Characterization of "Off-Target" Immune Modulation Induced by Live Attenuated Yellow Fever Vaccine

BACKGROUND

Live attenuated vaccines alter immune functions and are associated with beneficial outcomes. We previously demonstrated that live attenuated yellow fever virus (YFV) vaccine (LA-YF-Vax) dampens T-cell receptor (TCR) signaling in vitro via an RNA-based mechanism. We examined study participants before and after LA-YF-Vax to assess TCR-mediated functions in vivo.

METHODS

Serum samples and peripheral blood mononuclear cells (PBMCs) were obtained before and after LA-YF-Vax (with or without additional vaccines) or quadrivalent influenza vaccine. TCR-mediated activation was determined by interleukin 2 release or phosphorylation of the lymphocyte-specific Src kinase. TCR-regulating phosphatase (protein tyrosine phosphatase receptor type E [PTPRE]) expression was also measured.

RESULTS

Compared with prevaccination findings, LA-YF-Vax recipient PBMCs demonstrated transient reduction in interleukin 2 release after TCR stimulation and PTPRE levels, unlike in control participants who received quadrivalent influenza vaccine. YFV was detected in 8 of 14 participants after LA-YF-Vax. After incubation of healthy donor PBMCs in serum-derived extracellular vesicles prepared from LA-YF-Vax recipients, TCR signaling and PTPRE levels were reduced after vaccination, even in participants without detectable YFV RNA.

CONCLUSIONS

LA-YF-Vax reduces TCR functions and PTPRE levels after vaccination. Extracellular vesicles from serum recapitulated this effect in healthy cells. This likely contributes to the reduced immunogenicity for heterologous vaccines after LA-YF-Vax administration. Identification of specific immune mechanisms related to vaccines should contribute to understanding of the "off-target," beneficial effects of live vaccines.

Novel 2-indolinone derivatives as promising agents against respiratory syncytial and yellow fever viruses

Background: A vaccine or antiviral drug for respiratory syncytial virus (RSV) infections and a specific antiviral drug for yellow fever virus (YFV) infections has not yet been developed. Method: In this study, 2-indolinone-based N-(4-sulfamoylphenyl)hydrazinecarbothioamides were synthesized. Along with these new compounds, previously synthesized 2-indolinone-based N-(3-sulfamoylphenyl)hydrazinecarbothioamides were evaluated against various DNA and RNA viruses. Results: Some 2-indolinone compounds exhibited nontoxic and selective antiviral activities against RSV and YFV. Halogen substitution at the indole ring increased the anti-RSV activities. Moreover, 1-benzyl and 5-halogen or nitro-substituted compounds were the most effective compounds against YFV. Conclusion: Generally, the 3-sulfonamide-substituted compounds were determined to be more effective than 4-sulfonamide-substituted compounds against RSV and YFV.

[Investigation of oncolytic potential of vaccine strains of yellow fever and tick-borne encephalitis viruses against glioblastoma and pancreatic carcinoma cell lines]

INTRODUCTION

Flaviviruses, possessing natural neurotropicity could be used in glioblastoma therapy using attenuated strains or as a delivery system for antitumor agents in an inactivated form.

OBJECTIVE

To investigate the sensitivity of glioblastoma and pancreatic carcinoma cell lines to vaccine strains of yellow fever and tick-borne encephalitis viruses.

MATERIALS AND METHODS

Cell lines: glioblastoma GL-6, T98G, LN-229, pancreatic carcinoma MIA RaCa-2 and human pancreatic ductal carcinoma PANC-1. Viral strains: 17D yellow fever virus (YF), Sofjin tick-borne encephalitis virus (TBEV). Virus concentration were determined by plaque assay and quantitative PCR. Determination of cell sensitivity to viruses by MTT assay.

RESULTS

17D YF was effective only against pancreatic carcinoma tumor cells MIA Paca-2 and had a limited effect against PANC-1. In glioblastoma cell lines (LN229, GL6, T98G), virus had no oncolytic effect and the viral RNA concentration fell in the culture medium. Sofjin TBEV showed CPE50 against MIA Paca-2 and a very limited cytotoxic effect against PANC-1. However, it had no oncolytic effect against glioblastoma cell lines (LN229, T98G and GL6), although virus reproduction continued in these cultures. For the GL6 glioblastoma cell line, the viral RNA concentration at the level with the infection dose was determined within 13 days, despite medium replacement, while in the case of the LN229 cell line, the virus concentration increased from 1 × 109 to 1 × 1010 copies/ml.

CONCLUSION

Tumor behavior in organism is more complex and is determined by different microenvironmental factors and immune status. In the future, it is advisable to continue studying the antitumor oncolytic and immunomodulatory effects of viral strains 17D YF and Sofjin TBEV using in vivo models.

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.

Does the Presence or a High Titer of Yellow Fever Virus Antibodies Interfere with Pregnancy Outcomes in Women with Zika Virus Infection?

Zika virus (ZIKV) and yellow fever virus (YFV) originated in Africa and expanded to the Americas, where both are co-circulated. It is hypothesized that in areas of high circulation and vaccination coverage against YFV, children of pregnant women have a lower risk of microcephaly. We evaluated the presence and titers of antibodies and outcomes in women who had ZIKV infection during pregnancy. Pregnancy outcomes were classified as severe, moderate, and without any important outcome. An outcome was defined as severe if miscarriage, stillbirth, or microcephaly occurred, and moderate if low birth weight and/or preterm delivery occurred. If none of these events were identified, the pregnancy was defined as having no adverse effects. A sample of 172 pregnant women with an acute ZIKV infection confirmed during pregnancy were collected throughout 2016. About 89% (150 of 169) of them presented immunity against YFV, including 100% (09 of 09) of those who had severe outcomes, 84% (16 of 19) of those who had moderate outcomes, and 89% (125 of 141) of those who had non-outcomes. There was no difference between groups regarding the presence of anti-YFV antibodies (p = 0.65) and YFV titers (p = 0.6). We were unable to demonstrate a protective association between the presence or titers of YFV antibodies and protection against serious adverse outcomes from exposure to ZIKV in utero.

Broad-Spectrum Antiviral Activity of Influenza A Defective Interfering Particles against Respiratory Syncytial, Yellow Fever, and Zika Virus Replication In Vitro

New broadly acting and readily available antiviral agents are needed to combat existing and emerging viruses. Defective interfering particles (DIPs) of influenza A virus (IAV) are regarded as promising options for the prevention and treatment of IAV infections. Interestingly, IAV DIPs also inhibit unrelated viral infections by stimulating antiviral innate immunity. Here, we tested the ability of IAV DIPs to suppress respiratory syncytial, yellow fever and Zika virus infections in vitro. In human lung (A549) cells, IAV DIP co-infection inhibited the replication and spread of all three viruses. In contrast, we observed no antiviral activity in Vero cells, which are deficient in the production of interferon (IFN), demonstrating its importance for the antiviral effect. Further, in A549 cells, we observed an enhanced type-I and type-III IFN response upon co-infection that appears to explain the antiviral potential of IAV DIPs. Finally, a lack of antiviral activity in the presence of the Janus kinase 1/2 (JAK1/2) inhibitor ruxolitinib was detected. This revealed a dependency of the antiviral activity on the JAK/signal transducers and activators of transcription (STAT) signaling pathway. Overall, this study supports the notion that IAV DIPs may be used as broad-spectrum antivirals to treat infections with a variety of IFN-sensitive viruses, particularly respiratory viruses.

Molecular Characterization of Circulating Yellow Fever Viruses from Outbreak in Ghana, 2021-2022

Yellow fever virus, transmitted by infected Aedes spp. mosquitoes, causes an acute viral hemorrhagic disease. During October 2021-February 2022, a yellow fever outbreak in some communities in Ghana resulted in 70 confirmed cases with 35 deaths (case-fatality rate 50%). The outbreak started in a predominantly unvaccinated nomadic community in the Savannah region, from which 65% of the cases came. The molecular amplification methods we used for diagnosis produced full-length DNA sequences from 3 confirmed cases. Phylogenetic analysis characterized the 3 sequences within West Africa genotype II; strains shared a close homology with sequences from Cote d'Ivoire and Senegal. We deployed more sensitive advanced molecular diagnostic techniques, which enabled earlier detection, helped control spread, and improved case management. We urge increased efforts from health authorities to vaccinate vulnerable groups in difficult-to-access areas and to educate the population about potential risks for yellow fever infections.

3-[N,N-Bis(sulfonyl)amino]isoxazolines with Spiro-Annulated or 1,2-Annulated Cyclooctane Rings Inhibit Reproduction of Tick-Borne Encephalitis, Yellow Fever, and West Nile Viruses

Spirocyclic compounds containing heterocyclic moieties represent promising 3D scaffolds for modern drug design. In the search for novel anti-flaviviral agents, we have obtained a series of 3-[N,N-bis(sulfonyl)amino]isoxazolines containing spiro-annulated cyclooctane rings and assessed their antiviral activity against tick-borne encephalitis (TBEV), yellow fever (YFV), and West Nile (WNV) viruses. The structural analogs of spirocyclic compounds with a single sulfonyl group or 1,2-annulated cyclooctane ring were also investigated. Almost all the studied 3-[N,N-bis(sulfonyl)amino]isoxazolines revealed antiviral activity against TBEV and WNV. The most active against TBEV was spiro-isoxazoline derivative containing p-nitrophenyl groups in the sulfonyl part (EC₅₀ 2.0 ± 0.5 μM), while the highest potency against WNV was found for the compounds with lipophilic substituents in sulfonyl moiety, naphtyl being the most favorable one (EC₅₀ 1.3 ± 0.5 μM). In summary, two novel scaffolds of anti-flaviviral agents based on N,N-bis(sulfonyl)amino]isoxazoline were proposed, and the compounds of this type demonstrated activity against TBEV and WNV.

Kunjin Virus, Zika Virus, and Yellow Fever Virus Infections Have Distinct Effects on the Coding Transcriptome and Proteome of Brain-Derived U87 Cells

As obligate intracellular parasites, viruses rely heavily on host cells for replication, and therefore dysregulate several cellular processes for their benefit. In return, host cells activate multiple signaling pathways to limit viral replication and eradicate viruses. The present study explores the complex interplay between viruses and host cells through next generation RNA sequencing as well as mass spectrometry (SILAC). Both the coding transcriptome and the proteome of human brain-derived U87 cells infected with Kunjin virus, Zika virus, or Yellow Fever virus were compared to the transcriptome and the proteome of mock-infected cells. Changes in the abundance of several hundred mRNAs and proteins were found in each infection. Moreover, the alternative splicing of hundreds of mRNAs was found to be modulated upon viral infection. Interestingly, a significant disconnect between the changes in the transcriptome and those in the proteome of infected cells was observed. These findings provide a global view of the coding transcriptome and the proteome of Flavivirus-infected cells, leading to a better comprehension of Flavivirus-host interactions.

The Importance of Entomo-Virological Investigation of Yellow Fever Virus to Strengthen Surveillance in Brazil

The largest outbreak of sylvatic yellow fever virus (YFV) in eight decades was recorded in Brazil between 2016-2018. Besides human and NHP surveillance, the entomo-virological approach is considered as a complementary tool. For this study, a total of 2904 mosquitoes of the Aedes, Haemagogus and Sabethes genera were collected from six Brazilian states (Bahia, Goiás, Mato Grosso, Minas Gerais, Pará, and Tocantins) and grouped into 246 pools, which were tested for YFV using RT-qPCR. We detected 20 positive pools from Minas Gerais, 5 from Goiás, and 1 from Bahia, including 12 of Hg. janthinomys and 5 of Ae. albopictus. This is the first description of natural YFV infection in this species and warns of the likelihood of urban YFV re-emergence with Ae. albopictus as a potential bridge vector. Three YFV sequences from Hg. janthinomys from Goiás and one from Minas Gerais, as well as one from Ae. albopictus from Minas Gerais were clustered within the 2016-2018 outbreak clade, indicating YFV spread from Midwest and its infection in a main and likely novel bridging vector species. Entomo-virological surveillance is critical for YFV monitoring in Brazil, which could highlight the need to strengthen YFV surveillance, vaccination coverage, and vector control measures.

Tetrahydroquinazoline N-oxide derivatives inhibit reproduction of tick-borne and mosquito-borne flaviviruses

Tick-borne encephalitis virus (TBEV), yellow fever virus (YFV), and West Nile virus (WNV) are flaviviruses causing emerging arthropod-borne infections of a great public health concern. Clinically approved drugs are not available to complement or replace the existing vaccines, which do not provide sufficient coverage. Thus, the discovery and characterization of new antiflaviviral chemotypes would advance studies in this field. In this study, a series of tetrahydroquinazoline N-oxides was synthesized, and the antiviral activity of the compounds was assessed against TBEV, YFV, and WNV using the plaque reduction assay along with the cytotoxicity to the corresponding cell lines (porcine embryo kidney and Vero). Most of the studied compounds were active against TBEV (EC₅₀  2 to 33 μM) and WNV (EC₅₀  0.15 to 34 μM) and a few also demonstrated inhibitory activity against YFV (EC₅₀  0.18 to 41 μM). To investigate the potential mechanism of action of the synthesized compounds, time-of-addition (TOA) experiments and virus yield reduction assays were performed for TBEV. The TOA studies suggested that the antiviral activity of the compounds should affect the early stages of the viral replication cycle after cell entry. Compounds with tetrahydroquinazoline N-oxide scaffold show a broad spectrum of activity against flaviviruses and represent a promising chemotype for antiviral drug discovery.

Specialized cis-Acting RNA Elements Balance Genome Cyclization to Ensure Efficient Replication of Yellow Fever Virus

Genome cyclization is essential for viral RNA (vRNA) replication of the vertebrate-infecting flaviviruses, and yet its regulatory mechanisms are not fully understood. Yellow fever virus (YFV) is a notorious pathogenic flavivirus. Here, we demonstrated that a group of cis-acting RNA elements in YFV balance genome cyclization to govern efficient vRNA replication. It was shown that the downstream of the 5'-cyclization sequence hairpin (DCS-HP) is conserved in the YFV clade and is important for efficient YFV propagation. By using two different replicon systems, we found that the function of the DCS-HP is determined primarily by its secondary structure and, to a lesser extent, by its base-pair composition. By combining in vitro RNA binding and chemical probing assays, we found that the DCS-HP orchestrates the balance of genome cyclization through two different mechanisms, as follows: the DCS-HP assists the correct folding of the 5' end in a linear vRNA to promote genome cyclization, and it also limits the overstabilization of the circular form through a potential crowding effect, which is influenced by the size and shape of the DCS-HP structure. We also provided evidence that an A-rich sequence downstream of the DCS-HP enhances vRNA replication and contributes to the regulation of genome cyclization. Interestingly, diversified regulatory mechanisms of genome cyclization, involving both the downstream of the 5'-cyclization sequence (CS) and the upstream of the 3'-CS elements, were identified among different subgroups of the mosquito-borne flaviviruses. In summary, our work highlighted how YFV precisely controls the balance of genome cyclization to ensure viral replication. IMPORTANCE Yellow fever virus (YFV), the prototype of the Flavivirus genus, can cause devastating yellow fever disease. Although it is preventable by vaccination, there are still tens of thousands of yellow fever cases per year, and no approved antiviral medicine is available. However, the understandings about the regulatory mechanisms of YFV replication are obscure. In this study, by a combination of bioinformatics, reverse genetics, and biochemical approaches, it was shown that the downstream of the 5'-cyclization sequence hairpin (DCS-HP) promotes efficient YFV replication by modulating the conformational balance of viral RNA. Interestingly, we found specialized combinations for the downstream of the 5'-cyclization sequence (CS) and upstream of the 3'-CS elements in different groups of the mosquito-borne flaviviruses. Moreover, possible evolutionary relationships among the various downstream of the 5'-CS elements were implied. This work highlighted the complexity of RNA-based regulatory mechanisms in the flaviviruses and will facilitate the design of RNA structure-targeted antiviral therapies.

Experimental Yellow Fever in Squirrel Monkey: Characterization of Liver In Situ Immune Response

Non-human primates contribute to the spread of yellow fever virus (YFV) and the establishment of transmission cycles in endemic areas, such as Brazil. This study aims to investigate virological, histopathological and immunohistochemical findings in livers of squirrel monkeys (Saimiri spp.) infected with the YFV. Viremia occurred 1-30 days post infection (dpi) and the virus showed a predilection for the middle zone (Z2). The livers were jaundiced with subcapsular and hemorrhagic multifocal petechiae. Apoptosis, lytic and coagulative necrosis, steatosis and cellular edema were also observed. The immune response was characterized by the expression of S100, CD11b, CD57, CD4 and CD20; endothelial markers; stress and cell death; pro and anti-inflammatory cytokines, as well as Treg (IL-35) and IL-17 throughout the experimental period. Lesions during the severe phase of the disease were associated with excessive production of apoptotic pro-inflammatory cytokines, such as IFN-γ and TNF-α, released by inflammatory response cells (CD4+ and CD8+ T lymphocytes) and associated with high expression of molecules of adhesion in the inflammatory foci observed in Z2. Immunostaining of the local endothelium in vascular cells and the bile duct was intense, suggesting a fundamental role in liver damage and in the pathogenesis of the disease.

Ecological, Genetic, and Phylogenetic Aspects of YFV 2017-2019 Spread in Rio de Janeiro State

In Brazil, a yellow fever (YF) outbreak was reported in areas considered YF-free for decades. The low vaccination coverage and the increasing forest fragmentation, with the wide distribution of vector mosquitoes, have been related to yellow fever virus (YFV) transmission beyond endemic areas since 2016. Aiming to elucidate the molecular and phylogenetic aspects of YFV spread on a local scale, we generated 43 new YFV genomes sampled from humans, non-human primates (NHP), and primarily, mosquitoes from highly heterogenic areas in 15 localities from Rio de Janeiro (RJ) state during the YFV 2016-2019 outbreak in southeast Brazil. Our analysis revealed that the genetic diversity and spatial distribution of the sylvatic transmission of YFV in RJ originated from at least two introductions and followed two chains of dissemination, here named the YFV RJ-I and YFV RJ-II clades. They moved with similar dispersal speeds from the north to the south of the RJ state in parallel directions, separated by the Serra do Mar Mountain chain, with YFV RJ-I invading the north coast of São Paulo state. The YFV RJ-I clade showed a more significant heterogeneity across the entire polyprotein. The YFV RJ-II clade, with only two amino acid polymorphisms, mapped at NS1 (I1086V), present only in mosquitoes at the same locality and NS4A (I2176V), shared by all YFV clade RJ-II, suggests a recent clustering of YFV isolates collected from different hosts. Our analyses strengthen the role of surveillance, genomic analyses of YVF isolated from other hosts, and environmental studies into the strategies to forecast, control, and prevent yellow fever outbreaks.

Defective Interfering Particles with Broad-Acting Antiviral Activity for Dengue, Zika, Yellow Fever, Respiratory Syncytial and SARS-CoV-2 Virus Infection

More than 100 arboviruses, almost all of which have an RNA genome, cause disease in humans. RNA viruses are causing unprecedented health system challenges worldwide, many with little or no specific therapies or vaccines available. Certain species of mosquito can carry dengue virus (DENV), Zika virus (ZIKV) and yellow fever virus (YFV), where co-infection of these viruses has occurred. Here, we found that purified synthetic defective interfering particles (DIPs) derived from DENV type 2 (DENV-2) strongly suppressed replication of the aforementioned viruses, respiratory syncytial virus (RSV) and also the novel emerging virus SARS-CoV-2 in human cells. DENV DIPs produced in bioreactors, purified by column chromatography, and concentrated are virus-like particles that are about half the diameter of a typical DENV particle, but with similar ratios of the viral structural proteins envelope and capsid. Overall, DIP-treated cells inhibited DENV, ZIKV, YFV, RSV, and SARS-CoV-2 by at least 98% by mechanisms which included interferon (IFN)-dependent cellular antiviral responses. IMPORTANCE DIPs are spontaneously derived virus mutants with deletions in genes that block viral replication. DIPs play important roles in modulation of viral disease, innate immune responses, virus persistence and virus evolution. Here, we investigated the antiviral activity of highly purified synthetic DIPs derived from DENV, which were produced in bioreactors. DENV DIPs purified by column chromatography strongly inhibited five different RNA viruses, including DENV, ZIKV, YFV, RSV, and SARS-CoV-2 in human cells. DENV DIPs inhibited virus replication via delivery of a small, noninfectious viral RNA that activated cellular innate immunity, resulting in robust type 1 interferon responses. The work here presents a pathway for DIP production which is adaptable to Good Manufacturing Practice, so that their preclinical testing should be suitable for evaluation in subjects.

Fast surveillance response reveals the introduction of a new yellow fever virus sub-lineage in 2021, in Minas Gerais, Brazil

BACKGROUND

In Brazil, the yellow fever virus (YFV) is maintained in a sylvatic cycle involving wild mosquitoes and non-human primates (NHPs). The virus is endemic to the Amazon region; however, waves of epidemic expansion reaching other Brazilian states sporadically occur, eventually causing spillovers to humans.

OBJECTIVES

To report a surveillance effort that led to the first confirmation of YFV in NHPs in the state of Minas Gerais (MG), Southeast region, in 2021.

METHODS

A surveillance network was created, encompassing the technology of smartphone applications and coordinated actions of several research institutions and health services to monitor and investigate NHP epizootics.

FINDINGS

When alerts were spread through the network, samples from NHPs were collected and YFV infection confirmed by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and genome sequencing at an interval of only 10 days. Near-complete genomes were generated using the Nanopore MinION sequencer. Phylogenetic analysis indicated that viral genomes were related to the South American genotype I, clustering with a genome detected in the Amazon region (state of Pará) in 2017, named YFVPA/MG sub-lineage. Fast YFV confirmation potentialised vaccination campaigns.

MAIN CONCLUSIONS

A new YFV introduction was detected in MG 6 years after the beginning of the major outbreak reported in the state (2015-2018). The YFV strain was not related to the sub-lineages previously reported in MG. No human cases have been reported, suggesting the importance of coordinated surveillance of NHPs using available technologies and supporting laboratories to ensure a quick response and implementation of contingency measures to avoid YFV spillover to humans.

Risk assessment of urban yellow fever virus transmission in Kenya: is Aedes aegypti an efficient vector?

The absence of urban yellow fever epidemics in East Africa remains a mystery amidst the proliferation of Aedes aegypti in this region. To understand the transmission dynamics of the disease, we tested urban (Mombasa, Kisumu, and Nairobi) Aedes mosquito populations in Kenya for their susceptibility to an East African yellow fever virus (YFV) genotype. Overall, 22% (n = 805) of the Ae. aegypti that were orally challenged with an infectious dose of YFV had a midgut infection, with comparable rates for Mombasa and Kisumu (χ²= 0.35, df = 1, P = 0.55), but significantly lower rates for Nairobi (χ² ≥ 11.08, df = 1, P ≤ 0.0009). Variations in YFV susceptibility (midgut infection) among Ae. aegypti subspecies were not associated with discernable cytochrome c oxidase subunit 1 gene haplotypes. Remarkably, no YFV dissemination or transmission was observed among the orally challenged Ae. aegypti populations. Moreover, Ae. aegypti mosquitoes that were intrathoracically inoculated with YFV failed to transmit the virus via capillary feeding. In contrast, dissemination (oral exposure) and transmission (intrathoracic inoculation) of YFV was observed among a few peri-domestic Ae. bromeliae mosquitoes (n = 129) that were assessed from these urban areas. Our study highlights an inefficient urban Ae. aegypti population, and the potential for Ae. bromeliae in sustaining an urban YFV transmission in Kenya. An assessment of urban Ae. aegypti susceptibility to other YFV genotypes, and vector potential of urban Ae. bromeliae populations in Kenya is recommended to guide cost-effective vaccination.

Discovery of a 2′-Fluoro,2′-Bromouridine Phosphoramidate Prodrug Exhibiting Anti-Yellow Fever Virus Activity in Culture and in Mice

Yellow fever virus (YFV) is a potentially lethal, zoonotic, blood-borne flavivirus transmitted to humans and non-human primates by mosquitoes. Owing to multiple deadly epidemics, the WHO classifies YFV as a "high impact, high threat disease" with resurgent epidemic potential. At present, there are no approved antiviral therapies to combat YFV infection. Herein we report on 2'-halogen-modified nucleoside analogs as potential anti-YFV agents. Of 11 compounds evaluated, three showed great promise with low toxicity, high intracellular metabolism into the active nucleoside triphosphate form, and sub-micromolar anti-YFV activity. Notably, we investigated a 2'-fluoro,2'-bromouridine phosphate prodrug (C9), a known anti-HCV agent with good stability in human blood and favorable metabolism. Predictive modeling revealed that C9 could readily bind the active site of the YFV RdRp, conferring its anti-YFV activity. C9 displayed potent anti-YFV activity in primary human macrophages, 3D hepatocyte spheroids, and in mice. In an A129 murine model, shortly after infection, C9 significantly reduced YFV replication and protected against YFV-induced liver inflammation and pathology with no adverse effects. Collectively, this work identifies a potent new anti-YFV agent with strong therapeutic promise.

Bis(Benzofuran-1,3-N,N-heterocycle)s as Symmetric and Synthetic Drug Leads against Yellow Fever Virus

The yellow fever virus (YFV) is an emerging RNA virus and has caused large outbreaks in Africa and Central and South America. The virus is often transmitted through infected mosquitoes and spreads from area to area because of international travel. Being an acute viral hemorrhagic disease, yellow fever can be prevented by an effective, safe, and reliable vaccine, but not be eliminated. Currently, there is no antiviral drug available for its cure. Thus, two series of novel bis(benzofuran−1,3-imidazolidin-4-one)s and bis(benzofuran−1,3-benzimidazole)s were designed and synthesized for the development of anti-YFV lead candidates. Among 23 new bis-conjugated compounds, 4 of them inhibited YFV strain 17D (Stamaril) on Huh-7 cells in the cytopathic effect reduction assays. These conjugates exhibited the most compelling efficacy and selectivity with an EC50 of <3.54 μM and SI of >15.3. The results are valuable for the development of novel antiviral drug leads against emerging diseases.

Recurrent Episodes of Some Mosquito-Borne Viral Diseases in Nigeria: A Systematic Review and Meta-Analysis

Different ecological zones favor the breeding of Aedes species. The molecular epidemiology of dengue virus (DENV), yellow fever virus (YFV), and Chikungunya virus (CHIKV) was determined from outbreaks and surveillance activities in Nigeria. Twenty-eight DENV, twenty-five YFV, and two CHIKV sequences from Nigeria were retrieved from GenBank. Genotyping was performed with a genome detective typing tool. The evolutionary comparison was performed by the Maximum Likelihood method on MEGA. Chi-square was used to compare the association between the proportions of viral infections at different times. Six DENV-1 were detected in 1964, 1965, 1978, 2007, and 2018. Nineteen DENV-2 strains were reported, four belonging to sylvatic VI, one belonging to cosmopolitan II, and twelve to Asian I genotype V. DENV-2 genotype VI was detected in 1966, and genotypes II and V in 2019. All three DENV-3 were detected in 2018, while only one DENV-4 was identified in 2019. YFV was reported in 1946 and then in the 60s, 70s, 80s, 90s, 2018, and 2019 with reports to date. CHIKV is still circulating following its identification in 1964 and 1965. Recurrent episodes of dengue, Chikungunya, and yellow fever continue unabated. Vector control initiatives and immunization should be greatly sustained.

Categorization by Score of Mosquito Species (Diptera: Culicidae) Related to Yellow Fever Epizootics in Argentina

The mosquito-borne yellow fever virus (YFV) is the cause of a zoonotic disease, with both sylvatic and urban cycles. Some mosquito species have been associated directly with transmission of the virus in South America, although the importance given to each species varies depending on the bibliography, geographical location, or year of publication. For Argentina, few publications have assessed the involvement of mosquito species, especially those included in the sylvatic cycle. Therefore, the goal of our paper was to gather all the information available in South America and categorize all mosquito species potentially involved in the YFV transmission cycle in Argentina according to incriminating vector criteria. Based on three main characteristics ('Hosts', 'Mosquito vector', and 'YF outbreak'), we generated scales of importance by species, one exclusively for Argentina and another for all of South America, Sabethes albiprivus Theobald, 1903 was the most important species in Argentina; whereas the most important species in South America were Haemagogus janthinomys Dyar 1921, Hg. leucocelaenus Dyar and Shannon, 1924, and Sa. chloropterus Von Humboldt, 1819. Our review highlights the lack of research that evaluates the importance of these species for YFV transmission in Argentina, while serving as a starting point to establish priorities for research on the bionomics and vector status of these species.

Yellow Fever Molecular Diagnosis Using Urine Specimens during Acute and Convalescent Phases of the Disease

Prior studies have demonstrated prolonged presence of yellow fever virus (YFV) RNA in saliva and urine as an alternative to serum. To investigate the presence of YFV RNA in urine, we used RT-PCR for YFV screening in 60 urine samples collected from a large cohort of naturally infected yellow fever (YF) patients during acute and convalescent phases of YF infection from recent YF outbreaks in Brazil (2017 to 2018). Fifteen urine samples from acute phase infection (up to 15 days post-symptom onset) and four urine samples from convalescent phase infection (up to 69 days post-symptom onset), were YFV PCR-positive. We genotyped YFV detected in seven urine samples (five collected during the acute phase and two collected during the YF convalescent phase). Genotyping indicated the presence of YFV South American I genotype in these samples. To our knowledge, this is the first report of wild-type YFV RNA detection in the urine this far out from symptom onset (up to 69 DPS), including YFV RNA detection during the convalescent phase of YF infection. The detection of YFV RNA in urine is an indicative of YFV infection; however, the results of RT-PCR using urine as sample should be interpreted with care, since a negative result does not exclude the possibility of YFV infection. With a possible prolonged period of detection beyond the viremic phase, the use of urine samples coupled with serological tests, epidemiologic inquiry, and clinical assessment could provide a longer diagnostic window for laboratory YF diagnosis.

Yellow Fever: Roles of Animal Models and Arthropod Vector Studies in Understanding Epidemic Emergence

Yellow fever virus (YFV) is a mosquito-borne flavivirus circulating throughout the tropical and sub-tropical regions of Africa and South America. It is responsible for an estimated 30,000 deaths annually, and while there is a highly successful vaccine, coverage is incomplete, and there is no approved treatment for YFV infection. Despite advancements in the field, animal models for YFV infection remain scarce, and care must be taken to select an appropriate model for a given hypothesis. Small animal models require either adapted YFV strains or immunocompromised hosts. Non-human primates (NHPs) recapitulate human disease, but they require specialized facilities and training, are often in short supply and cost-prohibitive, and can present ethical concerns. The limitations in studying the mosquito vectors for YFV infection include inconsistency in the laboratory environment, the requirement for a high containment insectary, and difficulty in maintaining sylvatic mosquitoes. In this review, we discuss the roles of animal models and arthropod vector studies in understanding epidemic emergence.

A High-Throughput Yellow Fever Neutralization Assay

Quick and accurate detection of neutralizing antibodies (nAbs) against yellow fever is essential in serodiagnosis during outbreaks for surveillance and to evaluate vaccine efficacy in population-wide studies. All of this requires serological assays that can process a large number of samples in a highly standardized format. Albeit being laborious, time-consuming, and limited in throughput, the classical plaque reduction neutralization test (PRNT) is still considered the gold standard for the detection and quantification of nAbs due to its sensitivity and specificity. Here, we report the development of an alternative fluorescence-based serological assay (SNTFLUO) with an equally high sensitivity and specificity that is fit for high-throughput testing with the potential for automation. Finally, our novel SNTFLUO was cross-validated in several reference laboratories and against international WHO standards, showing its potential to be implemented in clinical use. SNTFLUO assays with similar performance are available for the Japanese encephalitis, Zika, and dengue viruses amenable to differential diagnostics. IMPORTANCE Fast and accurate detection of neutralizing antibodies (nAbs) against yellow fever virus (YFV) is key in yellow fever serodiagnosis, outbreak surveillance, and monitoring of vaccine efficacy. Although classical PRNT remains the gold standard for measuring YFV nAbs, this methodology suffers from inherent limitations such as low throughput and overall high labor intensity. We present a novel fluorescence-based serum neutralization test (SNTFLUO) with equally high sensitivity and specificity that is fit for processing a large number of samples in a highly standardized manner and has the potential to be implemented for clinical use. In addition, we present SNTFLUO assays with similar performance for Japanese encephalitis, Zika, and dengue viruses, opening new avenues for differential diagnostics.

Monoclonal Antibodies and Flaviviruses: a Possible Option?

M. P. Doyle, J. R. Genualdi, A. L. Bailey, N. Kose, et al. (mBio 13:e00512-22, 2022, https://doi.org/10.1128/mBio.00512-22), report on the cloning of a panel of fully human monoclonal antibodies (mAbs) directed against yellow fever virus (YFV). In particular, mAb YFV-136 is endowed with interesting cross-YFV substrain-neutralizing features. The importance of YFV-136 and other mAbs with similar characteristics is related not necessarily only to their possible future use in the clinic but also to their role in a better understanding of the biology of YFV (as well as of other flaviviruses) for the development of effective therapeutic and prophylactic strategies. The emergence and reemergence of different flaviviruses worldwide in the last decades certainly make this a compelling clinical priority.

Updating the Phylodynamics of Yellow Fever Virus 2016-2019 Brazilian Outbreak With New 2018 and 2019 São Paulo Genomes

The recent outbreak of yellow fever (YF) in São Paulo during 2016-2019 has been one of the most severe in the last decades, spreading to areas with low vaccine coverage. The aim of this study was to assess the genetic diversity of the yellow fever virus (YFV) from São Paulo 2016-2019 outbreak, integrating the available genomic data with new genomes from patients from the Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo (HCFMUSP). Using phylodynamics, we proposed the existence of new IE subclades, described their sequence signatures, and determined their locations and time of origin. Plasma or urine samples from acute severe YF cases (n = 56) with polymerase chain reaction (PCR) positive to YFV were submitted to viral genome amplification using 12 sets of primers. Thirty-nine amplified genomes were subsequently sequenced using next-generation sequencing (NGS). These 39 sequences, together with all the complete genomes publicly available, were aligned and used to determine nucleotide/amino acids substitutions and perform phylogenetic and phylodynamic analysis. All YFV genomes generated in this study belonged to the genotype South American I subgroup E. Twenty-one non-synonymous substitutions were identified among the new generated genomes. We analyzed two major clades of the genotypes IE, IE1, and IE2 and proposed the existence of subclades based on their sequence signatures. Also, we described the location and time of origin of these subclades. Overall, our findings provide an overview of YFV genomic characterization and phylodynamics of the 2016-2019 outbreak contributing to future virological and epidemiological studies.

Isolation of a Potently Neutralizing and Protective Human Monoclonal Antibody Targeting Yellow Fever Virus

Yellow fever virus (YFV) causes sporadic outbreaks of infection in South America and sub-Saharan Africa. While live-attenuated yellow fever virus vaccines based on three substrains of 17D are considered some of the most effective vaccines in use, problems with production and distribution have created large populations of unvaccinated, vulnerable individuals in areas of endemicity. To date, specific antiviral therapeutics have not been licensed for human use against YFV or any other related flavivirus. Recent advances in monoclonal antibody (mAb) technology have allowed the identification of numerous candidate therapeutics targeting highly pathogenic viruses, including many flaviviruses. Here, we sought to identify a highly neutralizing antibody targeting the YFV envelope (E) protein as a therapeutic candidate. We used human B cell hybridoma technology to isolate mAbs from circulating memory B cells from human YFV vaccine recipients. These antibodies bound to recombinant YFV E protein and recognized at least five major antigenic sites on E. Two mAbs (designated YFV-136 and YFV-121) recognized a shared antigenic site and neutralized the YFV-17D vaccine strain in vitro. YFV-136 also potently inhibited infection by multiple wild-type YFV strains, in part, at a postattachment step in the virus replication cycle. YFV-136 showed therapeutic protection in two animal models of YFV challenge, including hamsters and immunocompromised mice engrafted with human hepatocytes. These studies define features of the antigenic landscape of the YFV E protein recognized by the human B cell response and identify a therapeutic antibody candidate that inhibits infection and disease caused by highly virulent strains of YFV.

Genotype-specific features reduce the susceptibility of South American yellow fever virus strains to vaccine-induced antibodies

The resurgence of yellow fever in South America has prompted vaccination against the etiologic agent, yellow fever virus (YFV). Current vaccines are based on a live-attenuated YF-17D virus derived from a virulent African isolate. The capacity of these vaccines to induce neutralizing antibodies against the vaccine strain is used as a surrogate for protection. However, the sensitivity of genetically distinct South American strains to vaccine-induced antibodies is unknown. We show that antiviral potency of the polyclonal antibody response in vaccinees is attenuated against an emergent Brazilian strain. This reduction was attributable to amino acid changes at two sites in central domain II of the glycoprotein E, including multiple changes at the domain I-domain II hinge, which are unique to and shared among most South American YFV strains. Our findings call for a reevaluation of current approaches to YFV immunological surveillance in South America and suggest approaches for updating vaccines.

Epidemiology and Laboratory Diagnostics of Dengue, Yellow Fever, Zika, and Chikungunya Virus Infections in Africa

Arbovirus infections are widespread, and their disease burden has increased in the past decade. In Africa, arbovirus infections and fever with unknown etiology are common. Due to the lack of well-established epidemiologic surveillance systems and accurate differential diagnosis in most African countries, little is known about the prevalence of human arbovirus infections in Africa. The aim of this review is to summarize the available epidemiological data and diagnostic laboratory tools of infections with dengue, yellow fever, Zika, and chikungunya viruses, all transmitted by Aedes mosquitoes. Studies indicate that these arboviral infections are endemic in most of Africa. Surveillance of the incidence and prevalence of the infections would enable medical doctors to improve the diagnostic accuracy in patients with typical symptoms. If possible, arboviral diagnostic tests should be added to the routine healthcare systems. Healthcare providers should be informed about the prevalent arboviral diseases to identify possible cases.

Minireview: Epidemiological impact of arboviral diseases in Latin American countries, arbovirus-vector interactions and control strategies

Mosquitoes are the most crucial insects in public health due to their vector capacity and competence to transmit pathogens, including arboviruses, bacterias and parasites. Re-emerging and emerging arboviral diseases, such as yellow fever virus (YFV), dengue virus (DENV), zika virus (ZIKV), and chikungunya virus (CHIKV), constitute one of the most critical health public concerns in Latin America. These diseases present a significant incidence within the human settlements increasing morbidity and mortality events. Likewise, among the different genus of mosquito vectors of arboviruses, those of the most significant medical importance corresponds to Aedes and Culex. In Latin America, the mosquito vector species of YFV, DENV, ZIKV, and CHIKV are mainly Aedes aegypti and Ae. Albopictus. Ae. aegypti is recognized as the primary vector in urban environments, whereas Ae. albopictus, recently introduced in the Americas, is more prone to rural settings. This minireview focuses on what is known about the epidemiological impact of mosquito-borne diseases in Latin American countries, with particular emphasis on YFV, DENV, ZIKV and CHIKV, vector mosquitoes, geographic distribution, and vector-arbovirus interactions. Besides, it was analyzed how climate change and social factors have influenced the spread of arboviruses and the control strategies developed against mosquitoes in this continent.

Visualization of yellow fever virus infection in mice using a bioluminescent reporter virus

Yellow fever virus (YFV) is a re-emerging flavivirus, which can lead to severe clinical manifestations and high mortality, with no specific antiviral therapies available. The live-attenuated yellow fever vaccine 17D (YF17D) has been widely used for over eighty years. However, the emergence of yellow fever vaccine-associated viscerotropic disease (YFL-AVD) and yellow fever vaccine-associated neurotropic disease (YFL-AND) raised non-negligible concerns. Additionally, the attenuation mechanism of YF17D is still unclear. Thus, the development of convenient models is crucial to understand the mechanisms behind YF17D attenuation and its adverse effects. In this work, we generated a reporter YF17D expressing nano-luciferase (NLuc). In vitro and in vivo characterization demonstrated that the NLuc-YF17D shared similar biological properties with its parental strain and the NLuc activity can reflect viral infectivity reliably. Combined with in vivo bioluminescence imaging, a series of mice models of YF17D infection was established, which will be useful for the evaluation of antiviral medicines and novel vaccine candidates. Especially, we demonstrated that intraperitoneally (i.p.) infection of NLuc-YF17D in type I interferon receptor-deficient mice A129 resulted in outcomes resembling YEL-AVD and YEL-AND, evidenced by viral replication in multiple organs and invasion of the central neuronal system. Finally, in vitro and in vivo assays based on this reporter virus were established to evaluate the antiviral activities of validated antiviral agents. In conclusion, the bioluminescent reporter virus described herein provides a powerful platform to study YF17D attenuation and vaccine-associated diseases as well as to develop novel countermeasures against YFV.

Re-emergence of yellow fever in the neotropics - quo vadis?

Yellow fever virus (YFV) is the etiological agent of yellow fever (YF), an acute hemorrhagic vector-borne disease with a significant impact on public health, is endemic across tropical regions in Africa and South America. The virus is maintained in two ecologically and evolutionary distinct transmission cycles: an enzootic, sylvatic cycle, where the virus circulates between arboreal Aedes species mosquitoes and non-human primates, and a human or urban cycle, between humans and anthropophilic Aedes aegypti mosquitoes. While the urban transmission cycle has been eradicated by a highly efficacious licensed vaccine, the enzootic transmission cycle is not amenable to control interventions, leading to recurrent epizootics and spillover outbreaks into human populations. The nature of YF transmission dynamics is multifactorial and encompasses a complex system of biotic, abiotic, and anthropogenic factors rendering predictions of emergence highly speculative. The recent outbreaks in Africa and Brazil clearly remind us of the significant impact YF emergence events pose on human and animal health. The magnitude of the Brazilian outbreak and spillover in densely populated areas outside the recommended vaccination coverage areas raised the specter of human — to — human transmission and re-establishment of enzootic cycles outside the Amazon basin. Herein, we review the factors that influence the re-emergence potential of YFV in the neotropics and offer insights for a constellation of coordinated approaches to better predict and control future YF emergence events.

Yellow Fever Outbreak in Eastern Senegal, 2020-2021

Yellow fever virus remains a major threat in low resource countries in South America and Africa despite the existence of an effective vaccine. In Senegal and particularly in the eastern part of the country, periodic sylvatic circulation has been demonstrated with varying degrees of impact on populations in perpetual renewal. We report an outbreak that occurred from October 2020 to February 2021 in eastern Senegal, notified and managed through the synergistic effort yellow fever national surveillance implemented by the Senegalese Ministry of Health in collaboration with the World Health Organization, the countrywide 4S network set up by the Ministry of Health, the Institut Pasteur de Dakar, and the surveillance of arboviruses and hemorrhagic fever viruses in human and vector populations implemented since mid 2020 in eastern Senegal. Virological analyses highlighted the implication of sylvatic mosquito species in virus transmission. Genomic analysis showed a close relationship between the circulating strain in eastern Senegal, 2020, and another one from the West African lineage previously detected and sequenced two years ago from an unvaccinated Dutch traveler who visited the Gambia and Senegal before developing signs after returning to Europe. Moreover, genome analysis identified a 6-nucleotide deletion in the variable domain of the 3′UTR with potential impact on the biology of the viral strain that merits further investigations. Integrated surveillance of yellow fever virus but also of other arboviruses of public health interest is crucial in an ecosystem such as eastern Senegal.

Immunity and Viral Infections: Modulating Antiviral Response via CRISPR-Cas Systems

Viral infections cause a variety of acute and chronic human diseases, sometimes resulting in small local outbreaks, or in some cases spreading across the globe and leading to global pandemics. Understanding and exploiting virus-host interactions is instrumental for identifying host factors involved in viral replication, developing effective antiviral agents, and mitigating the severity of virus-borne infectious diseases. The diversity of CRISPR systems and CRISPR-based tools enables the specific modulation of innate immune responses and has contributed impressively to the fields of virology and immunology in a very short time. In this review, we describe the most recent advances in the use of CRISPR systems for basic and translational studies of virus-host interactions.

Mother-to-Child Transmission of Arboviruses during Breastfeeding: From Epidemiology to Cellular Mechanisms

Most viruses use several entry sites and modes of transmission to infect their host (parenteral, sexual, respiratory, oro-fecal, transplacental, transcutaneous, etc.). Some of them are known to be essentially transmitted via arthropod bites (mosquitoes, ticks, phlebotomes, sandflies, etc.), and are thus named arthropod-borne viruses, or arboviruses. During the last decades, several arboviruses have emerged or re-emerged in different countries in the form of notable outbreaks, resulting in a growing interest from scientific and medical communities as well as an increase in epidemiological studies. These studies have highlighted the existence of other modes of transmission. Among them, mother-to-child transmission (MTCT) during breastfeeding was highlighted for the vaccine strain of yellow fever virus (YFV) and Zika virus (ZIKV), and suggested for other arboviruses such as Chikungunya virus (CHIKV), dengue virus (DENV), and West Nile virus (WNV). In this review, we summarize all epidemiological and clinical clues that suggest the existence of breastfeeding as a neglected route for MTCT of arboviruses and we decipher some of the mechanisms that chronologically occur during MTCT via breastfeeding by focusing on ZIKV transmission process.

Brazilian Aedes aegypti as a Competent Vector for Multiple Complex Arboviral Coinfections

BACKGROUND

Aedes aegypti is a highly competent vector in the transmission of arboviruses, such as chikungunya, dengue, Zika, and yellow fever viruses, and causes single and coinfections in the populations of tropical countries.

METHODS

The infection rate, viral abundance (VA), vector competence (VC), disseminated infection, and survival rate were recorded after single and multiple infections of the vector with 15 combinations of chikungunya, dengue, Zika, and yellow fever arboviruses.

RESULTS

Infection rates were 100% in all single and multiple infection experiments, except in 1 triple coinfection that presented a rate of 50%. The VC and disseminated infection rate varied from 100% (in single and quadruple infections) to 40% (in dual and triple infections). The dual and triple coinfections altered the VC and/or VA of ≥1 arbovirus. The highest viral VAs were detected for a single infection with chikungunya. The VAs in quadruple infections were similar when compared with each respective single infection. A decrease in survival rates was observed in a few combinations.

CONCLUSIONS

A. aegypti was able to host all single and multiple arboviral coinfections. The interference of the chikungunya virus suggests that distinct arbovirus families may have a significant role in complex coinfections.

Process intensification for the production of yellow fever virus-like particles as potential recombinant vaccine antigen

Yellow fever (YF) is a life-threatening viral disease endemic in parts of Africa and Latin America. Although there is a very efficacious vaccine since the 1930s, YF still causes 29,000-60,000 annual deaths. During recent YF outbreaks there were issues of vaccine shortage of the current egg-derived vaccine; rare but fatal vaccine adverse effects occurred; and cases were imported to Asia, where the circulating mosquito vector could potentially start local transmission. Here we investigated the production of YF virus-like particles (VLPs) using stably transfected HEK293 cells. Process intensification was achieved by combining sequential FACS (fluorescence-activated cell sorting) rounds to enrich the stable cell pool in terms of high producers and the use of perfusion processes. At shaken-tube scale, FACS enrichment of cells allowed doubling VLP production, and pseudoperfusion cultivation (with daily medium exchange) further increased VLP production by 9.3-fold as compared to batch operation mode. At perfusion bioreactor scale, the use of an inclined settler as cell retention device showed operational advantages over an ATF system. A one-step steric exclusion chromatography purification allowed significant removal of impurities and is a promising technique for future integration of upstream and downstream operations. Characterization by different techniques confirmed the identity and 3D-structure of the purified VLPs.

Seroprevalence of arboviruses in Ecuador: Implications for improved surveillance

Introduction:

Arthropod-borne viruses (arboviruses) cause morbidity and mortality in humans and domestic animals worldwide. The percentage of population immunity or susceptibility to these viruses in Ecuador is unknown.

Objectives:

To investigate the proportion of Ecuadorian populations with IgG antibodies (Abs) (past exposure/immunity) and IgM Abs (current exposure) against flaviviruses and alphaviruses and to study the activity of these viruses in Ecuador.

Materials and methods:

During 2009-2011, we conducted a serosurvey for selected arboviruses in humans (n=1,842), equines (n=149), and sentinel hamsters (n=84) at two coastal locations and one in the Amazon basin (Eastern Ecuador) using enzyme-linked immunosorbent assay and hemagglutination inhibition test.

Results:

From 20.63% to 63.61% of humans showed IgG-antibodies for the flaviviruses: Dengue virus (DENV), yellow fever virus (YFV) Saint Louis encephalitis virus, and West Nile virus (WNV); from 4.67% to 8.63% showed IgG-Abs for the alphaviruses: Venezuelan

equine encephalitis virus, eastern equine encephalitis virus, and western equine encephalitis virus. IgM-Abs were found for DENV and WNV. Equines and hamsters showed antibodies to alphaviruses in all locations; two hamsters seroconverted to YFV in the Amazonia.

Conclusions:

The results show a YFV vaccination history and suggest the activity of arboviruses not included in the current surveillance scheme. Enhanced arbovirus and mosquito surveillance, as well as continued YFV vaccination and evaluation of its coverage/ effectiveness, are recommended.

Differential Yellow Fever Susceptibility in New World Nonhuman Primates, Comparison with Humans, and Implications for Surveillance

A major outbreak of yellow fever (YF) occurred in Brazil during 2016-2018. Epizootics in New World nonhuman primates are sentinel events for YF virus circulation. However, genus-specific susceptibilities and suitability for YF surveillance remain poorly understood. We obtained and compared epidemiologic, histopathologic, immunohistochemical, and molecular results from 93 human and 1,752 primate cases submitted during the recent YF outbreak in Brazil (2017), with the support of the Brazilian National YF Surveillance Program. We detected heterogeneous YF-associated profiles among the various genera of primates we analyzed. Alouatta primates were the most reliable sentinel; Sapajus and Callicebus primates had higher viral loads but lower proportional mortality rates. Callithrix primates were the least sensitive, showing lower viral loads, lower proportional mortality rates, and no demonstrable YF virus antigen or extensive lesions in liver, despite detectable viral RNA. These differences in susceptibility, viral load, and mortality rates should be considered in strategic surveillance of epizootics and control measures for YF.

What Constitutes Protective Immunity Following Yellow Fever Vaccination?

Yellow fever (YF) remains a threat to global health, with an increasing number of major outbreaks in the tropical areas of the world over the recent past. In light of this, the Eliminate Yellow Fever Epidemics Strategy was established with the aim of protecting one billion people at risk of YF through vaccination by the year 2026. The current YF vaccine gives excellent protection, but its use is limited by shortages in supply due to the difficulties in producing the vaccine. There are good grounds for believing that alternative fractional dosing regimens can produce strong protection and overcome the problem of supply shortages as less vaccine is required per person. However, immune responses to these vaccination approaches are yet to be fully understood. In addition, published data on immune responses following YF vaccination have mostly quantified neutralising antibody titers. However, vaccine-induced antibodies can confer immunity through other antibody effector functions beyond neutralisation, and an effective vaccine is also likely to induce strong and persistent memory T cell responses. This review highlights the gaps in knowledge in the characterisation of YF vaccine-induced protective immunity in the absence or presence of neutralising antibodies. The assessment of biophysical antibody characteristics and cell-mediated immunity following YF vaccination could help provide a comprehensive landscape of YF vaccine-induced immunity and a better understanding of correlates of protective immunity.

Natural Infection and Vertical Transmission of Zika Virus in Sylvatic Mosquitoes Aedes albopictus and Haemagogus leucocelaenus from Rio de Janeiro, Brazil

Zika virus (ZIKV) was recently introduced into the Western Hemisphere, where it is suspected to be transmitted mainly by Aedes aegypti in urban environments. ZIKV represents a public health problem as it has been implicated in congenital microcephaly in South America since 2015. Reports of ZIKV transmission in forested areas of Africa raises the possibility of its dispersal to non-human-modified environments in South America, where it is now endemic. The current study aimed to detect arboviruses in mosquitoes collected from areas with low human interference in Rio de Janeiro, Brazil. Using a sensitive pan-flavivirus RT-PCR, designed to detect the NS5 region, pools of Ae. albopictus and Haemagogus leucocelaenus, were positive for both ZIKV and yellow fever (YFV). Virus RNA was detected in pools of adult males and females reared from field-collected eggs. Findings presented here suggest natural vertical transmission and infection of ZIKV in Hg. leucocelaenus and Ae.albopitcus in Brazil.

Vaccination reshapes the virus-specific T cell repertoire in unexposed adults

We examined how baseline CD4+ T cell repertoire and precursor states impact responses to pathogen infection in humans using primary immunization with yellow fever virus (YFV) vaccine. YFV-specific T cells in unexposed individuals were identified by peptide-MHC tetramer staining and tracked pre- and post-vaccination by tetramers and TCR sequencing. A substantial number of YFV-reactive T cells expressed memory phenotype markers and contained expanded clones in the absence of exposure to YFV. After vaccination, pre-existing YFV-specific T cell populations with low clonal diversity underwent limited expansion, but rare populations with a reservoir of unexpanded TCRs generated robust responses. These altered dynamics reorganized the immunodominance hierarchy and resulted in an overall increase in higher avidity T cells. Thus, instead of further increasing the representation of dominant clones, YFV vaccination recruits rare and more responsive T cells. Our findings illustrate the impact of vaccines in prioritizing T cell responses and reveal repertoire reorganization as a key component of effective vaccination.

Preparation and application of yellow fever virus NS1 protein-specific monoclonal antibodies

Yellow fever is an acute infectious disease that is common in Africa and South America and causes thousands of deaths annually. However, there are very few studies on yellow fever virus (YFV) antigen detection kits. As a detection target, the nonstructural protein 1 (NS1) has been successfully used in the early diagnosis of dengue virus (a member of the Flaviviridae family) infection. In this study, we used monoclonal antibody technology to prepare anti-YFV NS1 monoclonal antibodies (MAbs) and identified their immunological properties. Next, we used two mouse MAbs that can recognize different epitopes of YFV NS1 as capture and detection antibodies to establish a YFV NS1 antigen-capture enzyme-linked immunosorbent assay (ELISA). The antigen-capture ELISA displayed exclusive specificity to YFV without cross-reaction with other related members of the flavivirus family, including the dengue virus, West Nile virus, Japanese encephalitis virus. Additionally, the detection sensitivity towards the YFV culture supernatant was 103 TCID50/mL and the detection positivity rate was 95% compared with reverse transcription-polymerase chain reaction. In conclusion, this newly developed NS1 antigen-capture ELISA with high sensitivity and specificity could be used as an efficient method for the early diagnosis of YFV infection in animals or humans.

[Experience of application of IgY-technology for laboratory diagnostics of viral infections.]

INTRODUCTION

The well-known advantages of class Y antibodies (IgY) from egg yolks of immunized hens in comparison with class G antibodies (IgG) of laboratory animals traditionally used in laboratory diagnosis of infectious diseases determine the stable interest of researchers in using IgY for these purposes (IgY technology). Over the past 20 years, the obvious benefits of IgY technology have been demonstrated for a number of viral and bacterial infections. Goals and objectives. Construction of ELISA systems based on specific IgY for laboratory diagnosis of infections caused by tick-borne encephalitis virus, yellow fever virus, poliovirus.

MATERIAL AND METHODS

Obtaining yolk preparations of immunized chickens, obtaining highly purified IgY preparations (salting out, affinity chromatography), constructing ELISA systems for determining virus-specific antigens, testing the parameters of ELISA systems.

RESULTS AND DISCUSSION

For the first time in laboratory practice, ELISA systems based on the use of specific polyclonal IgY were designed for laboratory diagnosis of topical human viral infections caused by flaviviruses and enteroviruses: determination of antigens of tick-borne encephalitis virus, yellow fever virus, 3 types of poliovirus. It was experimentally shown that these ELISA systems have high sensitivity and specificity, which allows them to be used for the semiquantitative and quantitative determination of antigens of these viruses in various materials (infected cell cultures, vaccines, etc.).

CONCLUSION

The ELISA systems developed on the basis of specific IgY for determination of viral antigens can be effectively used for laboratory diagnosis of a number of viral infections, for the validation and control of vaccine preparations.

Molecular Determinants of Flavivirus Virion Assembly

Virion assembly is an important step in the life cycle of all viruses. For viruses of the Flavivirus genus, a group of enveloped positive-sense RNA viruses, the assembly step represents one of the least understood processes in the viral life cycle. While assembly is primarily driven by the viral structural proteins, recent studies suggest that several nonstructural proteins also play key roles in coordinating the assembly and packaging of the viral genome. This review focuses on describing recent advances in our understanding of flavivirus virion assembly, including the intermolecular interactions between the viral structural (capsid) and nonstructural proteins (NS2A and NS2B-NS3), host factors, as well as features of the viral genomic RNA required for efficient flavivirus virion assembly.

Post-Vaccination Yellow Fever Antiserum Reduces Zika Virus in Embryoid Bodies When Placental Cells are Present

Zika virus (ZIKV) is a flavivirus that originated in Africa but emerged in Latin America in 2015. In this region, other flaviviruses such as Dengue (DENV), West Nile, and Yellow Fever virus (YFV) also circulate, allowing for possible antigenic cross-reactivity to impact viral infections and immune responses. Studies have found antibody-mediated enhancement between DENV and ZIKV, but the impact of YFV antibodies on ZIKV infection has not been fully explored. ZIKV infections cause congenital syndromes, such as microcephaly, necessitating further research into ZIKV vertical transmission through the placental barrier. Recent advancements in biomedical engineering have generated co-culture methods that allow for the in vitro recapitulation of the maternal–fetal interface. This study utilized a transwell assay, which was a co-culture model utilizing human placental syncytiotrophoblasts, fetal umbilical cells, and a differentiating embryoid body, to replicate the maternal–fetal axis. To determine if cross-reactive YFV vaccine antibodies impacted the pathogenesis of ZIKV across the maternal–fetal axis, syncytiotrophoblasts were inoculated with ZIKV or ZIKV incubated with YFV vaccine antisera, and the viral load was measured 72 h post-inoculation. Here, we report that BeWo and HUVEC cells were permissive to ZIKV and that the impact of YFV post-vaccination antibodies on ZIKV replication was cell line-dependent. Embryoid bodies were also permissive to ZIKV, and the presence of YFV antibodies collected 4–14 months post-vaccination reduced ZIKV infection when placental cells were present. However, when directly infected with ZIKV, the embryoid bodies displayed significantly increased viral loads in the presence of YFV antiserum taken 30 days post-vaccination. The data show that each of the cell lines and EBs have a unique response to ZIKV complexed with post-vaccination serum, suggesting there may be cell-specific mechanisms that impact congenital ZIKV infections. Since ZIKV infections can cause severe congenital syndromes, it is crucial to understand any potential enhancement or protection offered from cross-reactive, post-vaccination antibodies.

Consumptive coagulopathy of severe yellow fever occurs independently of hepatocellular tropism and massive hepatic injury

Fatal cases of yellow fever are preceded by the development of hemorrhagic complications. While yellow fever virus is known to infect hepatocytes, the relationship between hepatocyte infection and the development of hemorrhage is currently undefined. Here, we identified high concentrations of D-dimer in the blood of yellow fever patients, indicative of a process that involves the activation and consumption of clotting factors. We then developed a mouse model in which only transplanted human hepatocytes could be infected at high levels. By examining clotting parameters in this model, we determined that hepatocyte infection alone is insufficient to cause the activation and consumption of coagulation factors observed in severe cases of yellow fever in humans and nonhuman primates.

Yellow fever (YF) is a mosquito-transmitted viral disease that causes tens of thousands of deaths each year despite the long-standing deployment of an effective vaccine. In its most severe form, YF manifests as a hemorrhagic fever that causes severe damage to visceral organs. Although coagulopathy is a defining feature of severe YF in humans, the mechanism by which it develops remains uncertain. Hepatocytes are a major target of yellow fever virus (YFV) infection, and the coagulopathy in severe YF has long been attributed to massive hepatocyte infection and destruction that results in a defect in clotting factor synthesis. However, when we analyzed blood from Brazilian patients with severe YF, we found high concentrations of plasma D-dimer, a fibrin split product, suggestive of a concurrent consumptive process. To define the relationship between coagulopathy and hepatocellular tropism, we compared infection and disease in Fah^−/−, Rag2^−/−, and Il2rɣ^−/− mice engrafted with human hepatocytes (hFRG mice) and rhesus macaques using a highly pathogenic African YFV strain. YFV infection of macaques and hFRG mice caused substantial hepatocyte infection, liver damage, and coagulopathy as defined by virological, clinical, and pathological criteria. However, only macaques developed a consumptive coagulopathy whereas YFV-infected hFRG mice did not. Thus, infection of cell types other than hepatocytes likely contributes to the consumptive coagulopathy associated with severe YF in primates and humans. These findings expand our understanding of viral hemorrhagic disease and associated coagulopathy and suggest directions for clinical management of severe YF cases.

Identification of Novel Yellow Fever Class II Epitopes in YF-17D Vaccinees

Yellow fever virus (YFV) is a mosquito-borne member of the genus flavivirus, including other important human-pathogenic viruses, such as dengue, Japanese encephalitis, and Zika. Herein, we report identifying 129 YFV Class II epitopes in donors vaccinated with the live attenuated YFV vaccine (YFV-17D). A total of 1156 peptides predicted to bind 17 different common HLA-DRB1 allelic variants were tested using IFNγ ELISPOT assays in vitro re-stimulated peripheral blood mononuclear cells from twenty-six vaccinees. Overall, we detected responses against 215 YFV epitopes. We found that the capsid and envelope proteins, as well as the non-structural (NS) proteins NS3 and NS5, were the most targeted proteins by CD4⁺ T cells from YF-VAX vaccinated donors. In addition, we designed and validated by flow cytometry a CD4⁺ mega pool (MP) composed of structural and non-structural epitopes in an independent cohort of vaccinated donors. Overall, this study provides a comprehensive prediction and validation of YFV epitopes in a cohort of YF-17D vaccinated individuals. With the design of a CD4 epitope MP, we further provide a useful tool to detect ex vivo responses of YFV-specific CD4 T cells in small sample volumes.

Retinoic Acid Inducible Gene I and Protein Kinase R, but Not Stress Granules, Mediate the Proinflammatory Response to Yellow Fever Virus

Yellow fever virus (YFV) is an RNA virus primarily targeting the liver. Severe YF cases are responsible for hemorrhagic fever, plausibly precipitated by excessive proinflammatory cytokine response. Pathogen recognition receptors (PRRs), such as the cytoplasmic retinoic acid inducible gene I (RIG-I)-like receptors (RLRs), and the viral RNA sensor protein kinase R (PKR), are known to initiate a proinflammatory response upon recognition of viral genomes. Here, we sought to reveal the main determinants responsible for the acute cytokine expression occurring in human hepatocytes following YFV infection. Using a RIG-I-defective human hepatoma cell line, we found that RIG-I largely contributes to cytokine secretion upon YFV infection. In infected RIG-I-proficient hepatoma cells, RIG-I was localized in stress granules. These granules are large aggregates of stalled translation preinitiation complexes known to concentrate RLRs and PKR and are so far recognized as hubs orchestrating RNA virus sensing. Stable knockdown of PKR in hepatoma cells revealed that PKR contributes to both stress granule formation and cytokine induction upon YFV infection. However, stress granule disruption did not affect the cytokine response to YFV infection, as assessed by small interfering RNA (siRNA)-knockdown-mediated inhibition of stress granule assembly. Finally, no viral RNA was detected in stress granules using a fluorescence in situ hybridization approach coupled with immunofluorescence. Our findings suggest that both RIG-I and PKR mediate proinflammatory cytokine induction in YFV-infected hepatocytes, in a stress granule-independent manner. Therefore, by showing the uncoupling of the cytokine response from the stress granule formation, our model challenges the current view in which stress granules are required for the mounting of the acute antiviral response.IMPORTANCE Yellow fever is a mosquito-borne acute hemorrhagic disease caused by yellow fever virus (YFV). The mechanisms responsible for its pathogenesis remain largely unknown, although increased inflammation has been linked to worsened outcome. YFV targets the liver, where it primarily infects hepatocytes. We found that two RNA-sensing proteins, RIG-I and PKR, participate in the induction of proinflammatory mediators in human hepatocytes infected with YFV. We show that YFV infection promotes the formation of cytoplasmic structures, termed stress granules, in a PKR- but not RIG-I-dependent manner. While stress granules were previously postulated to be essential platforms for immune activation, we found that they are not required for the production of proinflammatory mediators upon YFV infection. Collectively, our work uncovered molecular events triggered by the replication of YFV, which could prove instrumental in clarifying the pathogenesis of the disease, with possible repercussions for disease management.

Ensuring the Safety of Yellow Fever Vaccination in Travelers-The Experience at a Large U.S. Academic Medical Center in Colorado

Background: Yellow fever (YF) virus has the potential to cause fatal outcomes among at-risk individuals visiting endemic areas. Vaccinating travelers who are at risk is necessary to prevent virus-related life-threatening complications. We lack data on the clinical features of persons seeking YF vaccination. We aim to describe the characteristics of a cohort of persons receiving the YF vaccine before travel. Methods: A retrospective analysis of 964 travelers receiving the YF vaccine (Stamaril^®) from Oct 2016 to Jul 2019 was performed at the University of Colorado Hospital, U.S. Percentages, means, and standard deviations were calculated. A multivariate logistic regression model was built to evaluate the association between receiving YF vaccination less than 10 days before departure and visiting friends and relatives (VFR). Results: The average age of the subjects was 39 ± 18 years with a range of nine months to 83 years. Persons who were 60 years of age and older represented 17%. Women consisted of 52%, and most of the travelers were Caucasians (64%). Travelers reported traveling to Africa (57%) or South America (40%). The primary destinations for travelers overall were Kenya (19%), Uganda (11%), and Tanzania (11%) in Africa; and Peru (14%) and Brazil (13%) in South America. The most common reasons for travel included leisure (44%), VFR (18%), and mission trips (10%). Comorbidities included a history of hematologic disorders (4%), HIV infection (2%), and diabetes mellitus (3%). The average duration between vaccine administration and travel was 43 days. Those VFR were two times more likely to receive the YF vaccination <10 days before departure. Conclusions: Identifying the type of travel, itinerary, and underlying medical conditions allows providers to administer the YF vaccine to travelers safely. There is a need to identify strategies to improve the timing of YF vaccination among VFR travelers.