Protective and immunological behavior of chimeric yellow fever dengue vaccine

Harnessing Pentameric Scaffold of Cholera Toxin B (CTB) for Design of Subvirion Recombinant Dengue Virus Vaccine

Dengue virus is an enveloped virus with an icosahedral assembly of envelope proteins (E). The E proteins are arranged as a head-to-tail homodimer, and domain III (EDIII) is placed at the edge of the dimer, converging to a pentamer interface. For a structure-based approach, cholera toxin B (CTB) was harnessed as a structural scaffold for the five-fold symmetry of EDIII. Pivoted by an RNA-mediated chaperone for the protein folding and assembly, CTB-EDIII of dengue serotype 1 (DV1) was successfully produced as soluble pentamers in an E. coli host with a high yield of about 28 mg/L. Immunization of mice with CTB-DV1EDIII elicited increased levels of neutralizing antibodies against infectious viruses compared to the control group immunized with DV1EDIII without CTB fusion. IgG isotype switching into a balanced Th1/Th2 response was also observed, probably triggered by the intrinsic adjuvant activity of CTB. Confirming the immune-enhancing potential of CTB in stabilizing the pentamer assembly of EDIII, this study introduces a low-cost bacterial production platform designed to augment the soluble production of subunit vaccine candidates, particularly those targeting flaviviruses.

Nanomedicine as a potential novel therapeutic approach against the dengue virus

Dengue is an arbovirus infection which is transmitted by Aedes mosquitoes. Its prompt detection and effective treatment is a global health challenge. Various nanoparticle-based vaccines have been formulated to present immunogen (antigens) to instigate an immune response or prevent virus spread, but no specific treatment has been devised. This review explores the role of nanomedicine-based therapeutic agents against dengue virus, taking into consideration the applicable dengue virus assays that are sensitive, specific, have a short turnaround time and are inexpensive. Various kinds of metallic, polymeric and lipid nanoparticles with safe and effective profiles present an alternative strategy that could provide a better remedy for eradicating the dengue virus.

Development of a Singleplex Real-Time Reverse Transcriptase PCR Assay for Pan-Dengue Virus Detection and Quantification

Dengue virus (DENV) infection is a significant global health problem. There are no specific therapeutics or widely available vaccines. Early diagnosis is critical for patient management. Viral RNA detection by multiplex RT-PCR using multiple pairs of primers/probes allowing the simultaneous detection of all four DENV serotypes is commonly used. However, increasing the number of primers in the RT-PCR reaction reduces the sensitivity of detection due to the increased possibility of primer dimer formation. Here, a one tube, singleplex real-time RT-PCR specific to DENV 3′-UTR was developed for the detection and quantification of pan-DENV with no cross reactivity to other flaviviruses. The sensitivity of DENV detection was as high as 96.9% in clinical specimens collected at the first day of hospitalization. Our assay provided equivalent PCR efficiency and RNA quantification among each DENV serotype. The assay’s performance was comparable with previously established real-time RT-PCR targeting coding sequences. Using both assays on the same specimens, our results indicate the presence of defective virus particles in the circulation of patients infected with all serotypes. Dual regions targeting RT-PCR enhanced the sensitivity of viral genome detection especially during the late acute phase when viremia rapidly decline and an incomplete viral genome was clinically evident.

Severe Acute Respiratory Syndrome Coronavirus 2 Variants—Possibility of Universal Vaccine Design: A Review

Both novel and conventional vaccination strategies have been implemented worldwide since the onset of coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Despite various medical advances in the treatment and prevention of the spread of this contagious disease, it remains a major public health threat with a high mortality rate. As several lethal SARS-CoV-2 variants continue to emerge, the development of several vaccines and medicines, each with certain advantages and disadvantages, is underway. Additionally, many modalities are at various stages of research and development or clinical trials. Here, we summarize emerging SARS-CoV-2 variants, including delta, omicron, and “stealth omicron,” as well as available oral drugs for COVID-19. We also discuss possible antigen candidates other than the receptor-binding domain protein for the development of a universal COVID-19 vaccine. The present review will serve as a helpful resource for future vaccine and drug development to combat COVID-19.

Prevention and control of dengue and Chikungunya in Colombia: A cost-effectiveness analysis

Background

Chikungunya and dengue are emerging diseases that have caused large outbreaks in various regions of the world. Both are both spread by Aedes aegypti and Aedes albopictus mosquitos. We developed a dynamic transmission model of chikungunya and dengue, calibrated to data from Colombia (June 2014 –December 2017).

Methodology/Principal findings

We evaluated the health benefits and cost-effectiveness of residual insecticide treatment, long-lasting insecticide-treated nets, routine dengue vaccination for children aged 9, catchup vaccination for individuals aged 10–19 or 10–29, and portfolios of these interventions. Model calibration resulted in 300 realistic transmission parameters sets that produced close matches to disease-specific incidence and deaths. Insecticide was the preferred intervention and was cost-effective. Insecticide averted an estimated 95 chikungunya cases and 114 dengue cases per 100,000 people, 61 deaths, and 4,523 disability-adjusted life years (DALYs). In sensitivity analysis, strategies that included dengue vaccination were cost-effective only when the vaccine cost was 14% of the current price.

Conclusions/Significance

Insecticide to prevent chikungunya and dengue in Colombia could generate significant health benefits and be cost-effective. Because of limits on diagnostic accuracy and vaccine efficacy, the cost of dengue testing and vaccination must decrease dramatically for such vaccination to be cost-effective in Colombia. The vectors for chikungunya and dengue have recently spread to new regions, highlighting the importance of understanding the effectiveness and cost-effectiveness of policies aimed at preventing these diseases.

Chikungunya and dengue are emerging diseases that have caused large outbreaks in various regions of the world. Both are both spread by Aedes aegypti and Aedes albopictus mosquitos. To evaluate the effectiveness and cost-effectiveness of interventions aimed at controlling either of these diseases, it is important to consider the potential effects on both diseases, as an intervention that reduces the mosquito population will reduce the spread of both diseases. We developed a dynamic transmission model of chikungunya and dengue, calibrated to data from Colombia. We evaluated the health benefits and cost-effectiveness of the following interventions: residual insecticide treatment, long-lasting insecticide-treated nets, routine dengue vaccination for children aged 9, catchup dengue vaccination for individuals aged 10–19 or 10–29, and portfolios of these interventions. In all vaccination scenarios, we considered testing for previous exposure to dengue. We found that insecticide to prevent chikungunya and dengue in Colombia could generate significant health benefits and be cost-effective. While the dengue vaccine was effective in preventing cases and deaths, costs of diagnostic testing and vaccination must decrease for dengue vaccination to be considered cost-effective.

[Infections and inflammation in the development of stroke]

The review systematizes data on the role of infectious diseases and systemic inflammation in the pathogenesis of stroke. Various risk factors for stroke associated with pro-inflammatory reactions and their contribution to the pathogenesis of cerebrovascular pathology are analyzed. The interaction of systemic inflammation with hemostasis disturbances and clots formation, activation of autoreactive clones of cytotoxic lymphocytes, the progression of endothelial damage, and other processes is shown. Along with infection, these factors increase the risk of stroke. The key mechanisms of the pathogenesis from the development of acute or chronic inflammation to the preconditions of stroke are presented. The mechanisms of the acting of the infectious process as a trigger factor and/or medium-term or long-term risk factors of stroke are described. A separate section is devoted to the mechanisms of developing cerebrovascular diseases after COVID-19. Identifying an increased risk of stroke due to infection can be of great preventive value. Understanding of this risk by specialists followed by correction of drug therapy and rehabilitation measures can reduce the incidence of cerebrovascular complications in infectious patients.

Seroprevalence of Flavivirus Neutralizing Antibodies in Thailand by High-Throughput Neutralization Assay: Endemic Circulation of Zika Virus before 2012

Thailand is a hyperendemic country for flavivirus infections in Southeast Asia. Although the reporting system for flavivirus surveillance in Thailand is well established, syndromic surveillance tends to underestimate the true epidemiological status of flaviviruses due to the majority of infections being asymptomatic. To accurately understand the prevalence of flaviviruses in endemic regions, we performed neutralization tests against multiple flaviviruses using 147 serum samples from healthy donors collected from four distinct regions in Thailand. Single-round infectious particles (SRIP) for six flaviviruses, dengue virus types 1 to 4 (DENV-1 to -4), Japanese encephalitis virus (JEV), and Zika virus (ZIKV), were used as antigens for developing a safe, high-throughput neutralization assay. Titers of neutralizing antibodies (NAbs) against the six flaviviruses revealed that DENV-1 and DENV-2, followed by ZIKV were the predominant circulating flaviviruses in a total of four regions, whereas the prevalence of NAbs against JEV varied among regions. Although the seroprevalence of ZIKV was low relative to that of DENV-1 and DENV-2, the findings strongly suggested that ZIKV has been circulating at a sustained level in Thailand since before 2012. These findings not only demonstrated the application of an SRIP-neutralization test in a serological study, but also elucidated the circulation and distribution trends of different flaviviruses in Thailand. IMPORTANCE Neutralization tests are the most reliable assay for flavivirus antibody detection; however, these assays are not suitable for high-throughput processing due to their time-consuming and labor-intensive nature. In this study, we developed single-round infectious particles (SRIPs) with a luciferase gene for dengue virus types 1 to 4, Japanese encephalitis virus, and Zika virus for use in a safe, high-throughput neutralization assay. We performed neutralization tests against multiple flaviviruses using 147 serum samples that were collected from healthy donors residing in four distinct regions of Thailand in 2011 to 2012. The assay was useful for surveys of flavivirus seroprevalence. The data revealed that dengue virus type 1 (DENV-1) and DENV-2 were the predominant circulating flaviviruses in Thailand and that Zika virus has been circulating at a sustained level in Thailand since before 2012.

Labyrinthopeptin A1 inhibits dengue and Zika virus infection by interfering with the viral phospholipid membrane

To date, there are no broad-spectrum antivirals available to treat infections with flaviviruses such as dengue (DENV) and Zika virus (ZIKV). In this study, we determine the broad antiviral activity of the lantibiotic Labyrinthopeptin A1. We show that Laby A1 inhibits all DENV serotypes and various ZIKV strains with IC₅₀ around 1 μM. The structurally related Laby A2 also displayed a consistent, but about tenfold lower, antiviral activity. Furthermore, Laby A1 inhibits many viruses from divergent families such as HIV, YFV, RSV and Punta Torovirus. Of interest, Laby A1 does not show activity against non-enveloped viruses. Its antiviral activity is independent of the cell line or the used evaluation method, and can also be observed in MDDC, a physiologically relevant primary cell type. Furthermore, Laby A1 demonstrates low cellular toxicity and has a more favorable SI compared to duramycin, a well-described lantibiotic with broad-spectrum antiviral activity. Time-of-drug addition experiments demonstrate that Laby A1 inhibits infection and entry processes of ZIKV and DENV. We reveal that Laby A1 performs its broad antiviral activity by interacting with a viral factor rather than a cellular factor, and that it has virucidal properties. Finally, using SPR interaction studies we demonstrate that Laby A1 interacts with several phospholipids (i.e. PE and PS) present in the viral envelope. Together with other recent Labyrinthopeptin antiviral publications, this work validates the activity of Laby A1 as broad antiviral entry inhibitor with a unique mechanism of action and demonstrates its potential value as antiviral agent against emerging flaviviruses.

A Continuous Model of Three Scenarios of the Infection Process with Delayed Immune Response Factors

The course of an infection was modeled as a controlled nonlinear process. Understanding the substantial differences observed in the trajectory of the disease caused by the new coronavirus SARS-CoV-2 is of critical importance at the moment. Numerous factors have been considered to explain the fact that symptoms vary highly among different people and the infection transmission rate varies among local populations. Virus replication within the host cell and the development of an immune response to virus antigens in the body are two interdependent processes, which have aftereffects and depend on the preexisting states of the cell and virus populations. Different scenarios with the same input parameters are necessary to consider for modeling the properties of the states. The efficiency of the immune response is the most important factor, including the time it takes to develop defense responses from three levels of the immune system, which is a complex system of the body. A computational description of infection scenarios was proposed on the basis of a delay differential equation with two values of the time lag. In the new model, transitions between phases of infectious disease depend on the initial virus dose and the delayed immune response to infection. A variation in the dose of the virus and response time can lead to a transition from an acute phase of the disease with overt symptoms to a chronic phase or fatal outcome. Asymptomatic transmission of viral infection was calculated and described in the model as a situation where the virus is rapidly and efficiently suppressed after a short replication phase, while still persisting in the body in minor amounts. An analysis of the model behavior is consistent with the theory that the initial number of virions can affect the quality of the immune response. The reasons that high individual differences are observed in the trajectory of COVID-19 disease and the formation of types of the immune response to coronavirus are still poorly understood. Known trajectories of hepatitis C virus (HCV) infection were used as a basis for model scenarios.

Data and Safety Monitoring of COVID-19 Vaccine Clinical Trials

To speed the development of vaccines against SARS-CoV-2, the United States Federal Government has funded multiple phase 3 trials of candidate vaccines. A single 11-member data and safety monitoring board (DSMB) monitors all government-funded trials to ensure coordinated oversight, promote harmonized designs, and allow shared insights related to safety across trials. DSMB reviews encompass 3 domains: (1) the conduct of trials, including overall and subgroup accrual and data quality and completeness; (2) safety, including individual events of concern and comparisons by randomized group; and (3) interim analyses of efficacy when event-driven milestones are met. Challenges have included the scale and pace of the trials, the frequency of safety events related to the combined enrollment of over 100 000 participants, many of whom are older adults or have comorbid conditions that place them at independent risk of serious health events, and the politicized environment in which the trials have taken place.

Vaccine-associated enhanced disease: Case definition and guidelines for data collection, analysis, and presentation of immunization safety data

This is a Brighton Collaboration Case Definition of the term “Vaccine Associated Enhanced Disease” to be utilized in the evaluation of adverse events following immunization. The Case Definition was developed by a group of experts convened by the Coalition for Epidemic Preparedness Innovations (CEPI) in the context of active development of vaccines for SARS-CoV-2 vaccines and other emerging pathogens. The case definition format of the Brighton Collaboration was followed to develop a consensus definition and defined levels of certainty, after an exhaustive review of the literature and expert consultation. The document underwent peer review by the Brighton Collaboration Network and by selected Expert Reviewers prior to submission.

Enhancement of Zika virus infection by antibodies from West Nile virus seropositive individuals with no history of clinical infection

Background

Recent outbreaks of Zika Virus (ZIKV) infection and associated microcephaly has raised multiple scientific questions. The close antigenic relatedness between flaviviruses makes diagnosis of specific infection difficult. This relatedness also raises the potential of Antibody Dependent Enhancement (ADE) via cross reactive antibodies to flaviviruses like West Nile Virus (WNV) and Dengue Virus (DENV). Asymptomatic WNV infections are endemic throughout the US creating a large proportion of the population that is seropositive for WNV antibodies. Whether these sero-positive individuals potentially carry ZIKV enhancing antibodies remains unknown.

Results

Serum samples obtained from human subjects with symptomatic or asymptomatic WNV infection from a WNV endemic region in Texas were tested for their ability to enhance or neutralize ZIKV infection. Sero-surveillance data demonstrated a ~ 7% prevalence for WNV antibodies in the population. Sera from both symptomatic and asymptomatic WNV seropositive donors effectively neutralized WNV and to some extent DENV infection. Interestingly, WNV+ sera failed to inhibit ZIKV while significantly enhancing infection. Conversely, ZIKV specific sera effectively neutralized ZIKV, with ADE only evident at lower concentrations. The enhancement of ZIKV via WNV antibody positive sera was likely due to non-neutralizing Envelope (E) antibodies as seen with monoclonal ZIKV E antibodies.

Conclusions

Overall, our findings suggest that WNV antibodies in the sera significantly enhance ZIKV infection in Fc receptor positive cells with limited neutralization activity. Further studies in more relevant models of ADE will be needed to confirm the relevance of these findings in vivo.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12865-020-00389-2.

The Impact of Serotype Cross-Protection on Vaccine Trials: DENVax as a Case Study

There is a growing public health need for effective preventive interventions against dengue, and a safe, effective and affordable dengue vaccine against the four serotypes would be a significant achievement for disease prevention and control. Two tetravalent dengue vaccines, Dengvaxia (CYD-TDV—Sanofi Pasteur) and DENVax (TAK 003—Takeda Pharmaceutical Company), have now completed phase 3 clinical trials. Although Dengvaxia resulted in serious adverse events and had to be restricted to individuals with prior dengue infections, DENVax has shown, at first glance, some encouraging results. Using the available data for the TAK 003 trial, we estimate, via the Bayesian approach, vaccine efficacy (VE) of the post-vaccination surveillance periods of 12 and 18 months. Although better measurement over a long time was expected for the second part of the post-vaccination surveillance, variation in serotype-specific efficacy needs careful consideration. Besides observing that individual serostatus prior to vaccination is determinant of DENVax vaccine efficacy, such as for Dengvaxia, we also noted, after comparing the VE estimations for 12- and 18-month periods, that vaccine efficacy is decreasing over time. The comparison of efficacies over time is informative and very important, and brings up the discussion of the role of temporary cross-immunity in dengue vaccine trials and the impact of serostatus prior to vaccination in the context of dengue fever epidemiology.

Current Status of COVID-19 (Pre)Clinical Vaccine Development

The current COVID-19 pandemic has a tremendous impact on daily life world-wide. Despite the ability to dampen the spread of SARS-CoV-2, the causative agent of the diseases, through restrictive interventions, it is believed that only effective vaccines will provide sufficient control over the disease and revert societal live back to normal. At present, a double-digit number of efforts are devoted to the development of a vaccine against COVID-19. Here, we provide an overview of these (pre)clinical efforts and provide background information on the technologies behind these vaccines. In addition, we discuss potential hurdles that need to be addressed prior to mass scale clinical translation of successful vaccine candidates.

Surveillance of adverse events following immunization in the late 2010s: an overview of the importance, tools, and challenges

Immunization is one of the most effective measures to protect individuals and the population against vaccine-preventable diseases. Vaccines are safe and effective products, but like any other drug they can cause adverse events, which tend to become more visible as the diseases are controlled, eliminated, or eradicated. This study analyzed activities in the surveillance of adverse events following immunization (AEFI) based on data from the scientific literature, websites of immunization programs and health andregulatory agencies, and the authors' expertise in the areas of immunizations and pharmacovigilance. With the increase in the number of vaccines in the basic immunization schedule and expansion of the population's access, it has become essential to establish an efficient surveillance system for AEFI in Brazil. However, underreporting of cases in Brazil and in other countries hinders the detection of AEFI, especially rare events. Constantly updated information on vaccines' risks and benefits allows immunization programs to provide rapid and clear responses to rumors of AEFI. This ensures the system's reliability, especially in the face of the growing antivaccine movement and the increasing influence of social media in public opinion.

Recent Advances in the Development of Virus-Like Particle-Based Flavivirus Vaccines

Flaviviruses include several medically important viruses, such as Zika virus (ZIKV), Dengue virus (DENV), West Nile virus (WNV) and Japanese encephalitis virus (JEV). They have expanded in geographic distribution and refocused international attention in recent years. Vaccination is one of the most effective public health strategies for combating flavivirus infections. In this review, we summarized virus-like particle (VLP)-based vaccines against the above four mentioned flaviviruses. Potential strategies to improve the efficacy of VLP-based flavivirus vaccines were also illustrated. The applications of flavivirus VLPs as tools for viral detection and antiviral drug screening were finally proposed.

The optimal age of vaccination against dengue in Brazil based on serotype-specific forces of infection derived from serological data

In this paper, we study a single serotype transmission model of dengue to determine the optimal vaccination age for Dengvaxia. The transmission dynamics are modelled with an age-dependent force of infection. The force of infection for each serotype is derived from the serological profile of dengue in Brazil without serotype distinction and from serotype-specific reported cases. The risk due to an infection is measured by the probability of requiring hospitalization based on Brazilian Ministry of Health data. The optimal vaccination age is determined for any number and combination of the four distinct dengue virus serotypes DENv1-4. The lifetime expected risk is adapted to include antibody dependent enhancement (ADE) and permanent cross-immunity after two heterologous infections. The risk is assumed to be serostatus-dependent. The optimal vaccination age is computed for constant, serostatus-specific vaccine efficacies. Additionally, the vaccination age is restricted to conform to the licence of Dengvaxia in Brazil and the achievable and minimal lifetime expected risks are compared. The optimal vaccination age obtained for the risk of hospitalization varies significantly with the assumptions relating to ADE and cross-immunity. Risk-free primary infections lead to higher optimal vaccination ages, as do asymptomatic third and fourth infections. Sometimes vaccination is not recommended at all, e.g. for any endemic area with a single serotype if primary infections are risk-free. Restricting the vaccination age to Dengvaxia licensed ages mostly leads to only a slightly higher lifetime expected risk and the vaccine should be administered as close as possible to the optimal vaccination age.

A dose-response study in mice of a tetravalent recombinant dengue envelope domain III protein secreted from insect cells

BACKGROUND

DENV is the most globally prevalent mosquito-transmitted virus. Induction of a broadly and potently immune response is desirable for dengue vaccine development.

METHODS

Several formulations of secreted tetravalent EDIII protein containing different amounts of antigen from eukaryotic cells were used to evaluate the immune responses in mice.

RESULTS

We demonstrated that the tetravalent protein induced humoral immunity against all four serotypes of DENV, even at the lowest dose assayed. Besides, cellular immunities against DENV-1 and DENV-2 were elicited by medium dose group. Importantly, the immune responses induced by the tetravalent protein were functional in clearing DENV-2 in circulation of mice.

CONCLUSIONS

We believe that the tetravalent secreted EDIII protein is a potential vaccine candidate against DENV and suggest further detailed studies of this formulation in nonhuman primates.

Adaptive Immunity to Dengue Virus: Slippery Slope or Solid Ground for Rational Vaccine Design?

The four serotypes of dengue virus are the most widespread causes of arboviral disease, currently placing half of the human population at risk of infection. Pre-existing immunity to one dengue virus serotype can predispose to severe disease following secondary infection with a different serotype. The phenomenon of immune enhancement has complicated vaccine development and likely explains the poor long-term safety profile of a recently licenced dengue vaccine. Therefore, alternative vaccine strategies should be considered. This review summarises studies dissecting the adaptive immune responses to dengue virus infection and (experimental) vaccination. In particular, we discuss the roles of (i) neutralising antibodies, (ii) antibodies to non-structural protein 1, and (iii) T cells in protection and pathogenesis. We also address how these findings could translate into next-generation vaccine approaches that mitigate the risk of enhanced dengue disease. Finally, we argue that the development of a safe and efficacious dengue vaccine is an attainable goal.

Interaction Between Virus-Like Particles (VLPs) and Pattern Recognition Receptors (PRRs) From Dendritic Cells (DCs): Toward Better Engineering of VLPs

Virus-like particles (VLPs) have been shown to be strong activators of dendritic cells (DCs). DCs are the most potent antigen presenting cells (APCs) and their activation prompts the priming of immunity mediators based on B and T cells. The first step for the activation of DCs is the binding of VLPs to pattern recognition receptors (PRRs) on the surface of DCs, followed by VLP internalization. Like wild-type viruses, VLPs use specific PRRs from the DC; however, these recognition interactions between VLPs and PRRs from DCs have not been thoroughly reviewed. In this review, we focused on the interaction between proteins that form VLPs and PRRs from DCs. Several proteins that form VLP contain glycosylations that allow the direct interaction with PRRs sensing carbohydrates, prompting DC maturation and leading to the development of strong adaptive immune responses. We also discussed how the knowledge of the molecular interaction between VLPs and PRRs from DCs can lead to the smart design of VLPs, whether based on the fusion of foreign epitopes or their chemical conjugation, as well as other modifications that have been shown to induce a stronger adaptive immune response and protection against infectious pathogens of importance in human and veterinary medicine. Finally, we address the use of VLPs as tools against cancer and allergic diseases.

Genetically modified live attenuated vaccine: A potential strategy to combat visceral leishmaniasis

Visceral leishmaniasis (VL) is caused by a protozoan parasite Leishmania donovani mainly influencing the population of tropical and subtropical regions across the globe. The arsenal of drugs available is limited, and prolonged use of such drugs makes parasite to become resistant. Therefore, it is very imperative to develop a safe, cost-effective and inexpensive vaccine against VL. Although in recent years, many strategies have been pursued by researchers, so far only some of the vaccine candidates reached for clinical trial and more than half of them are still in pipeline. There is now a broad consent among Leishmania researchers that the perseverance of parasite is very essential for eliciting a protective immune response and may perhaps be attained by live attenuated parasite vaccination. For making a live attenuated parasite, it is very essential to ensure that the parasite is deficient of virulence and should further study genetically modified parasites to perceive the mechanism of pathogenesis. So it is believed that in the near future, a complete understanding of the Leishmania genome will explore clear strategies to discover a novel vaccine. This review describes the need for a genetically modified live attenuated vaccine against VL, and obstacles associated with its development.

Phenotype and functionality of follicular helper T cells in patients with acute dengue infection

Background

The association of functionality and phenotype of follicular helper T cells (Tfh) with dengue virus (DENV) specific antibody responses and clinical disease severity has not been well studied.

Methods

We investigated the phenotype and functionality of Tfh cells and plasmablasts in adult patients (DF = 18, DHF = 22) with acute dengue (day 4 to 8 since onset of fever) of varying severity using multiparametric flowcytometry. The properties of Tfh cells were correlated with viraemia, disease severity, plasmablast responses and DENV-specific serum antibody responses. We further evaluated the kinetics of neutralizing antibodies (Neut50) throughout the course of illness in order to evaluate their association with clinical disease severity and viraemia.

Results

Tfh cells (especially those producing IL-21 and co-expressing PD-1 and ICOS) were found to be significantly expanded (p < 0.0001) and highly activated in patients with DHF compared to those with DF. The frequency of Tfh cells significantly correlated with DENV-specific IgG, NS1-specific antibodies and Neut50 antibody titres in patients with DHF but not in those with DF. Although the Neut50 titres increased during the course of acute secondary DENV infection, they showed differences based on serotype. For instance, the Neut50 titres were significantly higher during the latter part of illness in patients with DF compared to DHF in DENV1 infection, while in DENV2, patients with DHF had significantly higher titres. The viral loads during early illness did not correlate with the subsequent rise in the Neut50 antibody titres during any time point of illness.

Conclusions

The expansion of Tfh cells is associated with DHF and DENV-specific IgG, NS1-specific and neutralizing antibodies. Neut50 titres did not associate with disease severity or viraemia at the point of first presentation during the febrile phase, but later titres do show differential association with severity in patients with DENV1 compared to DENV2.

Assessment of the long-term efficacy of a dengue vaccine against symptomatic, virologically-confirmed dengue disease by baseline dengue serostatus

CYD-TDV is a live, attenuated, tetravalent dengue vaccine licensed in 21 countries. We undertook a post-hoc analysis of the long-term efficacy of CYD-TDV during the surveillance expansion phase (SEP) of two Phase III studies (CYD14 in the Asia-Pacific region; CYD15 in Latin America). The SEP included approximately Year 5 and the entire Year 6 of follow-up after the first study injection. Vaccine efficacy against symptomatic virologically-confirmed dengue (VCD) was assessed by participant age (any age, ≥9, <9, 2-5, and 6-8 years at the time of the first injection) and baseline dengue serostatus using a case-cohort framework. Baseline dengue serostatus was estimated by several methods including logistic regression-based multiple imputation (MI) to predict PRNT₅₀ with key predictor being Month 13 (M13) anti-non-structural protein (NS1) titers; superlearner-based imputation by targeted minimum loss based estimation (TMLE); and M13 anti-NS1 titer threshold 9 EU/mL (NS1 M13). There were 436 symptomatic VCD cases (CYD14: n = 360; CYD15: n = 76) during the SEP. Vaccine efficacy in seropositive participants aged ≥9 years was assessed by MI (47.9% [95% CI 19.4; 66.3]), TMLE (53.0% [95% CI 23; 71]), and NS1 M13 (52.4% [95% CI 30.8; 67.3]). Vaccine efficacy estimates were lower in seropositive individuals aged <9 years compared with individuals ≥9 years. Among seropositive individuals aged 2-5 and 6-8 years, vaccine efficacy across the different approaches for assessing serostatus ranged from between -25.7 to 36.9% and 44.4 to 64.7% during the SEP, respectively. In the pooled CYD14/15 data of seronegatives, vaccine efficacy was null to modest. In conclusion, CYD-TDV was shown to maintain efficacy against symptomatic VCD in seropositive participants aged ≥9 years up to six years after the first dose. Persistence of efficacy was also observed in seropositive participants aged 6-8 years.

The role of anti-flavivirus humoral immune response in protection and pathogenesis

Flavivirus infections are a public health threat in the world that requires the development of safe and effective vaccines. Therefore, the understanding of the anti-flavivirus humoral immune response is fundamental to future studies on flavivirus pathogenesis and the design of anti-flavivirus therapeutics. This review aims to provide an overview of the current understanding of the function and involvement of flavivirus proteins in the humoral immune response as well as the ability of the anti-envelope (anti-E) antibodies to interfere (neutralizing antibodies) or not (non-neutralizing antibodies) with viral infection, and how they can, in some circumstances enhance dengue virus infection on Fc gamma receptor (FcγR) bearing cells through a mechanism known as antibody-dependent enhancement (ADE). Thus, the dual role of the antibodies against E protein poses a formidable challenge for vaccine development. Also, we discuss the roles of antibody binding stoichiometry (the concentration, affinity, or epitope recognition) in the neutralization of flaviviruses and the "breathing" of flavivirus virions in the humoral immune response. Finally, the relevance of some specific antibodies in the design and improvement of effective vaccines is addressed.

Dengue: Status of current and under-development vaccines

Dengue is an emerging mosquito-borne viral infection with increasing reports of outbreaks. The clinical picture ranges from a benign febrile illness through to severe and potentially fatal manifestations. No specific anti-viral treatment exists, and therapy only consists of supportive care. During the last three decades, several attempts to develop an effective vaccine have been made. The first dengue vaccine to obtain licensure was Dengvaxia, which was authorized in 2015 and is currently available in over 20 countries. Its use has been approved with strict limitations regarding age and serostatus of the recipients, highlighting the necessity for a more safe and efficacious vaccine. At present several vaccine, candidates are undergoing clinical and pre-clinical trials. The most advanced candidates are TDV and TDV 003/005, two live-attenuated vaccines, but another 15 vaccines are under development, introducing novel immunization strategies to the traditional dengue vaccine scenario. This work reviews the current research status on dengue vaccines.

The Optimal Age of Vaccination Against Dengue with an Age-Dependent Biting Rate with Application to Brazil

In this paper we introduce a single serotype transmission model, including an age-dependent mosquito biting rate, to find the optimal vaccination age against dengue in Brazil with Dengvaxia. The optimal vaccination age and minimal lifetime expected risk of hospitalisation are found by adapting a method due to Hethcote (Math Biosci 89:29–52). Any number and combination of the four dengue serotypes DENv1–4 is considered. Successful vaccination against a serotype corresponds to a silent infection. The effects of antibody-dependent enhancement (ADE) and permanent cross-immunity after two heterologous infections are studied. ADE is assumed to imply risk-free primary infections, while permanent cross-immunity implies risk-free tertiary and quaternary infections. Data from trials of Dengvaxia indicate vaccine efficacy to be age and serostatus dependent and vaccination of seronegative individuals to induce an increased risk of hospitalisation. Some of the scenarios are therefore reconsidered taking these findings into account. The optimal vaccination age is compared to that achievable under the current age restriction of the vaccine. If vaccination is not considered to induce risk, optimal vaccination ages are very low. The assumption of ADE generally leads to a higher optimal vaccination age in this case. For a single serotype vaccination is not recommended in the case of ADE. Permanent cross-immunity results in a slightly lower optimal vaccination age. If vaccination induces a risk, the optimal vaccination ages are much higher, particularly for permanent cross-immunity. ADE has no effect on the optimal vaccination age when permanent cross-immunity is considered; otherwise, it leads to a slight increase in optimal vaccination age.

An observational prospective cohort study of the epidemiology of hospitalized patients with acute febrile illness in Indonesia

Background

The epidemiology of acute febrile illness, a common cause of hospitalization in Indonesia, has not been systematically studied.

Methodology/Principal findings

This prospective observational study enrolled febrile patients (temperature ≥38°C) aged ≥1 year from July 2013 until June 2016 at eight government referral teaching hospitals in seven provincial capitals in Indonesia. Patients were managed according to the hospital standard-of-care (SOC), and blood samples were drawn for molecular and serological assays. Clinical data, laboratory results, and specimens for additional tests were collected at enrollment, days 14–28, and at three months. Regular follow-up visits were then scheduled for every three months either until symptoms resolved or until one year. In total, this study included 1,486 adult and pediatric patients presenting with multi-organ (768, 51.7%), gastrointestinal (497, 33.0%), respiratory (114, 7.7%), constitutional (62, 4.2%), skin and soft-tissue (24, 1.6%), central nervous system (17, 1.1%), or genitourinary (4, 0.3%) manifestations. Microbiological diagnoses were found in 1,003/1,486 (67.5%) participants, of which 351/1,003 (35.0%) were not diagnosed during hospitalization using SOC diagnostic tests. Missed diagnoses included all cases caused by Rickettsia spp., chikungunya, influenza, and Seoul virus. The most common etiologic agents identified were dengue virus (467, 46.6%), Salmonella spp. (103, 10.3%), and Rickettsia spp. (103, 10.3%). The overall mortality was 89 (5.9%).

Conclusions/Significance

Febrile illness in Indonesia has various microbiologic etiologies and substantial overall mortality. Diagnostic limitations and lack of epidemiologic data resulted in potentially treatable, and at times fatal, diseases being missed.

In tropical countries like Indonesia, fever due to infectious disease is the most common reason for hospitalization. However, diagnoses are mostly unconfirmed, as diagnostic tests are not available or are not performed due to budget constraints. Consequently, many patients are only treated based on clinical syndromes. To gain a better understanding of the epidemiology of acute fever in Indonesia, we conducted a study at eight hospitals in the seven largest cities from 2013–2016. We enrolled 1,486 subjects aged ≥1 year with acute fever ≥38°C. Blood cultures were mandatory for all subjects, while cultures of other biological specimens, microscopic examinations, and rapid tests for specific pathogens were based on clinical judgment and availability. Retrospectively, we performed molecular and serological testing for a panel of bacterial and viral pathogens for systemic, respiratory, and diarrheal diseases. We found six pathogens to be the most prevalent: dengue virus (47%), Salmonella Typhi/Paratyphi (10%), Rickettsia typhi (10%), influenza virus (7%), Leptospira spp. (5%), and chikungunya virus (4%). Rickettsia typhi, influenza, and chikungunya had not been considered in the differential diagnosis of any subject at the hospitals. Thus, multiple pathogens were associated with acute febrile illnesses, and a subset of treatable cases were missed. This may have resulted in increased overall mortality.

Successful Vaccines

Vaccines are considered one of the most important advances in modern medicine and have greatly improved our quality of life by reducing or eliminating many serious infectious diseases. Successful vaccines have been developed against many of the most common human pathogens, and this success has not been dependent upon any one specific class of vaccine since subunit vaccines, non-replicating whole-virus or whole-bacteria vaccines, and attenuated live vaccines have all been effective for particular vaccine targets. After completing the initial immunization series, one common aspect of successful vaccines is that they induce long-term protective immunity. In contrast, several partially successful vaccines appear to induce protection that is relatively short-lived and it is likely that long-term protective immunity will be critical for making effective vaccines against our most challenging diseases such as AIDS and malaria.

Dengue proteins with their role in pathogenesis, and strategies for developing an effective anti-dengue treatment: A review

Dengue virus is an arbovirus belonging to class Flaviviridae Its clinical manifestation ranges from asymptomatic to extreme conditions (dengue hemorrhagic fever/dengue shock syndrome). A lot of research has been done on this ailment, yet there is no effective treatment available for the disease. This review provides the systematic understanding of all dengue proteins, role of its structural proteins (C-protein, E-protein, prM) in virus entry, assembly, and secretion in host cell, and nonstructural proteins (NS1, NS2a, NS2b, NS3, NS4a, NS4b, and NS5) in viral assembly, replication, and immune evasion during dengue progression and pathogenesis. Furthermore, the review has highlighted the controversies related to the only commercially available dengue vaccine, that is, Dengvaxia, and the risk associated with it. Lastly, it provides an insight regarding various approaches for developing an effective anti-dengue treatment.

Considering Genomic and Immunological Correlates of Protection for a Dengue Intervention

Over three billion are at risk of dengue infection with more than 100 million a year presenting with symptoms that can lead to deadly haemorrhagic disease. There are however no treatments available and the only licensed vaccine shows limited efficacy and is able to enhance the disease in some cases. These failures have mainly been due to the complex pathology and lack of understanding of the correlates of protection for dengue virus (DENV) infection. With increasing data suggesting both a protective and detrimental effect for antibodies and CD8 T-cells whilst having complex environmental dynamics. This review discusses the roles of genomic and immunological aspects of DENV infection, providing both a historical interpretation and fresh discussion on how this information can be used for the next generation of dengue interventions.

Dependency of Vaccine Efficacy on Preexposure and Age: A Closer Look at a Tetravalent Dengue Vaccine

Background

A recombinant, live-attenuated, tetravalent dengue vaccine (CYD-TDV) was licensed for children aged ≥9 years in a few countries, but the dependence of vaccine efficacy on baseline immunity status and age groups has not been fully characterized.

Methods

Combining the 2 phase 3 trials CYD14 and CYD15, we estimated the vaccine efficacy for each of the 4 serotypes of dengue virus (DENV), as well as all serotypes combined, simultaneously stratified by baseline immunity status and age group, while accounting for uncertainty in the baseline immunity status of subjects.

Results

Baseline seropositive subjects showed high efficacy for all serotypes: 70.2% (95% confidence interval [CI], 57.4%-80.1%) for dengue serotype 1 (DENV-1), 67.9% (95% CI, 49.9%-82.0%) for DENV-2, 77.5% (95% CI, 64.3%-90.2%) for DENV-3, 89.9% (95% CI, 79.8%-99.9%) for DENV-4, and 75.4% (95% CI, 68.3%-81.6%) overall. In contrast, baseline seronegative subjects showed moderate efficacy against DENV-4 (51.2% [95% CI, 20.0%-72.8%]) but no significant efficacy against other serotypes. Among seropositive children, the overall efficacy tended to increase with age: 35.9% (95% CI, -7.6% to 69.3%) for children ≤5 years old, 65.6% (95% CI, 40.3%-84.2%) for those 6-8 years old, 73.4% (95% CI, 62.6%-82.1%) for those 9-11 years old, and 80.6% (95% CI, 72.9%-87.3%) for those 12 years or older.

Conclusions

The CYD-TDV vaccine was highly efficacious for all dengue serotypes among children aged >5 years who have acquired baseline immunity from previous exposure. Increasing vaccine efficacy with age was not fully explained by increasing prevalence of baseline immunity with age.

A quinoline compound inhibits the replication of dengue virus serotypes 1-4 in Vero cells

BACKGROUND

The global occurrence of dengue, a mosquito-​borne viral disease caused by four distinct dengue viruses (DENV-1, -2, -3 and -4), is reported to have increased approximately 30-fold in the last 50 years, causing approximately 400 million infections a year. A limited use, sub-optimal live attenuated dengue vaccine has become available recently. It is becoming apparent that antibodies to DENVs can promote infection by Zika virus (ZIKV), a related mosquito-borne flavivirus. A drug to treat these flaviviral infections continues to be an unmet public health need.

METHODS

We screened an 'in-house' library of approximately 2,000 small molecules for inhibitors of cloned DENV-2 protease. Putative inhibitor binding to DENV-2 protease was analysed by in silico docking. Anti-DENV activity was analysed by monitoring viral antigen synthesis by ELISA, viral RNA synthesis by reverse-transcription​ coupled to real-time polymerase chain reaction and infectious virus production by plaque assay, in DENV-infected Vero cells.

RESULTS

A quinoline derivative, BT24, was identified for the first time as a potent inhibitor of the cloned DENV-2 protease (half maximal inhibitory concentration [IC₅₀]=0.5 µM). In silico analysis revealed that BT24 binds to an allosteric site in the vicinity of the active site of DENV-2 protease. Cell-based assays demonstrated that BT24 can inhibit all four DENVs in infected Vero cells.

CONCLUSIONS

BT24 is a DENV-2 protease inhibitor which manifests the capacity to inhibit the replication of all four DENVs in cultured cells. It may provide a lead for a pan-DENV inhibitory drug.

Projected costs associated with school-based screening to inform deployment of Dengvaxia: Vietnam as a case study

Background

After new analysis, Sanofi Pasteur now recommends their dengue vaccine (Dengvaxia) should only be given to individuals previously infected with dengue and the World Health Organization's recommendations regarding its use are currently being revised. As a result, the potential costs of performing large-scale individual dengue screening and/or dengue serosurveys have become an important consideration for decision making by policymakers in dengue-endemic areas.

Methods

We used an ingredients-based approach to estimate the financial costs for conducting both a school-based dengue serosurvey and school-based individual dengue screening within a typical province in Vietnam, using an existing commercial indirect immunoglobulin G enzyme-linked immunosorbent assay kit. This costing is hypothetical and based on estimates regarding the resources that would be required to perform such activities.

Results

We estimated that performing a school-based individual screening of 9-year-olds would cost US$9.25 per child tested or US$197,827 in total for a typical province. We also estimated that a school-based serosurvey would cost US$10,074, assuming one class from each of the grades that include 8- to 11-year-olds are sampled at each of the 12 selected schools across the province.

Conclusions

The study indicates that using this vaccine safely on a large-scale will incur noteworthy operational costs. It is crucial that these be considered in future cost-effectiveness analyses informing how and where the vaccine is deployed.

Yeast-produced subunit protein vaccine elicits broadly neutralizing antibodies that protect mice against Zika virus lethal infection

Zika virus (ZIKV) infection is a serious public health concern due to its ability to induce neurological defects and its potential for rapid transmission at a global scale. However, no vaccine is currently available to prevent ZIKV infection. Here, we report the development of a yeast-derived subunit protein vaccine for ZIKV. The envelope protein domain III (EDIII) of ZIKV was produced as a secretory protein in the yeast Pichia pastoris. The yeast-derived EDIII could inhibit ZIKV infection in vitro in a dose-dependent manner, suggesting that it had acquired an appropriate conformation to bind to cellular receptors of ZIKV. Immunization with recombinant EDIII protein effectively induced antigen-specific binding antibodies and cellular immune responses. The resulting anti-EDIII sera could efficiently neutralize ZIKV representative strains from both Asian and African lineages. Passive transfer with the anti-EDIII neutralizing sera could confer protection against lethal ZIKV challenge in mice. Importantly, we found that purified anti-EDIII antibodies did not cross-react with closely related dengue virus (DENV) and therefore did not enhance DENV infection. Collectively, our results demonstrate that yeast-produced EDIII is a safe and effective ZIKV vaccine candidate.

Serostatus testing and dengue vaccine cost-benefit thresholds

The World Health Organization (WHO) currently recommends pre-screening for past infection prior to administration of the only licensed dengue vaccine, CYD-TDV. Using a threshold modelling analysis, we identify settings where this guidance prohibits positive net-benefits, and are thus unfavourable. Generally, however, our model shows test-then-vaccinate strategies can improve CYD-TDV economic viability: effective testing reduces unnecessary vaccination costs while increasing health benefits. With sufficiently low testing cost, those trends outweigh additional screening costs, expanding the range of settings with positive net-benefits. This work highlights two aspects for further analysis of test-then-vaccinate strategies. We found that starting routine testing at younger ages could increase benefits; if real tests are shown to sufficiently address safety concerns, the manufacturer, regulators and WHO should revisit guidance restricting use to 9-years-and-older recipients. We also found that repeat testing could improve return-on-investment (ROI), despite increasing intervention costs. Thus, more detailed analyses should address questions on repeat testing and testing periodicity, in addition to real test sensitivity and specificity. Our results follow from a mathematical model relating ROI to epidemiology, intervention strategy, and costs for testing, vaccination and dengue infections. We applied this model to a range of strategies, costs and epidemiological settings pertinent to CYD-TDV. However, general trends may not apply locally, so we provide our model and analyses as an R package available via CRAN, denvax. To apply to their setting, decision-makers need only local estimates of age-specific seroprevalence and costs for secondary infections.

Dual roles for the ER membrane protein complex in flavivirus infection: viral entry and protein biogenesis

Hundreds of cellular host factors are required to support dengue virus infection, but their identity and roles are incompletely characterized. Here, we identify human host dependency factors required for efficient dengue virus-2 (DENV2) infection of human cells. We focused on two, TTC35 and TMEM111, which we previously demonstrated to be required for yellow fever virus (YFV) infection and others subsequently showed were also required by other flaviviruses. These proteins are components of the human endoplasmic reticulum membrane protein complex (EMC), which has roles in ER-associated protein biogenesis and lipid metabolism. We report that DENV, YFV and Zika virus (ZIKV) infections were strikingly inhibited, while West Nile virus infection was unchanged, in cells that lack EMC subunit 4. Furthermore, targeted depletion of EMC subunits in live mosquitoes significantly reduced DENV2 propagation in vivo. Using a novel uncoating assay, which measures interactions between host RNA-binding proteins and incoming viral RNA, we show that EMC is required at or prior to virus uncoating. Importantly, we uncovered a second and important role for the EMC. The complex is required for viral protein accumulation in a cell line harboring a ZIKV replicon, indicating that EMC participates in the complex process of viral protein biogenesis.

Yellow fever (YF) vaccination does not increase dengue severity: A retrospective study based on 11,448 dengue notifications in a YF and dengue endemic region

BACKGROUND

We study the association between prior yellow fever immunization and clinical outcomes of dengue infections in individuals of varying sexes and ages. Serological interactions between dengue virus and other flaviviruses could drive antibody dependent enhancement, which is associated with disease severity in dengue infections. This effect may influence disease severity in individuals subsequently affected by related flaviviruses, such as dengue. We compare the severity of dengue episodes between patients vaccinated and non-vaccinated against yellow fever.

METHODS

We evaluated the severity of 11,448 lab-confirmed dengue cases reported in São José do Rio Preto, Brazil, in 7370 YF vaccinated patients compared to 4043 unvaccinated patients. We regressed dengue severity against YF vaccine status and a number of demographic, clinical, and laboratory variables as controls. We also evaluated the association between YF vaccination status and the clinical and laboratory symptoms of dengue patients.

RESULTS

We did not find any evidence of increased risk for severe dengue in patients vaccinated against YF (odds ratio = 1.00; 95% confidence interval = 0.87-1.14). Most of the variables analyzed did not have a statistically significant association with YF vaccination status.

CONCLUSIONS

We found no evidence that YF vaccination in dengue-endemic areas increases the risk of severe dengue fever.

The possible role of cross-reactive dengue virus antibodies in Zika virus pathogenesis

Zika virus (ZIKV) has been known for decades to circulate in Africa and Asia. However, major complications of a ZIKV infection have recently become apparent for reasons that are still not fully elucidated. One of the hypotheses for the seemingly increased pathogenicity of ZIKV is that cross-reactive dengue antibodies can enhance a ZIKV infection through the principle of antibody-dependent enhancement (ADE). Recently, ADE in ZIKV infection has been studied, but conclusive evidence for the clinical importance of this principle in a ZIKV infection is lacking. Conversely, the widespread circulation of ZIKV in dengue virus (DENV)-endemic regions raises new questions about the potential contribution of ZIKV antibodies to DENV ADE. In this review, we summarize the results of the evidence to date and elaborate on other possible detrimental effects of cross-reactive flavivirus antibodies, both for ZIKV infection and the risk of ZIKV-related congenital anomalies, DENV infection, and dengue hemorrhagic fever.

Stachyonic Acid: A Dengue Virus Inhibitor from Basilicum polystachyon

Stachyonic acid A, arising from the first in-depth phytochemical investigation of the herb Basilicum polystachyon, was found to display potent inhibitory activity against dengue virus, with limited cytotoxicity. Andrographolide, a known dengue virus inhibitor and closely related labdane-type diterpene, is structurally more complex but displayed poor antiviral activity in the PRNT assay, and increased cytotoxicity in comparison. Furthermore, a Diels-Alder reaction with PTAD identified the active pharmacophore of stachyonic acid to be the conjugated diene.

Small Molecules Targeting the Flavivirus E Protein with Broad-Spectrum Activity and Antiviral Efficacy in Vivo

Vaccines and antivirals to combat dengue, Zika, and other flavivirus pathogens present a major, unmet medical need. Vaccine development has been severely challenged by the antigenic diversity of these viruses and the propensity of non-neutralizing, cross-reactive antibodies to facilitate cellular infection and increase disease severity. As an alternative, direct-acting antivirals targeting the flavivirus envelope protein, E, have the potential to act via an analogous mode of action without the risk of antibody-dependent enhancement of infection and disease. We previously discovered that structurally diverse small molecule inhibitors of the dengue virus E protein exhibit varying levels of antiviral activity against other flaviviruses in cell culture. Here, we demonstrate that the broad-spectrum activity of several cyanohydrazones against dengue, Zika, and Japanese encephalitis viruses is due to specific inhibition of E-mediated membrane fusion during viral entry and provide proof of concept for pharmacological inhibition of E as an antiviral strategy in vivo.

Identification of small molecule inhibitors targeting the Zika virus envelope protein

The recent emergence of Zika virus, a mosquito-borne flavivirus, in the Americas has shed light on the severe neurological diseases associated with infection, notably congenital microcephaly in newborns and Guillain-Barré syndrome in adults. Despite the recent focus on Zika virus, there are currently no approved vaccines or antiviral therapies available to treat or prevent infection. In this study we established a competitive amplified luminescent proximity homogeneous assay (ALPHAscreen) to identify small molecule inhibitors targeting the envelope protein of Zika virus (Zika E). We utilized this assay to screen two libraries of nearly 27,000 compounds and identified seven novel inhibitors of Zika E. Characterization of these primary screening leads demonstrated that inhibition of Zika virus occurs at non-cytotoxic concentrations for all seven lead compounds. In addition, we found that all seven lead compounds have potent activity against the closely related dengue virus 2 but not vesicular stomatitis virus, an unrelated enveloped virus. Biochemical experiments indicate that these compounds act by preventing E-mediated membrane fusion. This work highlights a new method for the discovery and optimization of direct-acting antivirals targeting the E protein of Zika and other flaviviruses.

A multi-country study of the economic burden of dengue fever based on patient-specific field surveys in Burkina Faso, Kenya, and Cambodia

BACKGROUND

Dengue fever is a rapidly growing public health problem in many parts of the tropics and sub-tropics in the world. While there are existing studies on the economic burden of dengue fever in some of dengue-endemic countries, cost components are often not standardized, making cross-country comparisons challenging. Furthermore, no such studies have been available in Africa.

METHODS/PRINCIPAL FINDINGS

A patient-specific survey questionnaire was developed and applied in Burkina Faso, Kenya, and Cambodia in a standardized format. Multiple interviews were carried out in order to capture the entire cost incurred during the period of dengue illness. Both private (patient's out-of-pocket) and public (non-private) expenditure were accessed to understand how the economic burden of dengue is distributed between private and non-private payers. A substantial number of dengue-confirmed patients were identified in all three countries: 414 in Burkina Faso, 149 in Kenya, and 254 in Cambodia. The average cost of illness for dengue fever was $26 (95% CI $23-$29) and $134 (95% CI $119-$152) per inpatient in Burkina Faso and Cambodia, respectively. In the case of outpatients, the average economic burden per episode was $13 (95% CI $23-$29) in Burkina Faso and $23 (95% CI $19-$28) in Kenya. Compared to Cambodia, public contributions were trivial in Burkina Faso and Kenya, reflecting that a majority of medical costs had to be directly borne by patients in the two countries.

CONCLUSIONS/SIGNIFICANCE

The cost of illness for dengue fever is significant in the three countries. In particular, the current study sheds light on the potential economic burden of the disease in Burkina Faso and Kenya where existing evidence is sparse in the context of dengue fever, and underscores the need to achieve Universal Health Coverage. Given the availability of the current (CYD-TDV) and second-generation dengue vaccines in the near future, our study outcomes can be used to guide decision makers in setting health policy priorities.

Next generation designer virus-like particle vaccines for dengue

INTRODUCTION

A safe and efficacious vaccine for dengue continues to be an unmet public health need. The recent licensing of a dengue vaccine (Dengvaxia) developed by Sanofi has brought to the fore the safety issue of vaccine-induced infection enhancement.

AREAS COVERED

This article focuses on two new yeast-produced tetravalent dengue envelope domain III-displaying virus-like particulate vaccine candidates reported in early 2018 and reviews the rationale underlying their design, and pre-clinical data which suggest that these may offer promising alternate options.

EXPERT COMMENTARY

These are the only vaccine candidates so far to have demonstrated the induction of primarily serotype-specific neutralizing antibodies to all dengue virus serotypes in experimental animals. Interestingly, these antibodies lack infection-enhancing potential when evaluated using the AG129 mouse model.

Transient Expression of Dengue Virus NS1 Antigen in Nicotiana benthamiana for Use as a Diagnostic Antigen

Dengue is a viral disease that represents a significant threat to global public health since billions of people are now at risk of infection by this mosquito-borne virus. The implementation of extensive screening tests is indispensable to control this disease, and the Dengue virus non-structural protein 1 (NS1) is a promising antigen for the serological diagnosis of dengue fever. Plant-based systems can be a safe and cost-effective alternative for the production of dengue virus antigens. In this work, two strategies to produce the dengue NS1 protein in Nicotiana benthamiana leaves were evaluated: Targeting NS1 to five different subcellular compartments to assess the best subcellular organelle for the expression and accumulation of NS1, and the addition of elastin-like polypeptide (ELP) or hydrophobin (HFBI) fusion tags to NS1. The transiently expressed proteins in N. benthamiana were quantified by Western blot analysis. The NS1 fused to ELP and targeted to the ER (NS1 ELP-ER) showed the highest yield (445 mg/kg), approximately a forty-fold increase in accumulation levels compared to the non-fused protein (NS1-ER), representing the first example of transient expression of DENV NS1 in plant. We also demonstrated that NS1 ELP-ER was successfully recognized by a monoclonal anti-dengue virus NS1 glycoprotein antibody, and by sera from dengue virus-infected patients. Interestingly, it was found that transient production of NS1-ER and NS1 ELP-ER using vacuum infiltration of whole plants, which is easier to scale up, rather than syringe infiltration of leaves, greatly improved the accumulation of NS1 proteins. The generated plant made NS1, even without extensive purification, showed potential to be used for the development of the NS1 diagnostic tests in resource-limited areas where dengue is endemic.

The Role of Host Cholesterol During Flavivirus Infection

In recent years the emergence and resurgence of arboviruses have generated a global health alert. Among arboviruses, Dengue (DENV), Zika (ZIKV), Yellow Fever (YFV), and West Nile (WNV) virus, belong to the genus Flavivirus, cause high viremia and occasionally fatal clinical disease in humans. Given the genetic austerity of the virus, they depend on cellular factors and organelles to complete its replication. One of the cellular components required for flavivirus infection is cholesterol. Cholesterol is an abundant lipid in biomembranes of eukaryotes cells and is necessary to maintain the cellular homeostasis. Recently, it has been reported, that cholesterol is fundamental during flavivirus infection in both mammal and insect vector models. During infection with DENV, ZIKV, YFV, and WNV the modulation of levels of host-cholesterol facilitates viral entry, replicative complexes formation, assembly, egress, and control of the interferon type I response. This modulation involves changes in cholesterol uptake with the concomitant regulation of cholesterol receptors as well as changes in cholesterol synthesis related to important modifications in cellular metabolism pathways. In view of the flavivirus dependence of cholesterol and the lack of an effective anti-flaviviral treatment, this cellular lipid has been proposed as a therapeutic target to treat infection using FDA-approved cholesterol-lowering drugs. This review aims to address the dependence of cholesterol by flaviviruses as well as the basis for anti flaviviral therapy using drugs which target is cholesterol synthesis or uptake.

Human antibodies targeting Zika virus NS1 provide protection against disease in a mouse model

Zika virus is a mosquito-borne flavivirus closely related to dengue virus that can cause severe disease in humans, including microcephaly in newborns and Guillain-Barré syndrome in adults. Specific treatments and vaccines for Zika virus are not currently available. Here, we isolate and characterize four monoclonal antibodies (mAbs) from an infected patient that target the non-structural protein NS1. We show that while these antibodies are non-neutralizing, NS1-specific mAbs can engage FcγR without inducing antibody dependent enhancement (ADE) of infection in vitro. Moreover, we demonstrate that mAb AA12 has protective efficacy against lethal challenges of African and Asian lineage strains of Zika virus in Stat2^–/– mice. Protection is Fc-dependent, as a mutated antibody unable to activate known Fc effector functions or complement is not protective in vivo. This study highlights the importance of the ZIKV NS1 protein as a potential vaccine antigen.

Zika virus infection can cause severe disease in humans and there are currently no specific treatments or vaccines. Here, Bailey et al. isolate antibodies recognizing non-structural protein NS1 and show that they protect mice from disease by an Fc-dependent, non-neutralizing mechanism.