Serological immune biomarker for disease severity in dengue-infected pediatric hospitalized patients.

Clinical manifestation of dengue disease ranges from asymptomatic, febrile fever without warning sign (DOS) to serious outcome dengue with warning sign (DWS) and severe disease (SD) leading to shock syndrome and death. The role of antibody response in natural dengue infection is complex and not completely understood. Here, we aimed to assess serological marker for disease severity. Antibody response of dengue-confirmed pediatric patients with acute secondary infection were evaluated against infecting virus, immature virus, and recombinant envelop protein. Immature virus antibody titers were significantly higher in DWS as compared to DOS (p = 0.0006). However, antibody titers against recombinant envelop protein were higher in DOS as compared to DWS, and antibody avidity was significantly higher against infecting virus in DOS. Serum samples of DOS patients displayed higher in vitro neutralization potential in plaque assay as compared to DWS, whereas DWS serum samples showed higher antibody-dependent enhancement in the in vitro enhancement assays. Thus, antibodies targeting immature virus can predict disease severity and could be used in early forecast of disease outcome using an enzyme-linked immunoassay assay system which is less laborious and cheaper than plaque assay system for correlates of protection and could help optimize medical care and resources.

Expression of dengue capsid-like particles in silkworm and display of envelope domain III of dengue virus serotype 2.

Dengue virus (DENV) is a considerable public health threat affecting millions of people globally. Vaccines for dengue are an important strategy to reduce the disease burden. We expressed capsid (C2) and envelope domain III of dengue virus serotype 2 (2EDIII) separately in the silkworm expression system. We conjugated them employing the monomeric streptavidin (mSA2) and biotin affinity to display the antigenic 2EDIII on the C2-forming capsid-like particle (CLP). Purified 2EDIII-displaying C2 (CLP/2EDIII) was immunogenic in BALB/c mice, eliciting neutralizing antibodies confirmed by a single-round infectious particle (SRIP) neutralization assay. Th1 cytokine levels were upregulated for the CLP/2EDIII group, and the anti-inflammatory IL-10 and pro-inflammatory IL-6 cytokine levels were also raised compared to the 2EDIII and the control groups. Elevated cytokine levels for CLP/2EDIII indicate the importance of displaying the 2EDIII as CLP/2EDIII rather than as an individual subunit. This study is the first to express the C2 protein as self-assembling CLP in vivo and 2EDIII separately in the silkworm expression system and conjugate them to form a monovalent CLP. Thus, this CLP/2EDIII display method may pave the way for an efficient tetravalent dengue vaccine candidate.

Simultaneous quantitation of neutralizing antibodies against all four dengue virus serotypes using optimized reporter virus particles.

Serum-neutralizing antibody titers are a critical measure of vaccine immunogenicity and are used to determine flavivirus seroprevalence in study populations. An effective dengue virus (DENV) vaccine must confer simultaneous protection against viruses grouped within four antigenic serotypes. Existing flavivirus neutralization assays, including the commonly used plaque/focus reduction neutralization titer (PRNT/FRNT) assay, require an individual assay for each virus, serotype, and strain and easily become a labor-intensive and time-consuming effort for large epidemiological studies or vaccine trials. Here, we describe a multiplex reporter virus particle neutralization titer (TetraPlex RVPNT) assay for DENV that allows simultaneous quantitative measures of antibody-mediated neutralization of infection against all four DENV serotypes in a single low-volume clinical sample and analyzed by flow cytometry. Comparative studies confirm that the neutralization titers of antibodies measured by the TetraPlex RVPNT assay are similar to FRNT/PRNT assay approaches performed separately for each viral strain. The use of this high-throughput approach enables the careful serological study in DENV endemic populations and vaccine recipients required to support the development of a safe and effective tetravalent DENV vaccine. IMPORTANCE: As a mediator of protection against dengue disease and a serological indicator of prior infection, the detection and quantification of neutralizing antibodies against DENV is an important "gold standard" tool. However, execution of traditional neutralizing antibody assays is often cumbersome and requires repeated application for each virus or serotype. The optimized RVPNT assay described here is high-throughput, easily multiplexed across multiple serotypes, and targets reporter viral particles that can be robustly produced for all four DENV serotypes. The use of this transformative RVPNT assay will support the expansion of neutralizing antibody datasets to answer research and public health questions often limited by the more cumbersome neutralizing antibody assays and the need for greater quantities of test serum.

Machine-learning-assisted high-throughput identification of potent and stable neutralizing antibodies against all four dengue virus serotypes.

Several computational methods have been developed to identify neutralizing antibodies (NAbs) covering four dengue virus serotypes (DENV-1 to DENV-4); however, limitations of the dataset and the resulting performance remain. Here, we developed a new computational framework to predict potent and stable NAbs against DENV-1 to DENV-4 using only antibody (CDR-H3) and epitope sequences as input. Specifically, our proposed computational framework employed sequence-based ML and molecular dynamic simulation (MD) methods to achieve more accurate identification. First, we built a novel dataset (n = 1108) by compiling the interactions of CDR-H3 and epitope sequences with the half maximum inhibitory concentration (IC50) values, which represent neutralizing activities. Second, we achieved an accurately predictive ML model that showed high AUC values of 0.879 and 0.885 by tenfold cross-validation and independent tests, respectively. Finally, our computational framework could be applied to filter approximately 2.5 million unseen antibodies into two final candidates that showed strong and stable binding to all four serotypes. In addition, the most potent and stable candidate (1B3B9_V21) was evaluated for its development potential as a therapeutic agent by molecular docking and MD simulations. This study provides an antibody computational approach to facilitate the high-throughput identification of NAbs and accelerate the development of therapeutic antibodies.

Serological Evidence of Zika Virus Infections in Sudan.

Little is known about the frequency of Zika virus (ZIKV) infections in Sudan. The aim of this study was to obtain data on the prevalence of ZIKV infections and the immunity of the population in the country. To this end, 198 sera obtained between December 2012 and January 2013 in different regions in Sudan were examined for neutralizing antibodies against ZIKV, dengue virus (DENV), and yellow fever virus (YFV). The sera were non-randomly selected. The neutralization titers were compared with each other and with the WHO 1st International Standard for anti-Asian lineage Zika virus antibody. Twenty-six sera neutralized ZIKV. One-third of these sera had higher neutralization titers against ZIKV than against DENV-2 and -3. Two sera showed higher neutralization titers than the WHO standard for ZIKV antibodies. These data suggest occasional ZIKV infections in Sudan. The low percentage of sera in this cohort that neutralized ZIKV indicates that, in the study period, the population was susceptible to ZIKV infection.

Immuno-Haematologic Aspects of Dengue Infection: Biologic Insights and Clinical Implications.

Dengue infection is caused by the dengue virus (DENV) and is transmitted to humans by infected female Aedes aegypti and Aedes albopictus mosquitoes. There are nearly 100 million new dengue cases yearly in more than 120 countries, with a five-fold increase in incidence over the past four decades. While many patients experience a mild illness, a subset suffer from severe disease, which can be fatal. Dysregulated immune responses are central to the pathogenesis of dengue, and haematologic manifestations are a prominent feature of severe disease. While thrombocytopaenia and coagulopathy are major causes of bleeding in severe dengue, leucocyte abnormalities are emerging as important markers of prognosis. In this review, we provide our perspective on the clinical aspects and pathophysiology of haematologic manifestations in dengue. We also discuss the key gaps in our current practice and areas to be addressed by future research.

Cross-Neutralizing Anti-Chikungunya and Anti-Dengue 2 IgG Antibodies from Patients and BALB/c Mice against Dengue and Chikungunya Viruses.

Dengue (DENV) and Chikungunya (CHIKV) viruses can be transmitted simultaneously by Aedes mosquitoes, and there may be co-infections in humans. However, how the adaptive immune response is modified in the host has yet to be known entirely. In this study, we analyzed the cross-reactivity and neutralizing activity of IgG antibodies against DENV and CHIKV in sera of patients from the Mexican Institute of Social Security in Veracruz, Mexico, collected in 2013 and 2015 and using IgG antibodies of BALB/c mice inoculated with DENV and/or CHIKV. Mice first inoculated with DENV and then with CHIKV produced IgG antibodies that neutralized both viruses. Mice were inoculated with CHIKV, and then with DENV; they had IgG antibodies with more significant anti-CHIKV IgG antibody neutralizing activity. However, the inoculation only with CHIKV resulted in better neutralization of DENV2. In sera obtained from patients in 2013, significant cross-reactivity and low anti-CHIKV IgG antibody neutralizing activity were observed. In CHIKV-positive 2015 sera, the anti-DENV IgG antibody neutralizing activity was high. These results suggest that CHIKV stimulates DENV2-induced memory responses and vice versa. Furthermore, cross-reactivity between the two viruses generated neutralizing antibodies, but exchanging CHIKV for DENV2 generated a better anti-CHIKV neutralizing response.

Dengue virus (DV) non-cross-reactive Omicron wave COVID-19 serums enhanced DV3 infectivity in vitro.

Introduction. In India, the SARS-CoV-2 Delta wave (2020-2021) faded away with the advent of the Omicron variants (2021-present). Dengue incidences were observed to be less in Southeast Asia during the active years of the pandemic (2020-2021). However, dengue virus type 3 (DV3) cases were increasingly reported in this region (including India) concurrent with the progression of the Omicron waves since 2022.Hypothesis. What could be the reason(s) behind this unusual DV3 surge after an overall dip in dengue incidences in many parts of Southeast Asia?Aim. We, therefore, investigated the current state of cross-reactivity of prevalent (Omicron era) SARS-CoV-2 serums with different DV serotypes and evaluated the impact of such serums on DV neutralization in cell culture.Methodology. Fifty-five COVID-19 serum samples (January-September 2022) and three pre-pandemic archived serum samples from apparently healthy individuals were tested for DV or SARS-CoV-2 IgM/IgG using the lateral flow immunoassays. DV1-4 virus neutralization tests (VNTs) were done with the SARS-CoV-2 antibody (Ab)-positive serums in Huh7 cells. DV3 envelope (env) gene was PCR amplified and sequenced for three archived DV isolates, one from 2017 and two from 2021.Results. SARS-CoV-2 Ab-positive samples constituted 74.5 % of the serums. Of these, 41.5 % were DV cross-reactive and 58.5 % were not. The DV cross-reactive serums neutralized all DV serotypes (DV1-4), as per previous results and this study. The DV non-cross-reactive serums (58.5 %) also cross-neutralized DV1, 2 and 4 but increased DV3 infectivity by means of antibody-dependent enhancement of infection as evident from significantly higher DV3 titres in VNT compared to control serums. The DV3 envelope was identical among the three isolates, including isolate 1 used in VNTs. Our results suggest that DV cross-reactivity of SARS-CoV-2 serums diminished with the shift from Delta to Omicron prevalence. Such COVID-19 serums (DV non-cross-reactive) might have played a major role in causing DV3 surge during the Omicron waves.Conclusion. Patients suspected of dengue or COVID-19 should be subjected to virus/antigen tests and serological tests for both the diseases for definitive diagnosis, prognosis and disease management.

Utility of the WHO dengue guidelines in pediatric immunological studies.

Dengue is a significant health problem due to the high burden of critical infections during outbreaks. In 1997, the World Health Organization (WHO) classified dengue as dengue fever (DF), dengue hemorrhagic fever (DHF), and dengue shock syndrome (DSS). It was revised in 2009 (updated in 2015), and the new guidelines recommended classifying patients as dengue without warning signs (DNS), dengue with warning signs (DWS), and severe dengue (SD). Although the utility of the revised 2009 classification for clinical studies is accepted, for immunological studies it needs to be clarified. We determined the usefulness of the 2009 classification for pediatric studies that analyze the circulating interleukin (IL)-6 and IL-8, two inflammatory cytokines. Plasma levels of IL-6 and IL-8 were evaluated in the acute and convalescent phases by flow cytometry in children with dengue classified using the 1997 and 2009 WHO guidelines. The plasma levels of IL-6 and IL-8 were elevated during the acute and decreased during convalescence, and both cytokines served as a good marker of acute dengue illness compared to convalescence. There were no differences in the plasma level of the evaluated cytokines among children with different clinical severity with any classification, except for the IL-8, which was higher in DWS than DNS. Based on the levels of IL-8, the 2009 classification identified DWS plus SD (hospital-treated children) compared to the DNS group [area under the curve (AUC): 0.7, p = 0.028]. These results support the utility of the revised 2009 (updated in 2015) classification in studies of immune markers in pediatric dengue.

Evaluation of in-house dengue real-time PCR assays in West Java, Indonesia.

Dengue is an infectious disease caused by infection of dengue virus (DENV) transmitted by Aedes aegypti and Aedes albopictus. In Indonesia, dengue commonly occurs with an increasing incidence rate annually. It is known that early detection of dengue infection is one of the keys to controlling this disease outbreak. Rapid and accurate early detection to diagnose dengue can be achieved by molecular tests, one of which is through a real-time PCR method. However, real-time PCR assay for dengue developed based on Indonesian DENV sequences has not been available. Therefore, we developed in-house dengue real-time PCR (SYBR- and TaqMan-based) assays and evaluated those assays in routine clinical testing in the community. These assays target the 3' UTR region of the four DENV serotypes and was found to be specific for DENV. The most sensitive assay was the TaqMan assay with the LOD95% of 482 copy/ml, followed by the SYBR assay with the LOD95% of 14,398 copy/ml. We recruited dengue suspected patients from three primary health care services in West Java, Indonesia to represent the community testing setting. Dengue infection was examined using the two in-house real-time PCR assays along with NS1, IgM, and IgG rapid diagnostic tests (RDT). In total, as many as 74 clinical specimens of dengue suspected patients were included in this study. Among those patients, 21 were positive for TaqMan assay, 17 were positive for SYBR assay, nine were positive for NS1 test, six were positive for both IgG and IgM tests, and 22 were positive for IgG test only. Compared with our in-house TaqMan assay, the sensitivity of NS1 test, IgM test, and IgG test were 42.86%, 14.29%, and 28.57% respectively. Among these three RDT tests, NS1 showed 100% specificity. Thus, our study confirmed that NS1 test showed high specificity, indicating that a positive result of NS1 can be confidently considered a dengue case. However, NS1, IgM, and IgG tests with RDT are not enough to diagnose a dengue case. We suggest applying the high sensitivity and specificity rRT-PCR test as the gold standard for early detection and antibody test as a follow-up test for rRT-PCR negative cases.

Retrospective study on the dengue fever outbreak in Puntland State, Somalia.

BACKGROUND: Dengue infection is a mosquito-borne, endemic viral disease, particularly in developing countries. Here, we report the results of the clinicodemographic, serologic profile and the monthly occurrence of a recent dengue fever outbreak in Puntland State (Somalia). METHODOLOGY: We analyzed the data of 956 dengue-suspected patients who were investigated using the rapid diagnostic testing (RDT) method for detecting NS1 (dengue virus non-structural protein) and IgM antibodies employing the SD Biosensor Dengue Dou NS Ag and IgM test kit (Germany) at the Puntland Public Health Referral Laboratory from November 21, 2022, to May 27, 2023. RESULTS: We found that 118 cases were positive for dengue among the suspected patients enrolled in the present study. Of these cases, 76.2% were dengue NSI positive, 13.6% were dengue IgM positive, and 10.2% were both NSI and IgM positive. The number of females and males in the confirmed cases was equal, and most (48.3%) were aged 20 years or less. 43.1% of them lived in the Nugal region, particularly in Garowe. Clinically, fever was the most frequent symptom (88.9%). The cases peaked in December 2022 but dropped from January to March, with a slight rise in February, and then increased in April and May 2023. CONCLUSION: This study highlights the clinicodemographic characteristics, seroprevalence, and monthly occurrence of dengue in Puntland. We recommend improving vector control measures, enhancing case management, strengthening dengue surveillance, developing an early warning system, and conducting future studies to characterize the circulating strains.

Multi-epitope peptide vaccines targeting dengue virus serotype 2 created via immunoinformatic analysis.

The Middle East has witnessed a greater spread of infectious Dengue viruses, with serotype 2 (DENV-2) being the most prevalent form. Through this work, multi-epitope peptide vaccines against DENV-2 that target E and nonstructural (NS1) proteins were generated through an immunoinformatic approach. MHC class I and II and LBL epitopes among NS1 and envelope E proteins sequences were predicted and their antigenicity, toxicity, and allergenicity were investigated. Studies of the population coverage denoted the high prevalence of NS1 and envelope-E epitopes among different countries where DENV-2 endemic. Further, both the CTL and HTL epitopes retrieved from NS1 epitopes exhibited high conservancies' percentages with other DENV serotypes (1, 3, and 4). Three vaccine constructs were created and the expected immune responses for the constructs were estimated using C-IMMSIM and HADDOCK (against TLR 2,3,4,5, and 7). Molecular dynamics simulation for vaccine construct 2 with TLR4 denoted high binding affinity and stability of the construct with the receptor which might foretell favorable in vivo interaction and immune responses.

Repurposing of therapeutic antibodies against dengue virus envelope protein receptor binding domain.

Dengue virus (DENV) is the leading cause of numerous deaths every year due to its high infectivity. In this study we have tried to target the DENV envelope protein receptor binding domain, the region crucial for binding to host receptors which leads to membrane fusion and entry of the viral genome into the human host cell. We have taken 13 known FDA approved antiviral therapeutic antibodies from therapeutic antibody database and tried to repurpose them against the DENV envelope protein. Based on the humanness analysis, 10 antibodies were selected against the DENV envelope protein. Computational affinity maturation of the 10 selected antibodies was performed to increase their binding affinity and specificity against the DENV envelope protein which ultimately led to 8 mutant antibodies having better binding affinity than the native ones. Molecular Dynamics (MD) simulation shows that, the stability of the complexes involving both the native and mutant antibodies were found to be the same although the binding energy between the protein and the respective antibodies was seen to improve upon computational affinity maturation. Contact analyses show similar robustness of the interaction for both the mutant and native antibodies during complex formation with the DENV envelope protein. This has led to the selection of total 18 antibodies including 10 natural and 8 affinity matured mutants which have a high probability of interacting with the DENV envelope protein. Finally, based on all these analyses along with heated MD simulation, Bamlanivimab, Etesivimab and Tixagevimab with a mutation of residue 100 of the heavy chain from serine to tyrosine were selected as prospective therapeutic antibodies to combat DENV infection. This study may open a new avenue in designing therapeutics to combat Dengue viral infection.

Impact of elevated IgE in protective immunity and immunopathology of dengue.

Dengue is a mosquito-transmitted infection endemic in tropical and subtropical locations of the world where nearly half of the world's population resides. The disease may present as mild febrile illness to severe and can even be fatal if untreated. There are four genetically related but antigenically distinct dengue virus (DENV) serotypes. Immune responses to DENV infection are in general protective but under certain conditions, they can also aggravate the disease. The importance of the cellular immune responses and the antibody responses involving IgG and IgM has been well-studied. In contrast, not much has been described on the potential role of hypersensitivity reactions involving IgE in dengue. Several studies have shown elevated levels of IgE in patients with dengue fever, but its involvement in the immune response against the virus and disease is unknown. Activation of mast cells (MCs) and basophils mediated through dengue-specific IgE could result in the release of mediators affecting dengue virus infection. The present review explores the relationships between the induction of IgE in dengue virus infection, and the potential role of MCs and basophils, exploring both protective and pathogenic aspects, including antibody-dependent enhancement (ADE) of infection in dengue.

Wolbachia mediates crosstalk between miRNA and Toll pathways to enhance resistance to dengue virus in Aedes aegypti.

The obligate endosymbiont Wolbachia induces pathogen interference in the primary disease vector Aedes aegypti, facilitating the utilization of Wolbachia-based mosquito control for arbovirus prevention, particularly against dengue virus (DENV). However, the mechanisms underlying Wolbachia-mediated virus blockade have not been fully elucidated. Here, we report that Wolbachia activates the host cytoplasmic miRNA biogenesis pathway to suppress DENV infection. Through the suppression of the long noncoding RNA aae-lnc-2268 by Wolbachia wAlbB, aae-miR-34-3p, a miRNA upregulated by the Wolbachia strains wAlbB and wMelPop, promoted the expression of the antiviral effector defensin and cecropin genes through the Toll pathway regulator MyD88. Notably, anti-DENV resistance induced by Wolbachia can be further enhanced, with the potential to achieve complete virus blockade by increasing the expression of aae-miR-34-3p in Ae. aegypti. Furthermore, the downregulation of aae-miR-34-3p compromised Wolbachia-mediated virus blockade. These findings reveal a novel mechanism by which Wolbachia establishes crosstalk between the cytoplasmic miRNA pathway and the Toll pathway via aae-miR-34-3p to strengthen antiviral immune responses against DENV. Our results will aid in the advancement of Wolbachia for arbovirus control by enhancing its virus-blocking efficiency.

Seroprevalence of Arboviruses in a Malaria Hyperendemic Area in Southern Mali.

Diagnostics for febrile illnesses other than malaria are not readily available in rural sub-Saharan Africa. This study assessed exposure to three mosquito-borne arboviruses-dengue virus (DENV), Zika virus (ZIKV), and chikungunya virus (CHIKV)-in southern Mali. Seroprevalence for DENV, CHIKV, and ZIKV was analyzed by detection of IgG antibodies and determined to be 77.2%, 31.2%, and 25.8%, respectively. Among study participants, 11.3% were IgG-positive for all three arboviruses. DENV had the highest seroprevalence rate at all sites; the highest seroprevalence of CHIKV and ZIKV was observed in Bamba. The seroprevalence for all three arboviruses increased with age, and the highest seroprevalence was observed among adults older than 50 years. The prevalence of Plasmodium spp. in the cohort was analyzed by microscopy and determined to be 44.5% (N = 600) with Plasmodium falciparum representing 95.1% of all infections. This study demonstrates the co-circulation of arboviruses in a region hyperendemic for malaria and highlights the needs for arbovirus diagnostics in rural sub-Saharan Africa.

A pre-vaccination immune metabolic interplay determines the protective antibody response to a dengue virus vaccine.

Protective immunity to dengue virus (DENV) requires antibody response to all four serotypes. Systems vaccinology identifies a multi-OMICs pre-vaccination signature and mechanisms predictive of broad antibody responses after immunization with a tetravalent live attenuated DENV vaccine candidate (Butantan-DV/TV003). Anti-inflammatory pathways, including TGF-ß signaling expressed by CD68low monocytes, and the metabolites phosphatidylcholine (PC) and phosphatidylethanolamine (PE) positively correlate with broadly neutralizing antibody responses against DENV. In contrast, expression of pro-inflammatory pathways and cytokines (IFN and IL-1) in CD68hi monocytes and primary and secondary bile acids negatively correlates with broad DENV-specific antibody responses. Induction of TGF-ß and IFNs is done respectively by PC/PE and bile acids in CD68low and CD68hi monocytes. The inhibition of viral sensing by PC/PE-induced TGF-ß is confirmed in vitro. Our studies show that the balance between metabolites and the pro- or anti-inflammatory state of innate immune cells drives broad and protective B cell response to a live attenuated dengue vaccine.

Evidences support that dengue virus can impart broad-spectrum immunity against betacoronaviruses in dengue endemic regions.

COVID-19 tended to be less aggressive in dengue endemic regions. Conversely, dengue cases plummeted in dengue endemic zones during the active years of the pandemic (2020-2021). We and others have demonstrated serological cross-reactivity between these two viruses of different families. We further demonstrated that COVID-19 serum samples that were cross-reactive in dengue virus (DV) serological tests, "cross-neutralized" all DV serotypes in Huh7 cells. Here we showed by co-immunoprecipitation (Co-IP) and atomic force microscopy (AFM) imaging that severe acute respiratory syndrome (SARS)-coronavirus (CoV)-2 (SARS-CoV-2) spike (S) protein subunit S1 and S2 monoclonal antibodies can indeed, bind to DV particles. Likewise, DV envelope antibodies (DV E Abs) showed high docking frequency with other human pathogenic beta-CoVs and murine hepatitis virus-1 (MHV-1). SARS-CoV-2 Ab didn't show docking or Co-IP with MHV-1 supporting poor cross-protection among CoVs. DV E Abs showed binding to MHV-1 (AFM, Co-IP, and immunofluorescence) and prepandemic dengue patients' serum samples even "cross-neutralized" MHV-1 plaques in cell culture. Furthermore, dengue serum samples showed marked inhibition potential in a surrogate virus-based competitive enzyme-linked immunosorbent assay, used for determining neutralizing Abs against SARS-CoV-2 S protein receptor-binding domain in COVID-19 serum samples. We therefore, provide multiple evidence as to why CoVs are epidemiologically less prevalent in highly dengue endemic regions globally.

Mechanisms of Flavivirus Cross-Protection against Yellow Fever in a Mouse Model.

The complete lack of yellow fever virus (YFV) in Asia, and the lack of urban YFV transmission in South America, despite the abundance of the peridomestic mosquito vector Aedes (Stegomyia.) aegypti is an enigma. An immunologically naïve population of over 2 billion resides in Asia, with most regions infested with the urban YF vector. One hypothesis for the lack of Asian YF, and absence of urban YF in the Americas for over 80 years, is that prior immunity to related flaviviruses like dengue (DENV) or Zika virus (ZIKV) modulates YFV infection and transmission dynamics. Here we utilized an interferon α/ß receptor knock-out mouse model to determine the role of pre-existing dengue-2 (DENV-2) and Zika virus (ZIKV) immunity in YF virus infection, and to determine mechanisms of cross-protection. We utilized African and Brazilian YF strains and found that DENV-2 and ZIKV immunity significantly suppresses YFV viremia in mice, but may or may not protect relative to disease outcomes. Cross-protection appears to be mediated mainly by humoral immune responses. These studies underscore the importance of re-assessing the risks associated with YF outbreak while accounting for prior immunity from flaviviruses that are endemic.

Primary exposure to Zika virus is linked with increased risk of symptomatic dengue virus infection with serotypes 2, 3, and 4, but not 1.

Infection with any of the four dengue virus serotypes (DENV1-4) can protect against or enhance subsequent dengue depending on preexisting antibodies and infecting serotype. Additionally, primary infection with the related flavivirus Zika virus (ZIKV) is associated with increased risk of DENV2 disease. Here, we measured how prior DENV and ZIKV immunity influenced risk of disease caused by DENV1-4 in a pediatric Nicaraguan cohort. Of 3412 participants in 2022, 10.6% experienced dengue cases caused by DENV1 (n = 139), DENV4 (n = 133), DENV3 (n = 54), DENV2 (n = 9), or an undetermined serotype (n = 39). Longitudinal clinical and serological data were used to define infection histories, and generalized linear and additive models adjusted for age, sex, time since last infection, and year, and repeat measurements were used to predict disease risk. Compared with flavivirus-naïve participants, primary ZIKV infection was associated with increased risk of disease caused by DENV4 (relative risk = 2.62, 95% confidence interval: 1.48 to 4.63) and DENV3 (2.90, 1.34 to 6.27), but not DENV1 infection. Primary DENV infection or DENV followed by ZIKV infection was also associated with increased risk of DENV4 disease. We reanalyzed 19 years of cohort data and demonstrated that prior flavivirus immunity and antibody titer had distinct associations with disease risk depending on incoming serotype. We thus find that prior ZIKV infection, like prior DENV infection, is associated with increased risk of disease with certain DENV serotypes. Cross-reactivity among flaviviruses should be considered when assessing vaccine safety and efficacy.