induced in response to DENV infection are involved in the immunopathogenesis of DHF/DSS. However, the role of viral factors during DENV infection remains unclear. Nonstructural protein 1 (NS1), which is secreted in the sera of patients, is a useful diagnostic marker for acute DENV infection. Nevertheless, the roles of NS1 and its antibodies in the pathogenesis of DHF/DSS are unclear. The focus of this review is to evaluate the possible contributions of NS1 and the antibodies it induces to vascular leakage and abnormal hemorrhage during DENV infection, which may provide clues to better understanding the pathogenesis of DHF/DSS.