Search Results (329)

Understanding host cell response to viral infection could lead to the identification of molecular targets that can be used for the development of diagnostics and therapeutics. In this study, we investigated human dendritic cell (DC) response to infections with Vaccinia (VAC) virus, a highly immunogenic poxvirus, and Venezuelan Equine Encephalitis (VEE) virus, a single-stranded positive-strand RNA alphavirus, using human gene expression microarrays. Comparative changes in DC mRNA expression resulting from infection by the two viruses at 1, 8, and 12 h post-infection (hpi) revealed distinct temporal dynamics. VAC infection triggered early and robust activation of pathways related to chromatin organization, DNA damage, and antigen presentation, while VEE infection exhibited delayed activation of immune signaling pathways, including interferon signaling and cytokine production. Shared pathways, such as interferon signaling and inflammasome activation, highlight universal antiviral responses and potential therapeutic targets. These findings provide a molecular framework affected by VAC and VEE that need to be validated with additional experiments, such as functional assays or in vivo studies. The specific up- or downregulation of these pathways at different time points likely dictates the overall outcome of the viral infection and could potentially lead to better understanding of the temporal regulatory dynamics of virus host response. Full article

Host receptors can detect traces of non-self-pathogenic RNAs within a sea of cellular mRNA molecules. In host cells, mRNA cap methylation occurs in the nucleus, generating Cap1 and Cap2 structures (m⁷GpppNm and m⁷GpppNmNm, respectively). By contrast, alphavirus genomes carry a Cap0 structure (m⁷GpppN), which lacks 2′-O-methylation. This difference in the structure of the host and viral caps serves as a molecular signature that enables discrimination between self and non-self RNAs. Several host immune sensors, such as RIG-I and IFIT1, recognize the alphavirus Cap0 structure and trigger an antiviral response to restrict viral replication. It has been proposed that IFIT1 sequesters aberrant RNAs, preventing their translation by host ribosomes and blocking viral protein synthesis. However, alphaviruses have evolved molecular strategies to circumvent IFIT1-mediated restriction and facilitate infection in mammalian cells. One such strategy involves the folding of a 5′ RNA structure that hides the cap from host immune sensors. This highlights the dynamic interplay between viral evasion tactics and host immune defenses. This review will discuss how specific modifications at the 5′ end of alphavirus RNA modulate host defenses and how a deeper understanding of the virus–host interaction may inform the development of novel vaccine strategies. Full article

The re-emergence of alphaviruses (family Togaviridae), such as chikungunya virus, poses significant public health risks, with direct impact on quality of life and work productivity. There are no approved antiviral drugs for the treatment of infections with alphaviruses. Several alphaviruses are classified as risk group 3 agents which require handling in high-containment laboratories. To facilitate antiviral screening efforts against alphaviruses, we established a high-throughput antiviral screening assay using reporter Sindbis virus [SINV-GFP; expresses the green fluorescent protein] as a surrogate model for more pathogenic alphaviruses. The assay has strong reproducibility and was validated by reference small-molecule antivirals with various mechanisms of action. The use of high-content imaging as a readout, as demonstrated here, allows for high-throughput antiviral screening and provides a tool for early-stage antiviral discovery against emerging alphavirus threats at a lower biosafety level. Full article

Venezuelan equine encephalitis virus (VEEV) is a mosquito-borne pathogen causing low mortality but high morbidity in humans, with 4–14% cases exhibiting neurological complications. While the cyclic GMP-AMP synthase–stimulator of interferon genes (cGAS–STING) pathway is canonically associated with double-stranded DNA (dsDNA) detection, it has been shown to respond to RNA viruses and subsequently limit viral pathogenesis. Several viruses antagonize this signaling cascade, underscoring the importance that cGAS–STING plays in host immunity. Previous studies regarding single-stranded RNA viruses revealed that cGAS–STING limits viral replication in Old World alphavirus chikungunya virus infections, but little is known about New World alphaviruses such as VEEV. Here, we investigate the impact that STING activation has on VEEV infection as a potential prophylactic and therapeutic intervention. VEEV infection alone did not induce STING phosphorylation at Ser366, but interferon-stimulated genes (ISGs) were upregulated during the late phase of infection. Loss of STING through siRNA showed a partial dependency on STING for ISG transcription, suggesting that STING activation may occur through a noncanonical process. Priming of the STING pathway prior to infection was found to be critical in limiting viral replication; however, targeting STING activation post-infection abrogated the antiviral effects that dsDNA had on VEEV. VEEV suppressed STING phosphorylation in a multiplicity of infection (MOI)-dependent manner with the most robust pSTING (Ser366) inhibition observed at an MOI of 10. Collectively, our results suggest that VEEV antagonizes canonical STING activation. Full article

Chronic arthritis following arthritogenic alphavirus infections presents symptoms resembling autoimmune rheumatic diseases, raising questions about the underlying mechanisms, including molecular mimicry and autoantibody production. This systematic review evaluated evidence supporting molecular mimicry and the potential role of autoantibodies as predictive biomarkers in alphavirus-induced chronic arthritis. A comprehensive search of PubMed, Scopus and Web of Science was conducted following PRISMA 2020 guidelines and PECO framework. Thirteen studies met the inclusion criteria: four computational studies assessing peptide homology between viral and human proteins, and nine clinical studies evaluating autoantibodies in chronic post-alphavirus arthritis. Computational analyses identified conserved alphavirus peptides with sequence and structural similarity to human proteins implicated in autoimmunity, supporting the hypothesis of molecular mimicry. However, most lacked experimental validation. Clinical studies showed variable detection of autoantibodies, rheumatoid factors, anti-cyclic citrullinated peptide, and antinuclear antibodies in chronic patients, though seropositivity rates were inconsistent and generally low. Only one study reported a significant association between autoantibody levels and disease chronicity. The findings suggest a potential autoimmune component in post-alphavirus arthritis driven by molecular mimicry, though current evidence remains inconclusive due to methodological heterogeneity and limited validation. Autoantibodies may contribute to pathogenesis but are not reliable predictors of chronicity. Future longitudinal studies with standardized assays and validation of computational findings in human models are needed. Full article

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus prevalent in more than 110 countries and regions, including Africa, Asia, the Americas, and Europe. It can cause acute fever, rash, and severe joint pain, and some patients may develop chronic arthritis, which significantly impairs quality of life. CHIKV infection can occasionally be fatal, with neurologic disease a particularly severe manifestation. Following its resurgence in 2005, CHIKV has emerged as a major threat to global public health. This review summarizes diagnostic techniques, advances in vaccine development, and the latest drug interventions for CHIKV. We also present an overview of the epidemiology, structure, and invasion mechanisms of epidemic hotspots in 2024–2025 and propose evidence-based strategies for effective prevention and control of CHIKV infection. Full article

Background: Madariaga virus (MADV), formerly known as the South American variant of Eastern Equine Encephalitis virus (EEEV), is an alphavirus that belongs to the Togaviridae family and has been periodically infecting equids in Venezuela since its first identification in 1975. This study reports the isolation and molecular characterization of MADV isolated from a horse in December 2024 in the context of MADV cases reported in Venezuela. Methods: Antibodies to the rabies virus were detected by indirect immunofluorescence, and to the Equine Infectious Anemia virus (EIAV) by passive immunodiffusion. MADV RNA was detected by qRT-PCR. The sequence of the complete viral genome was obtained by next-generation sequencing. Results: The sequence of this virus was highly similar to that of the only human case of MADV reported in the country in 2016, as well as to a sequence of a virus isolated from a horse in Colombia in 2002. The horse was found to be co-infected with EIAV. Conclusions: The continuous circulation of MADV in Venezuela warrants reinforcing the preventive measures against these alphaviruses, which ignore borders, and may cause important animal and human health concerns. Full article

One highly consequential presentation of Venezuelan equine encephalitis virus (VEEV) infection is encephalitis. Here we considered anti-inflammatory interventions to limit the effects of this using a BALB/c subcutaneously challenged mouse model of disease. This disease model nearly ubiquitously presents with severe encephalitis, where viral neuroinvasion correlates with much of the outward clinical signs of disease. A selection of already licenced, commonly used anti-inflammatory drugs were tested in mice developing encephalitis (starting treatment at $24 \mathrm{h}$ post challenge). Drug regimens were used that had previously been shown to have pharmacodynamic effects in mice for unrelated conditions. None of the treatment regimens tested reduced brain inflammation. A single anti-inflammatory drug (dexamethasone) was further tested utilising ascending doses in an effort to provide an effective anti-inflammatory regimen. Higher doses of dexamethasone ($20$ and $50 \mathrm{m}\mathrm{g}/\mathrm{k}\mathrm{g}$) reduced inflammatory markers in the brain and lowered weight loss and clinical signs early on during infection. However, the $50 \mathrm{m}\mathrm{g}/\mathrm{k}\mathrm{g}$ regimen also caused the disease to become more severe at later time points when compared to controls. When combined with the antiviral drug molnupiravir, the negative effects of the dexamethasone treatment ($20$ and $50 \mathrm{m}\mathrm{g}/\mathrm{k}\mathrm{g}$) were absent, and the positive disease severity-reducing effects remained. When combined with a specific VEEV monoclonal antibody (1A3B7), dexamethasone significantly reduced the antibody’s protective effects. These data present currently unique insights into how anti-inflammatory approaches might benefit patients with VEEV disease and where caution might be advised. Full article

Alphaviruses have historically been viewed as acute, self-limiting pathogens. However, growing evidence shows that viral RNA and antigens can persist in vertebrate hosts long after the resolution of acute infection, a phenomenon known as viral persistence. Viral persistence reflects a dynamic interplay between viral replication—including shifts from lytic to non-lytic infection—and host defenses, which together establish cellular and tissue niches that enable evasion of immune-mediated clearance. Within vertebrate hosts, alphaviruses exhibit broad tissue tropism, infecting diverse cell types that may differentially support long-term persistence. Emerging evidence suggests that viral persistence arises through three interconnected processes: (i) selective infection of specific cellular niches, (ii) reprogramming of host cellular pathways, and (iii) modulation of immune responses. Yet, the extent to which viral or host determinants shape this balance, and how persistence contributes to chronic disease, remains unresolved. Here, we synthesize current in vitro and in vivo evidence of alphavirus persistence in vertebrate hosts and discuss potential mechanisms by which alphaviruses establish and maintain persistent infection beyond the acute phase. We further underscore critical gaps in current knowledge and outline future research avenues essential for elucidating the mechanisms underlying alphavirus pathogenesis. Full article

Alphaviruses pose a growing global health threat, with Chikungunya virus (CHIKV) epidemics ongoing. Although several CHIKV vaccine candidates have progressed to late-stage clinical evaluation, none have yet achieved licensure or widespread availability. The CHIKV nonstructural proteins nsP2 and nsP4 encode essential enzymatic activities that represent key targets for antiviral development, yet the biochemical basis of nsP4 RNA-dependent RNA polymerase (RdRp) activity remains poorly understood. Here, we identify a minimal, functional precursor form of nsP4 derived from the nsP3–nsP4 polyprotein (P34) that is active in a cell-based RNA replicon system. Using synthetic, capped mRNAs, we show that cleavage of P34 by the nsP2 protease is required for robust reporter expression, and that a truncated form retaining only the C-terminal 50 residues of nsP3 (CT50-P34) supports near-wild-type replication. Unexpectedly, ubiquitin–nsP4 fusions failed to substitute for P34, likely reflecting the transient expression supported by our RNA-based system. We propose that precursor forms of nsP4 interact with the nsP1 dodecamer at the site of genome replication, where cleavage activates the RdRp and localization within the nsP1 dodecamer maintains nsP4 in its active conformation. Dissociation from the nsP1 dodecamer triggers a conformational switch to an inactive state. Together, these findings establish a tractable framework for interrogation of the assembly, activation, and regulation of the alphavirus polymerase. Full article

Background/Objectives: To this day, rabies remains a significant global threat. This threat remains even with the availability of vaccines for humans, wildlife, and domestic animals, which are used as part of a series of interventions to attempt to control the infection and disease. The number of annual human deaths from rabies globally remains significant, with infections being mainly caused by domestic dogs. Although a number of vaccines exist for domestic animals, most contain inactivated rabies virus with adjuvants. Methods: To investigate alternatives to conventional rabies vaccines for dogs and cats, we developed a novel, non-adjuvanted, low-volume (0.5 mL) vaccine, based on the Venezuelan equine encephalitis virus (VEEV) TC-83-derived RNA particle (RP) expressing the rabies glycoprotein (G). This novel vaccine combines the safety profile of a non-adjuvanted vaccine while inducing consistently high efficacy and an extended duration of immunity similar to that shown by adjuvanted vaccines. Results: In multiple studies, we demonstrated that young kittens and puppies can be safely vaccinated without serious adverse effects. In graded dose experiments with cats and dogs, the RNA particle vaccine induced neutralizing levels of antibodies. Additionally, in vaccination/challenge studies, 100% protection from virulent rabies was demonstrated in excess of three years post-vaccination from a single dose at 12 weeks of age in both dogs and cats. The safety of the RP-Rabies vaccine in dogs and cats as young as twelve weeks of age was demonstrated in field safety studies using two vaccine serials formulated at a field dose. Conclusions: Data from these studies suggest that the RP-Rabies vaccine offers an excellent alternative to current vaccines combining the safety of a non-adjuvanted vaccine in a low-volume, single dose with the induction of an extended duration of immunity of at least three years in both dogs and cats. Full article

Alphavirus chikungunya (CHIKV) is an arthropod-borne alphavirus of the Togaviridae family, transmitted primarily by Aedes aegypti and Ae. albopictus mosquitoes. CHIKV infection often results in debilitating manifestations that compromise quality of life and generate significant socioeconomic impacts. Recurrent epidemics in tropical and subtropical regions underscore the urgent need to better understand the host immune responses and their contribution to disease outcome. CHIKV establishes infection by overcoming the host’s initial immunological barriers. Innate immune cells, including fibroblasts, dendritic cells, macrophages, monocytes, neutrophils and natural killer (NK) cells, are among the first to respond to infection, ensuring a rapid antiviral defense and supporting the development of adaptive immune responses. However, excessive release of inflammatory mediators and prolonged infiltration of innate cells into joint tissues contribute to disease chronicity and the persistence of arthralgia. In this review, we provide a comprehensive synthesis of current evidence on innate cells that serve as targets for CHIKV infection, highlighting mechanisms that promote effective antiviral defense as well as those responsible for pathological inflammation and chronic disease and identifying key gaps that remain to be addressed. Full article

Omsk hemorrhagic fever is an acute zoonotic disease caused by Omsk hemorrhagic fever virus, a member of the genus Flavivirus (family Flaviviridae), with a reported case-fatality rate of approximately 3%. Historically confined to southwestern Siberia, ecological changes raise concerns about possible spread to non-endemic regions. Although no Omsk hemorrhagic fever cases have been reported in the Republic of Korea, the risk of accidental importation highlights the importance of establishing a reliable diagnostic protocol. We established and validated an institutionally developed diagnostic protocol employing real-time reverse transcription polymerase chain reaction targeting the NS2A and C genes of Omsk hemorrhagic fever virus. Primers and probes were designed from all available genomes to ensure broad strain coverage. Human ribonuclease P was used as an internal control to verify nucleic acid extraction and amplification. Using synthetic deoxyribonucleic acid fragments and in vitro-transcribed ribonucleic acid, assay performance was optimized, and analytical sensitivity was determined using probit analysis. The limits of detection were 74.50 copies/µL (threshold cycle 32.99) for NS2A and 70.41 copies/µL (threshold cycle 35.38) for C. Specificity testing using representative flaviviruses (West Nile virus, Yellow fever virus, Zika virus, St. Louis encephalitis virus, and Tick-borne encephalitis virus) and an alphavirus (Venezuelan equine encephalitis virus) demonstrated no cross-reactivity. The assay demonstrated high sensitivity, specificity, and reproducibility, supporting its potential application in national and international Omsk hemorrhagic fever virus surveillance systems. Full article