Ross River virus: Molecular and cellular aspects of disease pathogenesis

Requirement of Fc-Fc Gamma Receptor Interaction for Antibody-Based Protection against Emerging Virus Infections

Identification of therapeutics against emerging and re-emerging viruses remains a continued priority that is only reinforced by the recent SARS-CoV-2 pandemic. Advances in monoclonal antibody (mAb) isolation, characterization, and production make it a viable option for rapid treatment development. While mAbs are traditionally screened and selected based on potency of neutralization in vitro, it is clear that additional factors contribute to the in vivo efficacy of a mAb beyond viral neutralization. These factors include interactions with Fc receptors (FcRs) and complement that can enhance neutralization, clearance of infected cells, opsonization of virions, and modulation of the innate and adaptive immune response. In this review, we discuss recent studies, primarily using mouse models, that identified a role for Fc-FcγR interactions for optimal antibody-based protection against emerging and re-emerging virus infections.

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.

High-Dose Intravenous Immunoglobulins in the Treatment of Severe Acute Viral Pneumonia: The Known Mechanisms and Clinical Effects

The current outbreak of viral pneumonia, caused by novel coronavirus SARS-CoV-2, is the focus of worldwide attention. The WHO declared the COVID-19 outbreak a pandemic event on Mar 12, 2020, and the number of confirmed cases is still on the rise worldwide. While most infected individuals only experience mild symptoms or may even be asymptomatic, some patients rapidly progress to severe acute respiratory failure with substantial mortality, making it imperative to develop an efficient treatment for severe SARS-CoV-2 pneumonia alongside supportive care. So far, the optimal treatment strategy for severe COVID-19 remains unknown. Intravenous immunoglobulin (IVIg) is a blood product pooled from healthy donors with high concentrations of immunoglobulin G (IgG) and has been used in patients with autoimmune and inflammatory diseases for more than 30 years. In this review, we aim to highlight the known mechanisms of immunomodulatory effects of high-dose IVIg therapy, the immunopathological hypothesis of viral pneumonia, and the clinical evidence of IVIg therapy in viral pneumonia. We then make cautious therapeutic inferences about high-dose IVIg therapy in treating severe COVID-19. These inferences may provide relevant and useful insights in order to aid treatment for COVID-19.

Chikungunya outbreak (2015) in the Colombian Caribbean: Latent classes and gender differences in virus infection

Chikungunya virus (CHIKV), a mosquito-borne alphavirus of the Togaviridae family, is part of a group of emergent diseases, including arbovirus, constituting an increasing public health problem in tropical areas worldwide. CHIKV causes a severe and debilitating disease with high morbidity. The first Colombian autochthonous case was reported in the Colombian Caribbean region in September 2014. Within the next two to three months, the CHIKV outbreak reached its peak. Although the CHIKV pattern of clinical symptomatology has been documented in different epidemiological studies, understanding of the relationship between clinical symptomatology and variation in phenotypic response to CHIKV infection in humans remains limited. We performed a cross sectional study following 1160 individuals clinically diagnosed with CHIKV at the peak of the Chikungunya outbreak in the Colombian Caribbean region. We examined the relationship between symptomatology and diverse phenotypic responses. Latent Class Cluster Analysis (LCCA) models were used to characterize patients’ symptomatology and further identify subgroups of individuals with differential phenotypic response. We found that most individuals presented fever (94.4%), headache (73.28%) and general discomfort (59.4%), which are distinct clinical symptoms of a viral infection. Furthermore, 11/26 (43.2%) of the categorized symptoms were more frequent in women than in men. LCCA disclosed seven distinctive phenotypic response profiles in this population of CHIKV infected individuals. Interestingly, 282 (24.3%) individuals exhibited a lower symptomatic “extreme” phenotype and 74 (6.4%) patients were within the severe complex “extreme” phenotype. Although clinical symptomatology may be diverse, there are distinct symptoms or group of symptoms that can be correlated with differential phenotypic response and perhaps susceptibility to CHIKV infection, especially in the female population. This suggests that, comparatively to men, women are a CHIKV at-risk population. Further study is needed to validate these results and determine whether the distinct LCCA profiles are a result of the immune response or a mixture of genetic, lifestyle and environmental factors. Our findings could contribute to the development of machine learning approaches to characterizing CHIKV infection in other populations. Preliminary results have shown prediction models achieving up to 92% accuracy overall, with substantial sensitivity, specificity and accuracy values per LCCA-derived cluster.

The Chikungunya virus (CHIKV) infection is a mosquito-borne virus of the Togaviridae family, part of the arbovirus group of mosquito-transmitted pathogens. CHIKV causes a severe and debilitating disease with high morbidity. In this study, we comprehensively analysed clinical data from 1160 individuals from the Colombian Caribbean, who were diagnosed with CHIKV infection during the 2014 epidemic peak and before the Zika epidemic (registered back in 2015). Further, the presence of latent classes and predictors of CHIKV susceptibility and severity of the CHIKV infection were analysed. Although it is well known that people respond differently to infection, our results showed that these differences are not arbitrary and may come from the specific orchestration of our immune response and specific genetic makeup. For example, we identified that females infected with CHIKV exhibited significant and heterogeneous phenotypic response patterns compared to men. Overall, these results inform about potential predictors and outlining strategies to study the natural history of CHIKV infection. Future studies assessing the contribution of demographic, immunological and genetic factors to symptom co-occurrence could shed some light on the severity of the clinical symptomatology and, ultimately, lead to more accurate, more efficient and differential diagnosis. These results could contribute to the development of machine learning approaches to characterizing CHIKV infection in other populations and provide more accurate and differential diagnosis.

Increasing the Capping Efficiency of the Sindbis Virus nsP1 Protein Negatively Affects Viral Infection

Alphaviruses have been the cause of both localized outbreaks and large epidemics of severe disease. Currently, there are no strategies or vaccines which are either safe or effective for preventing alphaviral infection or treating alphaviral disease. This deficit of viable therapeutics highlights the need to better understand the mechanisms behind alphaviral infection in order to develop novel antiviral strategies for treatment of alphaviral disease. In particular, this report details a previously uncharacterized aspect of the alphaviral life cycle: the importance of noncapped genomic viral RNAs for alphaviral infection. This offers new insights into the mechanisms of alphaviral replication and the impact of the noncapped genomic RNAs on viral packaging.

Alphaviruses are arthropod-borne RNA viruses that are capable of causing severe disease and are a significant burden to public health. Alphaviral replication results in the production of both capped and noncapped viral genomic RNAs (ncgRNAs), which are packaged into virions during infections of vertebrate and invertebrate cells. However, the roles that the ncgRNAs play during alphaviral infection have yet to be exhaustively characterized. Here, the importance of the ncgRNAs to alphaviral infection was assessed by using mutations of the nsP1 protein of Sindbis virus (SINV), which altered the synthesis of the ncgRNAs during infection by modulating the protein’s capping efficiency. Specifically, point mutations at residues Y286A and N376A decreased capping efficiency whereas a point mutation at D355A increased the capping efficiency of the SINV genomic RNA during genuine viral infection. Viral growth kinetics levels were significantly reduced for the D355A mutant relative to wild-type infection, whereas the Y286A and N376A mutants showed modest decreases in growth kinetics. Overall genomic translation and nonstructural protein accumulation were found to correlate with increases and decreases in capping efficiency. However, genomic, minus-strand, and subgenomic viral RNA synthesis were largely unaffected by the modulation of alphaviral capping activity. In addition, translation of the subgenomic alphaviral RNA (vRNA) was found not to be impacted by changes in capping efficiency. The mechanism by which the decreased presence of ncgRNAs reduced viral growth kinetics levels operated through the impaired production of viral particles. Collectively, these data illustrate the importance of ncgRNAs to viral infection and suggest that they play an integral role in the production of viral progeny.

Ross River Virus (RRV) infection in horses and humans: a review

A fascinating and important arbovirus is Ross River Virus (RRV) which is endemic and epizootic in nature in certain parts of the world. RRV is a member of the genus Alphavirus within the Semliki Forest complex of the family Togaviridae, which also includes the Getah virus. The virus is responsible for causing disease both in humans as well as horses. Mosquito species (Aedes camptorhynchus and Aedes vigilax; Culex annulirostris) are the most important vector for this virus. In places of low temperature as well as low rainfall or where there is lack of habitat of mosquito there is also limitation in the transmission of the virus. Such probability is higher especially in temperate regions bordering endemic regions having sub-tropical climate. There is involvement of articular as well as non-articular cells in the replication of RRV. Levels of pro-inflammatory factors viz., tumor necrosis factor-alpha (TNF-α); interferon-gamma (IFN-γ); and macrophage chemo-attractant protein-1 (MAC-1) during disease pathogenesis have been found to be reduced. Reverse transcription-polymerase chain reaction (RT-PCR) is the most advanced molecular diagnostic tool along with epitope-blocking enzyme-linked immunosorbent assay (ELISA) for detecting RRV infection. Treatment for RRV infection is only supportive. Vaccination is not a fruitful approach. Precise data collection will help the researchers to understand the RRV disease dynamics and thereby designing effective prevention and control strategy. Advances in diagnosis, vaccine development and emerging/novel therapeutic regimens need to be explored to their full potential to tackle RRV infection and the disease it causes.

Proteomics profiling of chikungunya-infected Aedes albopictus C6/36 cells reveal important mosquito cell factors in virus replication

Chikungunya virus (CHIKV) is the only causative agent of CHIKV fever with persistent arthralgia, and in some cases may lead to neurological complications which can be highly fatal, therefore it poses severe health issues in many parts of the world. CHIKV transmission can be mediated via the Aedes albopictus mosquito; however, very little is currently known about the involvement of mosquito cellular factors during CHIKV-infection within the mosquito cells. Unravelling the neglected aspects of mosquito proteome changes in CHIKV-infected mosquito cells may increase our understanding on the differences in the host factors between arthropod and mammalian cells for successful replication of CHIKV. In this study, the CHIKV-infected C6/36 cells with differential cellular proteins expression were profiled using two-dimensional gel electrophoresis (2DE) coupled with the use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). 2DE analysis on CHIKV-infected C6/36 cells has shown 23 mosquito cellular proteins that are differentially regulated, and which are involved diverse biological pathways, such as protein folding and metabolic processes. Among those identified mosquito proteins, spermatogenesis-associated factor, enolase phosphatase e-1 and chaperonin-60kD have been found to regulate CHIKV infection. Furthermore, siRNA-mediated gene knockdown of these proteins has demonstrated the biological importance of these host proteins that mediate CHIKV infection. These findings have provided an insight to the importance of mosquito host factors in the replication of CHIKV, thus providing a potential channel for developing novel antiviral strategies against CHIKV transmission.

Chikungunya virus (CHIKV), a re-emerging mosquito-borne virus, is the main cause of CHIKV fever, persistent arthralgia and serious neurological complications which can be highly fatal; therefore, it poses serious health threats worldwide. Unraveling the underappreciated aspects of mosquito cellular factors that contribute to the replication processes of CHIKV was performed using two-dimensional gel electrophoresis (2DE) coupled with the use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The 2DE proteomics profiling of CHIKV-infected mosquito C6/36 cells has revealed twenty-three proteins that were differentially regulated upon CHIKV infection. These proteins are shown to be involved in diverse biological pathways and cellular processes. Notably, upon selected genes knockdown, spermatogenesis-associated factor, enolase phosphatase e-1 and chaperonin-60kD are found to be important during the replication processes of CHIKV. This study illustrates the importance of mosquito cellular factors in association with CHIKV infection in mosquito cells and reveals an interesting portal for developing novel antiviral strategies in CHIKV studies.

Ross River virus infection in a Thuringian traveller returning from south-east Australia

Ross River virus (RRV) is an arbovirus transmitted by Aedes and Culex mosquitos. It is endemic in Australia, New Zealand and south-east Asia. Clinical manifestation rates in adults range about 20-40%. Symptoms involve arthralgia, myalgia, lymphadenopathy, fever and rash. Here we report a case of RRV in a Thuringian traveller who visited the urban South-East of Australia.

Chikungunya and the eye: a review

Chikungunya is a self-limited, systemic viral infection that has been a major health problem since the past few years. Ocular manifestations of the disease have become more prevalent in the recent years. Currently, there is neither a specific treatment nor vaccine available for chikungunya fever. This review highlights the current understanding on the pathogenesis, systemic changes with an emphasis on ocular findings, laboratory investigations, and prevention and treatment of this disease.

Mosquito cellular factors and functions in mediating the infectious entry of chikungunya virus

Chikungunya virus (CHIKV) is an arthropod-borne virus responsible for recent epidemics in the Asia Pacific regions. A customized gene expression microarray of 18,760 transcripts known to target Aedes mosquito genome was used to identify host genes that are differentially regulated during the infectious entry process of CHIKV infection on C6/36 mosquito cells. Several genes such as epsin I (EPN1), epidermal growth factor receptor pathway substrate 15 (EPS15) and Huntingtin interacting protein I (HIP1) were identified to be differentially expressed during CHIKV infection and known to be involved in clathrin-mediated endocytosis (CME). Transmission electron microscopy analyses further revealed the presence of CHIKV particles within invaginations of the plasma membrane, resembling clathrin-coated pits. Characterization of vesicles involved in the endocytic trafficking processes of CHIKV revealed the translocation of the virus particles to the early endosomes and subsequently to the late endosomes and lysosomes. Treatment with receptor-mediated endocytosis inhibitor, monodansylcadaverine and clathrin-associated drug inhibitors, chlorpromazine and dynasore inhibited CHIKV entry, whereas no inhibition was observed with caveolin-related drug inhibitors. Inhibition of CHIKV entry upon treatment with low-endosomal pH inhibitors indicated that low pH is essential for viral entry processes. CHIKV entry by clathrin-mediated endocytosis was validated via overexpression of a dominant-negative mutant of Eps15, in which infectious entry was reduced, while siRNA-based knockdown of genes associated with CME, low endosomal pH and RAB trafficking proteins exhibited significant levels of CHIKV inhibition. This study revealed, for the first time, that the infectious entry of CHIKV into mosquito cells is mediated by the clathrin-dependent endocytic pathway.

Deciphering the much neglected aspects of cellular factors in contributing to the infectious entry of CHIKV into mosquito cells may enhance our understanding of the conservation or diversity of these host factors amongst mammalian and arthropod for successful CHIKV replication. The study revealed that the infectious entry of chikungunya virus (CHIKV) into mosquito cells is mediated by the clathrin-dependent endocytic pathway. A customized gene expression microarray known to target the Aedes mosquito genome was used to identify host genes that are differentially regulated upon CHIKV infection. A combination of bio-imaging studies and pharmacological inhibitors confirmed the involvement of clathrin-mediated endocytosis as well as the importance of low endosomal pH during CHIKV infectious entry. Furthermore, the clathrin heavy chain, Eps15, RAB5, RAB7 and vacuolar ATPase B are shown to be essential for the infectious entry process of CHIKV. This study aims to underline the importance of cellular factors, particularly those associated with clathrin-dependent endocytosis, in mediating the infectious entry of CHIKV into mosquito cells.

Arthritis after infection with Chikungunya virus

Chikungunya virus (CHIKV) is an emerging alphavirus responsible for several infectious outbreaks in the world. After an acute stage of illness characterised by a fever-arthralgia syndrome and rash, joint disorders due to CHIKV infection can sometimes persist for several months or years. Chronic arthritis after this emerging disease is well documented, and similarities to rheumatoid arthritis have been described. Knowledge of the geographical epidemiology of CHIKV infection is crucial for better control of the disease. Thus, recent outbreaks have led to several studies, which have highlighted the need for a better understanding of the clinical features of Chikungunya (CHIK) and beginning knowledge of the pathophysiogenesis, which can lead to further research.

Insights into the interplay between chikungunya virus and its human host

Chikungunya virus (CHIKV) is a re-emerging arbovirus known to cause chronic arthritis with rare cases of neurological and hepatic complications. Nevertheless, infections with CHIKV can result in high morbidity and mortality rates. CHIKV is considered endemic in countries across Asia and Africa, with Europe and America also experiencing autochthonous transmission. This review highlights recent contributions to our understanding of the interactions between CHIKV and the human host. We focus on key factors contributing to disease manifestations observed in murine and simian models of CHIKV infection. Comparisons between CHIKV and Sindbis virus, the prototypic alphavirus, as well as other well-studied alphaviruses, are raised in relation to virus replication efficiency and host cell responses to infection. Recent advances concerning the role of host innate and humoral immune responses are also discussed.

Evaluation of an inactivated Ross River virus vaccine in active and passive mouse immunization models and establishment of a correlate of protection

Ross River Virus has caused reported outbreaks of epidemic polyarthritis, a chronic debilitating disease associated with significant long-term morbidity in Australia and the Pacific region since the 1920s. To address this public health concern, a formalin- and UV-inactivated whole virus vaccine grown in animal protein-free cell culture was developed and tested in preclinical studies to evaluate immunogenicity and efficacy in animal models. After active immunizations, the vaccine dose-dependently induced antibodies and protected adult mice from viremia and interferon α/β receptor knock-out (IFN-α/βR(-/-)) mice from death and disease. In passive transfer studies, administration of human vaccinee sera followed by RRV challenge protected adult mice from viremia and young mice from development of arthritic signs similar to human RRV-induced disease. Based on the good correlation between antibody titers in human sera and protection of animals, a correlate of protection was defined. This is of particular importance for the evaluation of the vaccine because of the comparatively low annual incidence of RRV disease, which renders a classical efficacy trial impractical. Antibody-dependent enhancement of infection, did not occur in mice even at low to undetectable concentrations of vaccine-induced antibodies. Also, RRV vaccine-induced antibodies were partially cross-protective against infection with a related alphavirus, Chikungunya virus, and did not enhance infection. Based on these findings, the inactivated RRV vaccine is expected to be efficacious and protect humans from RRV disease.

Identification and characterization of a ross river virus variant that grows persistently in macrophages, shows altered disease kinetics in a mouse model, and exhibits resistance to type I interferon

Alphaviruses, such as chikungunya virus, o'nyong-nyong virus, and Ross River virus (RRV), cause outbreaks of human rheumatic disease worldwide. RRV is a positive-sense single-stranded RNA virus endemic to Australia and Papua New Guinea. In this study, we sought to establish an in vitro model of RRV evolution in response to cellular antiviral defense mechanisms. RRV was able to establish persistent infection in activated macrophages, and a small-plaque variant (RRV(PERS)) was isolated after several weeks of culture. Nucleotide sequence analysis of RRV(PERS) found several nucleotide differences in the nonstructural protein (nsP) region of the RRV(PERS) genome. A point mutation was also detected in the E2 gene. Compared to the parent virus (RRV-T48), RRV(PERS) showed significantly enhanced resistance to beta interferon (IFN-β)-stimulated antiviral activity. RRV(PERS) infection of RAW 264.7 macrophages induced lower levels of IFN-β expression and production than infection with RRV-T48. RRV(PERS) was also able to inhibit type I IFN signaling. Mice infected with RRV(PERS) exhibited significantly enhanced disease severity and mortality compared to mice infected with RRV-T48. These results provide strong evidence that the cellular antiviral response can direct selective pressure for viral sequence evolution that impacts on virus fitness and sensitivity to alpha/beta IFN (IFN-α/β).

Biology and pathogenesis of chikungunya virus

Chikungunya virus (CHIKV) is a re-emerging mosquito-borne alphavirus responsible for a recent, unexpectedly severe epidemic in countries of the Indian Ocean region. Although many alphaviruses have been well studied, little was known about the biology and pathogenesis of CHIKV at the time of the 2005 outbreak. Over the past 5 years there has been a multidisciplinary effort aimed at deciphering the clinical, physiopathological, immunological and virological features of CHIKV infection. This Review highlights some of the most recent advances in our understanding of the biology of CHIKV and its interactions with the host.

Epidemiology, clinical manifestations, and diagnosis of Chikungunya fever: lessons learned from the re-emerging epidemic

Chikungunya fever, caused by "Chikungunya virus," is an arbovirus disease transmitted by the bite of infected mosquitoes belonging to the genus Aedes. Chikungunya fever epidemics have been reported from several countries around the world. The disease that was silent for nearly 32 years re-emerged in the October 2005 outbreak in India that is still ongoing. The incubation period ranges from 3 to 12 days. The onset is usually abrupt and the acute stage is characterized by sudden onset with high-grade fever, severe arthralgias, myalgias, and skin rash. Swollen tender joints and crippling arthritis are usually evident. In the chronic stage, relapses that include sensation of fever, asthenia, exacerbation of arthralgias, inflammatory polyarthritis, and stiffness may be evident. Neurological, ocular, and mucocutaneous manifestations have also been described. Chronic arthritis may develop in about 15% of the patients. Viral culture is the gold standard for the diagnosis of Chikungunya fever. Reverse transcription polymerase chain reaction and real-time loop-mediated isothermal amplification have also been found to be useful. Serodiagnostic methods for the detection of immunoglobulin M and immunoglobulin G antibodies against Chikungunya virus are more frequently used. Chikungunya is a self-limiting disease; however, severe manifestations such as meningoencephalitis, fulminant hepatitis, and bleeding manifestations may sometimes be life-threatening. Treatment is symptomatic and supportive. Prevention by educating the community and public health officials, vector control measures appear to be the best approach at controlling Chikungunya fever as no commercially available vaccine is available for public use in India for this condition presently.

A nonhuman primate model of chikungunya disease

Chikungunya disease is a severely debilitating, mosquito-borne, viral illness that has reached epidemic proportions in Africa, Asia, and the islands of the Indian Ocean. A mutation enhancing the ability of the chikungunya virus (CHIKV) to infect and be transmitted by Aedes albopictus has increased the geographical range at risk for infection due to the continuing global spread of this mosquito. Research into disease pathogenesis, vaccine development, and therapeutic design has been hindered by the lack of appropriate animal models of this disease. The meticulous study reported in this issue of the JCI by Labadie et al. is one of the first reports describing CHIKV infection of adult immunocompetent nonhuman primates. Using traditional and modern molecular and immunological approaches, the authors demonstrate that macaques infected with CHIKV are a good model of human CHIKV infection and also show that persistent arthralgia in humans may be caused by persistent CHIKV infection of macrophages.

Antibody dependent enhancement of frog virus 3 infection

Background

Viruses included in the family Iridoviridae are large, icosahedral, dsDNA viruses that are subdivided into 5 genera. Frog virus 3 (FV3) is the type species of the genus Ranavirus and the best studied iridovirus at the molecular level. Typically, antibodies directed against a virus act to neutralize the virus and limit infection. Antibody dependent enhancement occurs when viral antibodies enhance infectivity of the virus rather than neutralize it.

Results

Here we show that anti-FV3 serum present at the time of FV3 infection enhances infectivity of the virus in two non-immune teleost cell lines. We found that antibody dependent enhancement of FV3 was dependent on the Fc portion of anti-FV3 antibodies but not related to complement. Furthermore, the presence of anti-FV3 serum during an FV3 infection in a non-immune mammalian cell line resulted in neutralization of the virus. Our results suggest that a cell surface receptor specific to teleost cell lines is responsible for the enhancement.

Conclusions

This report represents the first evidence of antibody dependent enhancement in iridoviruses. The data suggests that anti-FV3 serum can either neutralize or enhance viral infection and that enhancement is related to a novel antibody dependent enhancement pathway found in teleosts that is Fc dependent.

Amelioration of alphavirus-induced arthritis and myositis in a mouse model by treatment with bindarit, an inhibitor of monocyte chemotactic proteins

OBJECTIVE

Alphaviruses such as chikungunya virus, Sindbis virus, o'nyong-nyong virus, Mayaro virus, and Ross River virus (RRV), are commonly associated with arthralgias and overt arthritides worldwide. Understanding the processes by which arthritogenic viruses cause disease is a prerequisite in the quest for better treatments. In this regard, we have recently established that monocyte/macrophages are mediators of alphavirus-induced arthritis in mice. We hypothesized that chemokines associated with monocyte/macrophage recruitment may play an important role in disease. The aim of the present investigations was to determine whether bindarit, an inhibitor of monocyte chemotactic protein (MCP) synthesis, could ameliorate alphavirus-induced rheumatic disease in mice.

METHODS

Using our recently developed mouse model of RRV-induced arthritis, which has many characteristics of RRV disease (RRVD) in humans, the effects of bindarit treatment on RRVD in mice were determined via histologic analyses, immunohistochemistry, flow cytometry, real-time polymerase chain reaction analysis, enzyme-linked immunosorbent assay, and electrophoretic mobility shift assay.

RESULTS

Bindarit-treated RRV-infected mice developed mild disease and had substantially reduced tissue destruction and inflammatory cell recruitment as compared with untreated RRV-infected mice. The virus load in the tissues was not affected by bindarit treatment. Bindarit exhibited its activity by down-regulating MCPs, which in turn led to inhibition of cell infiltration and lower production of NF-kappaB and tumor necrosis factor alpha, which are involved in mediating tissue damage.

CONCLUSION

Our data support the use of inhibitors of MCP production in the treatment of arthritogenic alphavirus syndromes and suggest that bindarit may be useful in treating RRVD and other alphavirus-induced arthritides in humans.

Macrophage-derived proinflammatory factors contribute to the development of arthritis and myositis after infection with an arthrogenic alphavirus

Alphaviruses, such as chikungunya virus and Ross River virus (RRV), are associated with outbreaks of infectious rheumatic disease in humans worldwide. Using an established mouse model of disease that mimics RRV disease in humans, we showed that macrophage-derived factors are critical in the development of striated muscle and joint tissue damage. Histologic analyses of muscle and ankle joint tissues demonstrated a substantial reduction in inflammatory infiltrates in infected mice depleted of macrophages (i.e., "macrophage-depleted mice"). Levels of the proinflammatory factors tumor necrosis factor-alpha, interferon-gamma, and macrophage chemoattractant protein-1 were also dramatically reduced in tissue samples obtained from infected macrophage-depleted mice, compared with samples obtained from infected mice without macrophage depletion. These factors were also detected in the synovial fluid of patients with RRV-induced polyarthritis. Neutralization of these factors reduced the severity of disease in mice, whereas blocking nuclear factor kappaB by treatment with sulfasalazine ameliorated RRV inflammatory disease and tissue damage. To our knowledge, these findings are the first to demonstrate that macrophage-derived products play important roles in the development of arthritis and myositis triggered by alphavirus infection.

Alphavirus production is inhibited in neurofibromin 1-deficient cells through activated RAS signalling

Virus-host interactions essential for alphavirus pathogenesis are poorly understood. To address this shortcoming, we coupled retrovirus insertional mutagenesis and a cell survival selection strategy to generate clonal cell lines broadly resistant to Sindbis virus (SINV) and other alphaviruses. Resistant cells had significantly impaired SINV production relative to wild-type (WT) cells, although virus binding and fusion events were similar in both sets of cells. Analysis of the retroviral integration sites identified the neurofibromin 1 (NF1) gene as disrupted in alphavirus-resistant cell lines. Subsequent analysis indicated that expression of NF1 was significantly reduced in alphavirus-resistant cells. Importantly, independent down-regulation of NF1 expression in WT HEK 293 cells decreased virus production and increased cell viability during SINV infection, relative to infected WT cells. Additionally, we observed hyperactive RAS signalling in the resistant HEK 293 cells, which was anticipated because NF1 is a negative regulator of RAS. Expression of constitutively active RAS (HRAS-G12V) in a WT HEK 293 cell line resulted in a marked delay in virus production, compared with infected cells transfected with parental plasmid or dominant-negative RAS (HRAS-S17N). This work highlights novel host cell determinants required for alphavirus pathogenesis and suggests that RAS signalling may play an important role in neuronal susceptibility to SINV infection.

A luciferase-based screening method for inhibitors of alphavirus replication applied to nucleoside analogues

Several members of the widespread alphavirus group are pathogenic, but no therapy is available to treat these RNA virus infections. We report here a quantitative assay to screen for inhibitors of Semliki Forest virus (SFV) replication, and demonstrate the effects of 29 nucleosides on SFV and Sindbis virus replication. The anti-SFV assay developed is based on a SFV strain containing Renilla luciferase inserted after the nsP3 coding region, yielding a marker virus in which the luciferase is cleaved out during polyprotein processing. The reporter-gene assay was miniaturized, automated and validated, resulting in a Z' value of 0.52. [3H]uridine labeling for 1 h at the maximal viral RNA synthesis time point was used as a comparative method. Anti-SFV screening and counter-screening for cell viability led to the discovery of several new SFV inhibitors. 3'-amino-3'-deoxyadenosine was the most potent inhibitor in this set, with an IC50 value of 18 microM in the reporter-gene assay and 2 microM in RNA synthesis rate detection. Besides the 3'-substituted analogues, certain N6-substituted nucleosides had similar IC50 values for both SFV and Sindbis replication, suggesting the applicability of this methodology to alphaviruses in general.

Characterization of reemerging chikungunya virus

An unprecedented epidemic of chikungunya virus (CHIKV) infection recently started in countries of the Indian Ocean area, causing an acute and painful syndrome with strong fever, asthenia, skin rash, polyarthritis, and lethal cases of encephalitis. The basis for chikungunya disease and the tropism of CHIKV remain unknown. Here, we describe the replication characteristics of recent clinical CHIKV strains. Human epithelial and endothelial cells, primary fibroblasts and, to a lesser extent, monocyte-derived macrophages, were susceptible to infection and allowed viral production. In contrast, CHIKV did not replicate in lymphoid and monocytoid cell lines, primary lymphocytes and monocytes, or monocyte-derived dendritic cells. CHIKV replication was cytopathic and associated with an induction of apoptosis in infected cells. Chloroquine, bafilomycin-A1, and short hairpin RNAs against dynamin-2 inhibited viral production, indicating that viral entry occurs through pH-dependent endocytosis. CHIKV was highly sensitive to the antiviral activity of type I and II interferons. These results provide a general insight into the interaction between CHIKV and its mammalian host.

Chikungunya virus (CHIKV) is a reemerging alphavirus responsible for an unprecedented epidemic in countries of the Indian Ocean region, causing an acute and painful syndrome with strong fever, asthenia, skin rash, polyarthritis, and lethal cases of encephalitis. The most recent epidemic reemergences were documented in Kinshasa, (50,000 estimated cases in 1999–2000), in Indonesia (2001–2003), the Indian Ocean islands of Mayotte, Mauritius, Réunion, and the Seychelles (270,000 cases in 2005–2006 in La Réunion island), and in India (1.4 to 6.5 million estimated cases in 2006–2007). There is a critical lack of knowledge on the biology of CHIKV. In particular, virtually nothing is known about the interaction of CHIKV (and of most alpahaviruses) with human primary cells. We have studied the replication characteristics and the tropism of clinical CHIKV strains from La Réunion. We designed various assays and reagents to follow viral replication, and we report here that adherent cells (epithelial and endothelial cells, primary fibroblasts), as well as macrophages, are sensitive to infection. In contrast, blood cells did not allow viral replication. We also characterized viral entry pathways and sensitivity to interferons. These results provide a general insight into the interaction between CHIKV and its mammalian host. This paper is the result of a collaborative effort between numerous teams from Institut Pasteur, the Groupe Hospitalier Sud Réunion, and other institutions. Our aim was to establish a task force with multiple and complementary expertise on virology, immunology, and cell biology in order to characterize this enigmatic virus.

The molecular and cellular aspects of arthritis due to alphavirus infections: lesson learned from Ross River virus

Alphaviruses such as the Sindbis-group viruses, Scandinavian Ockelbo virus, the African Asian chikungunya virus, the African O'nyong-nyong virus, the South American Mayaro virus, and the Australasian Barmah Forest and Ross River viruses, are commonly associated with outbreaks of acute and persistent arthritis and arthralgia in humans. The mechanisms by which these viruses cause arthritis/arthralgia are poorly understood. This chapter summarizes our current understanding of viral arthritides using our newly developed mouse model of Ross River virus-induced joint and muscle inflammation.

Attenuating characteristics of DEN-2 PDK53 in flavivirus-naïve peripheral blood mononuclear cells

A live-attenuated DEN-2 virus, DEN-2 strain 16681-PDK53, has been found to be attenuated for both humans and mice with an unknown mechanism. To partially answer this question, responses of flavivirus-naïve primary human PBMC to infection with attenuated DEN-2 PDK53 (D2/IC-VV45R) virus and its parental, virulent DEN-2 16681 virus (D2/IC-30P-A) were investigated at the cellular and genetic levels using cDNA array analysis. Both DEN-2 viruses produced similar replication kinetics in flavivirus-naïve PBMC. In contrast, virulent DEN-2 virus caused a higher percentage of apoptotic death. A macro-array analysis showed that the virulent D2/IC-30P-A virus induced changes in the expression of a greater number of genes than did the attenuated D2/IC-VV45R virus, 31 genes versus 19 genes, respectively, by 24 h post-infection. Interestingly, both viruses stimulated cytokines known to be virulence factors for DEN virus infection, such as IL-1beta, IL-6, IL-8, IL-10, MIP-1beta, and MIP-1alpha. The virulent virus additionally up-regulates immune suppression factors and down-regulates immune activator and growth factors. In conclusion, our data demonstrated that D2-PDK53 effected less change in PBMC than D2-16681 in terms of observable cellular effect and expression of cytokine and chemokine related genes.

Retrospective survey of Chikungunya disease in Réunion Island hospital staff

Réunion Island (Indian Ocean) has been suffering from its first known Chikungunya virus (CHIKV) epidemic since February 2005. To achieve a better understanding of the disease, a questionnaire was drawn up for hospital staff members and their household. CHIKV infected about one-third of the studied population, the proportion increasing with age and being higher in women. Presence of a garden was associated with CHIKV infection. The geographical distribution of cases was concordant with insect vector Aedes albopictus distribution. The main clinical signs were arthralgia and fever. The disease evolved towards full recovery in 34.4% of cases, a relapse in 55.6%, or a chronic form in 10%. Paracetamol was used as a painkiller in 95% of cases, sometimes associated with non-steroidal anti-inflammatory drugs, corticoids, or traditional herbal medicine. The survey provided valuable information on the factors that favour transmission, the clinical signs, the importance of relapses and the therapies used.

Dengue virus (DENV) antibody-dependent enhancement of infection upregulates the production of anti-inflammatory cytokines, but suppresses anti-DENV free radical and pro-inflammatory cytokine production, in THP-1 cells

The immunopathogenesis of dengue haemorrhagic fever and dengue shock syndrome is thought to be mediated by a variety of host factors. Enhancing antibodies are one of the key regulating molecules. These antibodies, via antibody-dependent enhancement (ADE) of infection, are able to facilitate dengue virus (DENV) growth in Fc-bearing host cells. The mechanism of ADE-enhanced DENV production is believed to be mediated through increasing the infected-cell mass. In the present work, the effect of ADE infection was explored further, focusing on the post-entry events of ADE infection. It was hypothesized that the higher virus production in ADE infection compared with DENV infection may be due to the ability of this infection pathway to suppress key antiviral molecules. Therefore, the influence of ADE infection on pro- and anti-inflammatory cytokines, including interleukin-12 (IL-12), gamma interferon (IFN-gamma), tumour necrosis factor alpha (TNF-alpha), IL-6 and IL-10, was investigated and it was found that DENV infection via the Fc receptor-mediated pathway was able to suppress the transcription and translation of IL-12, IFN-gamma and TNF-alpha. In contrast, infection via this route facilitated expression and synthesis of the anti-inflammatory cytokines IL-6 and IL-10. Moreover, this study demonstrates that the ADE infection pathway also suppresses an innate anti-DENV mediator, nitric oxide radicals, by disrupting the transcription of the iNOS gene transcription factor, IRF-1, and blocking the activation of STAT-1. In conclusion, ADE infection not only facilitates the entry process, but also modifies innate and adaptive intracellular antiviral mechanisms, resulting in unrestricted DENV replication in THP-1 cells.

Infection and musculoskeletal conditions: Viral causes of arthritis

Several viruses cause postinfectious arthritis. The disease is a typical manifestation of arthritogenic alphaviruses, rubella virus and human parvovirus B19. In addition, arthritis is not uncommon after infection by HIV, cytomegalovirus, hepatitis B virus, hepatitis C virus, or Epstein-Barr virus (EBV). Also prolonged arthritis may result from viral infections, particularly with alphaviruses and human parvovirus B19. Viruses such as EBV and B19 may have significant roles in initiating chronic arthropathies, which in some cases may be indistinguishable from rheumatoid arthritis.