Persistent RNA virus infections: do PAMPS drive chronic disease?

Differential TLR-ERK1/2 activity promotes viral ssRNA and dsRNA mimic-induced dysregulated immunity in macrophages

RNA virus induced excessive inflammation and impaired antiviral interferon (IFN-I) responses are associated with severe disease. This innate immune response, also referred to as 'dysregulated immunity,' is caused by viral single-stranded RNA (ssRNA) and double-stranded-RNA (dsRNA) mediated exuberant inflammation and viral protein-induced IFN antagonism. However, key host factors and the underlying mechanism driving viral RNA-mediated dysregulated immunity are poorly defined. Here, using viral ssRNA and dsRNA mimics, which activate toll-like receptor 7 (TLR7) and TLR3, respectively, we evaluated the role of viral RNAs in causing dysregulated immunity. We show that murine bone marrow-derived macrophages (BMDMs) stimulated with TLR3 and TLR7 agonists induce differential inflammatory and antiviral cytokine response. TLR7 activation triggered a robust inflammatory cytokine/chemokine induction compared to TLR3 activation, whereas TLR3 stimulation induced significantly increased IFN/IFN stimulated gene (ISG) response relative to TLR7 activation. To define the mechanistic basis for dysregulated immunity, we examined cell-surface and endosomal TLR levels and downstream mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-kB) activation. We identified a significantly higher cell-surface and endosomal TLR7 expression compared to TLR3, which further correlated with early and robust MAPK (pERK1/2 and p-P38) and NF-kB activation in TLR7-stimulated macrophages. Furthermore, blocking EKR1/2, p38, and NF-kB activity reduced TLR3/7-induced inflammatory cytokine/chemokine levels, whereas only ERK1/2 inhibition enhanced viral RNA-mimic-induced IFN/ISG responses. Collectively, our results illustrate that high cell surface and endosomal TLR7 expression and robust ERK1/2 activation drive viral ssRNA mimic-induced excessive inflammatory and reduced IFN/ISG responses, and blocking ERK1/2 activity would mitigate viral-RNA/TLR-induced dysregulated immunity.

Characterization of Japanese Encephalitis Virus Isolated from Persistently Infected Mouse Embryo Cells

Japanese encephalitis virus (JEV) has a positive-sense single-stranded RNA genome and belongs to the genus Flavivirus of the family Flaviviridae. Persistent JEV infection was previously shown in pig blood cells, which act as a natural reservoir of this virus. We aimed to determine the pathogenicity factors involved in persistent JEV infection by analyzing the pathogenicity and genome sequences of a virus isolated from a persistent infection model. We established persistent JEV infections in cells by inoculating mouse fetus primary cell cultures with the Beijing-1 strain of JEV and then performing repeated infected cell passages, harvesting viruses after each passage while monitoring the plaque size over 100 generations. The virus growth rate was compared among Vero, C6/36, and Neuro-2a cells. The pathogenicity was examined in female ICR mice at several ages. Additionally, we determined the whole-genome sequences. The 134th Beijing-1-derived persistent virus (ME134) grew in Vero cells at a similar rate to the parent strain but did not grow well in C6/36 or Neuro-2a cells. No differences were observed in pathogenicity after intracerebral inoculation in mice of different ages, but the survival time was extended in older mice. Mutations in the persistent virus genomes were found across all regions but were mainly focused in the NS3, NS4b, and 3'NCR regions, with a 34-base-pair deletion found in the variable region. The short deletion in the 3'NCR region appeared to be responsible for the reduced pathogenicity and growth efficiency.

Murine Parainfluenza Virus Persists in Lung Innate Immune Cells Sustaining Chronic Lung Pathology

Respiratory viruses including the human parainfluenza viruses (hPIVs) are a constant burden to human health, with morbidity and mortality frequently increased after the acute phase of the infection. Although is proven that respiratory viruses can persist in vitro, the mechanisms of virus or viral products persistence, their sources, and their impact on chronic respiratory diseases in vivo are unknown. Here, we used Sendai virus (SeV) to model hPIV infection in mice and test whether virus persistence associates with the development of chronic lung disease. Following SeV infection, virus products were detected in lung macrophages, type 2 innate lymphoid cells (ILC2s) and dendritic cells for several weeks after the infectious virus was cleared. Cells containing viral protein showed strong upregulation of antiviral and type 2 inflammation-related genes that associate with the development of chronic post-viral lung diseases, including asthma. Lineage tracing of infected cells or cells derived from infected cells suggests that distinct functional groups of cells contribute to the chronic pathology. Importantly, targeted ablation of infected cells or those derived from infected cells significantly ameliorated chronic lung disease. Overall, we identified persistent infection of innate immune cells as a critical factor in the progression from acute to chronic post viral respiratory disease.

mAb therapy controls CNS-resident lyssavirus infection via a CD4 T cell-dependent mechanism

Infections with rabies virus (RABV) and related lyssaviruses are uniformly fatal once virus accesses the central nervous system (CNS) and causes disease signs. Current immunotherapies are thus focused on the early, pre-symptomatic stage of disease, with the goal of peripheral neutralization of virus to prevent CNS infection. Here, we evaluated the therapeutic efficacy of F11, an anti-lyssavirus human monoclonal antibody (mAb), on established lyssavirus infections. We show that a single dose of F11 limits viral load in the brain and reverses disease signs following infection with a lethal dose of lyssavirus, even when administered after initiation of robust virus replication in the CNS. Importantly, we found that F11-dependent neutralization is not sufficient to protect animals from mortality, and a CD4 T cell-dependent adaptive immune response is required for successful control of infection. F11 significantly changes the spectrum of leukocyte populations in the brain, and the FcRγ-binding function of F11 contributes to therapeutic efficacy. Thus, mAb therapy can drive potent neutralization-independent T cell-mediated effects, even against an established CNS infection by a lethal neurotropic virus.

Evolution and immunopathology of chikungunya virus informs therapeutic development

Chikungunya virus (CHIKV), a mosquito-borne alphavirus, is an emerging global threat identified in more than 60 countries across continents. The risk of CHIKV transmission is rising due to increased global interactions, year-round presence of mosquito vectors, and the ability of CHIKV to produce high host viral loads and undergo mutation. Although CHIKV disease is rarely fatal, it can progress to a chronic stage, during which patients experience severe debilitating arthritis that can last from several weeks to months or years. At present, there are no licensed vaccines or antiviral drugs for CHIKV disease, and treatment is primarily symptomatic. This Review provides an overview of CHIKV pathogenesis and explores the available therapeutic options and the most recent advances in novel therapeutic strategies against CHIKV infections.

Viral infections in orthopedics: A systematic review and classification proposal

BACKGROUND

Although the impact of microbial infections on orthopedic clinical outcomes is well recognized, the influence of viral infections on the musculoskeletal system might have been underestimated.

AIM

To systematically review the available evidence on risk factors and musculoskeletal manifestations following viral infections and to propose a pertinent classification scheme.

METHODS

We searched MEDLINE, Cochrane Central Register of Controlled Trials (CENTRAL), the Reference Citation Analysis (RCA), and Scopus for completed studies published before January 30, 2021, to evaluate risk factors and bone and joint manifestations of viral infection in animal models and patient registries. Quality assessment was performed using SYRCLE's risk of bias tool for animal studies, Moga score for case series, Wylde score for registry studies, and Newcastle-Ottawa Scale for case-control studies.

RESULTS

Six human and four animal studies were eligible for inclusion in the qualitative synthesis. Hepatitis C virus was implicated in several peri- and post-operative complications in patients without cirrhosis after major orthopedic surgery. Herpes virus may affect the integrity of lumbar discs, whereas Ross River and Chikungunya viruses provoke viral arthritis and bone loss.

CONCLUSION

Evidence of moderate strength suggested that viruses can cause moderate to severe arthritis and osteitis. Risk factors such as pre-existing rheumatologic disease contributed to higher disease severity and duration of symptoms. Therefore, based on our literature search, the proposed clinical and pathogenetic classification scheme is as follows: (1) Viral infections of bone or joint; (2) Active bone and joint inflammatory diseases secondary to viral infections in other organs or tissues; and (3) Viral infection as a risk factor for post-surgical bacterial infection.

A Virus Is a Community: Diversity within Negative-Sense RNA Virus Populations

Negative-sense RNA virus populations are composed of diverse viral components that interact to form a community and shape the outcome of virus infections. At the genomic level, RNA virus populations consist not only of a homogeneous population of standard viral genomes but also of an extremely large number of genome variants, termed viral quasispecies, and nonstandard viral genomes, which include copy-back viral genomes, deletion viral genomes, mini viral RNAs, and hypermutated RNAs. At the particle level, RNA virus populations are composed of pleomorphic particles, particles missing or having additional genomes, and single particles or particle aggregates. As we continue discovering more about the components of negative-sense RNA virus populations and their crucial functions during virus infection, it will become more important to study RNA virus populations as a whole rather than their individual parts. In this review, we will discuss what is known about the components of negative-sense RNA virus communities, speculate how the components of the virus community interact, and summarize what vaccines and antiviral therapies are being currently developed to target or harness these components.

Why does viral RNA sometimes persist after recovery from acute infections?

DNA viruses often persist in the body of their host, becoming latent and recurring many months or years later. By contrast, most RNA viruses cause acute infections that are cleared from the host as they lack the mechanisms to persist. However, it is becoming clear that viral RNA can persist after clinical recovery and elimination of detectable infectious virus. This persistence can either be asymptomatic or associated with late progressive disease or nonspecific lingering symptoms, such as may be the case following infection with Ebola or Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Why does viral RNA sometimes persist after recovery from an acute infection? Where does the RNA come from? And what are the consequences?

Long COVID: current status in Japan and knowledge about its molecular background

Even after recovering from coronavirus disease 2019 (COVID-19), patients can experience prolonged complaints, referred to as "long COVID". Similar to reports in Caucasians, a follow-up study in Japan revealed that fatigue, dyspnea, cough, anosmia/dysgeusia, and dyssomnia are common symptoms. Although the precise mode of long COVID remains elusive, multiple etiologies such as direct organ damage by infection with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), autoimmunity, prolonged inflammatory reactions, and psychiatric impairment seem to be involved. Notably, SARS-CoV-2 is neurotropic, and viral RNA and proteins are continuously detectable in multiple organs, including the brain. Viral proteins exert a number of different toxic effects on cells, suggesting that persistent infection is a key element for understanding long COVID. Here, we first reviewed the current status of long COVID in Japan, and then summarized literature that help us understand the molecular background of the symptoms. Finally, we discuss the feasibility of vaccination as a treatment for patients with long COVID.

Tolerance and Persistence of Ebola Virus in Primary Cells from Mops condylurus, a Potential Ebola Virus Reservoir

Although there have been documented Ebola virus disease outbreaks for more than 40 years, the natural reservoir host has not been identified. Recent studies provide evidence that the Angolan free-tailed bat (Mops condylurus), an insectivorous microbat, is a possible ebolavirus reservoir. To investigate the potential role of this bat species in the ecology of ebolaviruses, replication, tolerance, and persistence of Ebola virus (EBOV) were investigated in 10 different primary bat cell isolates from M. condylurus. Varying EBOV replication kinetics corresponded to the expression levels of the integral membrane protein NPC1. All primary cells were highly tolerant to EBOV infection without cytopathic effects. The observed persistent EBOV infection for 150 days in lung primary cells, without resultant selective pressure leading to virus mutation, indicate the intrinsic ability of EBOV to persist in this bat species. These results provide further evidence for this bat species to be a likely reservoir of ebolaviruses.

Human parainfluenza virus type 1 regulates cholesterol biosynthesis and establishes quiescent infection in human airway cells

Human parainfluenza virus type 1 (hPIV1) and 3 (hPIV3) cause seasonal epidemics, but little is known about their interaction with human airway cells. In this study, we determined cytopathology, replication, and progeny virion release from human airway cells during long-term infection in vitro. Both viruses readily established persistent infection without causing significant cytopathic effects. However, assembly and release of hPIV1 rapidly declined in sharp contrast to hPIV3 due to impaired viral ribonucleocapsid (vRNP) trafficking and virus assembly. Transcriptomic analysis revealed that both viruses induced similar levels of type I and III IFNs. However, hPIV1 induced specific ISGs stronger than hPIV3, such as MX2, which bound to hPIV1 vRNPs in infected cells. In addition, hPIV1 but not hPIV3 suppressed genes involved in lipid biogenesis and hPIV1 infection resulted in ubiquitination and degradation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, a rate limiting enzyme in cholesterol biosynthesis. Consequently, formation of cholesterol-rich lipid rafts was impaired in hPIV1 infected cells. These results indicate that hPIV1 is capable of regulating cholesterol biogenesis, which likely together with ISGs contributes to establishment of a quiescent infection.

Seasonal epidemics caused by parainfluenza viruses result in a significant burden of disease in children. These viruses infect airway epithelial cells and cause acute respiratory infection. Humans are the only known hosts for these viruses, but how these viruses are maintained within the population is not known. In this study, we analyzed human airway cells infected with type 1 and 3 parainfluenza viruses. Both viruses readily established persistent infection without causing major cytopathic effects. However, assembly and release of hPIV1 rapidly declined over time in sharp contrast to hPIV3. HPIV1 infected cells formed large aggregates of viral nucleocapsid at late time points, suggesting impaired nucleocapsid trafficking and virus assembly. Transcriptomic analysis of infected cells showed no major difference in IFN induction between the viruses, while hPIV1 induced elevated levels of interferon stimulated genes (ISGs) compared to hPIV3. Interestingly, hPIV1 infection specifically downregulated genes involved in cholesterol biogenesis. We also found that hPIV1 infection induced ubiquitination and degradation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, a rate limiting enzyme in cholesterol biosynthesis. These results suggest that induction of IFN-independent ISGs and suppression of cholesterol by hPIV1 likely play a role in establishing quiescent infection in human respiratory epithelial cells.

SARS-CoV-2: lessons from both the history of medicine and from the biological behavior of other well-known viruses

SARS-CoV-2 is the etiological agent of the current pandemic worldwide and its associated disease COVID-19. In this review, we have analyzed SARS-CoV-2 characteristics and those ones of other well-known RNA viruses viz. HIV, HCV and Influenza viruses, collecting their historical data, clinical manifestations and pathogenetic mechanisms. The aim of the work is obtaining useful insights and lessons for a better understanding of SARS-CoV-2. These pathogens present a distinct mode of transmission, as SARS-CoV-2 and Influenza viruses are airborne, whereas HIV and HCV are bloodborne. However, these viruses exhibit some potential similar clinical manifestations and pathogenetic mechanisms and their understanding may contribute to establishing preventive measures and new therapies against SARS-CoV-2.

Global emergence of West Nile virus: Threat & preparedness in special perspective to India

West Nile virus (WNV) is a mosquito-borne single-stranded RNA neurotropic virus within the family Flaviviridae. The virus was first reported in the West Nile province of Uganda in 1937. Since then, sporadic cases have been reported until the last two decades when it has emerged as a threat to public health. The emergence of WNV with more severity in recent times is intriguing. Considering this phenomenon, the WNV-affected areas of the world were distinguished as old versus new in a depicted world map. The present review showcases the historical and epidemiological perspectives of the virus, genetic diversity of prevailing lineages and clinical spectrum associated with its infection. Emergence of the virus has been discussed in special context to India because of co-circulation of different WNV lineages/strains along with other flaviviruses. Recent laboratory diagnostics, vaccine development and clinical management associated with WNV infection have also been discussed. Further, the research gaps, especially in context to India have been highlighted that may have a pivotal role in combating the spread of WNV.

RNA-dependent RNA polymerase (RdRp) inhibitors: The current landscape and repurposing for the COVID-19 pandemic

The widespread nature of several viruses is greatly credited to their rapidly altering RNA genomes that enable the infection to persist despite challenges presented by host cells. Within the RNA genome of infections is RNA-dependent RNA polymerase (RdRp), which is an essential enzyme that helps in RNA synthesis by catalysing the RNA template-dependent development of phosphodiester bonds. Therefore, RdRp is an important therapeutic target in RNA virus-caused diseases, including SARS-CoV-2. In this review, we describe the promising RdRp inhibitors that have been launched or are currently in clinical studies for the treatment of RNA virus infections. Structurally, nucleoside inhibitors (NIs) bind to the RdRp protein at the enzyme active site, and nonnucleoside inhibitors (NNIs) bind to the RdRp protein at allosteric sites. By reviewing these inhibitors, more precise guidelines for the development of more promising anti-RNA virus drugs should be set, and due to the current health emergency, they will eventually be used for COVID-19 treatment.

Antiviral Drug Targets of Single-Stranded RNA Viruses Causing Chronic Human Diseases

Ribonucleic acid (RNA) viruses associated with chronic diseases in humans are major threats to public health causing high mortality globally. The high mutation rate of RNA viruses helps them to escape the immune response and also is responsible for the development of drug resistance. Chronic infections caused by human immunodeficiency virus (HIV) and hepatitis viruses (HBV and HCV) lead to acquired immunodeficiency syndrome (AIDS) and hepatocellular carcinoma respectively, which are one of the major causes of human deaths. Effective preventative measures to limit chronic and re-emerging viral infections are absolutely necessary. Each class of antiviral agents targets a specific stage in the viral life cycle and inhibits them from its development and proliferation. Most often, antiviral drugs target a specific viral protein, therefore only a few broad-spectrum drugs are available. This review will be focused on the selected viral target proteins of pathogenic viruses containing single-stranded (ss) RNA genome that causes chronic infections in humans (e.g. HIV, HCV, Flaviviruses). In the recent past, an exponential increase in the number of available three-dimensional protein structures (>150000 in Protein Data Bank), allowed us to better understand the molecular mechanism of action of protein targets and antivirals. Advancements in the in silico approaches paved the way to design and develop several novels, highly specific small-molecule inhibitors targeting the viral proteins.

Long-Lived Skin-Resident Memory T Cells Contribute to Concomitant Immunity in Cutaneous Leishmaniasis

Memory T cells, which protect against reinfection in many diseases, have predominantly been characterized in models of acute viral or bacterial infection. In contrast, memory T cells are less well understood in diseases where pathogens persist following disease resolution, such as leishmaniasis, in spite of the fact that these infections often lead to immunity to reinfection, termed concomitant immunity. Defining the T cells that mediate concomitant immunity is an important step in developing vaccines for these diseases. One set of protective T cells are short-lived effector T cells requiring constant stimulation, which would be difficult to maintain by vaccination. However, parasite-independent memory T cells, including central memory T cells (Tcm) and skin-resident T cells (Trm) have recently been described in leishmaniasis. Given their location, Trm cells are particularly suited for protection, and were found to globally seed the skin following Leishmania infection or immunization. Upon challenge, Trm cells rapidly respond to reduce the parasite burden, suggesting that developing strategies to generate parasite-independent Trm cells will be an important step in the quest for a successful leishmaniasis vaccine.

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.

Clearance of Chikungunya Virus Infection in Lymphoid Tissues Is Promoted by Treatment with an Agonistic Anti-CD137 Antibody

CD137, a member of the tumor necrosis factor receptor superfamily of cell surface proteins, acts as a costimulatory receptor on T cells, natural killer cells, B cell subsets, and some dendritic cells. Agonistic anti-CD137 monoclonal antibody (MAb) therapy has been combined with other chemotherapeutic agents in human cancer trials. Based on its ability to promote tumor clearance, we hypothesized that anti-CD137 MAb might activate immune responses and resolve chronic viral infections. We evaluated anti-CD137 MAb therapy in a mouse infection model of chikungunya virus (CHIKV), an alphavirus that causes chronic polyarthritis in humans and is associated with reservoirs of CHIKV RNA that are not cleared efficiently by adaptive immune responses. Analysis of viral tropism revealed that CHIKV RNA was present preferentially in splenic B cells and follicular dendritic cells during the persistent phase of infection, and animals lacking B cells did not develop persistent CHIKV infection in lymphoid tissue. Anti-CD137 MAb treatment resulted in T cell-dependent clearance of CHIKV RNA in lymphoid tissue, although this effect was not observed in musculoskeletal tissue. The clearance of CHIKV RNA from lymphoid tissue by anti-CD137 MAb was associated with reductions in the numbers of germinal center B cells and follicular dendritic cells. Similar results were observed with anti-CD137 MAb treatment of mice infected with Mayaro virus, a related arthritogenic alphavirus. Thus, anti-CD137 MAb treatment promotes resolution of chronic alphavirus infection in lymphoid tissues by reducing the numbers of target cells for infection and persistence.IMPORTANCE Although CHIKV causes persistent infection in lymphoid and musculoskeletal tissues in multiple animals, the basis for this is poorly understood, which has hampered pharmacological efforts to promote viral clearance. Here, we evaluated the therapeutic effects on persistent CHIKV infection of an agonistic anti-CD137 MAb that can activate T cell and natural killer cell responses to clear tumors. We show that treatment with anti-CD137 MAb promotes the clearance of persistent alphavirus RNA from lymphoid but not musculoskeletal tissues. This occurs because anti-CD137 MAb-triggered T cells reduce the numbers of target germinal center B cells and follicular dendritic cells, which are the primary reservoirs for CHIKV in the spleen and lymph nodes. Our studies help to elucidate the basis for CHIKV persistence and begin to provide strategies that can clear long-term cellular reservoirs of infection.

Dermal and muscle fibroblasts and skeletal myofibers survive chikungunya virus infection and harbor persistent RNA

Chikungunya virus (CHIKV) is an arthritogenic alphavirus that acutely causes fever as well as severe joint and muscle pain. Chronic musculoskeletal pain persists in a substantial fraction of patients for months to years after the initial infection, yet we still have a poor understanding of what promotes chronic disease. While replicating virus has not been detected in joint-associated tissues of patients with persistent arthritis nor in various animal models at convalescent time points, viral RNA is detected months after acute infection. To identify the cells that might contribute to pathogenesis during this chronic phase, we developed a recombinant CHIKV that expresses Cre recombinase (CHIKV-3'-Cre). CHIKV-3'-Cre replicated in myoblasts and fibroblasts, and it induced arthritis during the acute phase in mice. Importantly, it also induced chronic disease, including persistent viral RNA and chronic myositis and synovitis similar to wild-type virus. CHIKV-3'-Cre infection of tdTomato reporter mice resulted in a population of tdTomato+ cells that persisted for at least 112 days. Immunofluorescence and flow cytometric profiling revealed that these tdTomato+ cells predominantly were myofibers and dermal and muscle fibroblasts. Treatment with an antibody against Mxra8, a recently defined host receptor for CHIKV, reduced the number of tdTomato+ cells in the chronic phase and diminished the levels of chronic viral RNA, implicating these tdTomato+ cells as the reservoir of chronic viral RNA. Finally, isolation and flow cytometry-based sorting of the tdTomato+ fibroblasts from the skin and ankle and analysis for viral RNA revealed that the tdTomato+ cells harbor most of the persistent CHIKV RNA at chronic time points. Therefore, this CHIKV-3'-Cre and tdTomato reporter mouse system identifies the cells that survive CHIKV infection in vivo and are enriched for persistent CHIKV RNA. This model represents a useful tool for studying CHIKV pathogenesis in the acute and chronic stages of disease.

The Clinical Features, Pathogenesis and Methotrexate Therapy of Chronic Chikungunya Arthritis

Chikungunya fever (CHIKF) is an emerging viral infection that has spread widely, along with its Aedes vectors, throughout the tropics and beyond, causing explosive epidemics of acute illness and persistent disabling arthritis. The rheumatic symptoms associated with chikungunya virus (CHIKV) infection include polyarthralgia, polyarthritis, morning stiffness, joint edema, and erythema. Chronic CHIK arthritis (CCA) often causes severe pain and associated disability. The pathogenesis of CCA is not well understood. Proposed hypotheses include the persistence of a low level of replicating virus in the joints, the persistence of viral RNA in the synovium, and the induction of autoimmunity. In this review, we describe the main hypotheses of CCA pathogenesis, some of which support methotrexate (MTX) treatment which has been shown to be effective in preliminary studies in CCA.

Orthohantaviruses belonging to three phylogroups all inhibit apoptosis in infected target cells

Orthohantaviruses, previously known as hantaviruses, are zoonotic viruses that can cause hantavirus pulmonary syndrome (HPS) and hemorrhagic fever with renal syndrome (HFRS) in humans. The HPS-causing Andes virus (ANDV) and the HFRS-causing Hantaan virus (HTNV) have anti-apoptotic effects. To investigate if this represents a general feature of orthohantaviruses, we analysed the capacity of six different orthohantaviruses – belonging to three distinct phylogroups and representing both pathogenic and non-pathogenic viruses – to inhibit apoptosis in infected cells. Primary human endothelial cells were infected with ANDV, HTNV, the HFRS-causing Puumala virus (PUUV) and Seoul virus, as well as the putative non-pathogenic Prospect Hill virus and Tula virus. Infected cells were then exposed to the apoptosis-inducing chemical staurosporine or to activated human NK cells exhibiting a high cytotoxic potential. Strikingly, all orthohantaviruses inhibited apoptosis in both settings. Moreover, we show that the nucleocapsid (N) protein from all examined orthohantaviruses are potential targets for caspase-3 and granzyme B. Recombinant N protein from ANDV, PUUV and the HFRS-causing Dobrava virus strongly inhibited granzyme B activity and also, to certain extent, caspase-3 activity. Taken together, this study demonstrates that six different orthohantaviruses inhibit apoptosis, suggesting this to be a general feature of orthohantaviruses likely serving as a mechanism of viral immune evasion.

Chikungunya Arthritis: Implications of Acute and Chronic Inflammation Mechanisms on Disease Management

In the past decade, arboviruses-arthropod-borne viruses-have been the focus of public health institutions worldwide following a spate of devastating outbreaks. Chikungunya virus, an arbovirus that belongs to the alphavirus genus, is a reemerging arthritogenic virus that has caused explosive outbreaks since 2006, notably on Réunion Island, and more recently in the Caribbean, South America, India, and Southeast Asia. The severity of arthritic disease caused by chikungunya virus has prompted public health authorities in affected countries to develop specific guidelines to tackle this pathogen. Chikungunya virus disease manifests first as an acute stage of severe joint inflammation and febrile illness, which later progresses to a chronic stage, during which patients may experience debilitating and persisting articular pain for extended periods. This review aims to provide a broad perspective on current knowledge of chikungunya virus pathogenesis by identifying key clinical and experimental studies that have contributed to our understanding of chikungunya virus to date. In addition, the review explores the practical aspects of treatment and management of both acute and chronic chikungunya virus based on clinical experience during chikungunya virus outbreaks. Finally, recent findings on potential therapeutic solutions-from antiviral agents to immunomodulators-are reviewed to provide both viral immunologists and clinical rheumatologists with a balanced perspective on the nature of a reemerging arboviral disease of significant public health concern, and insight into future therapeutic approaches to better address the treatment and management of chikungunya virus.

Lower temperatures reduce type I interferon activity and promote alphaviral arthritis

Chikungunya virus (CHIKV) belongs to a group of mosquito-borne alphaviruses associated with acute and chronic arthropathy, with peripheral and limb joints most commonly affected. Using a mouse model of CHIKV infection and arthritic disease, we show that CHIKV replication and the ensuing foot arthropathy were dramatically reduced when mice were housed at 30°C, rather than the conventional 22°C. The effect was not associated with a detectable fever, but was dependent on type I interferon responses. Bioinformatics analyses of RNA-Seq data after injection of poly(I:C)/jetPEI suggested the unfolded protein response and certain type I interferon responses are promoted when feet are slightly warmer. The ambient temperature thus appears able profoundly to effect anti-viral activity in the periphery, with clear consequences for alphaviral replication and the ensuing arthropathy. These observations may provide an explanation for why alphaviral arthropathies are largely restricted to joints of the limbs and the extremities.

Vertebrate Reservoirs of Arboviruses: Myth, Synonym of Amplifier, or Reality?

The rapid succession of the pandemic of arbovirus diseases, such as dengue, West Nile fever, chikungunya, and Zika fever, has intensified research on these and other arbovirus diseases worldwide. Investigating the unique mode of vector-borne transmission requires a clear understanding of the roles of vertebrates. One major obstacle to this understanding is the ambiguity of the arbovirus definition originally established by the World Health Organization. The paucity of pertinent information on arbovirus transmission at the time contributed to the notion that vertebrates played the role of reservoir in the arbovirus transmission cycle. Because this notion is a salient feature of the arbovirus definition, it is important to reexamine its validity. This review addresses controversial issues concerning vertebrate reservoirs and their role in arbovirus persistence in nature, examines the genesis of the problem from a historical perspective, discusses various unresolved issues from multiple points of view, assesses the present status of the notion in light of current knowledge, and provides options for a solution to resolve the issue.