Search Results (170)

Alphaviruses are mosquito-borne viruses that can infect the central nervous system (CNS) and cause encephalomyelitis, which is a rare but dangerous complication from infection. In mice, this can be studied in a model of infection with Sindbis virus (SINV), which infects neurons and causes neurological disease. Due to the non-renewable nature of neurons, the immune response in the CNS is specialized to prevent neuronal damage or death, even if they are infected. Therefore, insights into the nuances of antiviral immunity in the CNS provide a better understanding of disease pathogenesis and mechanisms of recovery. Type I interferons (IFNs) are critically important for survival; they are an innate antiviral defense mechanism that consists mainly of IFNα and IFNβ. Although both use the same receptor, type-specific differences between IFNα and IFNβ have been described in other contexts. To this end, Ifnb^−/− mice were used to elucidate the role of IFNβ in recovery from alphavirus encephalomyelitis. IFNβ-deficient mice have intact IFNα expression and downstream signaling, but symptomatic disease occurs earlier and is more severe. This is accompanied by increased virus replication in the early stages of infection. Microgliosis is reduced in Ifnb^−/− mice compared to wildtype, but inflammatory cytokine/chemokine levels are higher and associated with alterations in monocyte and NK cell recruitment into the CNS. Ifnb^−/− mice have no deficiencies in the expression of factors known to be required for viral clearance. Therefore, IFNβ modulates the early stages of the immune response and facilitates restriction of virus replication, contributing to delayed disease onset. 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

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

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

Alphaviruses are transmitted by Aedes mosquitoes and cause large-scale epidemics worldwide. Chikungunya virus (CHIKV) infection can cause febrile seizures known as chikungunya fever (CHIKF), which ultimately leads to severe joint pain and myalgia. While a vaccine has recently been introduced against CHIKV, at present, no anti-viral drug is available. CHIKV, like other alphaviruses, has a short 6K protein capable of forming an ion channel. Blocking this ion channel with drugs can therefore serve as a potential way to curtail CHIKV infection. To that end, we screened a repurposed drug library using three bacteria-based channel assays to detect blockers against 6K viroporin, yielding several hits. Interestingly, several of the blockers were able to inhibit the 6K protein from the similar Eastern equine encephalitis virus (EEEV), while others were not, pointing to structural specificity which may be explained by modeling studies. In conclusion, our study provides a starting point for developing a new route to potentially inhibit CHIKV. Full article

Sindbis virus (SINV), a prototype of the Alphavirus genus (family Togaviridae), is a globally distributed arbovirus causing febrile rash and debilitating arthritis in humans. Viral structural proteins—capsid (C), E1, and E2—are fundamental to the virion’s architecture, mediating all stages from assembly to host cell entry and pathogenesis, thus representing critical targets for study. This review consolidates the historical and current understanding of SINV structural biology, tracing progress from early microscopy to recent high-resolution cryo-electron microscopy (cryo-EM) and X-ray crystallography. We detail the virion’s precise T = 4 icosahedral architecture, composed of a nucleocapsid core and an outer glycoprotein shell. Key functional roles tied to protein structure are examined: the capsid’s dual capacity as a serine protease and an RNA-packaging scaffold that interacts with the E2 cytoplasmic tail; the E1 glycoprotein’s function as a class II fusion protein driving membrane fusion; and the E2 glycoprotein’s primary role in receptor binding, which dictates cellular tropism and serves as the main antigenic target. Furthermore, we connect these molecular structures to viral evolution and disease, analyzing how genetic variation among SINV genotypes, particularly in the E2 gene, influences host adaptation, immune evasion, and the clinical expression of arthritogenic and neurovirulent disease. In conclusion, the wealth of structural data on SINV offers a powerful paradigm for understanding alphavirus biology. However, critical gaps persist, including the high-resolution visualization of dynamic conformational states during viral entry and the specific molecular determinants of chronic disease. Addressing these challenges through integrative structural and functional studies is paramount. Such knowledge will be indispensable for the rational design of next-generation antiviral therapies and broadly protective vaccines against the ongoing threat posed by SINV and related pathogenic alphaviruses. Full article

Alphaviruses engage a diverse array of attachment factors and receptors during viral entry, resulting in a broad host range and disease spectrum, and thus presenting them as a major global public health concern. The development of effective antivirals against these arboviruses relies on a comprehensive understanding of the molecular interplay between these viruses and host cell factors, as well as the wide range of immune responses that ensue following viral infection. In this review, we present the current understanding of the complex landscape of alphavirus interaction with attachment factors and entry receptors, some of which are characterized structurally, while others are characterized biochemically. Additionally, we provide an overview of the molecular bases of epitope recognition by neutralizing and non-neutralizing antibodies against alphaviruses, and how icosahedral symmetry influences these interactions, such as occupancy and neutralization potency. We further discuss the structural bases of epitope recognition of a few pan-alphavirus antibodies, their potential therapeutic implications, and offer future perspectives on the development of effective therapeutics against clinically relevant alphaviruses. Full article

Self-amplifying RNA-based (saRNA) technology represents the last frontier in using synthetic RNA in vaccinology. Typically, saRNA consists of positive-strand RNA molecules of viral origin (almost exclusively from alphaviruses) where the sequences of structural proteins are replaced with the open reading frame coding the antigen of interest. For in vivo delivery, they are complexed with lipid nanoparticles (LNPs), just like current COVID-19 vaccines based on synthetic messenger RNA (mRNA). Given their ability to amplify themselves inside the cell, optimal intracellular levels of the immunogenic antigen can be achieved by delivering lower amounts of saRNA molecules compared to mRNA-based vaccines. However, the excessive intracellular accumulation of saRNA may represent a relevant drawback since, as already described in alphavirus-infected cells, the recipient cell may react by incorporating excessive RNA molecules into extracellular vesicles (EVs). These EVs can shed and enter neighboring as well as distant cells, where the EV-associated saRNA can start a new replication cycle. This mechanism could lead to an unwanted and unnecessary spread of saRNA throughout the body, posing relevant safety issues. This perspective article discusses the molecular mechanisms through which saRNAs can be transmitted among different cells/tissues. In addition, a simple way to control the possible excessive saRNA intercellular propagation through the co-expression of an EV-anchored protein inhibiting the saRNA replication is proposed. Based on current knowledge, a safety improvement of saRNA-based vaccines appears to be mandatory for their usage in healthy humans. Full article

Arboviruses transmitted by Aedes aegypti pose a significant challenge in Ecuador, as they are persistent, emerging, and re-emerging. During the SARS-CoV-2 pandemic, these diseases were temporarily overshadowed. This study aimed to detect and identify arbovirus species in mosquitoes collected from two communities in Manabí province—Caja Fuego (rural) and San Gregorio (marginal urban). A total of 468 mosquitoes were collected—385 from Caja Fuego and 83 from San Gregorio—and grouped into 72 pools. Samples were transported to CISeAL under proper biosafety protocols, homogenized, and analyzed using End-Point PCR, RT-PCR, and Sanger sequencing. The results revealed the presence of Flaviviruses and Alphaviruses. Of the 22 Flavivirus pools tested, 18 were positive, with PCR analysis specifically identifying dengue and Zika. Although no arbovirus was identified via RT-PCR, Sanger sequencing detected two Zika-positive samples. Notably, no official Zika cases were reported in 2023, suggesting a potential undetected risk of infection in human populations of Caja Fuego and San Gregorio. This study recommends the implementation of a surveillance campaign in collaboration with the Ecuadorian Ministry of Public Health to mitigate the risk. Full article

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that, since its re-emergence in 2004, has become recognised as a major public health concern throughout many tropical and sub-tropical regions of the world. Amongst the insights gained from studies on other alphaviruses, several key determinants of virulence have been identified, including one present at the P3 position in the nsP1/nsP2 cleavage domain of the S.A.AR86 Sindbis (SINV) strain. This strain is associated with neurovirulence in adult mice; however, when a threonine-to-isoleucine substitution is engineered at this P3 position, an attenuated phenotype results. A reverse genetics system was developed to evaluate the phenotype that resulted from the substitution of alanine, present at the P3 position in the wild-type CHIKV clone, with valine. The A533V-mutant CHIKV induced milder disease symptoms in the C57BL/6 mouse model than the wild-type virus, in terms of severity of inflammation, length of viraemic period, and histological changes. Furthermore, the induction of type I IFN occurred more rapidly in both CHIKV-infected cell cultures and the mouse model with the mutant CHIKV. Full article

Encephalitic alphaviruses, including eastern, Venezuelan, and western equine encephalitis virus (EEEV, VEEV, and WEEV, respectively) are New World alphaviruses primarily transmitted by mosquitos that cause debilitating and lethal central nervous system (CNS) disease in both humans and horses. Despite over one hundred years of research on these viruses, the underpinnings of the molecular mechanisms driving virally induced damage to the CNS remain unresolved. Moreover, virally induced encephalitis following exposure to these viruses causes catastrophic damage to the CNS, and survivors of infection often suffer from permanent neurological sequelae as a result of sustained neuroinflammation and neurological insults encountered. Animal models are undoubtedly invaluable tools in biomedical research, where physiologically relevant models are required to study pathogenesis and host–pathogen interactions. Here, we review the literature to examine nonhuman primate (NHP) and mouse models of infection for EEEV, VEEV, and WEEV. We provide a brief overview of relevant background information for each virus, including geography, epidemiology, and clinical disease. The primary focus of this review is to describe neuropathological features associated with CNS disease in NHP and mouse models of infection and compare CNS invasion and neuropathogenesis for aerosol, intranasal, and subcutaneous routes of exposure to EEEV, VEEV, and WEEV. Full article