Exploring Barmah Forest virus pathogenesis: molecular tools to investigate non-structural protein 3 nuclear localization and viral genomic determinants of replication.

Barmah Forest virus (BFV) is a mosquito-borne virus that causes arthralgia with accompanying rash, fever, and myalgia in humans. The virus is mainly found in Australia and has caused outbreaks associated with significant health concerns. As the sole representative of the Barmah Forest complex within the genus Alphavirus, BFV is not closely related genetically to other alphaviruses. Notably, basic knowledge of BFV molecular virology has not been well studied due to a lack of critical investigative tools such as an infectious clone. Here we describe the construction of an infectious BFV cDNA clone based on Genbank sequence and demonstrate that the clone-derived virus has in vitro and in vivo properties similar to naturally occurring virus, BFV field isolate 2193 (BFV2193-FI). A substitution in nsP4, V1911D, which was identified in the Genbank reference sequence, was found to inhibit virus rescue and replication. T1325P substitution in nsP2 selected during virus passaging was shown to be an adaptive mutation, compensating for the inhibitory effect of nsP4-V1911D. The two mutations were associated with changes in viral non-structural polyprotein processing and type I interferon (IFN) induction. Interestingly, a nuclear localization signal, active in mammalian but not mosquito cells, was identified in nsP3. A point mutation abolishing nsP3 nuclear localization attenuated BFV replication. This effect was more prominent in the presence of type I interferon signaling, suggesting nsP3 nuclear localization might be associated with IFN antagonism. Furthermore, abolishing nsP3 nuclear localization reduced virus replication in mice but did not significantly affect disease.IMPORTANCEBarmah Forest virus (BFV) is Australia's second most prevalent arbovirus, with approximately 1,000 cases reported annually. The clinical symptoms of BFV infection include rash, polyarthritis, arthralgia, and myalgia. As BFV is not closely related to other pathogenic alphaviruses or well-studied model viruses, our understanding of its molecular virology and mechanisms of pathogenesis is limited. There is also a lack of molecular tools essential for corresponding studies. Here we describe the construction of an infectious clone of BFV, variants harboring point mutations, and sequences encoding marker protein. In infected mammalian cells, nsP3 of BFV was located in the nuclei. This finding extends our understanding of the diverse mechanisms used by alphavirus replicase proteins to interact with host cells. Our novel observations highlight the complex synergy through which the viral replication machinery evolves to correct mutation errors within the viral genome.

LDL receptor in alphavirus entry: structural analysis and implications for antiviral therapy.

Various low-density lipoprotein receptors (LPRs) have been identified as entry factors for alphaviruses, and structures of the corresponding virion-receptor complexes have been determined. Here, we analyze the similarities and differences in the receptor binding modes of multiple alphaviruses to understand their ability to infect a wide range of hosts. We further discuss the challenges associated with the development of broad-spectrum treatment strategies against a diverse range of alphaviruses.

4'-Fluorouridine inhibits alphavirus replication and infection in vitro and in vivo.

Chikungunya virus (CHIKV) is an enveloped, positive-sense RNA virus that has re-emerged to cause millions of human infections worldwide. In humans, acute CHIKV infection causes fever and severe muscle and joint pain. Chronic and debilitating arthritis and joint pain can persist for months to years. To date, there are no approved antivirals against CHIKV. Recently, the ribonucleoside analog 4'-fluorouridine (4'-FlU) was reported as a highly potent orally available inhibitor of SARS-CoV-2, respiratory syncytial virus, and influenza virus replication. In this study, we assessed 4'-FlU's potency and breadth of inhibition against a panel of alphaviruses including CHIKV, and found that it broadly suppressed alphavirus production in cell culture. 4'-FlU acted on the viral RNA replication step, and the first 4 hours post-infection were the critical time for its antiviral effect. In vitro replication assays identified nsP4 as the target of inhibition. In vivo, treatment with 4'-FlU reduced disease signs, inflammatory responses, and viral tissue burden in mouse models of CHIKV and Mayaro virus infection. Treatment initiated at 2 hours post-infection was most effective; however, treatment initiated as late as 24-48 hours post-infection produced measurable antiviral effects in the CHIKV mouse model. 4'-FlU showed effective oral delivery in our mouse model and resulted in the accumulation of both 4'-FlU and its bioactive triphosphate form in tissues relevant to arthritogenic alphavirus pathogenesis. Together, our data indicate that 4'-FlU inhibits CHIKV infection in vitro and in vivo and is a promising oral therapeutic candidate against CHIKV infection.IMPORTANCEAlphaviruses including chikungunya virus (CHIKV) are mosquito-borne positive-strand RNA viruses that can cause various diseases in humans. Although compounds that inhibit CHIKV and other alphaviruses have been identified in vitro, there are no licensed antivirals against CHIKV. Here, we investigated a ribonucleoside analog, 4'-fluorouridine (4'-FlU), and demonstrated that it inhibited infectious virus production by several alphaviruses in vitro and reduced virus burden in mouse models of CHIKV and Mayaro virus infection. Our studies also indicated that 4'-FlU treatment reduced CHIKV-induced footpad swelling and reduced the production of pro-inflammatory cytokines. Inhibition in the mouse model correlated with effective oral delivery of 4'-FlU and accumulation of both 4'-FlU and its bioactive form in relevant tissues. In summary, 4'-FlU exhibits potential as a novel anti-alphavirus agent targeting the replication of viral RNA.

Enhanced and copper concentration dependent virucidal effect against SARS-CoV-2 of electrospun poly(vinylidene difluoride) filter materials.

Virucidal filter materials were prepared by electrospinning a solution of 28 wt % poly(vinylidene difluoride) in N,N-dimethylacetamide without and with the addition of 0.25 wt %, 0.75 wt %, 2.0 wt %, or 3.5 wt % Cu(NO3)2 · 2.5H2O as virucidal agent. The fabricated materials had a uniform and defect free fibrous structure and even distribution of copper nanoclusters. X-ray diffraction analysis showed that during the electrospinning process, Cu(NO3)2 · 2.5H2O changed into Cu2(NO3)(OH)3. Electrospun filter materials obtained by electrospinning were essentially macroporous. Smaller pores of copper nanoclusters containing materials resulted in higher particle filtration than those without copper nanoclusters. Electrospun filter material fabricated with the addition of 2.0 wt % and 3.5 wt % of Cu(NO3)2 · 2.5H2O in a spinning solution showed significant virucidal activity, and there was 2.5 ± 0.35 and 3.2 ± 0.30 logarithmic reduction in the concentration of infectious SARS-CoV-2 within 12 h, respectively. The electrospun filter materials were stable as they retained virucidal activity for three months.

Evidence of Differences in Cellular Regulation of Wolbachia-Mediated Viral Inhibition between Alphaviruses and Flaviviruses.

The intracellular bacterium Wolbachia is increasingly being utilised in control programs to limit the spread of arboviruses by Aedes mosquitoes. Achieving a better understanding of how Wolbachia strains can reduce viral replication/spread could be important for the long-term success of such programs. Previous studies have indicated that for some strains of Wolbachia, perturbations in lipid metabolism and cholesterol storage are vital in Wolbachia-mediated antiviral activity against the flaviviruses dengue and Zika; however, it has not yet been examined whether arboviruses in the alphavirus group are affected in the same way. Here, using the reporters for the alphavirus Semliki Forest virus (SFV) in Aedes albopictus cells, we found that Wolbachia strains wMel, wAu and wAlbB blocked viral replication/translation early in infection and that storage of cholesterol in lipid droplets is not key to this inhibition. Another alphavirus, o'nyong nyong virus (ONNV), was tested in both Aedes albopictus cells and in vivo in stable, transinfected Aedes aegypti mosquito lines. The strains wMel, wAu and wAlbB show strong antiviral activity against ONNV both in vitro and in vivo. Again, 2-hydroxypropyl-ß-cyclodextrin (2HPCD) was not able to rescue ONNV replication in cell lines, suggesting that the release of stored cholesterol caused by wMel is not able to rescue blockage of ONNV. Taken together, this study shows that alphaviruses appear to be inhibited early in replication/translation and that there may be differences in how alphaviruses are inhibited by Wolbachia in comparison to flaviviruses.

LDLR is used as a cell entry receptor by multiple alphaviruses.

Alphaviruses are arboviruses transmitted by mosquitoes and are pathogenic to humans and livestock, causing a substantial public health burden. So far, several receptors have been identified for alphavirus entry; however, they cannot explain the broad host range and tissue tropism of certain alphaviruses, such as Getah virus (GETV), indicating the existence of additional receptors. Here we identify the evolutionarily conserved low-density lipoprotein receptor (LDLR) as a new cell entry factor for GETV, Semliki Forest virus (SFV), Ross River virus (RRV) and Bebaru virus (BEBV). Ectopic expression of LDLR facilitates cellular binding and internalization of GETV, which is mediated by the interaction between the E2-E1 spike of GETV and the ligand-binding domain (LBD) of LDLR. Antibodies against LBD block GETV infection in cultured cells. In addition, the GST-LBD fusion protein inhibits GETV infection both in vitro and in vivo. Notably, we identify the key amino acids in LDLR-LBD that played a crucial role in viral entry; specific mutations in the CR4 and CR5 domain of LDLR-LBD reduce viral entry to cells by more than 20-fold. These findings suggest that targeting the LDLR-LBD could be a potential strategy for the development of antivirals against multiple alphaviruses.

FHL1 promotes chikungunya and o'nyong-nyong virus infection and pathogenesis with implications for alphavirus vaccine design.

Arthritogenic alphaviruses are positive-strand RNA viruses that cause debilitating musculoskeletal diseases affecting millions worldwide. A recent discovery identified the four-and-a-half-LIM domain protein 1 splice variant A (FHL1A) as a crucial host factor interacting with the hypervariable domain (HVD) of chikungunya virus (CHIKV) nonstructural protein 3 (nsP3). Here, we show that acute and chronic chikungunya disease in humans correlates with elevated levels of FHL1. We generated FHL1-/- mice, which when infected with CHIKV or o'nyong-nyong virus (ONNV) displayed reduced arthritis and myositis, fewer immune infiltrates, and reduced proinflammatory cytokine/chemokine outputs, compared to infected wild-type (WT) mice. Interestingly, disease signs were comparable in FHL1-/- and WT mice infected with arthritogenic alphaviruses Ross River virus (RRV) or Mayaro virus (MAYV). This aligns with pull-down assay data, which showed the ability of CHIKV and ONNV nsP3 to interact with FHL1, while RRV and MAYV nsP3s did not. We engineered a CHIKV mutant unable to bind FHL1 (CHIKV-ΔFHL1), which was avirulent in vivo. Following inoculation with CHIKV-ΔFHL1, mice were protected from disease upon challenge with CHIKV and ONNV, and viraemia was significantly reduced in RRV- and MAYV-challenged mice. Targeting FHL1-binding as an approach to vaccine design could lead to breakthroughs in mitigating alphaviral disease.

Validation of flavivirus infectious clones carrying fluorescent markers for antiviral drug screening and replication studies.

Flaviviruses have emerged as major arthropod-transmitted pathogens and represent an increasing public health problem worldwide. High-throughput screening can be facilitated using viruses that easily express detectable marker proteins. Therefore, developing molecular tools, such as reporter-carrying versions of flaviviruses, for studying viral replication and screening antiviral compounds represents a top priority. However, the engineering of flaviviruses carrying either fluorescent or luminescent reporters remains challenging due to the genetic instability caused by marker insertion; therefore, new approaches to overcome these limitations are needed. Here, we describe reverse genetic methods that include the design and validation of infectious clones of Zika, Kunjin, and Dengue viruses harboring different reporter genes for infection, rescue, imaging, and morphology using super-resolution microscopy. It was observed that different flavivirus constructs with identical designs displayed strikingly different genetic stabilities, and corresponding virions resembled wild-type virus particles in shape and size. A successful strategy was assessed to increase the stability of rescued reporter virus and permit antiviral drug screening based on quantitative automated fluorescence microscopy and replication studies.

The Synthetic Peptide GA-Hecate and Its Analogs Inhibit Multiple Steps of the Chikungunya Virus Infection Cycle In Vitro.

Chikungunya virus (CHIKV) belongs to the Alphavirus genus and is responsible for significant outbreaks worldwide. Currently, there is no approved antiviral therapy against CHIKV. Bioactive peptides have great potential for new drug development. Here, we evaluated the antiviral activity of the synthetic peptide GA-Hecate and its analogs PSSct1905 and PSSct1910 against CHIKV infection. Initial screening showed that all three peptides inhibited the CHIKV replication cycle in baby hamster kidney fibroblast cells (BHK-21) and human hepatocarcinoma epithelial cells (Huh-7). GA-Hecate and its analog PSSct1905 were the most active, demonstrating suppression of viral infection by more than 91%. The analog PSSct1905 exhibited a protective effect in cells against CHIKV infection. We also observed that the analogs PSSct1905 and PSSct1910 affected CHIKV entry into both cell lines, inhibiting viral attachment and internalization. Finally, all tested compounds presented antiviral activity on the post-entry steps of CHIKV infection in all cells evaluated. In conclusion, this study highlights the potential of the peptide GA-Hecate and its analogs as novel anti-CHIKV compounds targeting different stages of the viral replication cycle, warranting the development of GA-Hecate-based compounds with broad antiviral activity.

Mimicking superinfection exclusion disrupts alphavirus infection and transmission in the yellow fever mosquito Aedes aegypti.

Multiple viruses, including pathogenic viruses, bacteriophages, and even plant viruses, cause a phenomenon termed superinfection exclusion whereby a currently infected cell is resistant to secondary infection by the same or a closely related virus. In alphaviruses, this process is thought to be mediated, at least in part, by the viral protease (nsP2) which is responsible for processing the nonstructural polyproteins (P123 and P1234) into individual proteins (nsP1-nsP4), forming the viral replication complex. Taking a synthetic biology approach, we mimicked this naturally occurring phenomenon by generating a superinfection exclusion-like state in Aedes aegypti mosquitoes, rendering them refractory to alphavirus infection. By artificially expressing Sindbis virus (SINV) and chikungunya virus (CHIKV) nsP2 in mosquito cells and transgenic mosquitoes, we demonstrated a reduction in both SINV and CHIKV viral replication rates in cells following viral infection as well as reduced infection prevalence, viral titers, and transmission potential in mosquitoes.

Broadly neutralizing humanized SARS-CoV-2 antibody binds to a conserved epitope on Spike and provides antiviral protection through inhalation-based delivery in non-human primates.

The COVID-19 pandemic represents a global challenge that has impacted and is expected to continue to impact the lives and health of people across the world for the foreseeable future. The rollout of vaccines has provided highly anticipated relief, but effective therapeutics are required to further reduce the risk and severity of infections. Monoclonal antibodies have been shown to be effective as therapeutics for SARS-CoV-2, but as new variants of concern (VoC) continue to emerge, their utility and use have waned due to limited or no efficacy against these variants. Furthermore, cumbersome systemic administration limits easy and broad access to such drugs. As well, concentrations of systemically administered antibodies in the mucosal epithelium, a primary site of initial infection, are dependent on neonatal Fc receptor mediated transport and require high drug concentrations. To reduce the viral load more effectively in the lung, we developed an inhalable formulation of a SARS-CoV-2 neutralizing antibody binding to a conserved epitope on the Spike protein, ensuring pan-neutralizing properties. Administration of this antibody via a vibrating mesh nebulization device retained antibody integrity and resulted in effective distribution of the antibody in the upper and lower respiratory tract of non-human primates (NHP). In comparison with intravenous administration, significantly higher antibody concentrations can be obtained in the lung, resulting in highly effective reduction in viral load post SARS-CoV-2 challenge. This approach may reduce the barriers of access and uptake of antibody therapeutics in real-world clinical settings and provide a more effective blueprint for targeting existing and potentially emerging respiratory tract viruses.

Establishing Mixed Neuronal and Glial Cell Cultures from Embryonic Mouse Brains to Study Infection and Innate Immunity.

Models of the central nervous system (CNS) must recapitulate the complex network of interconnected cells found in vivo. The CNS consists primarily of neurons, astrocytes, oligodendrocytes, and microglia. Due to increasing efforts to replace and reduce animal use, a variety of in vitro cell culture systems have been developed to explore innate cell properties, which allow the development of therapeutics for CNS infections and pathologies. Whilst certain research questions can be addressed by human-based cell culture systems, such as (induced) pluripotent stem cells, working with human cells has its own limitations with regard to availability, costs, and ethics. Here, we describe a unique protocol for isolating and culturing cells from embryonic mouse brains. The resulting mixed neural cell cultures mimic several cell populations and interactions found in the brain in vivo. Compared to current equivalent methods, this protocol more closely mimics the characteristics of the brain and also garners more cells, thus allowing for more experimental conditions to be investigated from one pregnant mouse. Further, the protocol is relatively easy and highly reproducible. These cultures have been optimized for use at various scales, including 96-well based high throughput screens, 24-well microscopy analysis, and 6-well cultures for flow cytometry and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis. This culture method is a powerful tool to investigate infection and immunity within the context of some of the complexity of the CNS with the convenience of in vitro methods.

The Dimeric Peptide (KKYRYHLKPF)2K Shows Broad-Spectrum Antiviral Activity by Inhibiting Different Steps of Chikungunya and Zika Virus Infection.

Chikungunya virus (CHIKV) and Zika virus (ZIKV) are important disease-causing agents worldwide. Currently, there are no antiviral drugs or vaccines approved to treat these viruses. However, peptides have shown great potential for new drug development. A recent study described (p-BthTX-I)2K [(KKYRYHLKPF)2K], a peptide derived from the Bothropstoxin-I toxin in the venom of the Bothrops jararacussu snake, showed antiviral activity against SARS-CoV-2. In this study, we assessed the activity of this peptide against CHIKV and ZIKV and its antiviral action in the different stages of the viral replication cycle in vitro. We observed that (p-BthTX-I)2K impaired CHIKV infection by interfering with the early steps of the viral replication cycle, reducing CHIKV entry into BHK-21 cells specifically by reducing both the attachment and internalization steps. (p-BthTX-I)2K also inhibited the ZIKV replicative cycle in Vero cells. The peptide protected the cells against ZIKV infection and decreased the levels of the viral RNA and the NS3 protein of this virus at viral post-entry steps. In conclusion, this study highlights the potential of the (p-BthTX-I)2K peptide to be a novel broad-spectrum antiviral candidate that targets different steps of the replication cycle of both CHIKV and ZIKV.

Climate change and vector-borne diseases: a multi-omics approach of temperature-induced changes in the mosquito.

BACKGROUND: Climate change and globalization contribute to the expansion of mosquito vectors and their associated pathogens. Long spared, temperate regions have had to deal with the emergence of arboviruses traditionally confined to tropical regions. Chikungunya virus (CHIKV) was reported for the first time in Europe in 2007, causing a localized outbreak in Italy, which then recurred repeatedly over the years in other European localities. This raises the question of climate effects, particularly temperature, on the dynamics of vector-borne viruses. The objective of this study is to improve the understanding of the molecular mechanisms set up in the vector in response to temperature. METHODS: We combine three complementary approaches by examining Aedes albopictus mosquito gene expression (transcriptomics), bacterial flora (metagenomics) and CHIKV evolutionary dynamics (genomics) induced by viral infection and temperature changes. RESULTS: We show that temperature alters profoundly mosquito gene expression, bacterial microbiome and viral population diversity. We observe that (i) CHIKV infection upregulated most genes (mainly in immune and stress-related pathways) at 20°C but not at 28°C, (ii) CHIKV infection significantly increased the abundance of Enterobacteriaceae Serratia marcescens at 28°C and (iii) CHIKV evolutionary dynamics were different according to temperature. CONCLUSION: The substantial changes detected in the vectorial system (the vector and its bacterial microbiota, and the arbovirus) lead to temperature-specific adjustments to reach the ultimate goal of arbovirus transmission; at 20°C and 28°C, the Asian tiger mosquito Ae. albopictus was able to transmit CHIKV at the same efficiency. Therefore, CHIKV is likely to continue its expansion in the northern regions and could become a public health problem in more countries than those already affected in Europe.

Attenuation of Avian Flavivirus by Rewiring the Leucine and Serine Codons of Its E-NS1 Protein toward Stop Mutation To Redirect Virus Evolution.

Recently, a new strategy for attenuating RNA viruses by redirecting their evolution in sequence space was confirmed for Enterovirus and Influenza viruses. Using avian flavivirus as a model, the 69 serine and 53 leucine codons on the E-NS1 genes were modified to change evolutionary direction of the viral sequence space. This means that all codons encoding serine or leucine residues were substituted with codons that are only one base different from the three stop codons, resulting in the initial position of the virus genome in sequence space being closer to the detrimental areas to achieve attenuation by reducing viral adaptability. The growth curve and plaque size of CQW1-one-to-stop (CQW1-OTS) were similar to those of CQW1-wild type (CQW1-WT) in vitro, but attenuated proliferation was detected when treated with a mutagenic reagent (ribavirin). However, comparably high CQW1-OTS and CQW1-WT lethality rates were detected in 9-day-old duck embryos and 5-day-old ducklings, suggesting that this strategy works but with limitations. With that in mind, homologous hosts in nonsensitive age (25-day-old ducks) and heterologous hosts (3-week-old Kunming mice) were employed to investigate if CQW1-OTS was attenuated under host selection pressure. Minimal attenuation of CQW1-OTS in elder ducks and apparent attenuation in mice were reported, providing reduced viral titers, mild clinical signs, and lower specific infectivity. Collectively, we experimentally demonstrate that the attenuation strategy of redirecting virus evolution in sequence space works for flavivirus. Redirection of the virus is attenuated only under some outside pressure, such as heterologous hosts or antiviral drugs treatment, limiting its usage in flaviviruses. IMPORTANCE Flaviviruses are medically important arboviruses that threaten public health, but no approved treatments are currently available. Vaccines prevent flavivirus infection. We employed duck Tembusu virus (TMUV), a mosquito-borne flavivirus, to evaluate virus redirection. TMUV is native to birds and could infect mice by intracerebral injection, making it an experimental animal model to study flavivirus characteristics in vivo. The 69 serine and 53 leucine codons on the E-NS1 proteins of CQW1 were synonymously substituted to change evolutionary direction of the virus in sequence space. In vitro mutagen reagent treatment suppressed CQW1-OTS viral multiplication, but in vivo attenuation depended on host selective pressure. CQW1-OTS viral attenuation was observed in older ducks but not sensitive ducklings; considerable attenuation was also observed in heterogenous host (mice), which provides more selective pressure on viruses. Collectively, these data indicated that there are very important preconditions for application of evaluating whether this strategy shows application prospects in novel flavivirus vaccine development.

Activity, Template Preference, and Compatibility of Components of RNA Replicase of Eastern Equine Encephalitis Virus.

Eastern equine encephalitis virus (EEEV) usually cycles between Culiseta melanura mosquitoes and birds; however, it can also infect humans. EEEV has a positive-sense RNA genome that, in infected cells, serves as an mRNA for the P1234 polyprotein. P1234 undergoes a series of precise cleavage events producing four nonstructural proteins (nsP1-4) representing subunits of the RNA replicase. Here, we report the construction and properties of a trans-replicase for EEEV. The template RNA of EEEV was shown to be replicated by replicases of diverse alphaviruses. The EEEV replicase, on the other hand, demonstrated limited ability in replicating template RNAs originating from alphaviruses of the Semliki Forest virus complex. The replicase of EEEV was also successfully reconstructed from P123 and nsP4 components. The ability of EEEV P123 to form functional RNA replicases with heterologous nsP4s was more efficient using EEEV template RNA than heterologous alphavirus template RNA. This finding indicates that unlike with previously studied Semliki Forest complex alphaviruses, P123 and/or its processing products have a leading role in EEEV template RNA recognition. Infection of HEK293T cells harboring the EEEV template RNA with EEEV or Western equine encephalitis virus prominently activated expression of a reporter encoded in the template RNA; the effect was much smaller for infection with other alphaviruses and not detectable upon flavivirus infection. At the same time, EEEV infection resulted only in a limited activation of the template RNA of chikungunya virus. Thus, cells harboring reporter-carrying template RNAs can be used as sensitive and selective biosensors for different alphaviruses. IMPORTANCE Infection of EEEV in humans can cause serious neurologic disease with an approximately 30% fatality rate. Although human infections are rare, a record-breaking number was documented in 2019. The replication of EEEV has a unique requirement for host factors but is poorly studied, partly because the virus requires biosafety level 3 facilities which can limit the scope of experiments; at the same time, these studies are crucial for developing antiviral approaches. The EEEV trans-replicase developed here contributes significantly to research on EEEV, providing a safe and versatile tool for studying the virus RNA replication. Using this system, the compatibility of EEEV replicase components with counterparts from other alphaviruses was analyzed. The obtained data can be used to develop unique biosensors that provide alternative methods for detection, identification, quantitation, and neutralization of viable alphaviruses that are compatible with high throughput, semiautomated approaches.

Antibacterial and Antiviral Effects of Ag, Cu and Zn Metals, Respective Nanoparticles and Filter Materials Thereof against Coronavirus SARS-CoV-2 and Influenza A Virus.

Due to the high prevalence of infectious diseases and their concurrent outbreaks, there is a high interest in developing novel materials with antimicrobial properties. Antibacterial and antiviral properties of a range of metal-based nanoparticles (NPs) are a promising means to fight airborne diseases caused by viruses and bacteria. The aim of this study was to test antimicrobial metals and metal-based nanoparticles efficacy against three viruses, namely influenza A virus (H1N1; A/WSN/1933) and coronaviruses TGEV and SARS-CoV-2; and two bacteria, Escherichia coli and Staphylococcus aureus. The efficacy of ZnO, CuO, and Ag NPs and their respective metal salts, i.e., ZnSO4, CuSO4, and AgNO3, was evaluated in suspensions, and the compounds with the highest antiviral efficacy were chosen for incorporation into fibers of cellulose acetate (CA), using electrospinning to produce filter materials for face masks. Among the tested compounds, CuSO4 demonstrated the highest efficacy against influenza A virus and SARS-CoV-2 (1 h IC50 1.395 mg/L and 0.45 mg/L, respectively), followed by Zn salt and Ag salt. Therefore, Cu compounds were selected for incorporation into CA fibers to produce antiviral and antibacterial filter materials for face masks. CA fibers comprising CuSO4 decreased SARS-CoV-2 titer by 0.38 logarithms and influenza A virus titer by 1.08 logarithms after 5 min of contact; after 1 h of contact, SARS-COV-2 virus was completely inactivated. Developed CuO- and CuSO4-based filter materials also efficiently inactivated the bacteria Escherichia coli and Staphylococcus aureus. The metal NPs and respective metal salts were potent antibacterial and antiviral compounds that were successfully incorporated into the filter materials of face masks. New antibacterial and antiviral materials developed and characterized in this study are crucial in the context of the ongoing SARS-CoV-2 pandemic and beyond.

Toll-like receptor 4 and lipopolysaccharide from commensal microbes regulate Tembusu virus infection.

Unlike most flaviviruses transmitted by arthropods, Tembusu virus (TMUV) is still active during winter and causes outbreaks in some areas, indicating vector-independent spread of the virus. Gastrointestinal transmission might be one of the possible routes of vector-free transmission, which also means that the virus has to interact with more intestinal bacteria. Here, we found evidence that TMUV indeed can transmit through the digestive tract. Interestingly, using an established TMUV disease model by oral gavage combined with an antibiotic treatment, we revealed that a decrease in intestinal bacteria significantly reduced local TMUV proliferation in the intestine, revealing that the bacterial microbiome is important in TMUV infection. We found that lipopolysaccharide (LPS) present in the outer membrane of Gram-negative bacteria enhanced TMUV proliferation by promoting its attachment. Toll-like receptor 4 (TLR4), a cell surface receptor, can transmit signal from LPS. We confirmed colocalization of TLR4 with TMUV envelope (E) protein as well as their interaction in infected cells. Coherently, TMUV infection of susceptible cells was inhibited by an anti-TLR4 antibody, purified soluble TLR4 protein, and knockdown of TLR4 expression. LPS-enhanced TMUV proliferation could also be blocked by a TLR4 inhibitor. Meanwhile, pretreatment of duck primary cells with TMUV significantly impaired LPS-induced interleukin 6 production. Collectively, our study provides first insights into vector-free transmission mechanisms of flaviviruses.

G3BP/Rin-Binding Motifs Inserted into Flexible Regions of nsP2 Support RNA Replication of Chikungunya Virus.

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus. In infected cells, its positive-sense RNA genome is translated into polyproteins that are subsequently processed into four nonstructural proteins (nsP1 to 4), the virus-encoded subunits of the RNA replicase. However, for RNA replication, interactions between nsPs and host proteins are also needed. These interactions are mostly mediated through the intrinsically disordered C-terminal hypervariable domain (HVD) in nsP3. Duplicate FGDF motifs in the HVD are required for interaction with mammalian RasGAP SH3-binding proteins (G3BPs) and their mosquito homolog Rin; these interactions are crucial for CHIKV RNA replication. In this study, we inactivated G3BP/Rin-binding motifs in the HVD and inserted peptides containing either native or inactivated G3BP/Rin-binding motifs into flexible regions of nsP1, nsP2, or nsP4. Insertion of native motifs into nsP1 or nsP2 but not into the C terminus of nsP4 activated CHIKV RNA replication in human cells in a G3BP-dependent manner. In mosquito cells, activation also resulted from the insertion of inactive motifs after residue 8 or 466 in nsP2; however, the effect was significantly larger when the inserted sequence contained native motifs. Nonetheless, CHIKV mutants harboring mutations in the HVD and containing insertions of native motifs in nsP2 were not viable in mosquito cells. In contrast, mutant genomes containing native motifs after residue 466 or 618 in nsP2 replicated in BHK-21 cells, with the latter mutant forming infectious progeny. Thus, the binding of G3BPs to nsP2 can support CHIKV RNA replication and restore the infectivity of viruses lacking G3BP-binding motifs in the HVD of nsP3. IMPORTANCE CHIKV is a reemerging alphavirus that has spread throughout more than 60 countries and is the causative agent of chikungunya fever. No approved drugs or vaccines are available for the treatment or prevention of CHIKV infection. CHIKV replication depends on the ability of its replicase proteins to interact with host cell factors, and a better understanding of host cell factor roles in viral infection will increase our understanding of CHIKV RNA replication and provide new strategies for viral infection attenuation. Here, we demonstrate that the motifs required for the binding of host G3BP/Rin proteins remain functional when transferred from their natural location in nsP3 to different replicase proteins and may enable mutant viruses to complete a full replication cycle. To our knowledge, this is the first demonstration of interaction motifs for crucial host factors being successfully transferred from one replicase protein to another subunit of alphavirus replicase.