Microevolution and virulence of dengue viruses

Development of New Live-Attenuated Vaccine Candidates Lacking Antibody-Dependent Enhancement (ADE) Against Dengue

Dengue virus (DENV) threatens public health, especially in regions with tropical and subtropical climates. In 2024, the World Health Organisation reported 3.4 million confirmed dengue cases, with 16,000 severe cases and 3000 dengue-associated fatalities. The first licensed dengue vaccine, CYD-TDV (Dengvaxia®,Sanofi-Pasteur, Paris, France), is recommended by the WHO only for individuals aged 9-45 years with a prior history of dengue infection. However, being vaccinated with Dengvaxia® increases the risk of developing severe dengue infections in seronegative individuals. Recently, a second licensed dengue vaccine, Qdenga®,Takeda, Singen, Germany), was approved and recommended by the WHO to be administered only in highly dengue-endemic countries, as it was not shown to elicit a robust immune response against DENV-3 and DENV-4 serotypes in dengue seronegative individuals. Due to an imbalance in immune response against all four DENV serotypes, there is a higher risk of developing the antibody-dependent enhancement (ADE) effect, which could lead to severe dengue. This review has identified mutations throughout the DENV genome that were demonstrated to attenuate the virulence of DENV in either in vitro or in vivo studies. Several amino acid residues within the DENV prM and E proteins were identified to play important roles in ADE and modifying these ADE-linked residues is important in the rational design of novel live-attenuated dengue vaccine candidates. This review provides current insights to guide the development of a novel live-attenuated tetravalent dengue vaccine candidate that is effective against all DENV serotypes and safe from ADE. The efficacy and safety of the live-attenuated vaccine candidate should be further validated in in vivo studies.

Research progress of mosquito-borne virus mRNA vaccines

In recent years, mRNA vaccines have emerged as a leading technology for preventing infectious diseases due to their rapid development and high immunogenicity. These vaccines encode viral antigens, which are translated into antigenic proteins within host cells, inducing both humoral and cellular immune responses. This review systematically examines the progress in mRNA vaccine research for major mosquito-borne viruses, including dengue virus, Zika virus, Japanese encephalitis virus, Chikungunya virus, yellow fever virus, Rift Valley fever virus, and Venezuelan equine encephalitis virus. Enhancements in mRNA vaccine design, such as improvements to the 5' cap structure, 5'UTR, open reading frame, 3'UTR, and polyadenylation tail, have significantly increased mRNA stability and translation efficiency. Additionally, the use of lipid nanoparticles and polymer nanoparticles has greatly improved the delivery efficiency of mRNA vaccines. Currently, mRNA vaccines against mosquito-borne viruses are under development and clinical trials, showing promising protective effects. Future research should continue to optimize vaccine design and delivery systems to achieve broad-spectrum and long-lasting protection against various mosquito-borne virus infections.

Whole genome sequencing and phylogenetic analysis of dengue virus in Central Nepal from 2022 to 2023

BACKGROUND

In Nepal, dengue is an emerging disease of growing concern as outbreaks are increasing in both size and geographic reach and beginning to affect areas previously thought dengue-free. Dengue genomic surveillance has previously been limited within Nepal; however, with the increase in accessibility to sequencing technologies since the COVID-19 pandemic, it has recently become more feasible.

METHODS

This hospital-based retrospective study utilized banked samples from the 2022 and 2023 dengue seasons from Dhulikhel Hospital/Kathmandu University Hospital in Central Nepal. Next-generation sequencing was performed to obtain whole genome sequences of dengue virus which were analyzed phylogenetically using a maximum likelihood GTR + G model. Mutations were evaluated across viral particle region using the GISAID DengueServer.

RESULTS

We obtained 41 full-length sequences of DENV from 80 PCR-positive samples, including 24 sequences (58.5%) from 2022 and 17 sequences (41.5%) from 2023. We identified a shift in the majority serotype of our samples from DENV1 in 2022 to DENV3 in 2023, though 3 out of the 4 serotypes were identified in both years. Phylogenetic analysis revealed clusters within genotype III of DENV1 and genotype III of DENV3 closely related to strains from an outbreak of DENV in northern India in 2018-2019. DENV2 sequences fell into the cosmopolitan genotype IV-A1 and IV-B2 clades and were related to sequences from South and Southeast Asia and the USA, pointing to the global nature of dengue transmission. NS3 showed the highest frequency of mutation, whereas NS2B, NS4, NS5, and E were the most conserved. The most common mutations found were substitutions L17M and T20I in the 2 K peptide. A high number of mutations were observed in DENV3, followed by DENV2, with some mutations being unique to specific serotypes and others matching previously reported strains.

CONCLUSIONS

We identified possible clade shifts in the DENV1 and 2 populations and a rising prevalence of DENV3. Our study showed a high level of serotype diversity of DENV circulating in Central Nepal. Furthermore, our results indicate that DENV populations in Nepal are related to a geographically diverse set of sequences but are most strongly influenced by Indian strains of DENV.

Recent advances in the control of dengue fever using herbal and synthetic drugs

Dengue virus represents a global public health threat, being prevalent in tropical and subtropical regions, with an increasing geographical distribution and rising incidence worldwide. This mosquito-borne viral agent causes a wide range of clinical manifestations, from mild febrile illness to severe cases and potentially fatal outcomes due to hemorrhage and shock syndrome. The etiological agent, dengue virus (DENV), has four distinct serotypes, each capable of inducing severe clinical outcomes. The current therapeutic landscape remains limited, with management strategies mainly focused on supportive cares. However, recent advances in pharmaceutical research have yielded promising developments in anti-dengue drugs. Extensive investigations have been conducted on various synthetic compounds, including JNJ-1802, 1,4-pyran naphthoquinones, and arylnaphthalene lignan derivatives. Additionally, natural compounds derived from medicinal plants such as Hippophae rhamnoides, Azadirachta indica, and Cymbopogon citratus have demonstrated potential antiviral properties in both in vitro and in vivo studies, based on inhibition of DENV replication. However, none of these compounds are to date approved by the U.S. Food and Drug Administration (FDA). Although many vaccines have been recognized as candidates in various stages of clinical trials, only a limited number of these have demonstrated a protective efficacy against the infection. This aspect underscores the need for both highly effective immunization strategies and therapeutic interventions, whether derived from botanical sources or through synthetic manufacturing, that exhibit low adverse effects. This review examines innovative approaches to DENV prevention and treatment, encompassing both phytochemical and synthetic therapeutic strategies.

Molecular Epidemiology of Dengue Viruses in Lao People's Democratic Republic, 2020-2023

Dengue fever is a widespread mosquito-borne viral disease caused by infections with dengue virus (DENV). Since its initial detection in 1979, the disease has posed a significant public health threat to the Lao People's Democratic Republic (Lao PDR). Surveillance is crucial for understanding the circulation of DENV in endemic regions and identifying potential hot spots with higher-than-expected case numbers of dengue fever. In this study, we present the results from our surveillance activities in the Lao PDR spanning 2020-2023. While quarantine restrictions from the COVID-19 pandemic posed substantial disruptions to performing DENV surveillance, over 8800 samples were tested during this period, with a positive rate of close to 60%. Cases were reported from all three regions (northern, Central, and southern) of the Lao PDR. Three circulating serotypes (DENV-1, DENV-2, and DENV-4) were detected, with DENV-1 dominant in 2021 and 2022, while DENV-2 was dominant in 2020 and 2023. Phylogenetic analyses suggest that the genotypes of DENV-1, DENV-2, and DENV-4 were closely related to corresponding isolates from neighboring countries. These findings provide an update on the nature of DENV cases detected in the Lao PDR and underscore the critical importance of sustaining a robust surveillance network to track infections.

Advancements in dengue vaccines: A historical overview and pro-spects for following next-generation candidates

Dengue, caused by four serotypes of dengue viruses (DENV-1 to DENV-4), is the most prevalent and widely mosquito-borne viral disease affecting humans. Dengue virus (DENV) infection has been reported in over 100 countries, and approximately half of the world's population is now at risk. The paucity of universally licensed DENV vaccines highlights the urgent need to address this public health concern. Action and atten-tion to antibody-dependent enhancement increase the difficulty of vaccine development. With the worsen-ing dengue fever epidemic, Dengvaxia® (CYD-TDV) and Qdenga® (TAK-003) have been approved for use in specific populations in affected areas. However, these vaccines do not provide a balanced immune response to all four DENV serotypes and the vaccination cannot cover all populations. There is still a need to develop a safe, broad-spectrum, and effective vaccine to address the increasing number of dengue cases worldwide. This review provides an overview of the existing DENV vaccines, as well as potential candidates for future studies on DENV vaccine development, and discusses the challenges and possible solutions in the field.

Viruses and the Brain-A Relationship Prone to Trouble

Neurological disorders, some of which are associated with viral infections, are growing due to the aging and expanding population. Despite strong defenses of the central nervous system, some viruses have evolved ways to breach them, which often result in dire consequences. In this review, we recount the various ways by which different viruses can enter the CNS, and we describe the consequences of such invasions. Consequences may manifest as acute disease, such as encephalitis, meningitis, or result in long-term effects, such as neuromuscular dysfunction, as occurs in poliomyelitis. We discuss evidence for viral involvement in the causation of well-known chronic neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, as well as vascular dementia in the elderly. We also describe the approaches currently available to control a few of the neural viral infections. These include antivirals that are effective against human immunodeficiency virus and herpes simplex virus, as well as vaccines valuable for controlling rabies virus, poliomyelitis virus, and some flavivirus infections. There is an urgent need to better understand, at a molecular level, how viruses contribute to acute and, especially, chronic neurological diseases and to develop more precise and effective vaccines and therapies.

Functional Verification of Differentially Expressed Genes Following DENV2 Infection in Aedes aegypti

The dengue virus (DENV) is primarily transmitted by Aedes aegypti. Investigating genes associated with mosquito susceptibility to DENV2 offers a theoretical foundation for targeted interventions to regulate or block viral replication and transmission within mosquitoes. Based on the transcriptomic analyses of the midgut and salivary glands from Aedes aegypti infected with DENV2, alongside analyses of Aag2 cell infections, 24 genes potentially related to the regulation of Aedes aegypti infection with DENV2 were selected. By establishing transient transfection and overexpression models of Aedes aegypti Aag2 cells, and mosquito target gene interference models, the difference in viral load before and after treatment was compared, and the effects of DEGs on viral replication were evaluated. After overexpressing 24 DEGs in Aag2 cells, 19 DEGs showed a significant difference in DENV2 RNA copies in the cell supernatant (p < 0.05). In adult mosquitoes, knocking down defensin-A, defensin-A-like, and SMCT1 respectively reduced the DENV2 RNA copies, while knocking down UGT2B1 and ND4 respectively increased the DENV2 RNA copies. In this study, to assess the role of genes related to DENV2 replication, and transient transfection and overexpression models in Aag2 cells and mosquito gene knockdown models were established, and five genes, defensin-A, defensin-A-like, SMCT1, UGT2B1, and ND4, were found to have an impact on the replication of DENV2, providing a reference basis for studying the complex mechanism of mosquito-virus interactions.

Current status of the development of dengue vaccines

Dengue fever is caused by the mosquito-borne dengue virus (DENV), which is endemic in more than 100 countries. Annually, there are approximately 390 million dengue cases, with a small subset manifesting into severe illnesses, such as dengue haemorrhagic fever or dengue shock syndrome. Current treatment options for dengue infections remain supportive management due to the lack of an effective vaccine and clinically approved antiviral. Although the CYD-TDV (Dengvaxia®) vaccine with an overall vaccine efficacy of 60 % has been licensed for clinical use since 2015, it poses an elevated risk of severe dengue infections especially in dengue-naïve children below 9 years of age. The newly approved Qdenga vaccine was able to achieve an overall vaccine efficacy of 80 % after 12 months, but it was not able to provide a protective effect against DENV-3 in dengue naïve individuals. The Butantan-DV vaccine candidate is still undergoing phase 3 clinical trials for safety and efficacy evaluations in humans. Apart from live-attenuated vaccines, various other vaccine types are also currently being studied in preclinical and clinical studies. This review discusses the current status of dengue vaccine development.

Spatial-temporal distribution of chikungunya virus in Brazil: a review on the circulating viral genotypes and Aedes (Stegomyia) albopictus as a potential vector

Chikungunya virus (CHIKV) is mainly transmitted by the invasive mosquito Aedes (Stegomyia) aegypti in tropical and subtropical regions worldwide. However, genetic adaptations of the virus to the peri domestic mosquito vector Aedes (Stegomyia) albopictus has resulted in enhanced vector competence and associated epidemics and may contribute to further geographic expansion of CHIKV. However, evidence-based data on the relative role of Ae. albopictus in CHIKV transmission dynamics are scarce, especially in regions where Ae. aegypti is the main vector, such as in Brazil. Here, we review the CHIKV genotypes circulating in Brazil, spatial and temporal distribution of Chikungunya cases in Brazil, and susceptibility to infection and transmission (i.e., vector competence) of Ae. albopictus for CHIKV to better understand its relative contribution to the virus transmission dynamics.

Dengue virus genomic surveillance in the applying Wolbachia to eliminate dengue trial reveals genotypic efficacy and disruption of focal transmission

Release of Aedes aegypti mosquitoes infected with Wolbachia pipientis (wMel strain) is a biocontrol approach against Ae. aegypti-transmitted arboviruses. The Applying Wolbachia to Eliminate Dengue (AWED) cluster-randomised trial was conducted in Yogyakarta, Indonesia in 2018-2020 and provided pivotal evidence for the efficacy of wMel-Ae. aegypti mosquito population replacement in significantly reducing the incidence of virologically-confirmed dengue (VCD) across all four dengue virus (DENV) serotypes. Here, we sequenced the DENV genomes from 318 dengue cases detected in the AWED trial, with the aim of characterising DENV genetic diversity, measuring genotype-specific intervention effects, and inferring DENV transmission dynamics in wMel-treated and untreated areas of Yogyakarta. Phylogenomic analysis of all DENV sequences revealed the co-circulation of five endemic DENV genotypes: DENV-1 genotype I (12.5%) and IV (4.7%), DENV-2 Cosmopolitan (47%), DENV-3 genotype I (8.5%), and DENV-4 genotype II (25.7%), and one recently imported genotype, DENV-4 genotype I (1.6%). The diversity of genotypes detected among AWED trial participants enabled estimation of the genotype-specific protective efficacies of wMel, which were similar (± 10%) to the point estimates of the respective serotype-specific efficacies reported previously. This indicates that wMel afforded protection to all of the six genotypes detected in Yogyakarta. We show that within this substantial overall viral diversity, there was a strong spatial and temporal structure to the DENV genomic relationships, consistent with highly focal DENV transmission around the home in wMel-untreated areas and a near-total disruption of transmission by wMel. These findings can inform long-term monitoring of DENV transmission dynamics in Wolbachia-treated areas including Yogyakarta.

Genomic surveillance reveals a dengue 2 virus epidemic lineage with a marked decrease in sensitivity to Mosnodenvir

Dengue fever is the most important arbovirosis for public health, with more than 5 million cases worldwide in 2023. Mosnodenvir is the first anti-dengue compound with very high preclinical pan-serotype activity, currently undergoing phase 2 clinical evaluation. Here, by analyzing dengue virus (DENV) genomes from the 2023-2024 epidemic in the French Caribbean Islands, we show that they all exhibit mutation NS4B:V91A, previously associated with a marked decrease in sensitivity to mosnodenvir in vitro. Using antiviral activity tests on four clinical and reverse-genetic strains, we confirm a marked decrease in mosnodenvir sensitivity for DENV-2 ( > 1000 fold). Finally, combining phylogenetic analysis and experimental testing for resistance, we find that virus lineages with low sensitivity to mosnodenvir due to the V91A mutation likely emerged multiple times over the last 30 years in DENV-2 and DENV-3. These results call for increased genomic surveillance, in particular to track lineages with resistance mutations. These efforts should allow to better assess the activity profile of DENV treatments in development against circulating strains.

Detection of dengue virus serotype 4 in Panama after 23 years without circulation

Panama is a country with endemic Dengue virus (DENV) transmission since its reintroduction in 1993. The four serotypes have circulated in the country and the region of the Americas, however, DENV-4 confirmed autochthonous cases have not been identified since 2000, despite its circulation in neighboring countries. Here, we report DENV-4 detection in Panama in the last four-month period of 2023 with co-circulation of the other serotypes, this was associated with a peak of dengue cases during the dry season even though most dengue outbreaks are described in the rainy season. Complete genomes of DENV-4 allowed us to determine that cases were caused by DENV-4 genotype IIb, the same genotype as 23 years ago, with high similarity to DENV-4 sequences circulating in Nicaragua and El Salvador during 2023. This report shows the importance of maintaining serotype and genotype surveillance for early detection of new variants circulating in the country.

In silico fragment-based design and pharmacophore modelling of therapeutics against dengue virus envelope protein

Dengue virus, an arbovirus of genus Flavivirus, is an infectious disease causing organisms in the tropical environment leading to numerous deaths every year. No therapeutic is available against the virus till date with only symptomatic relief available. Here, we have tried to design therapeutic compounds from scratch by fragment based method followed by pharmacophore based modelling to find suitable similar structure molecules and validated the same by MD simulation, followed by binding energy calculations and ADMET analysis. The receptor binding region of the dengue envelope protein was considered as the target for prevention of viral host cell entry and thus infection. This resulted in the final selection of kanamycin as a stable binding molecule against the Dengue virus envelope protein receptor binding domain. This study results in selection of a single molecule having high binding energy and prominent stable interactions as determined by post simulation analyses. This study aims to provide a direction for development of small molecule therapeutics against the dengue virus in order to control infection. This study may open a new avenue in the arena of structure based and fragment based therapeutic design to obtain novel molecules with therapeutic potential.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40203-024-00262-9.

Molecular epidemiology and evolutionary characteristics of dengue virus 2 in East Africa

Despite the increasing burden of dengue, the regional emergence of the virus in Kenya has not been examined. This study investigates the genetic structure and regional spread of dengue virus-2 in Kenya. Viral RNA from acutely ill patients in Kenya was enriched and sequenced. Six new dengue-2 genomes were combined with 349 publicly available genomes and phylogenies used to infer gene flow between Kenya and other countries. Analyses indicate two dengue-2 Cosmopolitan genotype lineages circulating in Kenya, linked to recent outbreaks in coastal Kenya and Burkina Faso. Lineages circulating in Western, Southern, and Eastern Africa exhibiting similar evolutionary features are also reported. Phylogeography suggests importation of dengue-2 into Kenya from East and Southeast Asia and bidirectional geneflow. Additional lineages circulating in Africa are also imported from East and Southeast Asia. These findings underscore how intermittent importations from East and Southeast Asia drive dengue-2 circulation in Kenya and Africa more broadly.

Preclinical Evaluation of Novel Sterically Optimized VLP-Based Vaccines against All Four DENV Serotypes

Over the past few decades, dengue fever has emerged as a significant global health threat, affecting tropical and moderate climate regions. Current vaccines have practical limitations, there is a strong need for safer, more effective options. This study introduces novel vaccine candidates covering all four dengue virus (DENV) serotypes using virus-like particles (VLPs), a proven vaccine platform. The dengue virus envelope protein domain III (EDIII), the primary target of DENV-neutralizing antibodies, was either genetically fused or chemically coupled to bacteriophage-derived AP205-VLPs. To facilitate the incorporation of the large EDIII domain, AP205 monomers were dimerized, resulting in sterically optimized VLPs with 90 N- and C-termini. These vaccines induced high-affinity/avidity antibody titers in mice, and confirmed their protective potential by neutralizing different DENV serotypes in vitro. Administration of a tetravalent vaccine induced high neutralizing titers against all four serotypes without producing enhancing antibodies, at least not against DENV2. In conclusion, the vaccine candidates, especially when administered in a combined fashion, exhibit intriguing properties for potential use in the field, and exploring the possibility of conducting a preclinical challenge model to verify protection would be a logical next step.

Unraveling Dengue Virus Diversity in Asia: An Epidemiological Study through Genetic Sequences and Phylogenetic Analysis

Dengue virus (DENV) is the causative agent of dengue. Although most infected individuals are asymptomatic or present with only mild symptoms, severe manifestations could potentially devastate human populations in tropical and subtropical regions. In hyperendemic regions such as South Asia and Southeast Asia (SEA), all four DENV serotypes (DENV-1, DENV-2, DENV-3, and DENV-4) have been prevalent for several decades. Each DENV serotype is further divided into multiple genotypes, reflecting the extensive diversity of DENV. Historically, specific DENV genotypes were associated with particular geographical distributions within endemic regions. However, this epidemiological pattern has changed due to urbanization, globalization, and climate change. This review comprehensively traces the historical and recent genetic epidemiology of DENV in Asia from the first time DENV was identified in the 1950s to the present. We analyzed envelope sequences from a database covering 16 endemic countries across three distinct geographic regions in Asia. These countries included Bangladesh, Bhutan, India, Maldives, Nepal, Pakistan, and Sri Lanka from South Asia; Cambodia, Laos, Myanmar, Thailand, and Vietnam from Mainland SEA; and Indonesia, the Philippines, Malaysia, and Singapore from Maritime SEA. Additionally, we describe the phylogenetic relationships among DENV genotypes within each serotype, along with their geographic distribution, to enhance the understanding of DENV dynamics.

Regional Variation of the CD4 and CD8 T Cell Epitopes Conserved in Circulating Dengue Viruses and Shared with Potential Vaccine Candidates

As dengue expands globally and many vaccines are under trials, there is a growing recognition of the need for assessing T cell immunity in addition to assessing the functions of neutralizing antibodies during these endeavors. While several dengue-specific experimentally validated T cell epitopes are known, less is understood about which of these epitopes are conserved among circulating dengue viruses and also shared by potential vaccine candidates. As India emerges as the epicenter of the dengue disease burden and vaccine trials commence in this region, we have here aligned known dengue specific T cell epitopes, reported from other parts of the world with published polyprotein sequences of 107 dengue virus isolates available from India. Of the 1305 CD4 and 584 CD8 epitopes, we found that 24% and 41%, respectively, were conserved universally, whereas 27% and 13% were absent in any viral isolates. With these data, we catalogued epitopes conserved in circulating dengue viruses from India and matched them with each of the six vaccine candidates under consideration (TV003, TDEN, DPIV, CYD-TDV, DENVax and TVDV). Similar analyses with viruses from Thailand, Brazil and Mexico revealed regional overlaps and variations in these patterns. Thus, our study provides detailed and nuanced insights into regional variation that should be considered for itemization of T cell responses during dengue natural infection and vaccine design, testing and evaluation.

Genotype of dengue virus serotype 1 in relation to severe dengue in Guangzhou, China

Guangzhou has been the city most affected by the dengue virus (DENV) in China, with a predominance of DENV serotype 1 (DENV-1). Viral factors such as dengue serotype and genotype are associated with severe dengue (SD). However, none of the studies have investigated the relationship between DENV-1 genotypes and SD. To understand the association between DENV-1 genotypes and SD, the clinical manifestations of patients infected with different genotypes were investigated. A total of 122 patients with confirmed DENV-1 genotype infection were recruited for this study. The clinical manifestations, laboratory tests, and levels of inflammatory mediator factors were statistically analyzed to investigate the characteristics of clinical manifestations and immune response on the DENV-1 genotype. In the case of DENV-1 infection, the incidence of SD with genotype V infection was significantly higher than that with genotype I infection. Meanwhile, patients infected with genotype V were more common in ostealgia and bleeding significantly. In addition, levels of inflammatory mediator factors including IFN-γ, TNF-α, IL-10, and soluble vascular cell adhesion molecule 1 were higher in patients with SD infected with genotype V. Meanwhile, the concentrations of regulated upon activation normal T-cell expressed and secreted and growth-related gene alpha were lower in patients with SD infected with genotype V. The higher incidence of SD in patients infected with DENV-1 genotype V may be attributed to elevated cytokines and adhesion molecules, along with decreased chemokines.

Continued dominance of dengue virus serotype 2 during the recent Central India outbreaks (2019-2021) with evidence of genetic divergence

Central India faced major dengue outbreaks in 2019 and 2021. In the present study, we aimed to identify the dengue virus serotypes and genotypes circulating in Central India during the COVID pre-pandemic year (2019) and ongoing-pandemic year (2021). For this purpose, the suspected cases were first tested by serological assays. Sero-positive samples were then subjected to molecular diagnosis by RT-PCR and semi-nested PCR. The serotypes obtained were confirmed by nucleotide sequencing. A phylogenetic analysis of serotypes was performed to identify the circulating genotypes. All four DENV serotypes were detected during 2019 and 2021, with the predominance of DENV2. Cases with multiple DENV serotype infections were also identified, involving DENV-2 in all the coinfections. Genotyping revealed that DENV-1 (Genotype V, American/African), DENV-2 (Genotype IV, Cosmopolitan), DENV-3 (Genotype III, Cosmopolitan), and DENV-4 (Genotype I) were involved during both outbreaks. DENV-2 detected in 2019 and 2021 has diverged from the previous strains detected in Central India (2016 and 2018), which may account for the higher transmission of DENV-2 during these outbreaks. The detection of heterologous DENV serotypes with high transmission efficiency calls for continuous viral monitoring and surveillance, which will contribute to a better understanding of changing viral dynamics and transmission patterns.

Neurological Complications in Dengue Among Males of the Adult Age Group

Neurological problems are more frequently linked to dengue, a mosquito-transmitted virus common in tropical areas. This review study thoroughly examines the effects of dengue on adult males' neurological systems. Dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS) can develop in severe cases of dengue fever caused by the dengue virus (DENV). Unsettlingly, it is thought that a sizable portion of DENV infections impact the central nervous system (CNS), which calls into question the former theory that the DENV is not neurotropic. This review dissects the many neurological manifestations of dengue, spanning from encephalopathy, encephalitis, and other CNS implications to peripheral neuromuscular issues, through the systematic analysis of publications gathered from PubMed. The essay emphasizes the immunological reactions brought on by DENV infections and offers a deeper understanding of the pathophysiology. Given that they exhibit similar first symptoms, Zika and chikungunya are two more illnesses that must be distinguished from dengue. The mainstay of current diagnostic methods is serum and cerebrospinal fluid (CSF) tests, although supportive care is still used. This review highlights the importance of tracking neurological symptoms in dengue patients and encourages more studies in this area.

A Novel, Comprehensive A129 Mouse Model for Investigating Dengue Vaccines and Evaluating Pathogenesis

In search of a mouse model for use in evaluating dengue vaccines, we assessed A129 mice that lacked IFN-α/β receptors, rendering them susceptible to dengue virus (DENV) infection. To our knowledge, no reports have evaluated dengue vaccine efficiency using A129 mice. A129 mice were given a single intraperitoneal (IP) or subcutaneous (SC) injection of the vaccine, Dengvaxia. After 14 days of immunization via the IP or SC injection of Dengvaxia, the A129 mice exhibited notably elevated levels of anti-DENV immunoglobulin G and neutralizing antibodies (NAb) targeting all four DENV serotypes, with DENV-4 displaying the highest NAb levels. After challenge with DENV-2, Dengvaxia and mock-immunized mice survived, while only the mock group exhibited signs of morbidity. Viral genome levels in the serum and tissues (excluding the brain) were considerably lower in the immunized mice compared to those in the mock group. The SC administration of Dengvaxia resulted in lower viremia levels than IP administration did. Therefore, given that A129 mice manifest dengue-related morbidity, including viremia in the serum and other tissues, these mice represent a valuable model for investigating novel dengue vaccines and antiviral drugs and for exploring dengue pathogenesis.

Conessine inhibits enveloped viruses replication through up-regulating cholesterol level

Dengue virus (DENV) is one of the most prevalent arthropod-borne diseases. It may cause dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS), while no effective vaccines and drugs are available. Our study demonstrated that conessine exhibits broad antiviral activity against several enveloped viruses, including DENV, vesicular stomatitis virus, and herpes simplex virus. In addition, conessine has no direct destructive effect on the integrity or infectivity of virions. Both pre-treatment and post-treatment with conessine significantly reduce DENV replication. Pre-treatment with conessine disrupts the endocytosis of enveloped viruses, while post-treatment disturbs DENV RNA replication or translation at an early stage. Through screening differentially expressed genes by transcriptome sequencing, we found that conessine may affect cholesterol biosynthesis, metabolism or homeostasis. Finally, we confirmed that conessine inhibits virus replication through up-regulating cholesterol levels. Our work suggests that conessine could be developed as a prophylactic and therapeutic treatment for infectious diseases caused by enveloped viruses.

Homotypic antibodies target novel E glycoprotein domains after natural DENV 3 infection/vaccination

The envelope (E) glycoprotein is the primary target of type-specific (TS) neutralizing antibodies (nAbs) after infection with any of the four distinct dengue virus serotypes (DENV1-4). nAbs can be elicited to distinct structural E domains (EDs) I, II, or III. However, the relative contribution of these domain-specific antibodies is unclear. To identify the primary DENV3 nAb targets in sera after natural infection or vaccination, chimeric DENV1 recombinant encoding DENV3 EDI, EDII, or EDIII were generated. DENV3 EDII is the principal target of TS polyclonal nAb responses and encodes two or more neutralizing epitopes. In contrast, some were individuals vaccinated with a DENV3 monovalent vaccine-elicited serum TS nAbs targeting each ED in a subject-dependent fashion, with an emphasis on EDI and EDIII. Vaccine responses were also sensitive to DENV3 genotypic variation. This DENV1/3 panel allows the measurement of serum ED TS nAbs, revealing differences in TS nAb immunity after natural infection or vaccination.

Insights into dengue immunity from vaccine trials

The quest for an effective dengue vaccine has culminated in two approved vaccines and another that has completed phase 3 clinical trials. However, shortcomings exist in each, suggesting that the knowledge on dengue immunity used to develop these vaccines was incomplete. Vaccine trial findings could refine our understanding of dengue immunity, because these are experimentally derived, placebo-controlled data. Results from these trials suggest that neutralizing antibody titers alone are insufficient to inform protection against symptomatic infection, implicating a role for cellular immunity in protection. These findings have relevance for both future dengue vaccine development and application of current vaccines for maximal public health benefit.

Global and local evolutionary dynamics of Dengue virus serotypes 1, 3, and 4

Evolutionary studies on Dengue virus (DENV) in endemic regions are necessary since naturally occurring mutations may lead to genotypic variations or shifts in serotypes, which may lead to future outbreaks. Our study comprehends the evolutionary dynamics of DENV, using phylogenetic, molecular clock, skyline plots, network, selection pressure, and entropy analyses based on partial CprM gene sequences. We have collected 250 samples, 161 in 2017 and 89 in 2018. Details for the 2017 samples were published in our previous article and that of 2018 are presented in this study. Further evolutionary analysis was carried out using 800 sequences, which incorporate the study and global sequences from GenBank: DENV-1 (n = 240), DENV-3 (n = 374), and DENV-4 (n = 186), identified during 1944-2020, 1956-2020, and 1956-2021, respectively. Genotypes V, III, and I were identified as the predominant genotypes of the DENV-1, DENV-3, and DENV-4 serotypes, respectively. The rate of nucleotide substitution was found highest in DENV-3 (7.90 × 10-4 s/s/y), followed by DENV-4 (6.23 × 10-4 s/s/y) and DENV-1 (5.99 × 10-4 s/s/y). The Bayesian skyline plots of the Indian strains revealed dissimilar patterns amongst the population size of the three serotypes. Network analyses showed the presence of different clusters within the prevalent genotypes. The data presented in this study will assist in supplementing the measures for vaccine development against DENV.

Genotyping of dengue virus from infected tissue samples embedded in paraffin

Dengue has become one of the vector-borne diseases that affect humans worldwide. In Latin American countries, Colombia is historically one of the most affected by epidemics of this flavivirus. The underreporting of signs and symptoms of probable cases of dengue, the lack of characterization of the serotypes of the infection, and the few detailed studies of postmortem necropsies of patients are among other conditions that have delayed progress in the knowledge of the pathogenesis of the disease. This study presents the results of fragment sequencing assays on paraffin-embedded tissue samples from fatal DENV cases during the 2010 epidemic in Colombia. We found that the predominant serotype was DENV-2, with the Asian/American genotype of lineages 1 and 2. This work is one of the few reports of the circulating genotypes of dengue during the 2010 epidemic in Colombia, one of the most lethal dates in the country's history.

Moderation effects of serotype on dengue severity across pregnancy status in Mexico

BACKGROUND

Pregnancy increases a woman's risk of severe dengue. To the best of our knowledge, the moderation effect of the dengue serotype among pregnant women has not been studied in Mexico. This study explores how pregnancy interacted with the dengue serotype from 2012 to 2020 in Mexico.

METHOD

Information from 2469 notifying health units in Mexican municipalities was used for this cross-sectional analysis. Multiple logistic regression with interaction effects was chosen as the final model and sensitivity analysis was done to assess potential exposure misclassification of pregnancy status.

RESULTS

Pregnant women were found to have higher odds of severe dengue [1.50 (95% CI 1.41, 1.59)]. The odds of dengue severity varied for pregnant women with DENV-1 [1.45, (95% CI 1.21, 1.74)], DENV-2 [1.33, (95% CI 1.18, 1.53)] and DENV-4 [3.78, (95% CI 1.14, 12.59)]. While the odds of severe dengue were generally higher for pregnant women compared with non-pregnant women with DENV-1 and DENV-2, the odds of disease severity were much higher for those infected with the DENV-4 serotype.

CONCLUSION

The effect of pregnancy on severe dengue is moderated by the dengue serotype. Future studies on genetic diversification may potentially elucidate this serotype-specific effect among pregnant women in Mexico.

Association of Dengue Virus Serotypes 1&2 with Severe Dengue Having Deletions in Their 3′Untranslated Regions (3′UTRs)

Dengue virus infections are recorded as hyper-endemic in many countries, including India. Research pertaining to the reasons for frequent outbreaks and severe dengue is ongoing. Hyderabad city, India, has been recorded as a ‘hotspot’ for dengue virus infections. Dengue virus strains circulating over the past few years in Hyderabad city have been characterized at the molecular level to analyze the serotype/genotypes; 3′UTRs were further amplified and sequenced. The disease severity in patients infected with dengue virus strains with complete and 3′UTR deletion mutants was analyzed. Genotype I of the serotype 1 replaced genotype III, which has been circulating over the past few years in this region. Coincidentally, the number of dengue virus infections significantly increased in this region during the study period. Nucleotide sequence analysis suggested twenty-two and eight nucleotide deletions in the 3′UTR of DENV-1. The eight nucleotide deletions observed in the case of DENV-1 3′UTR were the first reported in this instance. A 50 nucleotide deletion was identified in the case of the serotype DENV-2. Importantly, these deletion mutants were found to cause severe dengue, even though they were found to be replication incompetent. This study emphasized the role of dengue virus 3′UTRs on severe dengue and emerging outbreaks.

An alternating transmission model between mice and mosquitoes for genetic study of dengue virus

Rapidly increased incidence and prevalence of dengue virus serotype 2 (DENV-2) in recent decades highlight the need for better understanding of the selective pressures that drive genetic and phenotypic changes in this virus. We simulated the transfer of DENV-2 between human hosts and mosquito vectors by horizontally transmitting the virus between suckling mice and Aedes aegypti (Linnaeus, Diptera: Culicidae). A total of 3 cycles of alternating transmission were performed and 3 passages of virus population were harvested from the infected sucking mice. The viral titer in mice brain and infectivity to mosquitoes of theses viral populations were tested. The genome of the viruses was also sequenced. Results showed that viral titer were similar and infection rate in the mosquitoes were not significantly different among those 3 passages. This in vivo model could be utilized to explore virus evolution and genetic variance in alternating transmission.

Epidemiological and genomic analysis of dengue cases in Guangzhou, China, from 2010 to 2019

With a long epidemic history and a large number of dengue cases, Guangzhou is a key city for controlling dengue in China. The demographic information regarding dengue cases, and the genomic characteristics of the envelope gene of dengue viruses, as well as the associations between these factors were investigated from 2010 to 2019, to improve the understanding of the epidemiology of dengue in Guangzhou. Demographic data on 44,385 dengue cases reported to the Notifiable Infectious Disease Report System were analyzed using IBM SPSS Statistics v. 20. Dengue virus isolates from patient sera were sequenced, and phylogenetic trees were constructed using PhyML 3.1. There was no statistical difference in the risk of dengue infection between males and females. Unlike other areas in which dengue is endemic, the infection risk in Guangzhou increased with age. Surveillance identified four serotypes responsible for dengue infections in Guangzhou. Serotype 1 remained prevalent for most of the study period, whereas serotypes 3 and 4 were prevalent in 2012 and 2010, respectively. Different serotypes underwent genotype and sublineage shifts. The epidemiological characteristics and phylogeny of dengue in Guangzhou suggested that although it has circulated in Guangzhou for decades, it has not been endemic in Guangzhou. Meanwhile, shifts in genotypes, rather than in serotypes, might have caused dengue epidemics in Guangzhou.

Vector Competence of a Coastal Population of Aedes aegypti for Dengue 2 and 3 Virus Serotypes in Kenya

Aedes aegypti is the primary vector of dengue, an arboviral disease caused by dengue virus (DENV) that exists as four distinct serotypes (DENV 1-4). While all four DENV serotypes circulate in Kenya, differential distribution of the serotypes in specific regions suggests virus transmission may differ among local vector populations. In this study, we tested the hypothesis that a coastal Ae. aegypti population (Rabai, Kilifi County) varies in its ability to transmit DENV-2 (predominant) and DENV-3 (less dominant) and that transmission is related to Ae. aegypti subspecies—domestic Ae. aegypti aegypti (Aaa) and sylvtic Ae. aegypti formosus (Aaf). We orally exposed F1 females (3-10 days old) to blood meals containing DENV-2 (10 5.30 pfu/ml) or DENV-3 (10 5.13 pfu/ml), tested them individually for infection (body), dissemination (legs), and transmission (saliva) at 7, 14, and 21 days postinfection (DPI), respectively, and compared the rates between the serotypes. We analyzed cytochrome c oxidase I gene (cox-I) sequences among DENV-susceptible and nonsusceptible cohorts. Of 489 mosquitoes tested (DENV-2: 240; DENV-3: 249), we found consistently higher but nonsignificant rates of infection (16% vs. 10%), dissemination (47% (18/38) vs. 35% (9/26)), and transmission (39% (7/18) vs. 11% (1/9)) for DENV-2 than DENV-3. However, DENV-2 exhibited a shorter extrinsic incubation period (EIP) for disseminated infection (7-DPI vs. 14-DPI) and transmission (14-DPI vs. 21-DPI) compared to DENV-3. Two cox-I lineages were recovered in phylogeny, one predominantly clustered with referenced Aaa and a minor lineage grouped with Aaf. Infected mosquitoes and those with disseminated infection were represented in both lineages; those that transmitted the viruses grouped with the Aaa-associated lineage only. We conclude that the coastal Ae. aegypti population is a competent vector for DENV-2 and DENV-3 likely driven by the domestic Aaa that is predominant. The shorter EIP to attain dissemination and transmission for DENV-2 could favour its transmission over DENV-3.

A Six Years (2010-2016) Longitudinal Survey of the Four Serotypes of Dengue Viruses in Lao PDR

Dengue fever is the most prevalent arthropod-borne viral infection of humans in tropical and subtropical countries. Since 1979, dengue has been reported to be endemic in the Lao People's Democratic Republic (PDR), as in many countries in Southeast Asia, with a complex circulation of the four dengue viruses' serotypes (DENV-1 to DENV-4). By sequencing the complete envelope protein, we explored a panel of samples from five Lao Provinces (Vientiane capital, Luangprabang, Bolikhamxay, Saravane, Attapeu) to enrich knowledge about the co-circulation of DENVs in Lao PDR between 2010 and 2016. Phylogenetic analyses highlighted the specific circulation of DENV-1 genotype I, DENV-2 genotype Asian I, DENV-4 genotype I and the co-circulation of DENV-3 genotype II and III. The continuous co-circulation of the four serotypes was underlined, with genotype or cluster shifts among DENV-3 and DENV-1. These data suggested the emergence or re-emergence of DENV strains associated with epidemic events, potentially linked to the exchanges within the territory and with neighboring countries. Indeed, the increasing local or regional connections favored the dissemination of new isolates or new clusters around the country. Since 2012, the surveillance and alert system created in Vientiane capital by the Institut Pasteur du Laos appears to be a strategic tool for monitoring the circulation of the four serotypes, especially in this endemic country, and allows for improving dengue epidemiological knowledge to anticipate epidemic events better.

Association of viral kinetics, infection history, NS1 protein with plasma leakage among Indonesian dengue infected patients

OBJECTIVES

Plasma leakage, a hallmark of disease in Dengue virus (DENV) infection, is an important clinical manifestation and is often associated with numerous factors such as viral factors. The aim of this study is to investigate the association of virus serotype, viral load kinetics, history of infection, and NS1 protein with plasma leakage.

METHODS

Subjects with fever ≤ 48 hours and positive DENV infection were included. Serial laboratory tests, viral load measurements, and ultrasonography examination to assess plasma leakage were performed.

RESULTS

DENV-3 was the most common serotype found in the plasma leakage group (35%). Patients with plasma leakage demonstrated a trend of higher viral load and a longer duration of viremia compared to those without. This was significantly observed on the fourth day of fever (p = 0.037). We found higher viral loads on specific days in patients with plasma leakage in both primary and secondary infections compared to those without. In addition, we also observed more rapid viral clearance in patients with secondary infection. NS1 protein, especially after 4 days of fever, was associated with higher peak viral load level, even though it was not statistically significant (p = 0.470). However, pairwise comparison demonstrated that peak viral load level in the group of patients with circulating NS1 detected for 7 days was significantly higher than the 5-day group (p = 0.037).

CONCLUSION

DENV-3 was the most common serotype to cause plasma leakage. Patients with plasma leakage showed a trend of higher viral load and a longer duration of viremia. Higher level of viral load was observed significantly on day 5 in patients with primary infection and more rapid viral clearance was observed in patients with secondary infection. Longer duration of circulating NS1 protein was also seen to be positively correlated with higher peak viral load level although not statistically significant.

Three highly variable genome regions of the four dengue virus serotypes can accurately recapitulate the CDS phylogeny

The circulation of the four-dengue virus (DENV) serotypes has significantly increased in recent years, accompanied by an increase in viral genetic diversity. In order to conduct disease surveillance and understand DENV evolution and its effects on virus transmission and disease, efficient and accurate methods for phylogenetic classification are required. Phylogenetic analysis of different viral genes sequences is the most used method, the envelope gene (E) being the most frequently selected target. We explored the genetic variability of the four DENV serotypes throughout their complete coding sequence (CDS) of sequences available in GenBank and used genomic regions of different variability rate to recapitulate the phylogeny obtained with the DENV CDS. Our results indicate that the use of high or low variable regions accurately recapitulate the phylogeny obtained with CDS of sequences from different DENV genotypes. However, when analyzing the phylogeny of a single genotype, highly variable regions performed better in recapitulating the distance branch length, topology, and support of the CDS phylogeny. The use of three concatenated highly variable regions was not statistically different in distance branch length and support to that obtained in CDS phylogeny.•This study demonstrated the ability of highly variable regions of the DENV genome to recapitulate the phylogeny obtained with the full coding sequence (CDS).•The use of genomic regions of high or low variability did not affect the performance in recapitulating the phylogeny obtained with CDS from different genotypes. However, when phylogeny was analyzed for sequences from a single genotype, highly variable regions performed better in recapitulating the distance branch length, topology, and support of the CDS phylogeny.•The use of concatenated highly variable genome regions represent a useful option for recapitulating genome-wide phylogenies in analyses of sequences belonging to the same DENV genotype.

Neurological Complications of Dengue Fever

PURPOSE OF REVIEW

To discuss the neurological complications of dengue virus (DENV) infection and their pathogenesis.

RECENT FINDINGS

Include recognition of the four different serotypes of DENV and their epidemiology as well as recognition of the expanded dengue syndrome encompassing multisystem involvement in the severe form of the disease including involvement of the central nervous system (CNS). DENV is a neurotropic virus with the ability to infect the supporting cells of the CNS. Neural injury during the acute stage of the infection results from direct neuro-invasion and/or the phenomenon of antibody-dependent enhancement, resulting in plasma leakage and coagulopathy. Immune mechanisms have been implicated in the development of the delayed neurological sequelae through molecular mimicry. A myriad of neurological syndromes has been described as a result of the involvement of the CNS, the peripheral nervous system (PNS), or both. Neurological manifestations in DENV infection are increasingly being recognized, some of which are potentially fatal if not treated promptly. DENV encephalopathy and encephalitis should be considered in the differential diagnosis of other acute febrile encephalopathies, autoimmune encephalitides, and in cases of encephalopathy/encephalitis related to SARS-CoV2 infection, especially in dengue-endemic areas. Acute disseminated encephalomyelitis (ADEM) may be occasionally encountered. Clinicians should be knowledgeable of the expanded dengue syndrome characterized by the concurrent compromise of cardiac, neurological, gastrointestinal, renal, and hematopopoietic systems. Isolated cranial nerve palsies occur rather uncommonly and are often steroid responsive. These neuropathies may result from the direct involvement of cranial nerve nuclei or nerve involvement or may be immune-mediated. Even if the diagnosis of dengue is confirmed, it is absolutely imperative to exclude other well-known causes of isolated cranial nerve palsies. Ischemic and hemorrhagic strokes may occur following dengue fever. The pathogenesis may be beyond the commonly observed thrombocytopenia and include cerebral vasculitis. Involvement of ocular blood vessels may cause maculopathy or retinal hemorrhages. Posterior reversible encephalopathy syndrome (PRES) is uncommon and possibly related to dysregulated cytokine release phenomena. Lastly, any patient developing acute neuromuscular weakness during the course or within a fortnight of remission from dengue fever must be screened for acute inflammatory demyelinating polyneuropathy (AIDP), hypokalemic paralysis, or acute myositis. Rarely, a Miller-Fisher-like syndrome with negative anti-GQ1b antibody may develop.

Genetic diversity and spatiotemporal dynamics of DENV-1 and DENV-2 infections during the 2012-2013 outbreak in Mexico

Dengue fever is caused by four related dengue virus serotypes, DENV-1 to DENV-4, where each serotype comprises distinct genotypes and lineages. The last major outbreak in Mexico occurred during 2012 and 2013, when 112,698 confirmed cases were reported (DENV-1 and DENV-2 were predominant). Following partial E, NS2A and NS5 gene sequencing, based on the virus genome variability, we analyzed 396 DENV-1 and 248 DENV-2 gene sequences from serum samples from dengue acute clinical cases from 13 Mexican states, Mutations were identified, and their genetic variability estimated, along with their evolutionary relationship with DENV sequences sampled globally. DENV-1 genotype V and DENV-2 Asian-American genotype V were the only genotypes circulating during the outbreak. Mutations in NS2A and NS5 proteins were widely disseminated and suggested local emergence of new lineages. Phylogeographic analysis suggested viral spread occurred from coastal regions, and tourist destinations, such as Yucatan and Quintana Roo, which played important roles in disseminating these lineages.

Molecular Characterization and Phylogenetic Analysis of the 2019 Dengue Outbreak in Wenzhou, China

In 2019, a dengue outbreak occurred with 290 confirmed cases in Wenzhou, a coastal city in southeast China. To identify the origin of the dengue virus (DENV) from this outbreak, viral RNA was extracted from four serum samples and sequenced for whole genome analysis. Then, phylogenetic analysis, gene mutation, secondary structure prediction, selection pressure analysis, and recombination analysis were performed. DENV strains Cam-03 and Cam-11 were isolated from patients traveling from Cambodia, while ZJWZ-18 and ZJWZ-62 strains were isolated from local patients without a record of traveling abroad. The whole genome sequence of all four strains was 10,735 nucleotides long. Phylogenetic tree analysis showed that the four strains belonged to genotype 1 of DENV-1, but the local Wenzhou strains and imported strains clustered in different branches. ZJWZ-18 and ZJWZ-62 were closely related to strain MF033254-Singapore-2016, and Cam-03 and Cam-11 were closely related to strain AB608788-China : Taiwan-1994. A comparison of the coding regions between the local strains and the DENV-1 standard strain (EU848545-Hawaii-1944) showed 82 amino acid mutations between the two strains. A total of 55 amino acid mutations were found between the coding regions of the local and imported strains. The overall secondary structure of the 3' UTR of the local strains had changed: apparent changes in the head and tail position were observed when compared to DENV-1 standard strain. Furthermore, selection pressure analysis and recombination detection using the 4 isolates and 41 reference strains showed two credible positive selection sites and eight credible recombination events, which warrant further studies. This study may enhance the understanding of viral replication, infection, evolution, virulence, and pathogenicity of DENV.

Dengue fever as a reemerging disease in upper Egypt: Diagnosis, vector surveillance and genetic diversity using RT-LAMP assay

Background

The recent increase in dengue virus (DENV) outbreaks and the absence of an effective vaccine have highlighted the importance of developing rapid and effective diagnostic surveillance tests and mosquito-based screening programs. To establish effective control measures for preventing future DENV transmission, the present study was established to identify the main mosquito vector involved in the dengue fever (DF) outbreak in Upper Egypt in 2016 and detect the diversity of dengue virus serotypes circulating in both humans and vectors.

Methods

We investigated the prevalence of DENV infection and circulating serotypes in the sera of 51 humans clinically suspected of DF and 1800 field-collected Aedes aegypti adult female mosquitoes grouped into 36 pooled samples. Both DENV non-structural protein (NS1) immunochromatographic strip assay and loop-mediated isothermal amplification (LAMP) were used for screening.

Results

Overall, the rate of DENV infection in both human sera and pooled mosquito homogenate was 33.3%, as revealed by rapid dipstick immunochromatographic analysis. However, higher detection rates were observed with RT-LAMP assay of 60.8% and 44.4% for humans and vector mosquitoes, respectively. DENV-1 was the most prevalent serotype in both populations. A combination of two, three, or even four circulating serotypes was found in 87.5% of total positive pooled mosquito samples and 83.87% of DENV-positive human sera.

Conclusion

The study reinforces the evidence of the reemergence of Aedes aegypti in Upper Egypt, inducing an outbreak of DENV. Mosquito-based surveillance of DENV infection is important to elucidate the viral activity rate and define serotype diversity to understand the virus dynamics in the reinfested area. Up to our knowledge, this is the first report of serotyping of DENV infection in an outbreak in Egypt using RT-LAMP assay.

Circulation of genotypes of dengue virus serotype 2 in Guangzhou over a period of 20 years

Background

The dengue epidemic in Guangzhou has imposed a rising burden on society and health infrastructure. Here, we present the genotype data for dengue virus serotype 2 (DENV-2) to improve understanding of this dengue epidemic.

Methods

We sequenced the envelope gene of DENV-2 obtained from patient serum samples and subsequently performed maximum-likelihood phylogenetic analysis using PhyMLv3.1, maximum clade credibility analysis using BEAST v.1.10.4, and selection pressure analysis using Datamonkey 2.0.

Results

The prevalent DENV-2 strains identified in Guangzhou region are related to those in Southeast Asian countries. In particular, the Malaysia/Indian subcontinent genotype is prevailing in Guangzhou with no apparent genotype shift having occurred over the past 20 years. However, episodic positive selection was detected at one site.

Conclusions

Local control of the DENV-2 epidemic in Guangzhou requires effective measures to prevent and monitor imported cases. Moreover, the shift between the Malaysia/Indian subcontinent genotype lineages, which originated at different time points, may account for the rise in DENV-2 cases in Guangzhou. Meanwhile, the low rate of dengue haemorrhagic fever in Guangzhou may be explained by the dominance of the less virulent Malaysia/Indian subcontinent genotype.

The RNA Secondary Structure Analysis Reveals Potential for Emergence of Pathogenic Flaviviruses

The Flavivirus genus is divided into four groups: Mosquito-borne flaviviruses, Tick-borne flaviviruses, no-known vector flaviviruses, and Insect specific flaviviruses. Millions of people are affected worldwide every year due to the flaviviral infections. The 5' UTR of the RNA genome plays a critical role in the biology of flaviviruses. To explore any correlation between the topology of the 5' UTR and pathogenesis, a global scale study of the RNA secondary structure of different groups of flaviviruses has been conducted. We found that most of the pathogenic flaviviruses, irrespective of their mode of transmission, tend to form a Y shaped topology in the Stem loop A of the 5' UTR. Some of the current non-pathogenic flaviviruses were also observed to form Y shaped structure. Based on this study, it has been proposed that the flaviviruses having the Y shaped topology in their 5' UTR regions may have the potential to become pathogenic.

Adaptive Evolution as a Driving Force of the Emergence and Re-Emergence of Mosquito-Borne Viral Diseases

Emerging and re-emerging mosquito-borne viral diseases impose a significant burden on global public health. The most common mosquito-borne viruses causing recent epidemics include flaviviruses in the family Flaviviridae, including Dengue virus (DENV), Zika virus (ZIKV), Japanese encephalitis virus (JEV) and West Nile virus (WNV) and Togaviridae viruses, such as chikungunya virus (CHIKV). Several factors may have contributed to the recent re-emergence and spread of mosquito-borne viral diseases. Among these important causes are the evolution of mosquito-borne viruses and the genetic mutations that make them more adaptive and virulent, leading to widespread epidemics. RNA viruses tend to acquire genetic diversity due to error-prone RNA-dependent RNA polymerases, thus promoting high mutation rates that support adaptation to environmental changes or host immunity. In this review, we discuss recent findings on the adaptive evolution of mosquito-borne viruses and their impact on viral infectivity, pathogenicity, vector fitness, transmissibility, epidemic potential and disease emergence.

Rapid molecular assays for the detection of the four dengue viruses in infected mosquitoes

The pantropic emergence of severe dengue disease can partly be attributed to the co-circulation of different dengue viruses (DENVs) in the same geographical location. Effective monitoring for circulation of each of the four DENVs is critical to inform disease mitigation strategies. In low resource settings, this can be effectively achieved by utilizing inexpensive, rapid, sensitive and specific assays to detect viruses in mosquito populations. In this study, we developed four rapid DENV tests with direct applicability for low-resource virus surveillance in mosquitoes. The test protocols utilize a novel sample preparation step, a single-temperature isothermal amplification, and a simple lateral flow detection. Analytical sensitivity testing demonstrated tests could detect down to 1,000 copies/µL of virus-specific DENV RNA, and analytical specificity testing indicated tests were highly specific for their respective virus, and did not detect closely related flaviviruses. All four DENV tests showed excellent diagnostic specificity and sensitivity when used for detection of both individually infected mosquitoes and infected mosquitoes in pools of uninfected mosquitoes. With individually infected mosquitoes, the rapid DENV-1, -2 and -3 tests showed 100% diagnostic sensitivity (95% CI = 69% to 100%, n=8 for DENV-1; n=10 for DENV 2,3) and the DENV-4 test showed 92% diagnostic sensitivity (CI: 62% to 100%, n=12) along with 100% diagnostic specificity (CI: 48-100%) for all four tests. Testing infected mosquito pools, the rapid DENV-2, -3 and -4 tests showed 100% diagnostic sensitivity (95% CI = 69% to 100%, n=10) and the DENV-1 test showed 90% diagnostic sensitivity (55.50% to 99.75%, n=10) together with 100% diagnostic specificity (CI: 48-100%). Our tests reduce the operational time required to perform mosquito infection status surveillance testing from > two hours to only 35 minutes, and have potential to improve accessibility of mosquito screening, improving monitoring and control strategies in low-income countries most affected by dengue outbreaks.

Rapid molecular assays for the detection of the four dengue viruses in infected mosquitoes

The pantropic emergence of severe dengue disease can partly be attributed to the co-circulation of different dengue viruses (DENVs) in the same geographical location. Effective monitoring for circulation of each of the four DENVs is critical to inform disease mitigation strategies. In low resource settings, this can be effectively achieved by utilizing inexpensive, rapid, sensitive and specific assays to detect viruses in mosquito populations. In this study, we developed four rapid DENV tests with direct applicability for low-resource virus surveillance in mosquitoes. The test protocols utilize a novel sample preparation step, a single-temperature isothermal amplification, and a simple lateral flow detection. Analytical sensitivity testing demonstrated tests could detect down to 1,000 copies/µL of virus-specific DENV RNA, and analytical specificity testing indicated tests were highly specific for their respective virus, and did not detect closely related flaviviruses. All four DENV tests showed excellent diagnostic specificity and sensitivity when used for detection of both individually infected mosquitoes and infected mosquitoes in pools of uninfected mosquitoes. With individually infected mosquitoes, the rapid DENV-1, -2 and -3 tests showed 100% diagnostic sensitivity (95% CI = 69% to 100%, n=8 for DENV-1; n=10 for DENV 2,3) and the DENV-4 test showed 92% diagnostic sensitivity (CI: 62% to 100%, n=12) along with 100% diagnostic specificity (CI: 48-100%) for all four tests. Testing infected mosquito pools, the rapid DENV-2, -3 and -4 tests showed 100% diagnostic sensitivity (95% CI = 69% to 100%, n=10) and the DENV-1 test showed 90% diagnostic sensitivity (55.50% to 99.75%, n=10) together with 100% diagnostic specificity (CI: 48-100%). Our tests reduce the operational time required to perform mosquito infection status surveillance testing from > two hours to only 35 minutes, and have potential to improve accessibility of mosquito screening, improving monitoring and control strategies in low-income countries most affected by dengue outbreaks.

Dengue Infection Susceptibility of Five Aedes aegypti Populations from Manaus (Brazil) after Challenge with Virus Serotypes 1–4

The successful spread and maintenance of the dengue virus (DENV) in mosquito vectors depends on their viral infection susceptibility, and parameters related to vector competence are the most valuable for measuring the risk of viral transmission by mosquitoes. These parameters may vary according to the viral serotype in circulation and in accordance with the geographic origin of the mosquito population that is being assessed. In this study, we investigated the effect of DENV serotypes (1–4) with regards to the infection susceptibility of five Brazilian Ae. aegypti populations from Manaus, the capital of the state of Amazonas, Brazil. Mosquitoes were challenged by oral infection with the DENV serotypes and then tested for the presence of the arbovirus using quantitative PCR at 14 days post-infection, which is the time point that corresponds to the extrinsic incubation period of Ae. aegypti when reared at 28 °C. Thus, we were able to determine the infection patterns for DENV-1, -2, -3 and -4 in the mosquito populations. The mosquitoes had both interpopulation and inter-serotype variation in their viral susceptibilities. All DENV serotypes showed a similar tendency to accumulate in the body in a greater amount than in the head/salivary gland (head/SG), which does not occur with other flaviviruses. For DENV-1, DENV-3, and DENV-4, the body viral load varied among populations, but the head/SG viral loads were similar. Differently for DENV-2, both body and head/SG viral loads varied among populations. As the lack of phenotypic homogeneity represents one of the most important reasons for the long-term fight against dengue incidence, we expect that this study will help us to understand the dynamics of the infection patterns that are triggered by the distinct serotypes of DENV in mosquitoes.

Updates on Dengue Vaccine and Antiviral: Where Are We Heading?

Approximately 100–400 million people from more than 100 countries in the tropical and subtropical world are affected by dengue infections. Recent scientific breakthroughs have brought new insights into novel strategies for the production of dengue antivirals and vaccines. The search for specific dengue inhibitors is expanding, and the mechanisms for evaluating the efficacy of novel drugs are currently established, allowing for expedited translation into human trials. Furthermore, in the aftermath of the only FDA-approved vaccine, Dengvaxia, a safer and more effective dengue vaccine candidate is making its way through the clinical trials. Until an effective antiviral therapy and licensed vaccine are available, disease monitoring and vector population control will be the mainstays of dengue prevention. In this article, we highlighted recent advances made in the perspectives of efforts made recently, in dengue vaccine development and dengue antiviral drug.

Using Background Sequencing Data to Anticipate DENV-1 Circulation in the Lao PDR

Since its first detection in 1979, dengue fever has been considered a major public health issue in the Lao People’s Democratic Republic (PDR). Dengue virus (DENV) serotype 1 was the cause of an epidemic in 2010–2011. Between 2012 and 2020, major outbreaks due successively to DENV-3, DENV-4 and recently DENV-2 have been recorded. However, DENV-1 still co-circulated in the country over this period. Here, we summarize epidemiological and molecular data of DENV-1 between 2016 and 2020 in the Lao PDR. Our data highlight the continuous circulation of DENV-1 in the country at levels ranging from 16% to 22% among serotyping tests. In addition, the phylogenetic analysis has revealed the circulation of DENV-1 genotype I at least since 2008 with a co-circulation of different clusters. Sequence data support independent DENV-1 introductions in the Lao PDR correlated with an active circulation of this serotype at the regional level in Southeast Asia. The maintenance of DENV-1 circulation over the last ten years supports a low level of immunity against this serotype within the Lao population. Thereby, the risk of a DENV-1 epidemic cannot be ruled out in the future, and this emphasizes the importance of maintaining an integrated surveillance approach to prevent major outbreaks.

Molecular Diagnosis of Dengue

Several protocols for genomic amplification using reverse transcription followed by polymerase chain reaction (RT-PCR), important in the identification of the infecting serotype, have been used in the rapid diagnosis of Dengue Virus (DENV) infections. The qualitative protocol described by Lanciotti et al. (J Clin Microbiol 30: 545-551, 1992) suggested by WHO detects the four DENV serotypes simultaneously in one procedure "semi-nested," generating amplified products with specific sizes in base pairs for each serotype and it has been the most used in the past two decades. However, advances in molecular diagnosis have enabled the development of RT-PCR in real time (qRT-PCR) based on the use of dyes and probes (SYBR green and TaqMan), which is performed in a single step and is capable of providing quantitative data. In addition to quantification, the advantages of qRT-PCR over conventional RT-PCR include speed, greater sensitivity and specificity, and low rate of false positives. Several protocols for the diagnosis and/or quantification of DENV have already been described. Non-PCR-based methods such as reverse transcription loop-mediated isothermal amplification have shown high sensitivities and specificities. RT-PCR and qRT-PCR techniques can be performed using serum, plasma, infected cells, mosquitoes, fresh, and paraffin-embedded tissues. However, despite fast and accurate, they are limited to samples collected during the acute phase of infection (up to 7 days after the onset of symptoms) and require specialized equipment and trained staff.

Current Trends and Limitations in Dengue Antiviral Research

Dengue is the most prevalent arthropod-borne viral disease worldwide and affects approximately 2.5 billion people living in over 100 countries. Increasing geographic expansion of Aedes aegypti mosquitoes (which transmit the virus) has made dengue a global health concern. There are currently no approved antivirals available to treat dengue, and the only approved vaccine used in some countries is limited to seropositive patients. Treatment of dengue, therefore, remains largely supportive to date; hence, research efforts are being intensified for the development of antivirals. The nonstructural proteins, 3 and 5 (NS3 and NS5), have been the major targets for dengue antiviral development due to their indispensable enzymatic and biological functions in the viral replication process. NS5 is the largest and most conserved nonstructural protein encoded by flaviviruses. Its multifunctionality makes it an attractive target for antiviral development, but research efforts have, this far, not resulted in the successful development of an antiviral targeting NS5. Increase in structural insights into the dengue NS5 protein will accelerate drug discovery efforts focused on NS5 as an antiviral target. In this review, we will give an overview of the current state of therapeutic development, with a focus on NS5 as a therapeutic target against dengue.