The researchers orally exposed laboratory colonies established from Salvador, Brazil to either the ancestral Oropouche strain BeAn 19991 or the contemporary outbreak strain 240023, using viral doses ranging from 10⁴ to 10⁶ PFU/mL. They then quantified viral replication in mosquito bodies, legs, and saliva, the standard steps for assessing vector competence: whether the virus infects the midgut, escapes into the hemocoel, and ultimately reaches the saliva in infectious form.

In Culex quinquefasciatus, the outbreak strain replicated less efficiently than the historical strain at low viral doses, although this difference disappeared at high infection doses. More decisively, regardless of strain or dose, vector competence was extremely low: only 0 to 1 percent of mosquitoes shed infectious Oropouche virus particles in their saliva after the extrinsic incubation period. These results indicate that Cx. quinquefasciatus is unlikely to sustain transmission of either viral strain under the conditions tested.

Aedes albopictus told a more nuanced story. The mosquitoes showed consistently higher body infection rates with the 240023 strain than with BeAn 19991, at both low and high doses, suggesting the reassortant virus infects this species more readily. Yet overall transmission potential remained limited: only 0 to 6.4 percent of leg or saliva samples were positive across strains and doses, meaning most infected mosquitoes never progressed to a transmissible state.

To evaluate the influence of mosquito genotype on infection outcomes, the team compared Ae. albopictus lines from Salvador City in Brazil and Houston in the United States. The higher infection rates of the 240023 strain held across both genotypes, but infectious saliva was detected only in the Salvador line, reaching up to 20 percent, and never in the Houston line, which stayed at 0 percent. This contrast suggests that local mosquito genetics shape whether higher infectivity translates into actual transmission potential.

Taken together, the findings indicate that the recent geographic expansion of Oropouche virus is unlikely to be driven by a vector shift from midges to these two mosquito species. The extremely low salivary shedding in Cx. quinquefasciatus and the limited transmission in Ae. albopictus, even with the contemporary strain, do not support the idea that mosquitoes are fueling the 2024 surge.

The authors do flag one forward-looking observation: the higher infectivity of the 240023 strain in Ae. albopictus across different mosquito lines may have implications if the virus further adapts to this species over time. That possibility remains speculative on the present evidence, and the study’s scope is confined to laboratory colonies and two mosquito species, so it cannot rule out roles for other vectors, other mosquito populations, or field conditions not reproduced in the lab.

As a laboratory vector-competence study with fixed viral doses and colony mosquitoes, the work measures potential rather than real-world transmission, and the observed differences in infection and salivary shedding carry the uncertainty inherent to small percentages and limited sample outcomes. Within those limits, the results argue against enhanced mosquito transmission as the explanation for Oropouche’s expansion, while leaving open the question of what actually drove the 2024 rise in cases beyond the Amazon region.

Subject of Research: Virology

Article Title: Vector competence of Aedes albopictus and Culex quinquefasciatus for Oropouche virus

Article References: Abu, A. E. I., Hua, X., Sattler, R., Becker, M. V., Forato, J., de Lima, S. T. S., Claro, I. M., Scachetti, G. C., Simões Mello, L. M., Sallum, M. A. M., Plante, K. S., Weaver, S. C., Proenca-Modena, J. L., de Souza, W. M., & Dickson, L. B. (2026). Vector competence of Aedes albopictus and Culex quinquefasciatus for Oropouche virus. PLOS Neglected Tropical Diseases, 20(10), e0014656. https://doi.org/10.1371/journal.pntd.0014656

Image Credits: AI Generated

DOI: 10.1371/journal.pntd.0014656

Keywords: Oropouche virus, Aedes albopictus, Culex quinquefasciatus, vector competence, arbovirus, reassortant strain, Brazil, mosquitoes, Culicoides paraensis, Oropouche fever, Vector, competence

The research team, led by Jwel Sharma and Ahmad Abdullah Mahdeen, applied a reverse-vaccinology strategy, an approach that begins with the pathogen’s genome and protein sequences rather than with whole, attenuated organisms. From the Oropouche virus proteome, the investigators focused on three key targets: the two surface glycoproteins, Gn and Gc, which mediate attachment to host cells, and the nucleocapsid protein, which encapsidates the viral RNA. These proteins are the primary molecules exposed to or recognized by the vertebrate immune system, making them logical sources of peptide fragments, or epitopes, that could be presented to immune cells.

The core of the design involved identifying short peptide sequences capable of being displayed by human major histocompatibility complex molecules. Cytotoxic T lymphocytes recognize peptides presented by MHC class I, while helper T cells respond to peptides presented by MHC class II; B cells, meanwhile, can bind exposed linear segments of proteins directly. The authors screened candidate epitopes from the Gn, Gc, and N proteins against a battery of predictive criteria, including predicted binding strength expressed as percentile rank, likelihood of provoking an antibody response as measured by antigenicity scores, and screening for potential allergenicity and toxicity. Only epitopes passing these filters were incorporated into the final construct, which was then linked together in an arrangement intended to maximize immune recognition.

A vaccine candidate is only useful if the resulting protein molecule is itself well behaved. The researchers therefore evaluated the biophysical properties of the assembled construct, and the results were encouraging. The protein received a negative GRAVY score of −0.432, a hydropathicity index indicating that the sequence is likely to be soluble in aqueous cellular environments rather than prone to aggregation. Stability assessments also suggested that the engineered protein would hold together under physiological conditions, an essential property for any subunit vaccine intended for production and purification at scale.

Structure prediction and validation formed the next stage of the analysis. Using computational modeling, the team generated a three-dimensional model of the vaccine protein and assessed its plausibility with standard tools. A Ramachandran plot analysis, which checks whether the backbone torsion angles of amino acids fall into geometrically allowed conformations, placed 91.86 percent of residues in the most favored regions, a strong indication that the model is structurally credible. The model also achieved a Z-score of −1.81, within the range expected for proteins of comparable size, further supporting the quality of the predicted fold. A well-validated structure matters because the shape of the vaccine protein determines how effectively immune receptors will engage it.

To gauge whether the construct could actually stimulate the innate immune system, the authors performed molecular docking against two human toll-like receptors, TLR-2 and TLR-4, which act as sentinels that recognize pathogen-associated molecular patterns and trigger inflammatory and adaptive responses. The docking simulations predicted favorable binding interactions for both receptors, with calculated binding energies of −1126.8 kilojoules per mole for the vaccine–TLR-2 complex and −1239.4 kilojoules per mole for the vaccine–TLR-4 complex. Large negative values indicate thermodynamically favorable associations, suggesting that the multiepitope construct would be capable of engaging these innate immune receptors if delivered in the body, which is precisely the engagement a subunit vaccine needs to launch a downstream adaptive response.

Docking alone captures a static snapshot, so the investigators extended their analysis to molecular dynamics simulations, which track how the protein complexes move and flex over time. Simulating both the free vaccine structure and the vaccine–TLR-4 complex, they examined indicators such as structural deviation, flexibility, and compactness across the trajectory. The results indicated that both systems remained dynamically stable and compact, meaning the vaccine protein neither unraveled nor displayed erratic behavior when bound to its receptor. Such stability during simulation is taken as evidence that the modeled interaction would persist under realistic physiological motion rather than existing only as a computational artifact.

Because the candidate is designed as a subunit vaccine, it must ultimately be produced by expressing the gene in a host organism, and the authors chose Escherichia coli K12 as the prospective manufacturing platform. To maximize yield, they performed codon optimization, rewriting the DNA sequence so that its codons match the translational preferences of the bacterial host. The optimized gene achieved a codon adaptation index of 1.0, the theoretical maximum, and a GC content within the optimal 30 to 70 percent window. These metrics indicate that the sequence would, in principle, be expressed efficiently, an important practical consideration for scaling up vaccine production.

Perhaps the most consequential predictions concern immunogenicity. Using an immune simulation platform, the team modeled how a vaccinated individual’s immune system would respond to the construct over time. The simulations predicted a robust response on both major arms of adaptive immunity: strong antibody-mediated protection, with elevated immunoglobulin G titers, and potent T cell-mediated responses, reflected in high levels of interferon-gamma, a cytokine characteristic of effective cellular immunity. The models also predicted the generation of memory cell populations, which are the basis of long-lasting protection and the ultimate goal of vaccination.

The authors are careful to frame these results as a promising starting point rather than a finished product. Every finding in the study is computational, from epitope selection to docking scores to immune simulation, and the entire pipeline rests on predictive algorithms that must ultimately be tested against biological reality. As the researchers note, experimental verification is required to confirm that the vaccine candidate is genuinely immunogenic and safe in laboratory and animal settings. Nevertheless, the work demonstrates how reverse vaccinology can compress the early stages of vaccine development into a purely digital exercise, rapidly triaging thousands of possible epitope combinations into a single prioritized construct. For a virus like Oropouche, which continues to emerge in regions with limited surveillance and no countermeasures, such computationally derived candidates provide a concrete, testable foundation on which wet-laboratory validation can now begin.

Subject of Research: Immunoinformatics design of a multiepitope subunit vaccine candidate against Oropouche virus

Article Title: An immunoinformatics-driven multiepitope subunit vaccine targeting Oropouche virus: Molecular docking, immune and dynamics simulation approaches

Article References: Sharma, J., & Mahdeen, A. A. (2026). An immunoinformatics-driven multiepitope subunit vaccine targeting Oropouche virus: Molecular docking, immune and dynamics simulation approaches. PLOS One, 21(10), e0360186. https://doi.org/10.1371/journal.pone.0360186

Image Credits: AI Generated

DOI: 10.1371/journal.pone.0360186

Keywords: Oropouche virus, reverse vaccinology, multiepitope vaccine, molecular docking, molecular dynamics simulation, TLR-2, TLR-4, MHC epitopes, immune simulation, codon optimization, subunit vaccine, PLOS One

The drug in question is favipiravir, a broad-spectrum nucleoside analogue that inhibits viral RNA-dependent RNA polymerases and is already approved for influenza treatment in several countries. The research team began by characterizing its activity against Oropouche virus in cultured Vero E6 cells, comparing it directly with ribavirin, another broad-spectrum antiviral. Favipiravir proved substantially more potent, with a mean half-maximal effective concentration of 28.4 micromolar compared with 115.7 micromolar for ribavirin. Untreated infected cells developed marked cytopathic effects, and ribavirin offered only limited protection, whereas favipiravir preserved cellular morphology in a dose-dependent fashion and robustly reduced infectious virus production. Time-of-addition experiments pinpointed the drug’s stage of action: treatment significantly reduced viral titers when administered at the time of infection or during early replication, but not at the maturation stage, consistent with favipiravir’s established mechanism of interfering with viral RNA synthesis during the post-entry replication phase.

The decisive test came in vivo. The researchers used a lethal Syrian hamster model, infecting animals intraperitoneally with 5.4 × 10⁵ plaque-forming units of the OROV TRVL 9760 strain. All vehicle-treated animals succumbed to infection by three days post-infection, without preceding overt clinical symptoms or weight loss—a fulminant course that underscores how aggressive lethal Oropouche disease can be in this model. In stark contrast, animals receiving high-dose favipiravir at 600 milligrams per kilogram per day, given orally twice daily beginning one hour before infection and continuing for six days, survived the entire 26-day observation period without any clinical signs and steadily gained weight. Lower doses of favipiravir and both tested doses of ribavirin conferred only partial protection, and notably, some animals in the ribavirin groups developed neurological symptoms, including ataxia, hindlimb weakness, and paralysis, after treatment ceased.

Virological measurements explained these divergent outcomes. Using plaque assays and reverse transcription quantitative PCR, the team tracked viral loads in serum, brain, liver, and spleen at multiple time points. Vehicle-treated animals carried high viral burdens in all tissues at two days post-infection. High-dose favipiravir, by contrast, suppressed viral replication so completely that no viral RNA or infectious virus was detectable in any tissue at any time point examined. The suboptimal regimens told a more cautionary story: although low-dose favipiravir and ribavirin reduced infectious virus in serum, liver, and spleen, infectious virus persisted in the brains of these animals at six and eight days post-infection, indicating incomplete clearance from the central nervous system that correlated with the delayed neurological disease observed after treatment withdrawal. The message is clear—insufficient antiviral pressure allows viral neuroinvasion, and neuroinvasion drives fatal disease.

Perhaps the most clinically encouraging finding concerns timing. In outbreak settings, patients rarely present before infection is already established, so a drug that works only as prophylaxis would be of limited value. The researchers therefore tested delayed treatment, initiating favipiravir at one hour before infection, at the time of infection, or at 6, 24, or 48 hours after infection. Strikingly, animals that began treatment as late as 24 hours post-infection were fully protected, with 100 percent survival and complete suppression of viral replication in systemic organs and the central nervous system. Even at 48 hours post-infection, when the therapeutic window was narrowing, favipiravir still conferred partial protection, with 50 percent survival and consistent weight gain among survivors. This therapeutic window, demonstrated in a model where untreated infection is uniformly lethal within days, substantially strengthens the case for favipiravir as a practical candidate for human Oropouche disease.

Beyond efficacy, the study’s second major contribution is mechanistic. To define the host responses associated with Oropouche virus pathogenesis and their modulation by antiviral therapy, the team performed tissue-resolved transcriptomic profiling—RNA sequencing of liver and brain collected at two days post-infection. Because the Syrian hamster genome remains less comprehensively annotated than the mouse genome, hamster genes were functionally annotated through their mouse orthologs. Principal component analysis revealed a clear transcriptional separation between infected and uninfected animals in both tissues, while favipiravir-treated animals clustered near uninfected controls, indicating that the infection-driven transcriptional upheaval was largely suppressed by the drug. This is, to the authors’ knowledge, the first in vivo, tissue-resolved transcriptomic framework of Oropouche virus infection.

The transcriptomic signatures in infected animals were distinctive and, in places, ominous. In the liver, where the virus replicated robustly, infection induced upregulation of genes involved in chemotaxis, cytokine signaling, myeloid cell differentiation, and interferon responses, alongside downregulation of metabolic pathways governing energy production and fatty acid metabolism. In the brain, antiviral and inflammatory programs were induced even more strongly, accompanied by pathways promoting immune cell recruitment. Quantitative PCR validation of selected interferon-stimulated genes—Cxcl10, Rsad2, and Isg15—confirmed strong induction at two days post-infection in both tissues of untreated animals, which was suppressed by both favipiravir and ribavirin at that early stage. At later time points, however, Rsad2 and Isg15 expression tended to remain elevated in ribavirin-treated animals, correlating with their persistent brain viral loads, whereas expression stayed low in favipiravir-treated animals. Interestingly, the canonical inflammatory cytokines Il6, Il10, and Tnf-alpha showed no significant changes at two days post-infection and did not track with viral replication, suggesting they are unlikely to be major drivers of Oropouche disease in this model.

The metabolic findings deserve particular attention. Although liver involvement is not a prominent feature of typical Oropouche fever, recent fatal human infections have been associated with markedly elevated aminotransferase levels and liver injury biomarkers, and independent studies have demonstrated hepatic infection and inflammatory responses in human liver organoids and an experimental mouse model. The simultaneous enrichment of pathways associated with positive regulation of innate immune responses and negative regulation of defense responses in high-burden animals suggests a complex, potentially dysregulated host response, in which sustained antiviral and inflammatory signaling coexists with regulatory mechanisms that constrain excessive immune activation. When viral replication remains high, such regulation appears insufficient. The concurrent downregulation of energetic, lipid metabolic, and mitochondrial pathways in the liver implies that cellular stress during high-burden infection may contribute to tissue dysfunction and injury, meaning that Oropouche pathogenesis likely reflects not only direct viral replication but also the interplay between persistent viral burden, dysregulated immunity, and disrupted metabolic homeostasis.

The authors are candid about the study’s limitations. The reliance on mouse orthologs for gene annotation means hamster-specific transcriptional features and genes lacking confident mouse orthologs may have been underrepresented. Additionally, because all vehicle-treated animals reached the humane endpoint before six days post-infection, direct comparisons of gene expression between untreated and treated animals at later time points were impossible, leaving some uncertainty about whether the later profiles reflect favipiravir’s effects or the absence of ongoing infection. These caveats notwithstanding, the study extends earlier work by Rodrigues and colleagues, who established the Syrian hamster as a relevant model of Oropouche pathogenesis, by integrating tissue-resolved transcriptomics with therapeutic intervention in a single experimental framework.

Translational considerations will shape what happens next. Favipiravir offers genuine advantages over other polymerase-targeting candidates such as 4′-fluorouridine, including oral bioavailability and prior clinical use against multiple viral diseases, and its demonstrated efficacy with delayed initiation enhances its relevance for outbreak settings where early diagnosis is difficult. Yet the drug carries known safety liabilities: teratogenic and embryotoxic effects, and an association with elevated serum uric acid and hyperuricemia. These concerns are especially pertinent for Oropouche virus, given the growing recognition of congenital and pregnancy-associated disease. The authors emphasize that further studies addressing pharmacokinetics, optimal dosing, treatment duration, and safety in relevant populations will be required before clinical application. Even so, the findings provide strong preclinical evidence that timely, potent antiviral intervention can prevent central nervous system invasion, suppress pathogenic inflammatory and metabolic programs, and avert lethal Oropouche disease—transforming the outlook for a pathogen that, until now, medicine could only watch.

Subject of Research: Favipiravir efficacy and host transcriptomic responses in lethal Oropouche virus infection

Article Title: Integrated in vivo and transcriptomic analyses of lethal Oropouche virus infection reveal suppression of pathogenic host responses by antiviral therapy

Article References: Sousa Moraes, C., Gonzalez, G., Sato, A., Miki, S., Inoue, A., Tabata, K., Kranrod, J. W., Kabamba, C. F., Ohnuma, A., Matsuno, K., Harada, R., Saito, S., Akimoto, N., Sasaki, M., Orba, Y., Hall, W. W., Sawa, H., & Itakura, Y. (2026). Integrated in vivo and transcriptomic analyses of lethal Oropouche virus infection reveal suppression of pathogenic host responses by antiviral therapy. PLOS Pathogens, 22(10), e1014647. https://doi.org/10.1371/journal.ppat.1014647

Image Credits: AI Generated

DOI: 10.1371/journal.ppat.1014647

Keywords: Oropouche virus, favipiravir, antiviral therapy, arbovirus, neuroinvasion, Syrian hamster model, transcriptomics, interferon response, ribavirin, PLOS Pathogens, emerging infectious disease, RNA virus

The 2024 Oropouche epidemic attracted worldwide attention for several reasons. The virus expanded geographically into regions where it had never before been detected, the number of reported cases rose substantially, and the first globally documented Oropouche-associated fatalities occurred. In parallel, several studies provided evidence of vertical transmission and raised concerns about the potential impact of maternal infection on fetal development and survival. Notably, pregnancy losses among Oropouche-infected women were reported in Brazil as far back as the 1980s, predating the current wave of warnings by decades. What has been missing, the authors argue, is a systematic strategy to move from suggestive case reports to robust causal inference.

The evidence that currently fuels concern comes largely from individual case reports. Researchers have described Oropouche virus RNA or antigens in placental and fetal tissues, and anti-Oropouche IgM antibodies have been detected in microcephalic newborns. These findings support the plausibility of vertical transmission, but they fall short of demonstrating that the virus actively replicates in fetal tissue, which would substantially strengthen the biological case for fetal injury. The authors emphasize that viral infections can damage tissue indirectly, for example through immune imbalance, yet direct evidence of replication remains the gold standard for establishing pathogenicity.

To close that gap, the framework proposes molecular techniques capable of detecting positive-sense viral RNA, the form of viral genetic material produced during active replication. Strand-specific reverse transcription PCR assays, designed to target complementary RNA and viral messenger RNA rather than the negative-sense genomic RNA packaged in virions, could provide evidence consistent with active Oropouche replication in placental or fetal samples. Complementing this, signal-amplified in situ hybridization methods such as RNAscope coupled with confocal microscopy, or PrimeFlow RNA assays combined with flow cytometry, could localize viral replication within tissues and identify which specific cell populations harbor replicating virus. Histopathological and immunohistochemical analyses using antibodies against non-structural viral proteins expressed only during replication could further link viral activity to tissue damage.

Animal models form the second pillar of the proposed framework. Previous studies have demonstrated vertical transmission of Oropouche virus and fetal impairment in mice, including infection with an ancestral viral strain. However, these results were consistently observed only in animals with impaired type I interferon signaling, suggesting that vertical transmission in this setting is context-dependent and limiting extrapolation to natural human infection. The authors point instead to golden hamsters, which have been proposed as a model for Oropouche pathogenesis and may represent a promising in vivo system for investigating fetal effects without genetic or immunological manipulation. They also suggest examining SJL mice, a strain likely more susceptible to viral infection, which gained attention during the Zika epidemic for their permissiveness to viral teratogenicity studies.

Non-human primates offer a third experimental avenue. These animals have been used successfully to investigate virus-associated fetal outcomes for other pathogens, including Zika virus and congenital cytomegalovirus, and could prove suitable for Oropouche studies. Intrauterine infection of immunocompetent animals would provide a proof-of-concept approach to evaluate the direct fetal consequences of Oropouche infection, a strategy previously applied to teratogenic viruses including Zika and Cache Valley virus, an orthobunyavirus in the same genus as Oropouche. Intracranial inoculation in neonatal animal models and embryonated chicken eggs could also be employed, as these approaches were previously used to characterize the teratogenic potential of other orthobunyaviruses such as Aino, Akabane and Cache Valley viruses.

The authors stress that any such experiments should use both historical and recently circulating Oropouche strains to detect possible differences in fetal effects between lineages, and should employ minimally passaged viruses to avoid adaptive mutations that would distort the wild-type phenotype. Testing at different stages of gestation would further clarify whether particular windows of pregnancy carry heightened risk, a question of direct clinical relevance for counseling pregnant women in endemic areas.

Viral reverse genetics represents a particularly promising tool within the framework, especially for probing the role of the type I interferon response. Because in vivo studies have shown possible vertical transmission only in animals lacking an adequate interferon response, and because interferon antagonism is an established pathogenicity mechanism of orthobunyaviruses, including the teratogenic Schmallenberg virus, the Oropouche NSs gene, which encodes a known type I interferon antagonist, becomes a prime suspect. Reverse genetics could be used to manipulate this gene, identify the residues and domains involved in interferon antagonism, and test whether these functions contribute to adverse fetal outcomes. Such findings could also inform genomic surveillance by identifying molecular signatures in circulating strains that are potentially associated with fetal injury.

On the epidemiological side, the framework calls for well-designed case-control studies, modeled on those conducted during the Zika epidemic, to estimate the likelihood of miscarriage or developmental abnormalities among Oropouche-infected pregnant women and to identify other risk factors, such as the most vulnerable gestational period. Prospective postnatal follow-up of exposed newborns would be timely for investigating potential later neurodevelopmental effects, including those occurring in the absence of microcephaly, a pattern documented in congenital Zika infection. Close immunological monitoring of infected pregnant women, focusing on type I and type III interferons and interferon-stimulated genes such as IFIT1, could reveal host factors that modulate vertical transmission. The authors acknowledge real obstacles: infections outside outbreak periods are rarely reported, outbreaks have historically been concentrated in remote areas, and the recent decline in transmission across several affected regions may limit participant recruitment. Multicenter studies and prospective surveillance strategies, they argue, are the practical answer.

The overarching message is one of scientific caution paired with methodological ambition. Despite recent advances in understanding Oropouche virus, its potential for vertical transmission and adverse fetal outcomes remains unproven, and establishing causality will require the deliberate integration of molecular virology, animal modeling, reverse genetics and epidemiology. The authors contend that such efforts are essential not only for resolving a pressing scientific uncertainty but also for improving surveillance strategies, guiding clinical management of pregnancies in endemic regions, and mitigating whatever impact Oropouche infection may ultimately prove to have on fetal health. As the virus continues to expand its footprint in the Americas, the framework offers a roadmap for converting alarming anecdotes into actionable evidence.

Subject of Research: Assessment of potential Oropouche virus-associated adverse fetal outcomes through experimental and epidemiological approaches

Article Title: A framework for assessing potential Oropouche virus-associated adverse fetal outcomes

Article References: Tanaka, L. F., Dutra, N. B. D. M., Lopes, T. R. R., Carmo, R. F., Oliveira-Filho, E. F. D., Gil, L. H. V. G., & Silva Júnior, J. V. J. (2026). A framework for assessing potential Oropouche virus-associated adverse fetal outcomes. BMC Infectious Diseases, 26(1), Article 1739. https://doi.org/10.1186/s12879-026-14420-1

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14420-1

Keywords: Oropouche virus, vertical transmission, adverse fetal outcomes, microcephaly, pregnancy, orthobunyavirus, type I interferon, reverse genetics, animal models, case-control studies, placental infection, neurodevelopment