Arthritogenic alphaviruses: new insights into arthritis and bone pathology

Pathogenicity and virulence of O'nyong-nyong virus: A less studied Togaviridae with pandemic potential

O'nyong-nyong virus (ONNV) is a neglected mosquito-borne alphavirus belonging to the Togaviridae family. ONNV is known to be responsible for sporadic outbreaks of acute febrile disease and polyarthralgia in Africa. As climate change increases the geographical range of known and potential new vectors, recent data indicate a possibility for ONNV to spread outside of the African continent and grow into a greater public health concern. In this review, we summarise the current knowledge on ONNV epidemiology, host-pathogen interactions, vector-virus responses, and insights into possible avenues to control risk of further epidemics. In this review, the limited ONNV literature is compared and correlated to other findings on mainly Old World alphaviruses. We highlight and discuss studies that investigate viral and host factors that determine viral-vector specificity, along with important mechanisms that determine severity and disease outcome of ONNV infection.

Chikungunya and Mayaro Viruses Induce Chronic Skeletal Muscle Atrophy Triggered by Pro-Inflammatory and Oxidative Response

Chikungunya (CHIKV) and Mayaro (MAYV) viruses are arthritogenic alphaviruses that promote an incapacitating and long-lasting inflammatory muscle-articular disease. Despite studies pointing out the importance of skeletal muscle (SkM) in viral pathogenesis, the long-term consequences on its physiology and the mechanism of persistence of symptoms are still poorly understood. Combining molecular, morphological, nuclear magnetic resonance imaging, and histological analysis, we conduct a temporal investigation of CHIKV and MAYV replication in a wild-type mice model, focusing on the impact on SkM composition, structure, and repair in the acute and late phases of infection. We found that viral replication and induced inflammation promote a rapid loss of muscle mass and reduction in fiber cross-sectional area by upregulation of muscle-specific E3 ubiquitin ligases MuRF1 and Atrogin-1 expression, both key regulators of SkM fibers atrophy. Despite a reduction in inflammation and clearance of infectious viral particles, SkM atrophy persists until 30 days post-infection. The genomic CHIKV and MAYV RNAs were still detected in SkM in the late phase, along with the upregulation of chemokines and anti-inflammatory cytokine expression. In agreement with the involvement of inflammatory mediators on induced atrophy, the neutralization of TNF and a reduction in oxidative stress using monomethyl fumarate, an agonist of Nrf2, decreases atrogen expression and atrophic fibers while increasing weight gain in treated mice. These data indicate that arthritogenic alphavirus infection could chronically impact body SkM composition and also harm repair machinery, contributing to a better understanding of mechanisms of arthritogenic alphavirus pathogenesis and with a description of potentially new targets of therapeutic intervention.

Unraveling the complex interplay: immunopathology and immune evasion strategies of alphaviruses with emphasis on neurological implications

Arthritogenic alphaviruses pose a significant public health concern due to their ability to cause joint inflammation, with emerging evidence of potential neurological consequences. In this review, we examine the immunopathology and immune evasion strategies employed by these viruses, highlighting their complex mechanisms of pathogenesis and neurological implications. We delve into how these viruses manipulate host immune responses, modulate inflammatory pathways, and potentially establish persistent infections. Further, we explore their ability to breach the blood-brain barrier, triggering neurological complications, and how co-infections exacerbate neurological outcomes. This review synthesizes current research to provide a comprehensive overview of the immunopathological mechanisms driving arthritogenic alphavirus infections and their impact on neurological health. By highlighting knowledge gaps, it underscores the need for research to unravel the complexities of virus-host interactions. This deeper understanding is crucial for developing targeted therapies to address both joint and neurological manifestations of these infections.

Rheumatoid arthritis patients harbour aberrant enteric bacteriophages with autoimmunity-provoking potential: a paired sibling study

OBJECTIVES

Viruses have been considered as important participants in the development of rheumatoid arthritis (RA). However, the profile of enteric virome and its role in RA remains elusive. This study aimed to investigate the atlas and involvement of virome in RA pathogenesis.

METHODS

Faecal samples from 30 pairs of RA and healthy siblings that minimise genetic interferences were collected for metagenomic sequencing. The α and β diversity of the virome and the virome-bacteriome interaction were analysed. The differential bacteriophages were identified, and their correlations with clinical and immunological features of RA were analysed. The potential involvement of these differential bacteriophages in RA pathogenesis was further investigated by auxiliary metabolic gene annotation and molecular mimicry study. The responses of CD4+ T cells and B cells to the mimotopes derived from the differential bacteriophages were systemically studied.

RESULTS

The composition of the enteric bacteriophageome was distorted in RA. The differentially presented bacteriophages correlated with the immunological features of RA, including anti-CCP autoantibody and HLA-DR shared epitope. Intriguingly, the glycerolipid and purine metabolic genes were highly active in the bacteriophages from RA. Moreover, peptides of RA-enriched phages, in particular Prevotella phage and Oscillibacter phage could provoke the autoimmune responses in CD4+ T cells and plasma cells via molecular mimicry of the disease-associated autoantigen epitopes, especially those of Bip.

CONCLUSIONS

This study provides new insights into enteric bacteriophageome in RA development. In particular, the aberrant bacteriophages demonstrated autoimmunity-provoking potential that would promote the occurrence of the disease.

Elevated Complement Activation Fragments and C1q-Binding Circulating Immune Complexes in Varied Phases of Chikungunya Virus Infection

Chikungunya virus (CHIKV) is a causative agent of a disease continuum, ranging from an acute transient chikungunya fever to chronic incapacitating viral arthralgia. The interaction between anti-CHIKV antibodies and the complement system has recently received attention. However, the contribution of complement activation in CHIKV-induced pathologies has not been fully elucidated. The present study was undertaken to delineate the possible contribution of complement activation in CHIKV-induced disease progression. In this study, using plasma specimens of chikungunya patients in the acute, chronic, and recovered phases of infection, we explicated the involvement of complement activation in CHIKV disease progression by ELISAs and Bio-Plex assays. Correlation analysis was carried out to demonstrate interrelation among C1q-binding IgG-containing circulating immune complexes (CIC-C1q), complement activation fragments (C3a, C5a, sC5b-9), and complement-modulated pro-inflammatory cytokines (IL-1β, IL-18, IL-6, and TNF-α). We detected elevated complement activation fragments, CIC-C1q, and complement-modulated cytokines in the varied patient groups compared with the healthy controls, indicating persistent activation of the complement system. Furthermore, we observed statistically significant correlations among CIC-C1q with complement activation fragments and C3a with complement modulatory cytokines IL-1β, IL-6, and IL-18 during the CHIKV disease progression. Taken together, the current data provide insight into the plausible association between CICs, complement activation, subsequent complement modulatory cytokine expression, and CHIKV etiopathology.

Essential role of the CCL2-CCR2 axis in Mayaro virus-induced disease

Mayaro virus (MAYV) is an emerging arbovirus member of the Togaviridae family and Alphavirus genus. MAYV infection causes an acute febrile illness accompanied by persistent polyarthralgia and myalgia. Understanding the mechanisms involved in arthritis caused by alphaviruses is necessary to develop specific therapies. In this work, we investigated the role of the CCL2/CCR2 axis in the pathogenesis of MAYV-induced disease. For this, wild-type (WT) C57BL/6J and CCR2-/- mice were infected with MAYV subcutaneously and evaluated for disease development. MAYV infection induced an acute inflammatory disease in WT mice. The immune response profile was characterized by an increase in the production of inflammatory mediators, such as IL-6, TNF, and CCL2. Higher levels of CCL2 at the local and systemic levels were followed by the significant recruitment of CCR2+ macrophages and a cellular response orchestrated by these cells. CCR2-/- mice showed an increase in CXCL-1 levels, followed by a replacement of the macrophage inflammatory infiltrate by neutrophils. Additionally, the absence of the CCR2 receptor protected mice from bone loss induced by MAYV. Accordingly, the silencing of CCL2 chemokine expression in vivo and the pharmacological blockade of CCR2 promoted a partial improvement in disease. Cell culture data support the mechanism underlying the bone pathology of MAYV, in which MAYV infection promotes a pro-osteoclastogenic microenvironment mediated by CCL2, IL-6, and TNF, which induces the migration and differentiation of osteoclast precursor cells. Overall, these data contribute to the understanding of the pathophysiology of MAYV infection and the identification future of specific therapeutic targets in MAYV-induced disease.IMPORTANCEThis work demonstrates the role of the CCL2/CCR2 axis in MAYV-induced disease. The infection of wild-type (WT) C57BL/6J and CCR2-/- mice was associated with high levels of CCL2, an important chemoattractant involved in the recruitment of macrophages, the main precursor of osteoclasts. In the absence of the CCR2 receptor, there is a mitigation of macrophage migration to the target organs of infection and protection of these mice against bone loss induced by MAYV infection. Much evidence has shown that host immune response factors contribute significantly to the tissue damage associated with alphavirus infections. Thus, this work highlights molecular and cellular targets involved in the pathogenesis of arthritis triggered by MAYV and identifies novel therapeutic possibilities directed to the host inflammatory response unleashed by MAYV.

Refined innate plasma signature after rVSVΔG-ZEBOV-GP immunization is shared among adult cohorts in Europe and North America

Background

During the last decade Ebola virus has caused several outbreaks in Africa. The recombinant vesicular stomatitis virus-vectored Zaire Ebola (rVSVΔG-ZEBOV-GP) vaccine has proved safe and immunogenic but is reactogenic. We previously identified the first innate plasma signature response after vaccination in Geneva as composed of five monocyte-related biomarkers peaking at day 1 post-immunization that correlates with adverse events, biological outcomes (haematological changes and viremia) and antibody titers. In this follow-up study, we sought to identify additional biomarkers in the same Geneva cohort and validate those identified markers in a US cohort.

Methods

Additional biomarkers were identified using multiplexed protein biomarker platform O-link and confirmed by Luminex. Principal component analysis (PCA) evaluated if these markers could explain a higher variability of the vaccine response (and thereby refined the initial signature). Multivariable and linear regression models evaluated the correlations of the main components with adverse events, biological outcomes, and antibody titers. External validation of the refined signature was conducted in a second cohort of US vaccinees (n=142).

Results

Eleven additional biomarkers peaked at day 1 post-immunization: MCP2, MCP3, MCP4, CXCL10, OSM, CX3CL1, MCSF, CXCL11, TRAIL, RANKL and IL15. PCA analysis retained three principal components (PC) that accounted for 79% of the vaccine response variability. PC1 and PC2 were very robust and had different biomarkers that contributed to their variability. PC1 better discriminated different doses, better defined the risk of fever and myalgia, while PC2 better defined the risk of headache. We also found new biomarkers that correlated with reactogenicity, including transient arthritis (MCP-2, CXCL10, CXCL11, CX3CL1, MCSF, IL-15, OSM). Several innate biomarkers are associated with antibody levels one and six months after vaccination. Refined PC1 correlated strongly in both data sets (Geneva: r = 0.97, P < 0.001; US: r = 0.99, P< 0.001).

Conclusion

Eleven additional biomarkers refined the previously found 5-biomarker Geneva signature. The refined signature better discriminated between different doses, was strongly associated with the risk of adverse events and with antibody responses and was validated in a separate cohort.

Human Synovial Mesenchymal Stem Cells Expressed Immunoregulatory Factors IDO and TSG6 in a Context of Arthritis Mediated by Alphaviruses

Infection by arthritogenic alphaviruses (aavs) can lead to reactive arthritis, which is characterized by inflammation and persistence of the virus; however, its mechanisms remain ill-characterized. Intriguingly, it has been shown that viral persistence still takes place in spite of robust innate and adaptive immune responses, characterized notably by the infiltration of macrophages (sources of TNF-alpha) as well as T/NK cells (sources of IFN-gamma) in the infected joint. Aavs are known to target mesenchymal stem cells (MSCs) in the synovium, and we herein tested the hypothesis that the infection of MSCs may promote the expression of immunoregulators to skew the anti-viral cellular immune responses. We compared the regulated expression via human synovial MSCs of pro-inflammatory mediators (e.g., IL-1β, IL6, CCL2, miR-221-3p) to that of immunoregulators (e.g., IDO, TSG6, GAS6, miR146a-5p). We used human synovial tissue-derived MSCs which were infected with O'Nyong-Nyong alphavirus (ONNV, class II aav) alone, or combined with recombinant human TNF-α or IFN-γ, to mimic the clinical settings. We confirmed via qPCR and immunofluorescence that ONNV infected human synovial tissue-derived MSCs. Interestingly, ONNV alone did not regulate the expression of pro-inflammatory mediators. In contrast, IDO, TSG6, and GAS6 mRNA expression were increased in response to ONNV infection alone, but particularly when combined with both recombinant cytokines. ONNV infection equally decreased miR-146a-5p and miR-221-3p in the untreated cells and abrogated the stimulatory activity of the recombinant TNF-α but not the IFN-gamma. Our study argues for a major immunoregulatory phenotype of MSCs infected with ONNV which may favor virus persistence in the inflamed joint.

Zika virus alters osteogenic lineage progression of human mesenchymal stromal cells

Arboviruses target bone forming osteoblasts and perturb bone remodeling via paracrine factors. We previously reported that Zika virus (ZIKV) infection of early-stage human mesenchymal stromal cells (MSCs) inhibited the osteogenic lineage commitment of MSCs. To understand the physiological interplay between bone development and ZIKV pathogenesis, we employed a primary in vitro model to examine the biological responses of MSCs to ZIKV infection at different stages of osteogenesis. Precommitted MSCs were infected at the late stage of osteogenic stimulation (Day 7) with ZIKV (multiplicity of infection of 5). We observe that MSCs infected at the late stage of differentiation are highly susceptible to ZIKV infection similar to previous observations with early stage infected MSCs (Day 0). However, in contrast to ZIKV infection at the early stage of differentiation, infection at a later stage significantly elevates the key osteogenic markers and calcium content. Comparative RNA sequencing (RNA-seq) of early and late stage infected MSCs reveals that ZIKV infection alters the mRNA transcriptome during osteogenic induction of MSCs (1251 genes). ZIKV infection provokes a robust antiviral response at both stages of osteogenic differentiation as reflected by the upregulation of interferon responsive genes (n > 140). ZIKV infection enhances the expression of immune-related genes in early stage MSCs while increasing cell cycle genes in late stage MSCs. Remarkably, ZIKA infection in early stage MSCs also activates lipid metabolism-related pathways. In conclusion, ZIKV infection has differentiation stage-dependent effects on MSCs and this mechanistic understanding may permit the development of new therapeutic or preventative measures for bone-related effects of ZIKV infection.

Advances in the Development of Small Molecule Antivirals against Equine Encephalitic Viruses

Venezuelan, western, and eastern equine encephalitic alphaviruses (VEEV, WEEV, and EEEV, respectively) are arboviruses that are highly pathogenic to equines and cause significant harm to infected humans. Currently, human alphavirus infection and the resulting diseases caused by them are unmitigated due to the absence of approved vaccines or therapeutics for general use. These circumstances, combined with the unpredictability of outbreaks-as exemplified by a 2019 EEE surge in the United States that claimed 19 patient lives-emphasize the risks posed by these viruses, especially for aerosolized VEEV and EEEV which are potential biothreats. Herein, small molecule inhibitors of VEEV, WEEV, and EEEV are reviewed that have been identified or advanced in the last five years since a comprehensive review was last performed. We organize structures according to host- versus virus-targeted mechanisms, highlight cellular and animal data that are milestones in the development pipeline, and provide a perspective on key considerations for the progression of compounds at early and later stages of advancement.

Zika virus infects human osteoclasts and blocks differentiation and bone resorption

Bone-related complications are commonly reported following arbovirus infection. These arboviruses are known to disturb bone-remodeling and induce inflammatory bone loss via increased activity of bone resorbing osteoclasts (OCs). We previously showed that Zika virus (ZIKV) could disturb the function of bone forming osteoblasts, but the susceptibility of OCs to ZIKV infection is not known. Here, we investigated the effect of ZIKV infection on osteoclastogenesis and report that infection of pre- and early OCs with ZIKV significantly reduced the osteoclast formation and bone resorption. Interestingly, infection of pre-OCs with a low dose ZIKV infection in the presence of flavivirus cross-reacting antibodies recapitulated the phenotype observed with a high viral dose, suggesting a role for antibody-dependent enhancement in ZIKV-associated bone pathology. In conclusion, we have characterized a primary in vitro model to study the role of osteoclastogenesis in ZIKV pathogenesis, which will help to identify possible new targets for developing therapeutic and preventive measures.

Anti-Alphaviral Alkaloids: Focus on Some Isoquinolines, Indoles and Quinolizidines

The discovery and the development of safe and efficient therapeutics against arthritogenic alphaviruses (e.g., chikungunya virus) remain a continuous challenge. Alkaloids are structurally diverse and naturally occurring compounds in plants, with a wide range of biological activities including beneficial effects against prominent pathogenic viruses and inflammation. In this short review, we discuss the effects of some alkaloids of three biologically relevant structural classes (isoquinolines, indoles and quinolizidines). Based on various experimental models (viral infections and chronic diseases), we highlight the immunomodulatory effects of these alkaloids. The data established the capacity of these alkaloids to interfere in host antiviral and inflammatory responses through key components (antiviral interferon response, ROS production, inflammatory signaling pathways and pro- and anti-inflammatory cytokines production) also involved in alphavirus infection and resulting inflammation. Thus, these data may provide a convincing perspective of research for the use of alkaloids as immunomodulators against arthritogenic alphavirus infection and induced inflammation.

Distinct Cellular Tropism and Immune Responses to Alphavirus Infection

Alphaviruses are emerging and reemerging viruses that cause disease syndromes ranging from incapacitating arthritis to potentially fatal encephalitis. While infection by arthritogenic and encephalitic alphaviruses results in distinct clinical manifestations, both virus groups induce robust innate and adaptive immune responses. However, differences in cellular tropism, type I interferon induction, immune cell recruitment, and B and T cell responses result in differential disease progression and outcome. In this review, we discuss aspects of immune responses that contribute to protective or pathogenic outcomes after alphavirus infection. Expected final online publication date for the Annual Review of Immunology, Volume 40 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Current Understanding of the Role of T Cells in Chikungunya, Dengue and Zika Infections

Arboviral infections such as Chikungunya (CHIKV), Dengue (DENV) and Zika (ZIKV) are a major disease burden in tropical and sub-tropical countries, and there are no effective vaccinations or therapeutic drugs available at this time. Understanding the role of the T cell response is very important when designing effective vaccines. Currently, comprehensive identification of T cell epitopes during a DENV infection shows that CD8 and CD4 T cells and their specific phenotypes play protective and pathogenic roles. The protective role of CD8 T cells in DENV is carried out through the killing of infected cells and the production of proinflammatory cytokines, as CD4 T cells enhance B cell and CD8 T cell activities. A limited number of studies attempted to identify the involvement of T cells in CHIKV and ZIKV infection. The identification of human immunodominant ZIKV viral epitopes responsive to specific T cells is scarce, and none have been identified for CHIKV. In CHIKV infection, CD8 T cells are activated during the acute phase in the lymph nodes/blood, and CD4 T cells are activated during the chronic phase in the joints/muscles. Studies on the role of T cells in ZIKV-neuropathogenesis are limited and need to be explored. Many studies have shown the modulating actions of T cells due to cross-reactivity between DENV-ZIKV co-infections and have repeated heterologous/homologous DENV infection, which is an important factor to consider when developing an effective vaccine.

Near-germline human monoclonal antibodies neutralize and protect against multiple arthritogenic alphaviruses

Arthritogenic alphaviruses are globally distributed, mosquito-transmitted viruses that cause rheumatological disease in humans and include Chikungunya virus (CHIKV), Mayaro virus (MAYV), and others. Although serological evidence suggests that some antibody-mediated heterologous immunity may be afforded by alphavirus infection, the extent to which broadly neutralizing antibodies that protect against multiple arthritogenic alphaviruses are elicited during natural infection remains unknown. Here, we describe the isolation and characterization of MAYV-reactive alphavirus monoclonal antibodies (mAbs) from a CHIKV-convalescent donor. We characterized 33 human mAbs that cross-reacted with CHIKV and MAYV and engaged multiple epitopes on the E1 and E2 glycoproteins. We identified five mAbs that target distinct regions of the B domain of E2 and potently neutralize multiple alphaviruses with differential breadth of inhibition. These broadly neutralizing mAbs (bNAbs) contain few somatic mutations and inferred germline-revertants retained neutralizing capacity. Two bNAbs, DC2.M16 and DC2.M357, protected against both CHIKV- and MAYV-induced musculoskeletal disease in mice. These findings enhance our understanding of the cross-reactive and cross-protective antibody response to human alphavirus infections.

Alphaviruses: Host pathogenesis, immune response, and vaccine & treatment updates

Human pathogens belonging to the Alphavirus genus, in the Togaviridae family, are transmitted primarily by mosquitoes. The signs and symptoms associated with these viruses include fever and polyarthralgia, defined as joint pain and inflammation, as well as encephalitis. In the last decade, our understanding of the interactions between members of the alphavirus genus and the human host has increased due to the re-appearance of the chikungunya virus (CHIKV) in Asia and Europe, as well as its emergence in the Americas. Alphaviruses affect host immunity through cytokines and the interferon response. Understanding alphavirus interactions with both the innate immune system as well as the various cells in the adaptive immune systems is critical to developing effective therapeutics. In this review, we summarize the latest research on alphavirus-host cell interactions, underlying infection mechanisms, and possible treatments.

Quercetin can reduce viral RNA level of O'nyong-nyong virus and resulting innate immune cytokine responses in cultured human synovial fibroblasts

O’nyong-nyong virus is an alphavirus closely related to chikungunya virus, causing arthralgia, rash and fever. Alphaviruses mainly target synovial fibroblasts and persists in the joints of patients, possibly leading to chronic arthritis. To date, no specific antiviral treatment is available for ONNV infection and induced-inflammation. Primary human synovial fibroblasts cells were used to assess infection by ONNV and the resulting cytokine responses. Phenolics (gallic acid, caffeic acid and chlorogenic acid, curcumin and quercetin) and a curcuminoids-rich extract from turmeric were tested for their antiviral and anti-inflammatory capacities. We showed that infection occurred in HSF cells and increased gene expression and protein secretion of two major proinflammatory CCL-2 and IL-1β markers. In ONNV-infected HSF cells (MOI 1), we found that non-cytotoxic concentrations of phenolics (10 µM) reduced the level of viral RNA (E1, E2, nsP1, nsP2) and downregulated CCL-2 and IL-1β expression and secretion. These results highlighted the high value of the flavonol quercetin to reduce viral RNA levels and inflammatory status induced by ONNV in HSF cells.

Differentiation-dependent susceptibility of human muscle cells to Zika virus infection

Muscle cells are potential targets of many arboviruses, such as Ross River, Dengue, Sindbis, and chikungunya viruses, that may be involved in the physiopathological course of the infection. During the recent outbreak of Zika virus (ZIKV), myalgia was one of the most frequently reported symptoms. We investigated the susceptibility of human muscle cells to ZIKV infection. Using an in vitro model of human primary myoblasts that can be differentiated into myotubes, we found that myoblasts can be productively infected by ZIKV. In contrast, myotubes were shown to be resistant to ZIKV infection, suggesting a differentiation-dependent susceptibility. Infection was accompanied by a caspase-independent cytopathic effect, associated with paraptosis-like cytoplasmic vacuolization. Proteomic profiling was performed 24h and 48h post-infection in cells infected with two different isolates. Proteome changes indicate that ZIKV infection induces an upregulation of proteins involved in the activation of the Interferon type I pathway, and a downregulation of protein synthesis. This work constitutes the first observation of primary human muscle cells susceptibility to ZIKV infection, and differentiation-dependent restriction of infection from myoblasts to myotubes. Since myoblasts constitute the reservoir of stem cells involved in reparation/regeneration in muscle tissue, the infection of muscle cells and the viral-induced alterations observed here could have consequences in ZIKV infection pathogenesis.

Muscle cells are potential targets of many arboviruses, such as Ross River, Dengue, Sindbis, and chikungunya viruses, and may be involved in the disease manifestation. During the recent outbreak of Zika virus (ZIKV), myalgia was one of the most frequently reported symptoms. We investigated the susceptibility of human muscle cells to ZIKV infection. Using an in vitro model of human muscle stem cells (myoblasts) that can be differentiated into differentiated muscle cells (myotubes), we found that myoblasts can be infected by ZIKV. In contrast, myotubes were shown to be resistant to ZIKV infection. Infection induced the death of infected cells. Protein levels 24h and 48h post-infection indicate that ZIKV infection induces an upregulation of proteins involved in the activation of the Interferon type I pathway, and a downregulation of protein synthesis. This work constitutes the first observation of primary human muscle cells susceptibility to ZIKV infection, muscle stem cells being susceptible while differentiated muscle cells are resistant. Since myoblasts constitute the reservoir of stem cells involved in reparation/regeneration in muscle tissue, the infection of muscle cells and the viral-induced alterations observed here could have consequences during ZIKV infection.

Agua Salud alphavirus defines a novel lineage of insect-specific alphaviruses discovered in the New World

The genus Alphavirus harbours mostly insect-transmitted viruses that cause severe disease in humans, livestock and wildlife. Thus far, only three alphaviruses with a host range restricted to insects have been found in mosquitoes from the Old World, namely Eilat virus (EILV), Taï Forest alphavirus (TALV) and Mwinilunga alphavirus (MWAV). In this study, we found a novel alphavirus in one Culex declarator mosquito sampled in Panama. The virus was isolated in C6/36 mosquito cells, and full genome sequencing revealed an 11 468 nt long genome with maximum pairwise nucleotide identity of 62.7 % to Sindbis virus. Phylogenetic analyses placed the virus as a solitary deep rooting lineage in a basal relationship to the Western equine encephalitis antigenic complex and to the clade comprising EILV, TALV and MWAV, indicating the detection of a novel alphavirus, tentatively named Agua Salud alphavirus (ASALV). No growth of ASALV was detected in vertebrate cell lines, including cell lines derived from ectothermic animals, and replication of ASALV was strongly impaired above 31 °C, suggesting that ASALV represents the first insect-restricted alphavirus of the New World.

Chronic Joint Pain 3 Years after Chikungunya Virus Infection Largely Characterized by Relapsing-remitting Symptoms

OBJECTIVE

To determine the frequency of chronic joint pain and stiffness 3 years after infection with chikungunya virus (CHIKV) in a Latin American cohort.

METHODS

A cross-sectional followup of 120 patients from an initial cohort of 500 patients who reported joint pain 2 years after infection from the Atlántico Department, Colombia. Patients were clinically diagnosed as having CHIKV during the 2014-2015 epidemic, and baseline and followup symptoms at 40 months were evaluated in serologically confirmed cases.

RESULTS

Of the initial 500 patients enrolled in the study, 482 had serologically confirmed chikungunya infection. From this group, 123 patients reported joint pain 20 months after infection, and 54% of those patients reported continued joint pain 40 months after infection. Therefore, 1 out of every 8 people who tested serologically positive for CHIKV infection had persistent joint pain 3 years after infection. Participants who followed up in person were predominantly adult (mean ± SD age 51 ± 14 yrs) and female (86%). The most common type of pain reported in these patients at 40 months post-infection was pain with periods of relief and subsequent reoccurrence, and over 75% reported stiffness after immobility, with 39% experiencing morning stiffness.

CONCLUSION

To our knowledge, this is the first report to describe persistent joint pain and stiffness 40 months after viral infection. The high frequency of chronic disease highlights the need to develop prevention and treatment methods. Further studies should be conducted to understand the similarities between post-chikungunya joint pain and rheumatoid arthritis.

Arboviruses and Muscle Disorders: From Disease to Cell Biology

Infections due to arboviruses (arthropod-borne viruses) have dramatically increased worldwide during the last few years. In humans, symptoms associated with acute infection of most arboviruses are often described as "dengue-like syndrome", including fever, rash, conjunctivitis, arthralgia, and muscular symptoms such as myalgia, myositis, or rhabdomyolysis. In some cases, muscular symptoms may persist over months, especially following flavivirus and alphavirus infections. However, in humans the cellular targets of infection in muscle have been rarely identified. Animal models provide insights to elucidate pathological mechanisms through studying viral tropism, viral-induced inflammation, or potential viral persistence in the muscle compartment. The tropism of arboviruses for muscle cells as well as the viral-induced cytopathic effect and cellular alterations can be confirmed in vitro using cellular models. This review describes the link between muscle alterations and arbovirus infection, and the underlying mechanisms.

High-Throughput Fluorescence-Based Screen Identifies the Neuronal MicroRNA miR-124 as a Positive Regulator of Alphavirus Infection

MicroRNAs (miRNAs) are small regulatory RNAs which act by modulating the expression of target genes. In addition to their role in maintaining essential physiological functions in the cell, miRNAs can also regulate viral infections. They can do so directly by targeting RNAs of viral origin or indirectly by targeting host mRNAs, and this can result in a positive or negative outcome for the virus. Here, we performed a fluorescence-based miRNA genome-wide screen in order to identify cellular miRNAs involved in the regulation of arbovirus infection in human cells. We identified 16 miRNAs showing a positive effect on Sindbis virus (SINV) expressing green fluorescent protein (GFP), among which were a number of neuron-specific ones such as miR-124. We confirmed that overexpression of miR-124 increases both SINV structural protein translation and viral production and that this effect is mediated by its seed sequence. We further demonstrated that the SINV genome possesses a binding site for miR-124. Both inhibition of miR-124 and silent mutations to disrupt this binding site in the viral RNA abolished positive regulation. We also proved that miR-124 inhibition reduces SINV infection in human differentiated neuronal cells. Finally, we showed that the proviral effect of miR-124 is conserved in other alphaviruses, as its inhibition reduces chikungunya virus (CHIKV) production in human cells. Altogether, our work expands the panel of positive regulation of the viral cycle by direct binding of host miRNAs to the viral RNA and provides new insights into the role of cellular miRNAs as regulators of alphavirus infection.IMPORTANCE Arthropod-borne (arbo) viruses are part of a class of pathogens that are transmitted to their final hosts by insects. Because of climate change, the habitat of some of these insects, such as mosquitoes, is shifting, thereby facilitating the emergence of viral epidemics. Among the pathologies associated with arbovirus infection, neurological diseases such as meningitis and encephalitis represent a significant health burden. Using a genome-wide miRNA screen, we identified neuronal miR-124 as a positive regulator of the Sindbis and chikungunya alphaviruses. We also showed that this effect was in part direct, thereby opening novel avenues to treat alphavirus infections.

A possible role for autoimmunity through molecular mimicry in alphavirus mediated arthritis

Alphaviral infections are foremost in causing debilitating clinical outcomes in humans characterized by rheumatic arthritis like conditions. Though the presence of virus in joints and associated inflammation has been implicated as one of the reasons for the acute and chronic polyarthritis post alphaviral infections, the basis for rheumatic like outcomes is not clear. Through an in silico analysis, we have investigated the possibility of an autoimmune process mediated through molecular mimicry in alphaviral infection induced pathogenicity. Interestingly, sequence alignment of the structural polyproteins belonging to arthritogenic alphaviruses revealed conserved regions which share homology with human proteins implicated in rheumatoid arthritis (RA). These conserved regions were predicted to exhibit binding to HLA class II alleles, showcasing their potential to incite T cell help. Molecular docking of the viral peptide and the corresponding homologous region in the human protein onto HLA-DRB1 revealed strong similarities in their binding patterns. Linear and conformational B cell epitope prediction analyses showed that these potential mimics have high propensity to elicit an efficient B cell response. We thus propose that the origin of polyarthritis post-arthritogenic alphaviral infections may also be mediated through a hitherto unknown autoimmune response due to the presence of cross-reactive epitopes between viral and human proteins.

Imaging of Emerging Infectious Diseases

Purpose of Review

Emerging infectious diseases have seen a record increase in prevalence, and understanding their management is critical in an increasingly global community. In this paper, we review current literature detailing the role of radiology in the diagnosis and treatment of the Ebola (EVD), Zika (ZVD), Chikungunya (CHIKF), H1N1, Middle East Respiratory (MERS), and Severe Acute Respiratory Syndrome (SARS) viruses.

Recent Findings

Complex protocols are required to safely use portable imaging in EVD to prevent nosocomial spread of disease. In ZVD, antenatal ultrasound can detect fetal abnormalities early, allowing implementation of care and support to affected families. Imaging is useful in assessing the extent of involvement of chronic CHIKF and monitoring treatment effect. Chest radiography and CT play a more direct role in the diagnosis and monitoring of the viral infections with primarily respiratory manifestations (H1N1, MERS, and SARS).

Summary

Radiology plays a variable role in emerging infectious diseases, requiring an understanding of disease transmission and safe imaging practices, as well as imaging features that affect clinical management.

Molecular Basis of Arthritogenic Alphavirus Receptor MXRA8 Binding to Chikungunya Virus Envelope Protein

Arthritogenic alphaviruses, such as Chikungunya virus (CHIKV), cause severe and debilitating rheumatic diseases worldwide, resulting in severe morbidity and economic costs. Recently, MXRA8 was reported as an entry receptor. Here, we present the crystal structures of the mouse MXRA8, human MXRA8 in complex with the CHIKV E protein, and the cryo-electron microscopy structure of human MXRA8 and CHIKV virus-like particle. MXRA8 has two Ig-like domains with unique structural topologies. This receptor binds in the "canyon" between two protomers of the E spike on the surface of the virion. The atomic details at the interface between the two binding entities reveal that both the two domains and the hinge region of MXRA8 are involved in interaction with CHIKV E1-E2 residues from two protomers. Notably, the stalk region of MXRA8 is critical for CHIKV virus entry. This finding provides important information regarding the development of therapeutic countermeasures against those arthritogenic alphaviruses.

Animal model of arthritis and myositis induced by the Mayaro virus

BACKGROUND

The Mayaro virus (MAYV) is an endemic arbovirus in South American countries, where it is responsible for sporadic outbreaks of Mayaro fever. Clinical manifestations include fever, headache, ocular pain, rash, myalgia, and debilitating and persistent polyarthralgia. Understanding the mechanisms associated with MAYV-induced arthritis is of great importance due to the potential for its emergence, urbanization and dispersion to other regions.

METHODS

15-day old Balb/c mice were infected by two distinct pathways, below the forelimb and in the rear footpad. Animals were observed for a period of 21 days. During this time, they were monitored every 24 hours for disease signs, such as weight loss and muscle weakness. Histological damage in the muscles and joints was evaluated 3, 7, 10, 15 and 20 days post-infection. The cytokine profile in serum and muscles during MAYV infection was evaluated by flow cytometry at different post-infection times. For pain analysis, the animals were submitted to the von Frey test and titre in different organs was evaluated throughout the study to obtain viral kinetics.

FINDINGS

Infection by two distinct pathways, below the forelimb and in the rear footpad, resulted in a homogeneous viral spread and the development of acute disease in animals. Clinical signs were observed such as ruffled fur, hunched posture, eye irritation and slight gait alteration. In the physical test, both groups presented loss of resistance, which was associated with histopathological damage, including myositis, arthritis, tenosynovitis and periostitis. The immune response was characterized by a strong inflammatory response mediated by the cytokines TNF-α, IL-6 and INF-γ and chemokine MCP-1, followed by the action of IL-10 and IL-4 cytokines.

INTERPRETATION

The results showed that Balb/c mice represent a promising model to study mechanisms involved in MAYV pathogenesis and for future antiviral testing.

Rev-erb Agonist Inhibits Chikungunya and O'nyong'nyong Virus Replication

Chikungunya virus (CHIKV), an alphavirus spread by Aedes spp. mosquitos, causes severe inflammation and joint pain, progressing to a chronic arthralgic state in a subset of patients. Due to recent global epidemics of CHIKV and the potential for related viruses to cause outbreaks, multiple approaches to combat these pathogens are of interest. We report that SR9009, a synthetic agonist of nuclear receptors Rev-erb α/β, inhibits replication of multiple alphaviruses (CHIKV and O'nyong'nyong virus) mainly by suppressing structural protein synthesis, although viral RNA accumulation is relatively unimpeded. Furthermore, SR9009 reduces the inflammatory response in cultured murine macrophages exposed to alphavirus-infected cells.

Chikungunya fever: a threat to global public health

Chikungunya fever is an emerging arbovirus infection, representing a serious public health problem. Its etiological agent is the Chikungunya virus (CHIKV). Transmission of this virus is mainly vector by mosquitoes of the genus Aedes, although transmission by blood transfusions and vertical transmission has also been reported. The disease presents high morbidity caused mainly by the arthralgia and arthritis generated. Cardiovascular and neurological manifestations have also been reported. The severity of the infection seems to be directly associated with the action of the virus, but also with the decompensation of preexisting comorbidities. Currently, there are no therapeutic products neither vaccines licensed to the infection CHIKV control, although several vaccine candidates are being evaluated and human polyvalent immunoglobulins anti-CHIKV had been tested. Antibodies can protect against the infection, but in sub-neutralizing concentrations can augment virus infection and exacerbate disease severity. So, the prevention still depends on the use of personal protection measures and vector control, which are only minimally effective.

Increased Proinflammatory Cytokine Levels in Prolonged Arthralgia in Ross River Virus Infection

Ross River virus, a mosquitoborne alphavirus, causes epidemic polyarthritis in Australia and the Pacific region. We analyzed serum cytokine, chemokine, and growth factor levels in travelers returning to Germany from Australia. Serum samples showed elevated concentrations in the acute phase of the illness and, more pronounced, in the long-lasting convalescent phase.

Ultrasonography of Hands and Wrists in the Diagnosis of Complications of Chikungunya Fever

The purpose of this series was to describe the ultrasonographic and radiographic manifestations of changes to the hands and wrists in 50 patients with chronic musculoskeletal symptoms secondary to Chikungunya fever during the 2016 outbreak that occurred in Rio de Janeiro, Brazil. Most of the plain radiographs were normal (62%). The most common ultrasonographic findings were small joint synovitis (84%), wrist synovitis (74%), finger tenosynovitis (70%), and cellulitis (50%). In most cases, power Doppler did not show an increase in synovial vascular flow. The plain radiographs showed no specific findings, whereas the ultrasound images revealed synovial compromise and neural thickening.

Fingolimod treatment abrogates chikungunya virus-induced arthralgia

Chikungunya virus (CHIKV) is one of the many rheumatic arthropod-borne alphaviruses responsible for debilitating joint inflammation in humans. Despite the severity in many endemic regions, clinically approved intervention targeting the virus remains unavailable. CD4⁺ T cells have been shown to mediate CHIKV-induced joint inflammation in mice. We demonstrate here that transfer of splenic CD4⁺ T cells from virus-infected C57BL/6 mice into virus-infected T cell receptor-deficient (TCR^-/-) mice recapitulated severe joint pathology including inflammation, vascular leakages, subcutaneous edema, and skeletal muscle necrosis. Proteome-wide screening identified dominant CD4⁺ T cell epitopes in nsP1 and E2 viral antigens. Transfer of nsP1- or E2-specific primary CD4⁺ T cell lines into CHIKV-infected TCR^-/- recipients led to severe joint inflammation and vascular leakage. This pathogenic role of virus-specific CD4⁺ T cells in CHIKV infections led to the assessment of clinically approved T cell-suppressive drugs for disease intervention. Although drugs targeting interleukin-2 pathway were ineffective, treatment with fingolimod, an agonist of sphingosine 1-phosphate receptor, successfully abrogated joint pathology in CHIKV-infected animals by blocking the migration of CD4⁺ T cells into the joints without any effect on viral replication. These results set the stage for further clinical evaluation of fingolimod in the treatment of CHIKV-induced joint pathologies.

Endemic Australian arboviruses of human health significance

Each year many thousands of cases of human arbovirus infection are notified within Australia, acquired either within Australia or when travelling overseas1. These cause diseases varying from fever and aches, to debilitating joint disease, to encephalitis and death. The arboviruses endemic to Australia are all maintained in a cycle between mosquitoes (and rarely midges) and a bird or mammalian host2. As such, the virus activity is dependent on rainfall and temperature conditions that are conducive to mosquito breeding, and to virus replication and amplification (Figure 1). Those conditions being met, there have to be suitable amplifying animal hosts nearby, and their absence is one of the factors that protects most of the larger urban populations in Australia. Then, of course, humans have to be exposed to the infected mosquitoes to get disease.

Chikungunya Virus: Pathophysiology, Mechanism, and Modeling

Chikungunya virus (CHIKV), a mosquito-transmitted alphavirus, is recurring in epidemic waves. In the past decade and a half, the disease has resurged in several countries around the globe, with outbreaks becoming increasingly severe. Though CHIKV was first isolated in 1952, there remain significant gaps in knowledge of CHIKV biology, pathogenesis, transmission, and mechanism. Diagnosis is largely simplified and based on symptoms, while treatment is supportive rather than curative. Here we present an overview of the disease, the challenges that lie ahead for future research, and what directions current studies are headed towards, with emphasis on improvement of current animal models and potential use of 3D models.

Chikungunya vaccines in development

Chikungunya virus has become a global health threat, spreading to the industrial world of Europe and the Americas; no treatment or prophylactic vaccine is available. Since the late 1960s much effort has been put into the development of a vaccine, and several heterogeneous strategies have already been explored. Only two candidates have recently qualified to enter clinical phase II trials, a chikungunya virus-like particle-based vaccine and a recombinant live attenuated measles virus-vectored vaccine.

This review focuses on the current status of vaccine development against chikungunya virus in humans and discusses the diversity of immunization strategies, results of recent human trials and promising vaccine candidates.

The osteogenic cell surface marker BRIL/IFITM5 is dispensable for bone development and homeostasis in mice

BRIL (bone-restricted IFITM-like), is a short transmembrane protein expressed almost exclusively in osteoblasts. Although much is known about its bone-restricted gene expression pattern and protein biochemical and topological features, little information is available for BRIL physiological function. Two autosomal dominant forms of osteogenesis imperfecta (OI) are caused by distinct, but recurrent mutations in the BRIL gene. Yet, the underlying mechanisms by which those mutations lead to OI are still poorly understood. A previous report indicated that BRIL knockout (KO) mice had bone deformities, shortened long bones, and reproductive problems. Here we generated and systematically analyzed the skeletal phenotype of a new global Bril KO/LacZ knockin mouse model. KO mice reproduced and thrived normally up to 12 month of age. The skeletal phenotype of KO and WT littermates was assessed at embryonic (E13.5 to E18.5) and postnatal (2 days, 3 weeks, 3 months and 8 months) time-points. Embryos from E13.5 through to E18.5 showed significant X-Gal staining in all skeletal elements without any apparent patterning anomalies. Although bone deformities were never observed at any postnatal ages, minor and transient differences were noted in terms of bone length and static uCT parameters, but not systematically across all ages and genders. These changes, however, were not accompanied by significant alteration in bone material properties as assessed by a 3-point bending test. In addition, no changes were detected in circulating serum markers of bone turnover (P1NP, CTX-I, and osteocalcin). Gene expression monitoring also revealed no major impact of the loss of BRIL. Further, when mice were challenged with a surgically-induced fracture in tibia, bones repaired equally well in the KO mice as compared to WT. Finally, we showed that BRIL C-terminus is not a bona fide binding site for calcium. In conclusion, our in depth analysis suggest that skeletal patterning, bone mass accrual and remodeling in mice proceeded independent of BRIL.

Ultrasound of ankles in the diagnosis of complications of chikungunya fever

Objective

To describe the main ultrasound findings of chikungunya fever in the ankle.

Materials and Methods

This was a cross-sectional observational study involving 52 patients referred to the Hospital Universitário Pedro Ernesto and presenting with clinical and biochemical evidence of chikungunya fever. The examinations were performed by a radiologist with more than 20 years of experience in ultrasound.

Results

The predominant gender was female (in 88.5%), and the mean age was 58.4 years. The majority (61.5%) of the patients came from the northern part of the city of Rio de Janeiro, and 46.2% were using corticosteroids to treat inflammatory symptoms. The most common alterations observed by ultrasound were joint effusion (in 69.2%), tenosynovitis (in 59.6%), cellulitis (in 46.2%), Kager's fat pad thickening (in 29.9%), myositis (of the soleus or flexor hallucis longus muscle) (in 17.3%), retrocalcaneal bursitis (in 5.8%), tendon ruptures (in 3.8%), and increased vascular flow on power Doppler (in 3.8%).

Conclusion

Signs of synovitis and tenosynovitis were the main ultrasound findings in a predominantly female population with a mean age of 58.4 years. Further studies are needed in order to define the role of ultrasound in the follow-up of such patients.

A Review of Chikungunya Virus-induced Arthralgia: Clinical Manifestations, Therapeutics, and Pathogenesis

Background:

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus that circulates predominantly in tropical and subtropical regions, potentially affecting over 1 billion people. Recently, an outbreak began in the western hemisphere and has resulted in over 1.8 million reported suspected cases. Infection often results in severe fever, rash and debilitating polyarthralgia lasting weeks to months. Additionally, the current literature reports that CHIKV can result in a severe chronic arthralgia and/or arthritis that can last months to years following the initial infection.

Objective:

The purpose of this review is to evaluate the literature and summarize the current state of knowledge regarding CHIKV-associated disease, including clinical presentation, diagnosis, risk factors for development of severe disease, treatment, and pathogenesis in human patients. Additionally, recommendations are presented regarding avenues for clinical research to help further elucidate the pathogenesis of joint disease associated with CHIKV infection.

Conclusion:

While there is an association between initial CHIKV infection and acute disease, a causal relationship with development of chronic arthralgia has not been established at this time. Potential causes of chronic CHIKV-induced arthritis have been postulated, including viral persistence, induction of autoimmune disease, and exacerbation of pre-existing joint disease. While there are numerous reports of chronic CHIKV-associated arthralgia and/or arthritis, there is currently no evidence of a definitive link between initial infection and development of chronic disease. Additional, prospective clinical research on CHIKV-associated disease is necessary to further determine the potential role of virus and development of chronic joint disease.

The Interferon-Stimulated Gene IFITM3 Restricts Infection and Pathogenesis of Arthritogenic and Encephalitic Alphaviruses

Host cells respond to viral infections by producing type I interferon (IFN), which induces the expression of hundreds of interferon-stimulated genes (ISGs). Although ISGs mediate a protective state against many pathogens, the antiviral functions of the majority of these genes have not been identified. IFITM3 is a small transmembrane ISG that restricts a broad range of viruses, including orthomyxoviruses, flaviviruses, filoviruses, and coronaviruses. Here, we show that alphavirus infection is increased in Ifitm3(-/-) and Ifitm locus deletion (Ifitm-del) fibroblasts and, reciprocally, reduced in fibroblasts transcomplemented with Ifitm3. Mechanistic studies showed that Ifitm3 did not affect viral binding or entry but inhibited pH-dependent fusion. In a murine model of chikungunya virus arthritis, Ifitm3(-/-) mice sustained greater joint swelling in the ipsilateral ankle at days 3 and 7 postinfection, and this correlated with higher levels of proinflammatory cytokines and viral burden. Flow cytometric analysis suggested that Ifitm3(-/-) macrophages from the spleen were infected at greater levels than observed in wild-type (WT) mice, results that were supported by experiments with Ifitm3(-/-) bone marrow-derived macrophages. Ifitm3(-/-) mice also were more susceptible than WT mice to lethal alphavirus infection with Venezuelan equine encephalitis virus, and this was associated with greater viral burden in multiple organs. Collectively, our data define an antiviral role for Ifitm3 in restricting infection of multiple alphaviruses.

IMPORTANCE

The interferon-induced transmembrane protein 3 (IFITM3) inhibits infection of multiple families of viruses in cell culture. Compared to other viruses, much less is known about the antiviral effect of IFITM3 on alphaviruses. In this study, we characterized the antiviral activity of mouse Ifitm3 against arthritogenic and encephalitic alphaviruses using cells and animals with a targeted gene deletion of Ifitm3 as well as deficient cells transcomplemented with Ifitm3. Based on extensive virological analysis, we demonstrate greater levels of alphavirus infection and disease pathogenesis when Ifitm3 expression is absent. Our data establish an inhibitory role for Ifitm3 in controlling infection of alphaviruses.

Fc receptors in antibody-dependent enhancement of viral infections

Sensitization of the humoral immune response to invading viruses and production of antiviral antibodies forms part of the host antiviral repertoire. Paradoxically, for a number of viral pathogens, under certain conditions, antibodies provide an attractive means of enhanced virus entry and replication in a number of cell types. Known as antibody‐dependent enhancement (ADE) of infection, the phenomenon occurs when virus‐antibody immunocomplexes interact with cells bearing complement or Fc receptors, promoting internalization of the virus and increasing infection. Frequently associated with exacerbation of viral disease, ADE of infection presents a major obstacle to the prevention of viral disease by vaccination and is thought to be partly responsible for the adverse effects of novel antiviral therapeutics such as intravenous immunoglobulins. There is a growing body of work examining the intracellular signaling pathways and epitopes responsible for mediating ADE, with a view to aiding rational design of antiviral strategies. With in vitro studies also confirming ADE as a feature of infection for a growing number of viruses, challenges remain in understanding the multilayered molecular mechanisms of ADE and its effect on viral pathogenesis.

Rainbow trout (Oncorhynchus mykiss) muscle satellite cells are targets of salmonid alphavirus infection

Sleeping disease in rainbow trout is characterized by an abnormal swimming behaviour of the fish which stay on their side at the bottom of the tanks. This sign is due to extensive necrosis and atrophy of red skeletal muscle induced by the sleeping disease virus (SDV), also called salmonid alphavirus 2. Infections of humans with arthritogenic alphaviruses, such as Chikungunya virus (CHIKV), are global causes of debilitating musculoskeletal diseases. The mechanisms by which the virus causes these pathologies are poorly understood due to the restrictive availability of animal models capable of reproducing the full spectrum of the disease. Nevertheless, it has been shown that CHIKV exhibits a particular tropism for muscle stem cells also known as satellite cells. Thus, SDV and its host constitute a relevant model to study in details the virus-induced muscle atrophy, the pathophysiological consequences of the infection of a particular cell-type in the skeletal muscle, and the regeneration of the muscle tissue in survivors together with the possible virus persistence. To study a putative SDV tropism for that particular cell type, we established an in vivo and ex vivo rainbow trout model of SDV-induced atrophy of the skeletal muscle. This experimental model allows reproducing the full panel of clinical signs observed during a natural infection since the transmission of the virus is arthropod-borne independent. The virus tropism in the muscle tissue was studied by immunohistochemistry together with the kinetics of the muscle atrophy, and the muscle regeneration post-infection was observed. In parallel, an ex vivo model of SDV infection of rainbow trout satellite cells was developed and virus replication and persistence in that particular cell type was followed up to 73 days post-infection. These results constitute the first observation of a specific SDV tropism for the muscle satellite cells.

The pathogenesis of chronic chikungunya: evolving concepts

Chikungunya virus (CHIKV) re-emerged and caused an outbreak in the Caribbean and the Americas. CHIKV can cause incapacitating arthralgia, which may be evolved in chronic arthritis that is similar to rheumatoid arthritis that lasts for months or years. This review provides an overview of known and hypothesized mechanisms that CHIKV uses to promote chronic arthritis. We hypothesized that the chronic inflammatory response that is stimulated by persisting CHIKV replication in the joints results in the arthritic symptoms seen in patients. Most hypotheses proposed in this review need to be tested or confirmed, which may help in the development of new specific treatments and vaccines against CHIKV that will not only combat viral persistence but also prevent tissue damage.

Mayaro virus: a neglected arbovirus of the Americas

Mayaro virus is a neglected tropical arbovirus that causes a mild, self-limited febrile syndrome, sometimes accompanied by a highly incapacitating arthralgia. First isolated in Trinidad and Tobago in 1954, it was reported in several countries within the tropical regions of South and Central America. Human infections are accidental spillover of the enzootic cycle. Little epidemiological data are available due to inadequate surveillance and the generic nature of clinical manifestations resulting in the misdiagnosis with other viral fevers. Despite its restricted distribution, Mayaro fever may become a public health issue due to their urbanization potential. Accurate epidemiological data are urgently needed to access the real distribution of this virus guiding public health policies better.

Early Events in Chikungunya Virus Infection-From Virus Cell Binding to Membrane Fusion

Chikungunya virus (CHIKV) is a rapidly emerging mosquito-borne alphavirus causing millions of infections in the tropical and subtropical regions of the world. CHIKV infection often leads to an acute self-limited febrile illness with debilitating myalgia and arthralgia. A potential long-term complication of CHIKV infection is severe joint pain, which can last for months to years. There are no vaccines or specific therapeutics available to prevent or treat infection. This review describes the critical steps in CHIKV cell entry. We summarize the latest studies on the virus-cell tropism, virus-receptor binding, internalization, membrane fusion and review the molecules and compounds that have been described to interfere with virus cell entry. The aim of the review is to give the reader a state-of-the-art overview on CHIKV cell entry and to provide an outlook on potential new avenues in CHIKV research.