Yellow Fever Virus: Knowledge Gaps Impeding the Fight Against an Old Foe

Mitochondrial hyperactivity and reactive oxygen species drive innate immunity to the yellow fever virus-17D live-attenuated vaccine

The yellow fever virus 17D (YFV-17D) live attenuated vaccine is considered one of the most successful vaccines ever generated associated with high antiviral immunity, yet the signaling mechanisms that drive the response in infected cells are not understood. Here, we provide a molecular understanding of how metabolic stress and innate immune responses are linked to drive type I IFN expression in response to YFV-17D infection. Comparison of YFV-17D replication with its parental virus, YFV-Asibi, and a related dengue virus revealed that IFN expression requires RIG-I-Like Receptor signaling through MAVS, as expected. However, YFV-17D uniquely induces mitochondrial respiration and major metabolic perturbations, including hyperactivation of electron transport to fuel ATP synthase. Mitochondrial hyperactivity generates reactive oxygen species (ROS) including peroxynitrite, blocking of which abrogated MAVS oligomerization and IFN expression in non-immune cells without reducing YFV-17D replication. Scavenging ROS in YFV-17D-infected human dendritic cells increased cell viability yet globally prevented expression of IFN signaling pathways. Thus, adaptation of YFV-17D for high growth imparts mitochondrial hyperactivity to meet energy demands, resulting in generation of ROS as the critical messengers that convert a blunted IFN response into maximal activation of innate immunity essential for vaccine effectiveness.

Identification of potential inhibitors targeting yellow fever virus helicase through ligand and structure-based computational studies

Yellow fever is a flavivirus having plus-sensed RNA which encodes a single polyprotein. Host proteases cut this polyprotein into seven nonstructural proteins including a vital NS3 protein. The present study aims to identify the most effective inhibitor against the helicase (NS3) using different advanced ligand and structure-based computational studies. A set of 300 ligands was selected against helicase by chemical structural similarity model, which are similar to S-adenosyl-l-cysteine using infiniSee. This tool screens billions of compounds through a similarity search from in-built chemical spaces (CHEMriya, Galaxi, KnowledgeSpace and REALSpace). The pharmacophore was designed from ligands in the library that showed same features. According to the sequence of ligands, six compounds (29, 87, 99, 116, 148, and 208) were taken for pharmacophore designing against helicase protein. Subsequently, compounds from the library which showed the best pharmacophore shared-features were docked using FlexX functionality of SeeSAR and their optibrium properties were analyzed. Afterward, their ADME was improved by replacing the unfavorable fragments, which resulted in the generation of new compounds. The selected best compounds (301, 302, 303 and 304) were docked using SeeSAR and their pharmacokinetics and toxicological properties were evaluated using SwissADME. The optimal inhibitor for yellow fever helicase was 2-amino-N-(4-(dimethylamino)thiazol-2-yl)-4-methyloxazole-5-carboxamide (302), which exhibits promising potential for drug development.

Pathogenesis and clinical management of arboviral diseases

Arboviral diseases are viral infections transmitted to humans through the bites of arthropods, such as mosquitoes, often causing a variety of pathologies associated with high levels of morbidity and mortality. Over the past decades, these infections have proven to be a significant challenge to health systems worldwide, particularly following the considerable geographic expansion of the dengue virus (DENV) and its most recent outbreak in Latin America as well as the difficult-to-control outbreaks of yellow fever virus (YFV), chikungunya virus (CHIKV), and Zika virus (ZIKV), leaving behind a substantial portion of the population with complications related to these infections. Currently, the world is experiencing a period of intense globalization, which, combined with global warming, directly contributes to wider dissemination of arbovirus vectors across the globe. Consequently, all continents remain on high alert for potential new outbreaks. Thus, this review aims to provide a comprehensive understanding of the pathogenesis of the four main arboviruses today (DENV, ZIKV, YFV, and CHIKV) discussing their viral characteristics, immune responses, and mechanisms of viral evasion, as well as important clinical aspects for patient management. This includes associated symptoms, laboratory tests, treatments, existing or developing vaccines and the main associated complications, thus integrating a broad historical, scientific and clinical approach.

Structural Virology: The Key Determinants in Development of Antiviral Therapeutics

Structural virology has emerged as the foundation for the development of effective antiviral therapeutics. It is pivotal in providing crucial insights into the three-dimensional frame of viruses and viral proteins at atomic-level or near-atomic-level resolution. Structure-based assessment of viral components, including capsids, envelope proteins, replication machinery, and host interaction interfaces, is instrumental in unraveling the multiplex mechanisms of viral infection, replication, and pathogenesis. The structural elucidation of viral enzymes, including proteases, polymerases, and integrases, has been essential in combating viruses like HIV-1 and HIV-2, SARS-CoV-2, and influenza. Techniques including X-ray crystallography, Nuclear Magnetic Resonance spectroscopy, Cryo-electron Microscopy, and Cryo-electron Tomography have revolutionized the field of virology and significantly aided in the discovery of antiviral therapeutics. The ubiquity of chronic viral infections, along with the emergence and reemergence of new viral threats necessitate the development of novel antiviral strategies and agents, while the extensive structural diversity of viruses and their high mutation rates further underscore the critical need for structural analysis of viral proteins to aid antiviral development. This review highlights the significance of structure-based investigations for bridging the gap between structure and function, thus facilitating the development of effective antiviral therapeutics, vaccines, and antibodies for tackling emerging viral threats.

Advancing canopy-level entomological surveillance to monitor vector-borne and zoonotic disease dynamics

Faced with the increased frequency of zoonotic spillover in recent decades, emerging vector-borne diseases from nonhuman primates pose a significant threat to global public health. Understanding transmission dynamics driven by arthropod vectors between wildlife populations is critical for surveillance, modeling, and mitigation. Elevated canopy-level sampling is a valuable approach for elucidating vector behavior and sylvatic transmission. However, this is underused in many regions because of the logistical and mechanical challenges of repurposing ground-based trapping for the forest canopy. We review methods of canopy-level entomological surveillance, present case studies, and identify opportunities to integrate new technologies. Paired with robust experimental design, canopy-level trapping can complement existing surveillance of emerging zoonotic diseases and provide critical insights into the role of vectors driving spillover risks.

[Non-alphabetic viral hepatitis]

The liver is the target of various viruses that can cause significant damage, impair function and potentially threaten a patient's life. While the "alphabetic" hepatitis viruses A, B, C, D, and E are well-characterized, and their impact on liver function well-documented, many emerging and re-emerging viruses, some of which are considered by the WHO to be potential pandemic threats, also infect the liver. In this review, we describe the current state of knowledge regarding liver infections caused by major non-alphabetic hepatotropic viruses and their effects on liver functions.

Epidemic Outbreaks Related to Yellow Fever Viruses

Epidemic outbreaks related to yellow fever viruses, added to the climate of fear resulting from the COVID-19 pandemic, raise a spectrum of concern and need for preparation in different research, epidemiology, and health groups. This question refers to conditions of: molecular analysis of the virus, its dissemination potential, vectors, mutational speed rate, evolutionary potential, and potential damage to individuals and populations.With regard to the yellow fever virus, such questions are even more pressing due to its successful history of colonization in America, originating from regions of Africa, and becoming endemic in both continents.Through the study of viral history and epidemiology, we seek to establish bases that allow us to analyze or avoid future problems and questions.This analysis of the past generates a future fear associated with a very real possibility:What are the chances of yellow fever spreading in densely populated regions of Asia?What are the chances of the emergence of a new pandemic caused by a virus that is already so well established on the planet?And in an associated way, the questions arise: How to avoid the possibility of a new epidemic? Is the vaccine associated with defense against this virus effective? Is the production of such a vaccine reliable and widespread in case of future deleterious events? All of these issues are relevant and worthy of analysis and response in future events, with a view to maximizing the health of the general population and mitigating human and economic damage.

Viral Live-Attenuated Vaccines (LAVs): Past and Future Directions

Viral infections continue to pose a significant threat to the health of both humans and animals. Currently, live attenuated vaccines (LAVs) remain the most efficacious and widely utilized tool for combating viral infections. Conventional LAVs involve the adaptation of virulent viruses to novel hosts, cell cultures, or suboptimal environments, resulting in a reduction in pathogenicity while retaining immunogenicity. This process entails directed evolution of the virus to enhance its replication efficiency under these modified conditions. In this review, the development of traditional animal-adapted and cold-adapted LAVs is specially discussed. Additionally, the factors that contribute to virus attenuation from a viral lifecycle perspective are summarized. Finally, we propose future directions for next-generation LAVs.

Flow Cytometry as Immunoassay Tool for Research on Yellow Fever Virus

Flow cytometry is a sensitive and practical technique that can be applied in both basic and clinical research. It allows extracting quantitative and multiparametric valuable information to assist in the study of cell immunophenotyping, morphological complexity, location and/or expression of extra and intracellular molecules involved in metabolic and proliferative pathways, inflammation, viability, and cell death, among others. The parameters are analyzed by labeling antigens of yellow fever virus and/or cells with fluorescent specific monoclonal antibodies or dyes for immunophenotyping and data acquisition using a flow cytometer. In translational research, flow cytometry is a useful tool in tracking and monitoring the etiology, evolution, and outcome of several infectious diseases, such as yellow fever (YF), with the aim of benefiting human health through detection of intracellular viral antigen and vaccine efficacy trials, as well as characterization, quantification, and monitoring of immune cells subpopulations and their biological functions quality. In the last 10 years we have been facing the re-emergence of YF, considered an endemic disease caused by arbovirus in continents including South America. Unfortunately, severe forms of the disease are still associated with increased mortality. Even with the availability of effective vaccines, gaps about understanding the immune pathophysiology and clinical management are still considered a huge challenge for the scientific community. Therefore, such tool has the potential to aggregate in flavivirus setting, being effective in tracking infection in different biological culture systems, animal and human models, as well as in searching for new antiviral drugs and vaccine efficacy.

Evaluation of Yellow Fever Virus Infection in Aedes aegypti Mosquitoes from Pakistan with Distinct Knockdown Resistance Genotypes

BACKGROUND

Yellow fever (YF) is an acute hemorrhagic disease endemic to Africa and Latin America; however, no cases have been reported in Asian regions with high Aedes aegypti infestation. Factors such as environmental conditions and genetic variations in the yellow fever virus (YFV) strains and mosquito populations may explain this absence. Mosquito populations have undergone strong selective pressure owing to the excessive use of insecticides. This pressure has led to the spread of alterations, such as knockdown-resistant mutations (kdr), which, while conferring resistance to pyrethroids, also induce various physiological side effects in the insect. Therefore, it is important to investigate whether the presence of kdr mutations influences the infectivity of YFV mosquitoes. This study evaluated the susceptibility of Ae. aegypti from Pakistan with distinct kdr genotypes to different YFV strains under laboratory conditions.

METHODS

Ae. aegypti from a Pakistani colony were exposed to YFV strains (PR4408/2008 and ES504/2017) along with the Rockefeller strain. After 14 days, RNA and DNA were extracted for viral RNA detection (qPCR) and kdr genotyping (TaqMan qPCR and HRM for T1520I and F1534C SNPs).

RESULTS

Pakistani Ae. aegypti were orally susceptible to YFV, with infection rates of 83.7% (PR4408/2008) and 61.3% (ES504), respectively, similar to Rockefeller. Two kdr genotypes (II + CC and TI + FC) were identified, with no significant differences in viral infection or dissemination rates.

CONCLUSIONS

The Ae. aegypti population from Asia is capable of YFV infection and dissemination, regardless of kdr genotype.

Hydroxychloroquine is associated with lower seroconversion upon 17DD-Yellow fever primovaccination in patients with primary Sjögren's syndrome

The present study aimed at investigating whether the hydroxychloroquine (HCQ) treatment would impact the neutralizing antibody production, viremia levels and the kinetics of serum soluble mediators upon planned 17DD-Yellow Fever (YF) primovaccination (Bio-Manguinhos-FIOCRUZ) of primary Sjögren's syndrome (pSS). A total of 34 pSS patients and 23 healthy controls (HC) were enrolled. The pSS group was further categorized according to the use of HCQ (HCQ and Non-HCQ). The YF-plaque reduction neutralization test (PRNT ≥1:50), YF viremia (RNAnemia) and serum biomarkers analyses were performed at baseline and subsequent time-points (Day0/Day3-4/Day5-6/Day7/Day14-D28). The pSS group showed PRNT titers and seropositivity rates similar to those observed for HC (GeoMean = 238 vs 440, p = .11; 82% vs 96%, p = .13). However, the HCQ subgroup exhibited lower seroconversion rates as compared to HC (GeoMean = 161 vs 440, p = .04; 69% vs 96%, p = .02) and Non-HQC (GeoMean = 161 vs 337, p = .582; 69% vs 94%, p = .049). No differences in YF viremia were observed amongst subgroups. Serum biomarkers analyses demonstrated that HCQ subgroup exhibited increased levels of CCL2, CXL10, IL-6, IFN-γ, IL1-Ra, IL-9, IL-10, and IL-2 at baseline and displayed a consistent increase of several biomarkers along the kinetics timeline up to D14-28. These results indicated that HCQ subgroup exhibited a deficiency in assembling YF-specific immune response elicited by 17DD-YF primovaccination as compared to Non-HCQ subgroup. Our findings suggested that hydroxychloroquine is associated with a decrease in the humoral immune response after 17DD-YF primovaccination.

DENV and ZIKV infection: Species specificity and broad cell tropism

Nearly one-third of countries worldwide have reported cases of Dengue virus (DENV) and Zika virus (ZIKV) infections, highlighting the significant threat these viruses pose to global public health. As members of the Flavivirus genus within the Flaviviridae family, DENV and ZIKV have demonstrated the ability to infect a wide range of cell lines from multiple species in vitro. However, the range of susceptible animal models is notably limited, and field studies indicate that their capacity to infect host organisms is highly restricted, with a very narrow range of target cells in vivo. The virus's ability to hijack host cellular machinery plays a crucial role in determining its cellular and species specificity. In this review, we examine how DENV and ZIKV exploit host cells to facilitate their replication, offering new insights that could inform the development of antiviral drugs and therapeutic targets.

Clinical Relevance of Oxidative Stress Biomarkers in Human Flavivirus Infections as Predictors of Disease Progression and Severity

Several Flaviviridae constitute an emerging threat to global health because of their continuing spread and the expansion of vector habitats, largely driven by climate change and intensified global travel. Infections can result in severe neurological or visceral pathologies. The relationship between oxidative stress (OS), an imbalance between generated reactive oxygen species and the antioxidant defences of the host, and flavivirus infection has been repeatedly demonstrated in in vitro and animal studies, but measuring biomarkers of oxidative stress in vivo could prove useful in clinical patient management. We summarise the knowledge and prospects of measuring peripheral OS biomarker levels for clinical case management and correlation with disease severity in six important human flavivirus infections (dengue virus (DENV), Japanese encephalitis virus, West Nile virus (WNV), tick-borne encephalitis virus (TBEV), yellow fever virus and zika virus). We searched the Medline and Web of Science databases for 'Oxidative Stress' AND 'Biomarkers' AND 'Flavivirus', combined with 'clinical', 'in vivo/in vivo', 'patient' and/or 'disease' and included 43 peer-reviewed publications. Correlation between OS and infection has been studied in all six Flaviviridae, but most clinically relevant data are available for DENV, TBEV and WNV. Plasma protein carbonyls, glutathione peroxidase activity and nitrogen monoxide are promising prognostic markers, but their measurement would benefit from methodological harmonisation. Future studies should investigate a broad range of OS biomarkers as predictors of clinically relevant outcomes. We advocate the validation and use of universal or disease-specific oxidative stress indexes that incorporate the most significant outcomes into one, easy-to-use clinical determinant.

Duration of post-vaccination immunity to yellow fever in volunteers ten years after a dose-response study - A complementary study

A single dose of standard yellow fever (YF) vaccine is considered to provide life-long protection. In this study, we evaluate the seropositivity conferred by lower doses 10 years post-vaccination. In 2009, Bio-Manguinhos/Fiocruz performed a dose-response study with the 17DD yellow fever vaccine, administering the vaccine in the usual mean dose of 27.476 IU and in decreasing doses (10.447 IU, 3.013 IU, 587 IU, 158 IU and 31 IU), with the usual volume and route (0,5 ml subcutaneous). The decreasing doses were obtained by dilution in the laboratory of the manufacturer and the lots in test had standard quality control and were produced by good manufacturing practices (GMP). Around 30 days after the vaccination, doses down to 587 IU had similar immunogenicity and the 158 IU and 31 IU were inferior to the full dose. The seropositivity was maintained for 10 months, except on the 31 IU group. Eight years after, 85 % of 318 participants evaluated in a follow-up, maintained seropositivity that was similar across groups. Consistently, antibody titers in the reduced-dose groups were also comparable to those of the full-dose group. The current study, 10 years later, showed similarity between the vaccine groups (six arms who received the YF vaccine in decreasing doses: 27.476 IU, 10.447 IU, 3.013 IU, 587 IU, 158 IU, 31 IU) both in relation of seropositivity and in the evaluation of the geometric mean titers. The seropositivity rates across subgroups were 83,1%, 90 %, 87 %, 93 %, 83,8% and 85 %, correspondingly. These findings provides further support to the long-term immunogenicity of lower doses. Clinical trial registry: NCT04416477.

A safer cell-based yellow fever live attenuated vaccine protects mice against YFV infection

The live attenuated yellow fever vaccine (YF17D) has caused controversial safety issues in history with low-yield problems, which has led to a large population being unable to be vaccinated and vaccine shortage in facing recent outbreaks. Here, we report a safer live attenuated vaccine candidate, YF17D-Δ77, which contains 77 nucleotides deletion in the 3' untranslated region (3' UTR) of the YF17D genome. YF17D-Δ77 exhibited no neurotropism and decreased viscerotropism and caused significantly lower lethality in mice compared to YF17D. Mechanistically, the deletion enhanced the sensitivity of the virus to type I and type II interferon responses, which hindered viral replication. Encouragingly, YF17D-Δ77 provided comparable immune protection in mice as did YF17D. Even 10 PFU of YF17D-Δ77 completely protected mice against YFV-Asibi challenge. In addition, the Δ77 mutation showed excellent stability after successive passages in Vero cells. Collectively, the data suggest that further development of YF17D-Δ77 as vaccine candidate is warranted.

Phage Display Revealed the Complex Structure of the Epitope of the Monoclonal Antibody 10H10

The annual number of reported human cases of flavivirus infections continues to increase. Measures taken by local healthcare systems and international organizations are not fully successful. In this regard, new approaches to treatment and prevention of flavivirus infections are relevant. One promising approach is to use monoclonal antibody preparations. The mouse mAb 10H10 is capable of interacting with viruses belonging to the genus Orthoflavivirus which are pathogenic to humans. ELISA and molecular modeling data can indicate that mAb 10H10 recognizes the fusion loop region of E protein. The KD of interaction between the mAb 10H10 and recombinant analogs of the E protein of the tick-borne encephalitis (TBEV), Zika (ZIKV) and dengue (DENV) viruses range from 1.5 to 4 nM. The aim of this study was to map the epitope of this antibody using phage display technology. After three rounds of biopanning, 60 individual phage clones were chosen. The amino acid sequences of the selected peptides were conveniently divided into five groups. Based on the selected peptides, bacteriophages were obtained carrying peptides on the surfaces of the pIII and pVIII proteins, which were tested for binding to the antibody in ELISA. Thus, the epitope of the mAb 10H10 is the highly conserved region 98-DRGWGNXXGLFGK-110 of the flavivirus E protein. The structures of the complexes of the identified peptides with the antibody paratope are proposed using the molecular docking and dynamics methods.

Mitochondrial Hyperactivity and Reactive Oxygen Species Drive Innate Immunity to the Yellow Fever Virus-17D Live-Attenuated Vaccine

The yellow fever virus 17D (YFV-17D) live attenuated vaccine is considered one of the successful vaccines ever generated associated with high antiviral immunity, yet the signaling mechanisms that drive the response in infected cells are not understood. Here, we provide a molecular understanding of how metabolic stress and innate immune responses are linked to drive type I IFN expression in response to YFV-17D infection. Comparison of YFV-17D replication with its parental virus, YFV-Asibi, and a related dengue virus revealed that IFN expression requires RIG-I-like Receptor signaling through MAVS, as expected. However, YFV-17D uniquely induces mitochondrial respiration and major metabolic perturbations, including hyperactivation of electron transport to fuel ATP synthase. Mitochondrial hyperactivity generates reactive oxygen species (mROS) and peroxynitrite, blocking of which abrogated IFN expression in non-immune cells without reducing YFV-17D replication. Scavenging ROS in YFV-17D-infected human dendritic cells increased cell viability yet globally prevented expression of IFN signaling pathways. Thus, adaptation of YFV-17D for high growth uniquely imparts mitochondrial hyperactivity generating mROS and peroxynitrite as the critical messengers that convert a blunted IFN response into maximal activation of innate immunity essential for vaccine effectiveness.

Novel Pyrazino[1,2-a]indole-1,3(2H,4H)-dione Derivatives Targeting the Replication of Flaviviridae Viruses: Structural and Mechanistic Insights

Infections with Flaviviridae viruses, such as hepatitis C (HCV), dengue (DENV), and yellow fever (YFV) viruses, are major public health problems worldwide. In the case of HCV, treatment is associated with drug resistance and high costs, while there is no clinically approved therapy for DENV and YFV. Consequently, there is still a need for new chemotherapies with alternative modes of action. We have previously identified novel 2-hydroxypyrazino[1,2-a]indole-1,3(2H,4H)-diones as metal-chelating inhibitors targeting HCV RNA replication. Here, by utilizing a structure-based approach, we rationally designed a second series of compounds by introducing various substituents at the indole core structure and at the imidic nitrogen, to improve specificity against the RNA-dependent RNA polymerase (RdRp). The resulting derivatives were evaluated for their potency against HCV genotype 1b, DENV2, and YFV-17D using stable replicon cell lines. The most favorable substitution was nitro at position 6 of the indole ring (compound 36), conferring EC50 1.6 μM against HCV 1b and 2.57 μΜ against HCV 1a, with a high selectivity index. Compound 52, carrying the acetohydroxamic acid functionality (-CH2CONHOH) on the imidic nitrogen, and compound 78, the methyl-substituted molecule at the position 4 indolediketopiperazine counterpart, were the most effective against DENV and YFV, respectively. Interestingly, compound 36 had a high genetic barrier to resistance and only one resistance mutation was detected, T181I in NS5B, suggesting that the compound target HCV RdRp is in accordance with our predicted model.

Structural Insights into the Dynamic Assembly of a YFV sNS1 Tetramer

Yellow fever virus (YFV) infections can cause severe diseases in humans, resulting in mass casualties in Africa and the Americas each year. Secretory NS1 (sNS1) is thought to be used as a diagnostic marker of flavivirus infections, playing an essential role in the flavivirus life cycle, but little is known about the composition and structure of YFV sNS1. Here, we present that the recombinant YFV sNS1 exists in a heterogeneous mixture of oligomerizations, predominantly in the tetrameric form. The cryoEM structures show that the YFV tetramer of sNS1 is stacked by the hydrophobic interaction between β-roll domains and greasy fingers. According to the 3D variability analysis, the tetramer is in a semi-stable state that may contain multiple conformations with dynamic changes. We believe that our study provides critical insights into the oligomerization of NS1 and will aid the development of NS1-based diagnoses and therapies.

Zafirlukast, as a viral inactivator, potently inhibits infection of several flaviviruses, including Zika virus, dengue virus, and yellow fever virus

Zika virus (ZIKV) is one of the mosquito-borne flaviviruses that exhibits a unique tropism to nervous systems and is associated with Guillain-Barre syndrome and congenital Zika syndrome (CZS). Dengue virus (DENV) and yellow fever virus (YFV), the other two mosquito-borne flaviviruses, have also been circulating for a long time and cause severe diseases, such as dengue hemorrhagic fever and yellow fever, respectively. However, there are no safe and effective antiviral drugs approved for the treatment of infections or coinfections of these flaviviruses. Here, we found that zafirlukast, a pregnancy-safe leukotriene receptor antagonist, exhibited potent antiviral activity against infections of ZIKV strains from different lineages in different cell lines, as well as against infections of DENV-2 and YFV 17D. Mechanistic studies demonstrated that zafirlukast directly and irreversibly inactivated these flaviviruses by disrupting the integrity of the virions, leading to the loss of viral infectivity, hence inhibiting the entry step of virus infection. Considering its efficacy against flaviviruses, its safety for pregnant women, and its neuroprotective effect, zafirlukast is a promising candidate for prophylaxis and treatment of infections or coinfections of ZIKV, DENV, and YFV, even in pregnant women.

A proposed One Health approach to control yellow fever outbreaks in Uganda

Yellow Fever (YF) is an acute viral hemorrhagic disease. Uganda is located within the Africa YF belt. Between 2019 and 2022, the Ugandan Health Authorities reported at least one outbreak of YF annually with an estimated 892 suspected cases, on average per year. The persistent recurrence of this disease raises significant concerns about the efficacy of current response strategies and prevention approaches. YF has been recognized as a One Health issue due to its interrelatedness with the animal and environmental domains. Monkeys have been recognized as the virus primary reservoir. The YF virus is transmitted through bites of infected Aedes or Haemagogus species mosquitoes between monkeys and humans. Human activities, monkey health, and environmental health issues (e.g., climate change and land use) impact YF incidence in Uganda. Additionally, disease control programs for other tropical diseases, such as mosquitoes control programs for malaria, impact YF incidence.This review adopts the One Health approach to highlight the limitations in the existing segmented YF control and prevention strategies in Uganda, including the limited health sector surveillance, the geographically localized outbreak response efforts, the lack of a comprehensive vaccination program, the limited collaboration and communication among relevant national and international agencies, and the inadequate vector control practices. Through a One Health approach, we propose establishing a YF elimination taskforce. This taskforce would oversee coordination of YF elimination initiatives, including implementing a comprehensive surveillance system, conducting mass YF vaccination campaigns, integrating mosquito management strategies, and enhancing risk communication. It is anticipated that adopting the One Health approach will reduce the risk of YF incidence and outbreaks.

Evaluation of humoral immune response after yellow fever infection: an observational study on patients from the 2017-2018 sylvatic outbreak in Brazil

Between 2016 and 2018, Brazil experienced major sylvatic yellow fever (YF) outbreaks that caused hundreds of casualties, with Minas Gerais (MG) being the most affected state. These outbreaks provided a unique opportunity to assess the immune response triggered by the wild-type (WT) yellow fever virus (YFV) in humans. The plaque reduction neutralization test (PRNT) is currently the standard method to assess the humoral immune response to YFV by measuring neutralizing antibodies (nAbs). The present study aimed to evaluate the humoral immune response of patients from the 2017-2018 sylvatic YF outbreak in MG with different disease outcomes by using PRNTs with a WT YFV strain, isolated from the 2017-2018 outbreak, and a vaccine YFV strain. Samples from naturally infected YF patients were tested, in comparison with healthy vaccinees. Results showed that both groups presented different levels of nAb against the WT and vaccine strains, and the levels of neutralization against the strains varied homotypically and heterotypically. Results based on the geometric mean titers (GMTs) suggest that the humoral immune response after a natural infection of YFV can reach higher levels than that induced by vaccination (GMT of patients against WT YFV compared to GMT of vaccinees, P < 0.0001). These findings suggest that the humoral immune responses triggered by the vaccine and WT strains of YFV are different, possibly due to genetic and antigenic differences between these viruses. Therefore, current means of assessing the immune response in naturally infected YF individuals and immunological surveillance methods in areas with intense viral circulation may need to be updated.IMPORTANCEYellow fever is a deadly febrile disease caused by the YFV. Despite the existence of effective vaccines, this disease still represents a public health concern worldwide. Much is known about the immune response against the vaccine strains of the YFV, but recent studies have shown that it differs from that induced by WT strains. The extent of this difference and the mechanisms behind it are still unclear. Thus, studies aimed to better understand the immune response against this virus are relevant and necessary. The present study evaluated levels of neutralizing antibodies of yellow fever patients from recent outbreaks in Brazil, in comparison with healthy vaccinees, using plaque reduction neutralization tests with WT and vaccine YFV strains. Results showed that the humoral immune response in naturally infected patients was higher than that induced by vaccination, thus providing new insights into the immune response triggered against these viruses.

Circulation of yellow fever virus in Benin city, Edo state Nigeria

Yellow fever (YF) is one of the most acute viral hemorrhagic diseases of the 18th and 19th centuries, which continues to cause severe morbidity and mortality in Africa. After 21 years of no reported cases of yellow fever in Nigeria, till 2017 where a case was confirmed in Kwara State, also in November 2018,WHO was informed of a cluster of suspected yellow fever cases and deaths in Edo state, Nigeria. The study was among all age group attending health centres in Benin City, Edo state. A total of 280 blood samples were collected from consented febrile patients and were screened for antibodies to Zika virus using rapid diagnostic test (RDT) kits. Blood samples positive to Zika virus (IgM/IgG RDT), were subjected to molecular characterization. Using the flavividae family primers, six (6) samples where confirmed positive by Hemi-nested reverse transcription PCR (hnRT-PCR) sequencing. Nucleotide sequence blast revealed the sequenceswere similar to Yellow fever virus strains. Phylogenetic analysis revealed that the yellow fever virus sequences are closely related to the African strains. Despite the safe and effective yellow fever vaccine, yellow fever virus is seen to be in circulation, hence the need for continues mass vaccination.

Perceptions of yellow fever emergency mass vaccinations among vulnerable groups in Uganda: A qualitative study

BACKGROUND

Yellow fever (YF), a mosquito-borne viral hemorrhagic fever, is endemic in Uganda and causes frequent outbreaks. A total of 1.6 million people were vaccinated during emergency mass immunization campaigns in 2011 and 2016. This study explored local perceptions of YF emergency mass immunization among vulnerable groups to inform future vaccination campaigns.

METHODOLOGY

In this qualitative study, we conducted 43 semi-structured interviews, 4 focus group discussions, and 10 expert interviews with 76 participants. Data were collected in six affected districts with emergency mass vaccination. We included vulnerable groups (people ≥ 65 years and pregnant women) who are typically excluded from YF vaccination except during mass immunization. Data analysis was conducted using grounded theory. Inductive coding was utilized, progressing through open, axial, and selective coding.

PRINCIPAL FINDINGS

Participants relied on community sources for information about the YF mass vaccination. Information was disseminated door-to-door, in community spaces, during religious gatherings, and on the radio. However, most respondents had no knowledge of the vaccine, and it was unclear to them whether a booster dose was required. In addition, the simultaneous presidential election during the mass vaccination campaign led to suspicion and resistance to vaccination. The lack of reliable and trustworthy information and the politicization of vaccination campaigns reinforced mistrust of YF vaccines.

CONCLUSIONS/SIGNIFICANCE

People in remote areas affected by YF outbreaks rely on community sources of information. We therefore recommend improving health education, communication, and engagement through respected and trusted community members. Vaccination campaigns can never be seen as detached from political systems and power relations.

Comprehensive landscape of neutralizing antibody and cell-mediated response elicited by the 1/5 fractional dose of 17DD-YF primary vaccination in adults

The present study aimed at evaluating the YF-specific neutralizing antibody profile besides a multiparametric analysis of phenotypic/functional features of cell-mediated response elicited by the 1/5 fractional dose of 17DD-YF vaccine, administered as a single subcutaneous injection. The immunological parameters of each volunteer was monitored at two time points, referred as: before (Day 0) [Non-Vaccinated, NV(D0)] and after vaccination (Day 30-45) [Primary Vaccinees, PV(D30-45)]. Data demonstrated high levels of neutralizing antibodies for PV(D30-45) leading to a seropositivity rate of 93%. A broad increase of systemic soluble mediators with a mixed profile was also observed for PV(D30-45), with IFN-γ and TNF-α presenting the highest baseline fold changes. Integrative network mapping of soluble mediators showed increased correlation numbers in PV(D30-45) as compared to NV(D0) (532vs398). Moreover, PV(D30-45) exhibited increased levels of Terminal Effector (CD45RA+CCR7-) CD4+ and CD8+ T-cells and Non-Classical memory B-cells (IgD+CD27+). Dimensionality reduction of Mass Cytometry data further support these findings. A polyfunctional cytokine profile (TNF-α/IFN-γ/IL-10/IL-17/IL-2) of T and B-cells was observed upon in vitro antigen recall. Mapping and kinetics timeline of soluble mediator signatures for PV(D30-45) further confirmed the polyfunctional profile upon long-term in vitro culture, mediated by increased levels of IFN-γ and TNF-α along with decreased production of IL-10. These findings suggest novel insights of correlates of protection elicited by the 1/5 fractional dose of 17DD-YF vaccine.

Immune response induced by standard and fractional doses of 17DD yellow fever vaccine

The re-emergence of yellow fever (YF) urged new mass vaccination campaigns and, in 2017, the World Health Organization approved the use of the fractional dose (FD) of the YF vaccine due to stock shortage. In an observational cross-sectional investigation, we have assessed viremia, antibodies, soluble mediators and effector and memory T and B-cells induced by primary vaccination of volunteers with FD and standard dose (SD). Similar viremia and levels of antibodies and soluble markers were induced early after immunization. However, a faster decrease in the latter was observed after SD. The FD led to a sustained expansion of helper T-cells and an increased expression of activation markers on T-cells early after vaccination. Although with different kinetics, expansion of plasma cells was induced upon SD and FD immunization. Integrative analysis reveals that FD induces a more complex network involving follicular helper T cells and B-cells than SD. Our findings substantiate that FD can replace SD inducing robust correlates of protective immune response against YF.

Yellow fever virus infection in human hepatocyte cells triggers an imbalance in redox homeostasis with increased reactive oxygen species production, oxidative stress, and decreased antioxidant enzymes

Yellow fever (YF) presents a wide spectrum of severity, with clinical manifestations in humans ranging from febrile and self-limited to fatal cases. Although YF is an old disease for which an effective and safe vaccine exists, little is known about the viral- and host-specific mechanisms that contribute to liver pathology. Several studies have demonstrated that oxidative stress triggered by viral infections contributes to pathogenesis. We evaluated whether yellow fever virus (YFV), when infecting human hepatocytes cells, could trigger an imbalance in redox homeostasis, culminating in oxidative stress. YFV infection resulted in a significant increase in reactive oxygen species (ROS) levels from 2 to 4 days post infection (dpi). When measuring oxidative parameters at 4 dpi, YFV infection caused oxidative damage to lipids, proteins, and DNA, evidenced by an increase in lipid peroxidation/8-isoprostane, carbonyl protein, and 8-hydroxy-2'-deoxyguanosine, respectively. Furthermore, there was a significant reduction in the activity of the antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx), in addition to a reduction in the ratio of reduced to oxidized glutathione (GSH/GSSG), indicating a pro-oxidant environment. However, no changes were observed in the enzymatic activity of the enzyme catalase (CAT) or in the gene expression of SOD isoforms (1/2/3), CAT, or GPx. Therefore, our results show that YFV infection generates an imbalance in redox homeostasis, with the overproduction of ROS and depletion of antioxidant enzymes, which induces oxidative damage to cellular constituents. Moreover, as it has been demonstrated that oxidative stress is a conspicuous event in YFV infection, therapeutic strategies based on antioxidant biopharmaceuticals may be new targets for the treatment of YF.

YELLOW ALERT: Persistent Yellow Fever Virus Circulation among Non-Human Primates in Urban Areas of Minas Gerais State, Brazil (2021-2023)

Yellow fever virus (YFV) is the agent of yellow fever (YF), which affects both humans and non-human primates (NHP). Neotropical NHP are highly susceptible to YFV and considered sentinels for YFV circulation. Brazil faced a significant YF outbreak in 2017-2018, with over 2000 human cases and 2000 epizootics cases, mainly in the State of Minas Gerais, Brazil. This study aimed to investigate whether YFV circulation persisted in NHP after the human outbreak had subsided. To this end, NHP carcass samples collected in Minas Gerais from 2021 to 2023 were screened for YFV. RNA was extracted from tissue fragments and used in RT-qPCR targeting the YFV 5'UTR. Liver and lung samples from 166 animals were tested, and the detection of the β-actin mRNA was used to ensure adequacy of RNA isolation. YFV RNA was detected in the liver of 18 NHP carcasses collected mainly from urban areas in 2021 and 2022. YFV positive NHP were mostly represented by Callithrix, from 5 out of the 12 grouped municipalities (mesoregions) in Minas Gerais state. These findings reveal the continued YFV circulation in NHP in urban areas of Minas Gerais during 2021 and 2022, with the attendant risk of re-establishing the urban YFV cycle.

Ocular Manifestations of Flavivirus Infections

Flaviviruses are a group of positive-sense, single-stranded RNA viruses predominantly transmitted by arthropods (mainly mosquitoes) that cause severe endemic infections and epidemics on a global scale. They represent a major cause of systemic morbidity and death and are expanding worldwide. Among this group, dengue fever, the West Nile virus, yellow fever, Japanese Encephalitis, and, recently, the Zika virus have been linked to a spectrum of ocular manifestations. These manifestations encompass subconjunctival hemorrhages and conjunctivitis, anterior and posterior uveitis (inclusive of vitritis, chorioretinitis, and retinal vasculitis), maculopathy, retinal hemorrhages, and optic neuritis. Clinical diagnosis of these infectious diseases is primarily based on epidemiological data, history, systemic symptoms and signs, and the pattern of ocular involvement. Diagnosis confirmation relies on laboratory testing, including RT-PCR and serological testing. Ocular involvement typically follows a self-limited course but can result in irreversible visual impairment. Effective treatments of flavivirus infections are currently unavailable. Prevention remains the mainstay for arthropod vector and zoonotic disease control. Effective vaccines are available only for the yellow fever virus, dengue virus, and Japanese Encephalitis virus. This review comprehensively summarizes the current knowledge regarding the ophthalmic manifestations of the foremost flavivirus-associated human diseases.

Exploring structural antigens of yellow fever virus to design multi-epitope subunit vaccine candidate by utilizing an immuno-informatics approach

BACKGROUND

Yellow fever is a mosquito-borne viral hemorrhagic disease transmitted by several species of virus-infected mosquitoes endemic to tropical regions of Central and South America and Africa. Earlier in the twentieth century, mass vaccination integrated with mosquito control was implemented to eradicate the yellow fever virus. However, regular outbreaks occur in these regions which pose a threat to travelers and residents of Africa and South America. There is no specific antiviral therapy, but there can be an effective peptide-based vaccine candidate to combat infection caused by the virus. Therefore, the study aims to design a multi-epitope-based subunit vaccine (MESV) construct against the yellow fever virus to reduce the time and cost using reverse vaccinology (RV) approach.

METHODS

Yellow fever virus contains 10,233 nucleotides that encode for 10 proteins (C, prM, E, NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5) including 3 structural and 7 non-structural proteins. Structural proteins-precursor membrane protein (prM) and envelope protein (E)-were taken as a target for B cell and T cell epitope screening. Further, various immunoinformatics approaches were employed to FASTA sequences of structural proteins to retrieve B cell and T cell epitopes. MESV was constructed from these epitopes based on allergenicity, antigenicity and immunogenicity, toxicity, conservancy, and population coverage followed by structure prediction. The efficacy of the MESV construct to bind with human TLR-3, TLR-4, and TLR-8 were evaluated using molecular docking and simulation studies. Finally, in-silico cloning of vaccine construct was performed withpBR322 Escherichia coli expression system using codon optimization.

RESULTS

Predicted epitopes evaluated and selected for MESV construction were found stable, non-allergenic, highly antigenic, and global population coverage of 68.03% according to in-silico analysis. However, this can be further tested in in-vitro and in-vivo investigations. Epitopes were sequentially merged to construct a MESV consisting of 393 amino acids using adjuvant and linkers. Molecular docking and simulation studies revealed stable and high-affinity interactions. Furthermore, in-silico immune response graphs showed effective immune response generation. Finally, higher CAI value ensured high gene expression of vaccine in the host cell.

CONCLUSION

The designed MESV construct in the present in-silico study can be effective in generating an immune response against the yellow fever virus. Therefore, to prevent yellow fever, it can be an effective vaccine candidate. However, further downstream, in-vitro study is required.

Tiratricol inhibits yellow fever virus replication through targeting viral RNA-dependent RNA polymerase of NS5

Yellow fever virus (YFV) infection is a major public concern that threatens a large population in South America and Africa. No specific antiviral drugs are available for treating yellow fever. Here, we report that tiratricol (triiodothyroacetic acid, TRIAC), a clinically approved drug used to treat thyroid hormone resistance syndrome (THRS), is a potent YFV inhibitor both in host cells and in animal models.An in vitro study demonstrates that TRIAC remarkably suppresses viral RNA synthesis and protein expression in a dose-dependent manner in human hepatoma cell lines (Huh-7) with an EC50 value of 2.07 μM and a CC50 value of 385.77 μM respectively. The surface plasmon resonance assay and molecular docking analysis indicate that TRIAC hinders viral replication by binding to the RNA-dependent RNA polymerase (RdRp) domain of viral nonstructural protein NS5, probably through interacting with the active sites of RdRp.The inhibitory effect of TRIAC in vivo is also confirmed in 3-week old C57BL/6 mice challenged with YFV infection, from which the survival of the mice as well as lesions and infection in their tissues and serum issignificantly promoted following oral administration of TRIAC (0.2 mg/kg/day). Additionally, TRIAC shows a broad-spectrum antiviral activity against multiple flaviviruses such as TBEV, WNV,ZIKV, andJEV in vitro. Our data demonstrate that the TH analogue TRIAC is an effective anti-YFV compound and may act as a potential therapeutic candidate for the treatment of YFV infection if its clinical importance is determined in patients in future.

Serological evidence for potential yellow fever virus infection in non-human primates, southeastern Mexico

BACKGROUND

Arthropod-borne flaviviruses like dengue virus (DENV) and yellow fever virus (YFV) are major human pathogens. In Latin America, YFV is maintained in sylvatic cycles involving non-human primates (NHP) and forest-dwelling mosquitos. YFV supposedly does not circulate north of Panama.

METHODS

We conducted a serologic study for flaviviruses and other emerging viruses in NHP from southeastern Mexico. A total of thirty sera of black-handed spider monkeys (Ateles geoffroyi, n = 25), black howler monkeys (Alouatta pigra, n = 3), and mantled howler monkeys (Al. palliata, n = 2) sampled in 2012 and 2018 were screened by an indirect immunofluorescence assay (IFA) to detected IgG antibodies against DENV, YFV, Zika virus (ZIKV), West Nile virus (WNV), Rift Valley fever virus, Crimean-Congo hemorrhagic fever virus, Middle East respiratory syndrome coronavirus, and Zaire Ebola virus, and confirmed by plaque reduction neutralization tests (PRNT90) representing all mosquito-borne flavivirus serocomplexes circulating in the Americas.

RESULTS

A total of 16 sera (53.3%; 95% CI, 34.3-71.7) showed IFA reactivity to at least one tested flavivirus with end-point titers ranging from 1:100 to 1:1000. No serum reacted with other viruses. Monotypic and high mean PRNT90 endpoint YFV titers of 1:246 were found in 3 black-handed spider monkey sera (10.0%; 95% CI, 2.1-26.5) sampled in 2018 in Tabasco, compared to all other flaviviruses tested. Monotypic endpoint PRNT90 titers of 1:28 for Ilheus virus and 1:22 for WNV in serum of black howler monkeys sampled in 2018 in Tabasco suggested additional flavivirus exposure.

CONCLUSIONS

Our findings may suggest unnoticed YFV circulation. Intensification of YFV surveillance in NHP and vectors is warranted in Mexico and potentially other areas considered free of yellow fever.

Membrane-proximal motifs encode differences in signaling strength between type I and III interferon receptors

Interferons (IFNs) play crucial roles in antiviral defenses. Despite using the same Janus-activated kinase (JAK)-signal transducer and activator of transcription (STAT) signaling cascade, type I and III IFN receptors differ in the magnitude and dynamics of their signaling in terms of STAT phosphorylation, gene transcription, and antiviral responses. These differences are not due to ligand-binding affinity and receptor abundance. Here, we investigated the ability of the intracellular domains (ICDs) of IFN receptors to differentiate between type I and III IFN signaling. We engineered synthetic, heterodimeric type I and III IFN receptors that were stably expressed at similar amounts in human cells and responded to a common ligand. We found that our synthetic type I IFN receptors stimulated STAT phosphorylation and gene expression to greater extents than did the corresponding type III IFN receptors. Furthermore, we identified short "box motifs" within ICDs that bind to JAK1 that were sufficient to encode differences between the type I and III IFN receptors. Together, our results indicate that specific regions within the ICDs of IFN receptor subunits encode different downstream signaling strengths that enable type I and III IFN receptors to produce distinct signaling outcomes.

Novel Lipophilic Hydroxamates Based on Spirocarbocyclic Hydantoin Scaffolds with Potent Antiviral and Trypanocidal Activity

Flaviviridae infections, such as those caused by hepatitis C (HCV) and dengue viruses (DENVs), represent global health risks. Infected people are in danger of developing chronic liver failure or hemorrhagic fever, both of which can be fatal if not treated. The tropical parasites Trypanosoma brucei and Trypanosoma cruzi cause enormous socioeconomic burdens in Sub-Saharan Africa and Latin America. Anti-HCV chemotherapy has severe adverse effects and is expensive, whereas dengue has no clinically authorized treatment. Antiparasitic medicines are often toxic and difficult to administer, and treatment failures are widely reported. There is an urgent need for new chemotherapies. Based on our previous research, we have undertaken structural modification of lead compound V with the goal of producing derivatives with both antiviral and trypanocidal activity. The novel spirocarbocyclic-substituted hydantoin analogs were designed, synthesized, and tested for antiviral activity against three HCV genotypes (1b, 3a, 4a), DENV, yellow fever virus (YFV), and two trypanosome species (T. brucei, T. cruzi). The optimization was successful and led to compounds with significant antiviral and trypanocidal activity and exceptional selectivity. Several modifications were made to further investigate the structure-activity relationships (SARs) and confirm the critical role of lipophilicity and conformational degrees of freedom.

Ecological drivers of sustained enzootic yellow fever virus transmission in Brazil, 2017-2021

Beginning December 2016, sylvatic yellow fever (YF) outbreaks spread into southeastern Brazil, and Minas Gerais state experienced two sylvatic YF waves (2017 and 2018). Following these massive YF waves, we screened 187 free-living non-human primate (NHPs) carcasses collected throughout the state between January 2019 and June 2021 for YF virus (YFV) using RTqPCR. One sample belonging to a Callithrix, collected in June 2020, was positive for YFV. The viral strain belonged to the same lineage associated with 2017-2018 outbreaks, showing the continued enzootic circulation of YFV in the state. Next, using data from 781 NHPs carcasses collected in 2017-18, we used generalized additive mixed models (GAMMs) to identify the spatiotemporal and host-level drivers of YFV infection and intensity (an estimation of genomic viral load in the liver of infected NHP). Our GAMMs explained 65% and 68% of variation in virus infection and intensity, respectively, and uncovered strong temporal and spatial patterns for YFV infection and intensity. NHP infection was higher in the eastern part of Minas Gerais state, where 2017-2018 outbreaks affecting humans and NHPs were concentrated. The odds of YFV infection were significantly lower in NHPs from urban areas than from urban-rural or rural areas, while infection intensity was significantly lower in NHPs from urban areas or the urban-rural interface relative to rural areas. Both YFV infection and intensity were higher during the warm/rainy season compared to the cold/dry season. The higher YFV intensity in NHPs in warm/rainy periods could be a result of higher exposure to vectors and/or higher virus titers in vectors during this time resulting in the delivery of a higher virus dose and higher viral replication levels within NHPs. Further studies are needed to better test this hypothesis and further compare the dynamics of YFV enzootic cycles between different seasons.

Flaviviruses and the Traveler: Around the World and to Your Stage. A Review of West Nile, Yellow Fever, Dengue, and Zika Viruses for the Practicing Pathologist

Flaviviruses are a genus of single-stranded RNA viruses that impose an important and growing burden to human health. There are over 3 billion individuals living in areas where flaviviruses are endemic. Flaviviruses and their arthropod vectors (which include mosquitoes and ticks) take advantage of global travel to expand their distribution and cause severe disease in humans, and they can be grouped according to their vector and pathogenicity. The mosquito-borne flaviviruses cause a spectrum of diseases from encephalitis to hepatitis and vascular shock syndrome, congenital abnormalities, and fetal death. Neurotropic infections such as Zika virus and West Nile virus cross the blood-brain barrier and infect neurons and other cells, leading to meningoencephalitis. In the hemorrhagic fever clade, there are yellow fever virus, the prototypical hemorrhagic fever virus that infects hepatocytes, and dengue virus, which infects cells of the reticuloendothelial system and can lead to a dramatic plasma cell leakage and shock syndrome. Zika virus also causes congenital infections and fetal death and is the first and only example of a teratogenic arbovirus in humans. Diagnostic testing for flaviviruses broadly includes the detection of viral RNA in serum (particularly within the first 10 days of symptoms), viral isolation by cell culture (rarely performed due to complexity and biosafety concerns), and histopathologic evaluation with immunohistochemistry and molecular testing on formalin-fixed paraffin-embedded tissue blocks. This review focuses on 4 mosquito-borne flaviviruses-West Nile, yellow fever, dengue, and Zika virus-and discusses the mechanisms of transmission, the role of travel in geographic distribution and epidemic emergence, and the clinical and histopathologic features of each. Finally, prevention strategies such as vector control and vaccination are discussed.

Mechanism of Immune Evasion in Mosquito-Borne Diseases

In recent decades, mosquito-borne illnesses have emerged as a major health burden in many tropical regions. These diseases, such as malaria, dengue fever, chikungunya, yellow fever, Zika virus infection, Rift Valley fever, Japanese encephalitis, and West Nile virus infection, are transmitted through the bite of infected mosquitoes. These pathogens have been shown to interfere with the host's immune system through adaptive and innate immune mechanisms, as well as the human circulatory system. Crucial immune checkpoints such as antigen presentation, T cell activation, differentiation, and proinflammatory response play a vital role in the host cell's response to pathogenic infection. Furthermore, these immune evasions have the potential to stimulate the human immune system, resulting in other associated non-communicable diseases. This review aims to advance our understanding of mosquito-borne diseases and the immune evasion mechanisms by associated pathogens. Moreover, it highlights the adverse outcomes of mosquito-borne disease.

Serum soluble mediators as prognostic biomarkers for morbidity, disease outcome, and late-relapsing hepatitis in yellow fever patients

This study described a soluble mediator storm in acute Yellow Fever/YF infection along the kinetic timeline towards convalescent disease. The analyses of the YF Viral RNAnemia, chemokines, cytokines, and growth factors were performed in YF patients at acute/(D1-15) and convalescent/(D16-315) phases. Patients with acute YF infection displayed a trimodal viremia profile spreading along D3, D6, and D8-14. A massive storm of mediators was observed in acute YF. Higher levels of mediators were observed in YF with higher morbidity scores, patients under intensive care, and those progressing to death than in YF patients who progress to late-relapsing hepatitis/L-Hep. A unimodal peak of biomarkers around D4-6 with a progressive decrease towards D181-315 was observed in non-L-Hep patients, while a bimodal pattern with a second peak around D61-90 was associated with L-Hep. This study provided a comprehensive landscape of evidence that distinct immune responses drive pathogenesis, disease progression, and L-Hep in YF patients.

A Perspective on Current Flavivirus Vaccine Development: A Brief Review

The flavivirus genus contains several clinically important pathogens that account for tremendous global suffering. Primarily transmitted by mosquitos or ticks, these viruses can cause severe and potentially fatal diseases ranging from hemorrhagic fevers to encephalitis. The extensive global burden is predominantly caused by six flaviviruses: dengue, Zika, West Nile, yellow fever, Japanese encephalitis and tick-borne encephalitis. Several vaccines have been developed, and many more are currently being tested in clinical trials. However, flavivirus vaccine development is still confronted with many shortcomings and challenges. With the use of the existing literature, we have studied these hurdles as well as the signs of progress made in flavivirus vaccinology in the context of future development strategies. Moreover, all current licensed and phase-trial flavivirus vaccines have been gathered and discussed based on their vaccine type. Furthermore, potentially relevant vaccine types without any candidates in clinical testing are explored in this review as well. Over the past decades, several modern vaccine types have expanded the field of vaccinology, potentially providing alternative solutions for flavivirus vaccines. These vaccine types offer different development strategies as opposed to traditional vaccines. The included vaccine types were live-attenuated, inactivated, subunit, VLPs, viral vector-based, epitope-based, DNA and mRNA vaccines. Each vaccine type offers different advantages, some more suitable for flaviviruses than others. Additional studies are needed to overcome the barriers currently faced by flavivirus vaccine development, but many potential solutions are currently being explored.

Recent Advancements in Mosquito-Borne Flavivirus Vaccine Development

Lately, the global incidence of flavivirus infection has been increasing dramatically and presents formidable challenges for public health systems around the world. Most clinically significant flaviviruses are mosquito-borne, such as the four serotypes of dengue virus, Zika virus, West Nile virus, Japanese encephalitis virus and yellow fever virus. Until now, no effective antiflaviviral drugs are available to fight flaviviral infection; thus, a highly immunogenic vaccine would be the most effective weapon to control the diseases. In recent years, flavivirus vaccine research has made major breakthroughs with several vaccine candidates showing encouraging results in preclinical and clinical trials. This review summarizes the current advancement, safety, efficacy, advantages and disadvantages of vaccines against mosquito-borne flaviviruses posing significant threats to human health.

Safety and immunogenicity following co-administration of Yellow fever vaccine with Tick-borne encephalitis or Japanese encephalitis vaccines: Results from an open label, non-randomized clinical trial

BACKGROUND

Flavivirus infections pose a significant global health burden underscoring the need for the development of safe and effective vaccination strategies. Available flavivirus vaccines are from time to time concomitantly delivered to individuals. Co-administration of different vaccines saves time and visits to health care units and vaccine clinics. It serves to provide protection against multiple pathogens in a shorter time-span; e.g., for individuals travelling to different endemic areas. However, safety and immunogenicity-related responses have not been appropriately evaluated upon concomitant delivery of these vaccines. Therefore, we performed an open label, non-randomized clinical trial studying the safety and immunogenicity following concomitant delivery of the yellow fever virus (YFV) vaccine with tick-borne encephalitis virus (TBEV) and Japanese encephalitis virus (JE) virus vaccines.

METHODS AND FINDINGS

Following screening, healthy study participants were enrolled into different cohorts receiving either TBEV and YFV vaccines, JEV and YFV vaccines, or in control groups receiving only the TBEV, JEV, or YFV vaccine. Concomitant delivery was given in the same or different upper arms for comparison in the co-vaccination cohorts. Adverse effects were recorded throughout the study period and blood samples were taken before and at multiple time-points following vaccination to evaluate immunological responses to the vaccines. Adverse events were predominantly mild in the study groups. Four serious adverse events (SAE) were reported, none of them deemed related to vaccination. The development of neutralizing antibodies (nAbs) against TBEV, JEV, or YFV was not affected by the concomitant vaccination strategy. Concomitant vaccination in the same or different upper arms did not significantly affect safety or immunogenicity-related outcomes. Exploratory studies on immunological effects were additionally performed and included studies of lymphocyte activation, correlates associated with germinal center activation, and plasmablast expansion.

CONCLUSIONS

Inactivated TBEV or JEV vaccines can be co-administered with the live attenuated YFV vaccine without an increased risk of adverse events and without reduced development of nAbs to the respective viruses. The vaccines can be delivered in the same upper arm without negative outcome. In a broader perspective, the results add valuable information for simultaneous administration of live and inactivated flavivirus vaccines in general.

TRIAL REGISTRATION

Eudra CT 2017-002137-32.

Arthropod-Borne Flaviviruses in Pregnancy

Flaviviruses are a diverse group of enveloped RNA viruses that cause significant clinical manifestations in the pregnancy and postpartum periods. This review highlights the epidemiology, pathophysiology, clinical features, diagnosis, and prevention of the key arthropod-borne flaviviruses of concern in pregnancy and the neonatal period-Zika, Dengue, Japanese encephalitis, West Nile, and Yellow fever viruses. Increased disease severity during pregnancy, risk of congenital malformations, and manifestations of postnatal infection vary widely amongst this virus family and may be quite marked. Laboratory confirmation of infection is complex, especially due to the reliance on serology for which flavivirus cross-reactivity challenges diagnostic specificity. As such, a thorough clinical history including relevant geographic exposures and prior vaccinations is paramount for accurate diagnosis. Novel vaccines are eagerly anticipated to ameliorate the impact of these flaviviruses, particularly neuroinvasive disease manifestations and congenital infection, with consideration of vaccine safety in pregnant women and children pivotal. Moving forward, the geographical spread of flaviviruses, as for other zoonoses, will be heavily influenced by climate change due to the potential expansion of vector and reservoir host habitats. Ongoing 'One Health' engagement across the human-animal-environment interface is critical to detect and responding to emergent flavivirus epidemics.

Potential Mammalian Vector-Borne Diseases in Live and Wet Markets in Indonesia and Myanmar

Vector-borne diseases spread from wild animals and their associated ectoparasites to humans and domesticated animals. Wildlife markets are recognized as important areas where this transfer can take place. We assessed the potential for spreading vector-borne diseases in two live and wet markets in Myanmar (Mong La, on the Myanmar-China border) and Indonesia (Sukahaji in Bandung on the island of Java) by making an inventory of all live and freshly killed wild mammals for sale. For eight mammal families, we quantified the number of animals on offer, and we used a heatmap cluster analysis to map vector-borne diseases that these families may carry. In Myanmar, we observed large numbers of wild pigs and deer (potentially carrying West Nile and various encephalitis viruses) whereas in Indonesia we observed Old World fruit bats (potentially carrying Chikungunya and encephalitis viruses) and squirrels (potentially carrying West Nile and encephalitis viruses). The trade in Indonesia was dominated by live mammals offered for sale as pets, and only Old World fruit bats and squirrels traded for traditional Asian medicine were killed in the markets. The trade in Myanmar was more geared towards wild meat (e.g., wild pigs, deer, primates) and traditional Asian medicine (squirrels). The combined risks of vector-borne diseases spreading from traded animals to human health highlight the need for an integrated approach protecting public health, economic interests and biodiversity.

Re-thinking yellow fever vaccines: fighting old foes with new generation vaccines

Despite the existence of a highly efficient yellow fever vaccine, yellow fever reemergence throughout Africa and the Americas has put 900 million people in 47 countries at risk of contracting the disease. Although the vaccine has been key to controlling yellow fever epidemics, its live-attenuated nature comes with a range of contraindications that prompts advising against its administration to pregnant and lactating women, immunocompromised individuals, and those with hypersensitivity to chicken egg proteins. Additionally, large outbreaks have highlighted problems with insufficient vaccine supply, whereby manufacturers rely on slow traditional manufacturing processes that prevent them from ramping up production. These limitations have contributed to an inadequate control of yellow fever and have favored the pursuit of novel yellow fever vaccine candidates that aim to circumvent the licensed vaccine's restrictions. Here, we review the live-attenuated vaccine's limitations and explore the epitome of a yellow fever vaccine, whilst scrutinizing next-generation vaccine candidates.

Assessing the efficacy of male Wolbachia-infected mosquito deployments to reduce dengue incidence in Singapore: study protocol for a cluster-randomized controlled trial

BACKGROUND

Dengue is a severe environmental public health challenge in tropical and subtropical regions. In Singapore, decreasing seroprevalence and herd immunity due to successful vector control has paradoxically led to increased transmission potential of the dengue virus. We have previously demonstrated that incompatible insect technique coupled with sterile insect technique (IIT-SIT), which involves the release of X-ray-irradiated male Wolbachia-infected mosquitoes, reduced the Aedes aegypti population by 98% and dengue incidence by 88%. This novel vector control tool is expected to be able to complement current vector control to mitigate the increasing threat of dengue on a larger scale. We propose a multi-site protocol to study the efficacy of IIT-SIT at reducing dengue incidence.

METHODS/DESIGN

The study is designed as a parallel, two-arm, non-blinded cluster-randomized (CR) controlled trial to be conducted in high-rise public housing estates in Singapore, an equatorial city-state. The aim is to determine whether large-scale deployment of male Wolbachia-infected Ae. aegypti mosquitoes can significantly reduce dengue incidence in intervention clusters. We will use the CR design, with the study area comprising 15 clusters with a total area of 10.9 km2, covering approximately 722,204 residents in 1713 apartment blocks. Eight clusters will be randomly selected to receive the intervention, while the other seven will serve as non-intervention clusters. Intervention efficacy will be estimated through two primary endpoints: (1) odds ratio of Wolbachia exposure distribution (i.e., probability of living in an intervention cluster) among laboratory-confirmed reported dengue cases compared to test-negative controls and (2) laboratory-confirmed reported dengue counts normalized by population size in intervention versus non-intervention clusters.

DISCUSSION

This study will provide evidence from a multi-site, randomized controlled trial for the efficacy of IIT-SIT in reducing dengue incidence. The trial will provide valuable information to estimate intervention efficacy for this novel vector control approach and guide plans for integration into national vector control programs in dengue-endemic settings.

TRIAL REGISTRATION

ClinicalTrials.gov, identifier: NCT05505682 . Registered on 16 August 2022. Retrospectively registered.

Establishment of Vero cell lines persistently harboring a yellow fever virus 17D subgenomic replicon

Yellow fever virus (YFV), a member of the genus Flavivirus, family Flaviviridae, is the etiological agent for an acute viral hemorrhagic disease, yellow fever. Although effective live attenuated vaccines based on the strain YFV 17D are currently available, no specific antiviral drug is available, and the disease remains a major public health concern. Hence, the discovery and development of antiviral drugs should lead to great benefits in controlling the disease. To provide a screening platform for antiviral agents targeting YFV RNA translation/replication, we have established and characterized two Vero cell lines that persistently harbor a subgenomic replicon derived from YFV 17D-204 (referred to as replicon cells). The replicon carries YFV nucleotides (1 - 176 and 2382-10,862) and a green fluorescent protein (GFP)-Zeocin resistance fusion gene as a selection marker and indicator of persistent replication. Immunofluorescence analysis revealed that both replicon cells and YFV 17D-infected cells showed similar distribution patterns of viral NS4B protein and replication intermediate, double-stranded RNA. Sequencing analysis of persistent replicons from the two replicon cell lines suggested that their nucleotide sequences did not vary greatly following multiple passages. We examined the effect of five agents, the antiviral cytokines interferon-β and -γ, the nucleoside analog ribavirin, the squalene synthase inhibitor zaragozic acid A, and the antibiotic rifapentine, a recently reported entry and replication inhibitor against YFV, on the persistent replication in the two replicon cell lines. These agents were selected because they inhibited both production of YFV 17D and transient replication of a luciferase-expressing replicon in Vero cells, without greatly affecting cell viability. We found that each of the agents decreased GFP fluorescence in the replicon cells, albeit to varying degrees. The agents other than rifapentine also showed a decrease in viral RNA levels in the replicon cells comparable to that seen for GFP fluorescence. These results indicate that persistent replication is susceptible to each of these five agents, although their mechanisms of action may differ. Taken together, these results provide evidence that translation/replication of the replicon in the replicon cells mimics that of the viral genome upon YFV 17D infection, indicating that the replicon cell lines can serve as a useful tool for high-throughput antiviral drug screening.

Rifapentine is an entry and replication inhibitor against yellow fever virus both in vitro and in vivo

Yellow fever virus (YFV) infection is a major public concern that threatens a large population in South America and Africa. No specific anti-YFV drugs are available till now. Here, we report that rifapentine is a potent YFV inhibitor in various cell lines by high-throughput drugs screening, acting at both cell entry and replication steps. Kinetic test and binding assay suggest that rifapentine interferes the viral attachment to the target cells. The application of YFV replicon and surface plasmon resonance assay indicates that rifapentine suppresses viral replication by binding to the RNA-dependent RNA polymerase (RdRp) domain of viral nonstructural protein NS5. Further molecular docking suggests that it might interact with the active centre of RdRp. Rifapentine significantly improves the survival rate, alleviates clinical signs, and reduces virus load and injury in targeted organs both in YFV-infected type I interferon receptor knockout A129^−/− and wild-type C57 mice. The antiviral effect in vivo is robust during both prophylactic intervention and therapeutic treatment, and the activity is superior to sofosbuvir, a previously reported YFV inhibitor in mice. Our data show that rifapentine may serve as an effective anti-YFV agent, providing promising prospects in the development of YFV pharmacotherapy.