Highly Pathogenic Swine Getah Virus in Blue Foxes, Eastern China, 2017

Development and application of a colloidal-gold immunochromatographic strip for detecting Getah virus antibodies

Getah virus (GETV) is a re-emerging mosquito-borne alphavirus that is highly pathogenic, mainly to pigs and horses. There are no vaccines or treatments available for GETV in swine in China. Therefore, the development of a simple, rapid, specific, and sensitive serological assay for GETV antibodies is essential for the prevention and control of GETV. Current antibody monitoring methods are time-consuming, expensive, and dependent on specialized instrumentation, and these features are not conducive to rapid detection in clinical samples. To address these problem, we developed immunochromatographic test strips (ICTS) using eukaryotically expressed soluble recombinant p62-E1 protein of GETV as a labelled antigen, which has good detection sensitivity and no cross-reactivity with other common porcine virus-positive sera. The ICTS is highly compatible with IFA and ELISA and can be stored for 1 month at 37 °C and for at least 3 months at room temperature. Hence, p62-E1-based ICTS is a rapid, accurate, and convenient method for rapid on-site detection of GETV antibodies. KEY POINTS: • We established a rapid antibody detection method that can monitor GETV infection • We developed colloidal gold test strips with high sensitivity and specificity • The development of colloidal gold test strips will aid in the field serologic detection of GETV.

Getah virus capsid protein undergoes co-condensation with viral genomic RNA to facilitate virion assembly

Getah virus (GETV) belongs to the Alphavirus genus in the Togaviridae family and is a zoonotic arbovirus causing disease in both humans and animals. The capsid protein (CP) of GETV regulates the viral core assembly, but the mechanism underlying this process is poorly understood. In this study, we demonstrate that CP undergoes liquid-liquid phase separation (LLPS) with the GETV genome RNA (gRNA) in vitro and forms cytoplasmic puncta in cells. Two regions of GETV gRNA (nucleotides 1-4000 and 5000-8000) enhance CP droplet formation in vitro and the lysine-rich Link region of CP is essential for its phase separation. CP(K/R) mutant with all lysines in the Link region replaced by arginines exhibits improved LLPS versus wild type (WT) CP, but CP(K/E) mutant with lysines substituted by glutamic acids virtually loses condensation ability. Consistently, recombinant virus mutant with CP(K/R) possesses significantly higher gRNA binding affinity, virion assembly efficiency and infectivity than the virus with WT-CP. Overall, our findings provide new insights into the understanding of GETV assembly and development of new antiviral drugs against alphaviruses.

Development of a monoclonal antibody specifically recognizing a linear epitope on the capsid protein of the emerging Group III Getah virus

Getah virus (GETV) is an emerging mosquito-borne alphavirus that can infect horses, pigs and other animals. Given the public health threat posed by GETV, research on its pathogenesis, diagnosis and prevention is urgently needed. In the current study, prokaryotic expression systems were used to express the capsid protein of GETV. This protein was then used to immunize BALB/c mice in order to generate monoclonal antibodies (mAbs). Subsequently, hybridoma cells secreting a mAb (2B11-4) against the capsid protein were obtained using the hybridoma technique. A B cell linear epitope, 18-PAYRPWR-24, located at the capsid protein's N-terminal region was identified using western blotting analysis with the produced mAb, 2B11-4. Sequence alignment indicated that this epitope was highly conserved in group III (GIII) strains of GETV, but varied among the other genotypes. Western blotting showed that mAb 2B11-4 could discriminate Group III GETVs from other genotypes. This study describes the preparation of a mAb against the GETV capsid protein and the identification of the specific localization of B-cell epitopes, and will contribute towards a better understanding of the biological importance of the GETV capsid protein. It will also pave the way for developing immunological detection methods and genotype diagnosis for GETVs.

The roles of 6K protein on Getah virus replication and pathogenicity

Alphavirus is a type of arbovirus that can infect both humans and animals. The amino acid sequence of the 6K protein, being one of the structural proteins of the alphavirus, is not conserved. Deletion of this protein will result in varying effects on different alphaviruses. Our study focuses on the function of the Getah virus (GETV) 6K protein in infected cells and mice. We successfully constructed infectious clone plasmids and created resulting viruses (rGETV and rGETV-Δ6K). Our comprehensive microscopic analysis revealed that the 6 K protein mainly stays in the endoplasmic reticulum. In addition, rGETV-Δ6K has lower thermal stability and sensitivity to temperature than GETV. Although the deletion of the 6K protein does not reduce virion production in ST cells, it affects the release of virions from host cells by inhibiting the process of E2 protein transportation to the plasma membrane. Subsequent in vivo testing demonstrated that neonatal mice infected with rGETV-Δ6K had a lower virus content, less significant pathological changes in tissue slices, and milder disease than those infected with the wild-type virus. Our results indicate that the 6K protein effectively reduces the viral titer by influencing the release of viral particles. Furthermore, the 6K protein play a role in the clinical manifestation of GETV disease.

Transcriptome screening identifies TIPARP as an antiviral host factor against the Getah virus

IMPORTANCE

Alphaviruses threaten public health continuously, and Getah virus (GETV) is a re-emerging alphavirus that can potentially infect humans. Approved antiviral drugs and vaccines against alphaviruses are few available, but several host antiviral factors have been reported. Here, we used GETV as a model of alphaviruses to screen for additional host factors. Tetrachlorodibenzo-p-dioxin-inducible poly(ADP ribose) polymerase was identified to inhibit GETV replication by inducing ubiquitination of the glycoprotein E2, causing its degradation by recruiting the E3 ubiquitin ligase membrane-associated RING-CH8 (MARCH8). Using GETV as a model virus, focusing on the relationship between viral structural proteins and host factors to screen antiviral host factors provides new insights for antiviral studies on alphaviruses.

The Isolation and Characterization of a Novel Group III-Classified Getah Virus from a Commercial Modified Live Vaccine against PRRSV

As an epizootic causative agent, the Getah virus (GETV) can cause moderate illness in horses, lethal disease in foxes, and reproductive disorders and fetal death in pigs. Due to the wide range of hosts and multiple routes of transmission, GETV has become a growing potential threat to the global livestock industry, and even to public health. More attention and research on GETV are urgently needed. In this study, we successfully isolated a novel GETV strain, named BJ0304, from a commercial live vaccine against porcine reproductive and respiratory syndrome virus (PRRSV) and determined its growth kinetics. Then, genetic and phylogenetic analyses were performed. The results revealed that BJ0304 was clustered into Group III, and it was most related to the GETV-V1 strain based on the complete genome sequence. Furthermore, the pathogenicity of the isolate was assessed and found to be a low virulent strain in mice relative to its closest homolog GETV-V1. Finally, mutation and glycosylation analysis showed that a unique mutation (171 T > I) at one amino acid of E2, which affected the glycosylation of E2, may be associated with viral pathogenicity. In summary, the general characteristic of a novel Group III-classified GETV-BJ0304 isolated from commercial live PRRSV vaccine was defined and then mutation/glycosylation-related potential virulence factor was discussed. This study highlights the complexity of GETV transmission routes in swine and the need for more surveillance on commercial animal vaccines, contributes to the understanding of genetic characterization of clinical isolates, provides possible virulence factors in favor of unveiling the viral pathogenesis, and eventually lays the foundation for the prevention and control of GETV.

The host transcriptome change involved in the inhibitory effect of exogenous interferon-γ on Getah virus replication

Introduction

Getah virus (GETV) has become a growing potential threat to the global livestock industry and public health. However, little is known about the viral pathogenesis and immune escape mechanisms, leading to ineffective control measures.

Methods

In this study, the antiviral activity of exogenous interferons (IFNs) was assessed by using western blotting (WB), real-time quantitative PCR (RT-qPCR) and indirect immunofluorescence assay (IFA). The comparative transcriptomics among mock- and GETV-infected (MOI = 0.1) ST cells with or without IFN-γ was performed by RNA-seq, and then the transcriptome profiling of GETV-infected ST cells and key pathways and putative factors involved in inhibitory effect of IFN-γ on GETV replication were analyzed by bioinformatics methods and RT-qPCR.

Results

The results showed that treatment with IFN-γ could suppress GETV replication, and the inhibitory effect lasted for at least 48 h, while the exogenous IFN-α/ω and IFN-λ3 treatments failed to inhibit the viral infection and early replication in vitro. Furthermore, the blueprint of virus-host interaction was plotted by RNA-seq and RT-qPCR, showing systemic activation of inflammatory, apoptotic, and antiviral pathways in response to GETV infection, indicating viral hijacking and inhibition of innate host immunity such as IFN-I/III responses. Last and most importantly, activation of the JAK-STAT signaling pathway and complement and coagulation cascades may be a primary driver for IFN-γ-mediated inhibition of GETV replication.

Discussion

These findings revealed that GETV possessed the capability of viral immune escape and indicated that IFN-γ aided in the prevention and control of GETV, implying the potential molecular mechanism of suppression of GETV by IFN-γ, all of which warrant emphasis or further clarification.

Development of a recombinant reporter Getah virus for antiviral drug screening assays

Getah virus (GETV), is an often neglected and re-emerging mosquito-borne RNA virus. GETV can cause illness accompanied with high fever, rash, incapacitating arthralgia and chronic arthritis or encephalitic disease in affected animals. Currently, there is no specific treatment or vaccine against GETV infection. In this study, we developed three recombinant viruses by inserting different reporter protein genes between the Cap and pE2 genes. The reporter viruses exhibited high replication capacity similar to the parental virus. The rGECiLOV and rGECGFP viruses were genetically stable within at least ten rounds of passages in BHK-21 cells. We confirmed that the reporter virus, rGECGFP, facilitated the antiviral assays against GETV by testing it with the known inhibitor, ribavirin. It was also found that the compound, doxycycline, showed an inhibitory effect on GETV replication. In addition, rGECGFP was found to be an authentic mimic of the parental virus infection in 3-day-old mice, but with milder pathogenicity. The reporter viruses will contribute to the assessment of viral replication and proliferation, tracking and elucidating of alphavirus-host interactions. In addition, they will help in the screening of potential antiviral compounds.

Evaluating the mosquito host range of Getah virus and the vector competence of selected medically important mosquitoes in Getah virus transmission

BACKGROUND

The Getah virus (GETV) is a mosquito-borne Alphavirus (family Togaviridae) that is of significant importance in veterinary medicine. It has been associated with major polyarthritis outbreaks in animals, but there are insufficient data on its clinical symptoms in humans. Serological evidence of GETV exposure and the risk of zoonotic transmission makes GETV a potentially medically relevant arbovirus. However, minimal emphasis has been placed on investigating GETV vector transmission, which limits current knowledge of the factors facilitating the spread and outbreaks of GETV.

METHODS

To examine the range of the mosquito hosts of GETV, we selected medically important mosquitoes, assessed them in vitro and in vivo and determined their relative competence in virus transmission. The susceptibility and growth kinetics of GETVs in various mosquito-derived cell lines were also determined and quantified using plaque assays. Vector competency assays were also conducted, and quantitative reverse transcription-PCR and plaque assays were used to determine the susceptibility and transmission capacity of each mosquito species evaluated in this study.

RESULTS

GETV infection in all of the investigated mosquito cell lines resulted in detectable cytopathic effects. GETV reproduced the fastest in Culex tritaeniorhynchus- and Aedes albopictus-derived cell lines, as evidenced by the highest exponential titers we observed. Regarding viral RNA copy numbers, mosquito susceptibility to infection, spread, and transmission varied significantly between species. The highest vector competency indices for infection, dissemination and transmission were obtained for Cx. tritaeniorhynchus. This is the first study to investigate the ability of Ae. albopictus and Anopheles stephensi to transmit GETV, and the results emphasize the role and capacity of other mosquito species to transmit GETV upon exposure to GETV, in addition to the perceived vectors from which GETV has been isolated in nature.

CONCLUSIONS

This study highlights the importance of GETV vector competency studies to determine all possible transmission vectors, especially in endemic regions.

Early Genomic Surveillance and Phylogeographic Analysis of Getah Virus, a Reemerging Arbovirus, in Livestock in China

Getah virus (GETV) mainly causes disease in livestock and may pose an epidemic risk due to its expanding host range and the potential of long-distance dispersal through animal trade. Here, we used metagenomic next-generation sequencing (mNGS) to identify GETV as the pathogen responsible for reemerging swine disease in China and subsequently estimated key epidemiological parameters using phylodynamic and spatially-explicit phylogeographic approaches. The GETV isolates were able to replicate in a variety of cell lines, including human cells, and showed high pathogenicity in a mouse model, suggesting the potential for more mammal hosts. We obtained 16 complete genomes and 79 E2 gene sequences from viral strains collected in China from 2016 to 2021 through large-scale surveillance among livestock, pets, and mosquitoes. Our phylogenetic analysis revealed that three major GETV lineages are responsible for the current epidemic in livestock in China. We identified three potential positively selected sites and mutations of interest in E2, which may impact the transmissibility and pathogenicity of the virus. Phylodynamic inference of the GETV demographic dynamics identified an association between livestock meat consumption and the evolution of viral genetic diversity. Finally, phylogeographic reconstruction of GETV dispersal indicated that the sampled lineages have preferentially circulated within areas associated with relatively higher mean annual temperature and pig population density. Our results highlight the importance of continuous surveillance of GETV among livestock in southern Chinese regions associated with relatively high temperatures. IMPORTANCE Although livestock is known to be the primary reservoir of Getah virus (GETV) in Asian countries, where identification is largely based on serology, the evolutionary history and spatial epidemiology of GETV in these regions remain largely unknown. Through our sequencing efforts, we provided robust support for lineage delineation of GETV and identified three major lineages that are responsible for the current epidemic in livestock in China. We further analyzed genomic and epidemiological data to reconstruct the recent demographic and dispersal history of GETV in domestic animals in China and to explore the impact of environmental factors on its genetic diversity and its diffusion. Notably, except for livestock meat consumption, other pig-related factors such as the evolution of live pig transport and pork production do not show a significant association with the evolution of viral genetic diversity, pointing out that further studies should investigate the potential contribution of other host species to the GETV outbreak. Our analysis of GETV demonstrates the need for wider animal species surveillance and provides a baseline for future studies of the molecular epidemiology and early warning of emerging arboviruses in China.

Surveillance of Getah virus in mosquitoes and racehorses from 2016 to 2019 at a training center in Ibaraki Prefecture, Japan, a site of several previous Getah virus outbreaks

Mosquitoes and EDTA-treated blood samples from febrile racehorses were investigated for Getah virus infection from 2016 to 2019 at the Miho Training Center, where several outbreaks of Getah virus have occurred. We collected 5557 mosquitoes and 331 blood samples from febrile horses in this study. The most frequently captured mosquito species was Culex tritaeniorhynchus (51.9%), followed by Aedes vexans nipponii (14.2%) and Anopheles sinensis (11.2%). Getah virus was detected in mosquitoes (Aedes vexans nipponii) in 2016 (strain 16-0810-26) but not in 2017-2019. Six of 74 febrile horses in 2016 and one of 69 in 2019 tested positive for Getah virus; none of the horses tested positive in 2017 or 2018. Phylogenetic and sequence analysis showed that strain 16-0810-26 was closely related to strains that had been isolated from horses and a pig around the training center in 2014-2016 but have not been detected in samples collected at the training center since 2017. In contrast, the strain isolated from the infected horse in 2019 (19-I-703) was genetically distinct from the strains isolated from horses and a pig in 2014-2016 and was more closely related to a strain isolated in 1978 at the training center. The source of strain 19-I-703 is unclear, but the virus was not detected in other horses sampled in 2019. In summary, we found that the distribution of mosquito species present at the training center had not changed significantly since 1979, and although a small outbreak of Getah virus infection occurred among horses at the training center in 2016, limited Getah virus activity was detected in mosquitoes and horses at the training center from 2017 to 2019.

Diversity of viral communities in faecal samples of farmed red foxes

Emerging and existing viruses from various human and animal samples have been studied and analyzed using viral metagenomics, which has proven to be an effective technique. Foxes, as a kind of significant economic animal, are widely raised in China. Viruses carried by foxes may potentially infect humans or other animals. There are currently very few studies of faecal virome in farmed foxes. Using viral metagenomics, we evaluated the faecal virome of twenty-four foxes collected from the same farm in Jilin Province, China. Some sequences more closely related to the families Parvoviridae, Picornaviridae, Smacoviridae, Anelloviridae, and Herpesviridae were detected in the faecal sample. The main animal viruses that infect farmed red foxes were parvovirus and picornavirus. Five smacovirus strains were found and provided evidence for genetic diversity in the genus Smacoviridae. In addition, some viruses infecting avian species or rats were detected in this study. The study helped us better understand faecal virome in farmed red foxes and assisted in the surveillance and prevention of viral diseases in these animals.

Seroconversion of anti-Getah virus antibody among Japanese native Noma horses around 2012

Getah virus (GETV), an arthropod-borne virus transmitted by mosquitoes, has been isolated from several animals. GETV infection in horses shows clinical signs such as fever, rash, and edema in the leg. Noma horses are one of the eight Japanese native horses. The present study aimed to clarify the occurrence of GETV infection in Noma horses. Serum samples collected from Noma horses were analyzed using a virus neutralization test and enzyme-linked immunosorbent assay and showed that the anti-GETV antibody titers in the samples collected in 2017 were significantly higher than those collected in 2012. We concluded that a seroconversion of anti-GETV antibodies was occurred in the Noma horse population around 2012, providing evidence of the GETV epidemic in Japan circa 2012.

Development and application of an indirect ELISA for detecting equine IgG antibodies against Getah virus with recombinant E2 domain protein

Getah virus (GETV) disease is a mosquito-borne infectious disease that causes fever, aseptic meningitis, and abortion in a variety of animals. Currently, the epidemic trend of GETV disease increases seriously worldwide, especially in China, posing a potential threat to animal safety and public health. However, there are few reports about the epidemiological investigation of GETV disease in China as well as a lack of commercial diagnostic kit for GETV antibody. Therefore, the establishment of a rapid, sensitive and suitable GETV antibody detection method for large-scale samples is an urgent request to fully understand the prevalence of GETV disease. Here, a recombinant plasmid pET22b-GETV-E2d that contained the domain of GETV-E2 (E2d) fused to His-tag was constructed to express recombinant protein E2d (rE2d) in Escherichia coli. The rE2d was mainly expressed in inclusion bodies. And it was purified successfully by nickel affinity column so that it could be used to develop an indirect ELISA (rE2d-ELISA). After optimizing reaction conditions of rE2d-ELISA, the cut-off value was determined as 0.396 with 100 equine sera tested by virus neutralization test (VNT). Furthermore, rE2d-ELISA method showed the positive rate of IgG antibodies against GETV was 54.3% based on testing 646 clinical serum samples obtained in Xinjiang whereas the overall coincidence rate between rE2d-ELISA and VNT was 94.0%, with 98.2% sensitivity and 92.6% specificity. The findings suggest that the developed IgG ELISA employing recombinant E2d promises was an efficient and low-cost type of antibody detection method for horse, which will benefit for prevention of GETV outbreaks in horses.

Establishment of a reverse transcription real-time quantitative PCR method for Getah virus detection and its application for epidemiological investigation in Shandong, China

Getah virus (GETV) is a mosquito-borne, single-stranded, positive-sense RNA virus belonging to the genus Alphavirus of the family Togaviridae. Natural infections of GETV have been identified in a variety of vertebrate species, with pathogenicity mainly in swine, horses, bovines, and foxes. The increasing spectrum of infection and the characteristic causing abortions in pregnant animals pose a serious threat to public health and the livestock economy. Therefore, there is an urgent need to establish a method that can be used for epidemiological investigation in multiple animals. In this study, a real-time reverse transcription fluorescent quantitative PCR (RT-qPCR) method combined with plaque assay was established for GETV with specific primers designed for the highly conserved region of GETV Nsp1 gene. The results showed that after optimizing the condition of RT-qPCR reaction, the minimum detection limit of the assay established in this study was 7.73 PFU/mL, and there was a good linear relationship between viral load and Cq value with a correlation coefficient (R²) of 0.998. Moreover, the method has good specificity, sensitivity, and repeatability. The established RT-qPCR is 100-fold more sensitive than the conventional RT-PCR. The best cutoff value for the method was determined to be 37.59 by receiver operating characteristic (ROC) curve analysis. The area under the curve (AUC) was 0.956. Meanwhile, we collected 2,847 serum specimens from swine, horses, bovines, sheep, and 17,080 mosquito specimens in Shandong Province in 2022. The positive detection rates by RT-qPCR were 1%, 1%, 0.2%, 0%, and 3%, respectively. In conclusion, the method was used for epidemiological investigation, which has extensive application prospects.

Getah Virus (Alphavirus): An Emerging, Spreading Zoonotic Virus

Getah virus (GETV) is a zoonotic virus transmitted by mosquitoes, belonging to the Togaviridae family, Alphavirus genus. It was first isolated from mosquitoes in Malaysia in 1955, being widespread in island countries in the South Pacific region. Since the beginning of the 21st century, GETV expanded its range and geographical distribution from low-latitude tropical regions to 60° north latitude, being isolated from 17 different species of mosquitoes belonging to five genera of Culicidae (Culex, Anopheles, Armigeres, Aedes and Mansonia), as well as from midges in Eurasia. Molecular genetic evolution analysis revealed large molecular differences between the mosquitoes currently circulating Eurasia and those in the South Pacific in 1950s. The number of disease outbreaks caused by GETV in animals is increasing alongside the types of animals infected, from horses and pigs to cattle, blue foxes and red pandas. The disease burden is severely underestimated, and the economic cost to livestock production remains unknown. Herein, we review GETV temporal and spatial distribution, molecular genetic evolution, transmission and data on disease outbreaks. This work provides a reference for public health workers engaged in GETV research and zoonotic disease prevention and control.

Viral metagenomics unveiled extensive communications of viruses within giant pandas and their associated organisms in the same ecosystem

Cross-species transmission events were commonplace, with numerous cases of host-switching during the viral evolutionary history, but relatively little evidence for onward transmission in different species living in the same ecosystem. For understanding the communications of viruses in giant pandas (Ailuropoda melanoleuca) and their associated organisms, based on a large size of samples (N = 2305) collected between 2015 and 2020 from giant panda (N = 776) and other four giant panda-associated organisms in the same ecosystem, red pandas (N = 700), stray cats (N = 32), wild rats (N = 42), and mosquitoes (N = 755), viromics was used for the virus identification and subsequent virus traceability. The results showed that a feline panleukopenia virus (FPV) was found in giant pandas with clinical signs of vomiting and mild diarrhea. Meanwhile, the same FPV strain was also prevalent in the healthy red panda (Ailurus fulgens) population. From the viromes of the five different organisms, 250 virus genomes were determined. Our data revealed that besides FPV, other putative pathogenic viruses, such as red panda amdoparvoviruses (RPAVs) and Getah viruses (GETVs) were responsible for previous disease or death of some red pandas. We also demonstrated that a number of viruses were involved in potential interspecies jumping events between giant pandas and their associated species. Collectively, our results shed light on the genetic diversity and relationship of diverse viral pathogens in 'Giant pandas-Associated animals-Arthropods' and report some cases of possible viral host-switching among these host species living in the same ecosystem.

Genomic and In Vitro Phenotypic Comparisons of Epidemic and Non-Epidemic Getah Virus Strains

Getah virus is an emerging mosquito-borne animal pathogen. Four phylogenetic groups of GETV, Group I (GI), GII, GIII and GIV, were identified. However, only the GETV GIII was associated with disease epidemics suggesting possible virulence difference in this virus group. Here, we compared the genetic and in vitro phenotypic characteristics between the epidemic and non-epidemic GETV. Our complete coding genome sequence analyses revealed several amino acid substitutions unique to the GETV GIII and GIV groups, which were found mainly in the hypervariable domain of nsP3 and E2 proteins. Replication kinetics of the epidemic (GIII MI-110 and GIII 14-I-605) and non-epidemic GETV strains (prototype GI MM2021 and GIV B254) were compared in mammalian Vero cells and mosquito C6/36 and U4.4 cells. In all cells used, both epidemic GETV GIII MI-110 and GIII 14-I-605 strains showed replication rates and mean maximum titers at least 2.7-fold and 2.3-fold higher than those of GIV B254, respectively (Bonferroni posttest, p < 0.01). In Vero cells, the epidemic GETV strains caused more pronounced cytopathic effects in comparison to the GIV B254. Our findings suggest that higher virus replication competency that produces higher virus titers during infection may be the main determinant of virulence and epidemic potential of GETV.

Construction and characterization of a full-length infectious clone of Getah virus in vivo

Getah virus (GETV) is a mosquito-borne virus of the genus Alphavirus in the family Togaviridae and, in recent years, it has caused several outbreaks in animals. The molecular basis for GETV pathogenicity is not well understood. Therefore, a reverse genetic system of GETV is needed to produce genetically modified viruses for the study of the viral replication and its pathogenic mechanism. Here, we generated a CMV-driven infectious cDNA clone based on a previously isolated GETV strain, GX201808 (pGETV-GX). Transfection of pGETV-GX into BHK-21 ​cells resulted in the recovery of a recombinant virus (rGETV-GX) which showed similar growth characteristics to its parental virus. Then three-day-old mice were experimentally infected with either the parental or recombinant virus. The recombinant virus showed milder pathogenicity than the parental virus in the mice. Based on the established CMV-driven cDNA clone, subgenomic promoter and two restriction enzyme sites (BamHI and EcoRI) were introduced into the region between E1 protein and 3′UTR. Then the green fluorescent protein (GFP), red fluorescent protein (RFP) and improved light-oxygen-voltage (iLOV) genes were inserted into the restriction enzyme sites. Transfection of the constructs carrying the reporter genes into BHK-21 ​cells proved the rescue of the recombinant reporter viruses. Taken together, the establishment of a reverse genetic system for GETV provides a valuable tool for the study of the virus life cycle, and to aid the development of genetically engineered GETVs as vectors for foreign gene expression.

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Generation and recovery of a CMV-driven infectious cDNA clone of GETV isolate, GX201808 (pGETV-GX).

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The recombinant virus showed milder pathogenicity than the parental virus in a mouse model.

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The Getah virus infectious clone can be used as a vector for expressing reporter genes.

Structure of infective Getah virus at 2.8 Å resolution determined by cryo-electron microscopy

Getah virus (GETV), a member of the genus alphavirus, is a mosquito-borne pathogen that can cause pyrexia and reproductive losses in animals. Although antibodies to GETV have been found in over 10% of healthy people, there are no reports of clinical symptoms associated with GETV. The biological and pathological properties of GETV are largely unknown and antiviral or vaccine treatments against GETV are still unavailable due to a lack of knowledge of the structure of the GETV virion. Here, we present the structure of infective GETV at a resolution of 2.8 Å with the atomic models of the capsid protein and the envelope glycoproteins E1 and E2. We have identified numerous glycosylation and S-acylation sites in E1 and E2. The surface-exposed glycans indicate a possible impact on viral immune evasion and host cell invasion. The S-acylation sites might be involved in stabilizing the transmembrane assembly of E1 and E2. In addition, a cholesterol and a phospholipid molecule are observed in a transmembrane hydrophobic pocket, together with two more cholesterols surrounding the pocket. The cholesterol and phospholipid stabilize the hydrophobic pocket in the viral envelope membrane. The structural information will assist structure-based antiviral and vaccine screening, design, and optimization.

Structural Insights into Alphavirus Assembly Revealed by the Cryo-EM Structure of Getah Virus

Getah virus (GETV) is a member of the alphavirus genus, and it infects a variety of animal species, including horses, pigs, cattle, and foxes. Human infection with this virus has also been reported. The structure of GETV has not yet been determined. In this study, we report the cryo-EM structure of GETV at a resolution of 3.5 Å. This structure reveals conformational polymorphism of the envelope glycoproteins E1 and E2 at icosahedral 3-fold and quasi-3-fold axes, which is believed to be a necessary organization in forming a curvature surface of virions. In our density map, three extra densities are identified, one of which is believed a “pocket factor”; the other two are located by domain D of E2, and they may maintain the stability of E1/E2 heterodimers. We also identify three N-glycosylations at E1 N141, E2 N200, and E2 N262, which might be associated with receptor binding and membrane fusion. The resolving of the structure of GETV provides new insights into the structure and assembly of alphaviruses and lays a basis for studying the differences of biology and pathogenicity between arthritogenic and encephalitic alphaviruses.

Group IV Getah Virus in Culex Mosquitoes, Malaysia

A new Getah virus (GETV) strain, B254, was isolated from Culex fuscocephalus mosquitoes captured at Mount Ophir, Malaysia, in 2012. Phylogenetic analyses revealed that GETV B254 is distinct from the old Malaysia GETV MM2021 strain but closely related to group IV GETV from Russia (LEIV16275Mag), China (YN12031), and Thailand (GETV/SW/Thailand/2017).

Molecular and Serological Surveillance of Getah Virus in the Xinjiang Uygur Autonomous Region, China, 2017-2020

The Getah virus (GETV), a mosquito-borne RNA virus, is widely distributed in Oceania and Asia. GETV is not the only pathogenic to horses, pigs, cattle, foxes and boars, but it can also cause fever in humans. Since its first reported case in Chinese mainland in 2017, the number of GETV-affected provinces has increased to seventeen till now. Therefore, we performed an epidemiologic investigation of GETV in the Xinjiang region, located in northwestern China, during the period of 2017–2020. ELISA was used to analyze 3299 serum samples collected from thoroughbred horse, local horse, sheep, goat, cattle, and pigs, with thoroughbred horse (74.8%), local horse (67.3%), goat (11.7%), sheep (10.0%), cattle (25.1%) and pigs (51.1%) being positive for anti-GETV antibodies. Interestingly, the neutralizing antibody titer in horses was much higher than in other species. Four samples from horses and pigs were positive for GETV according to RT-PCR. Furthermore, from the serum of a local horse, we isolated GETV which was designated as strain XJ-2019-07, and determined its complete genome sequence. From the phylogenetic relationships, it belongs to the Group III lineage. This is the first evidence of GETV associated to domestic animals in Xinjiang. Overall, GETV is prevalent in Xinjiang and probably has been for several years. Since no vaccine against GETV is available in China, detection and monitoring strategies should be improved in horses and pigs, especially imported and farmed, in order to prevent economic losses.

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We firstly reported the epidemiology and isolation of GETV infection in livestock in Xinjiang.

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GETV is prevalent in Xinjiang and probably has been for several years.

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Since no vaccine against GETV is available in China, detection and monitoring strategies should be improved in horses and pigs, especially imported and farmed, in order to prevent economic losses.

Origin, genetic diversity, adaptive evolution and transmission dynamics of Getah virus

As a member of the Alphavirus, Getah virus (GETV) was becoming more serious and posing a serious threat to animal safety and public health. However, the circulation, distribution and evolution of GETV is not well understood. Hence, we integrated a variety of bioinformatic methodologies, from genomic alterations to systematic analysis, phylogeography, selection, adaptive analysis, prediction of protein modification, structural biology and molecular dynamics simulations to understand the characteristics of GETV. The results of phylogeography and molecular evolution show that due to the lack of vaccine, GETV is rapidly expanding its host range and geographical distribution at a high evolutionary rate. We also predicted the important modification sites, and identified the adaptive and active selection sites. Finally, the analysis of spatial structure and function showed that six adaptive sites may be related to the structural stability, receptor binding ability, immunogenicity and immune evasion of the virus, respectively. The data from this study have important implications for the understanding of ongoing GETV outbreaks worldwide and will guide future efforts to develop effective preventive and control measures against GETV. In particular, biosafety measures should be strengthened immediately to prevent GETV from becoming a pandemic, especially in China, South Korea and Japan.

Development of a reverse transcription recombinase-aided amplification assay for detection of Getah virus

GETV, an arbo-borne zoonotic virus of the genus Alphavirus, which causes diarrhea and reproduction disorders in swine, lead to serious economic losses to the swine industry in China. At present, the existing methods for GETV detection are time-consuming and low sensitivity, so, a rapid, accurate and sensitive GETV detection method is urgently needed. In this study, a fluorescent reverse transcription recombinase-assisted amplification method (RT-RAA) was successfully established for the rapid detection of GETV. The sensitivity of this method to GETV was 8 copies/reaction and 20 TCID₅₀/reaction. No cross-reaction with other viruses. A total of 118 samples were prepared for GETV detection using fluorescent RT-RAA and SYBR Green I RT-qPCR, the coincidence rate of the two methods was 100%. The results suggest that the RT-RAA method is rapid, sensitive and specific for GETV detection and can be applied in the clinical.

Complete genetic dissection and cell type-specific replication of old world alphaviruses, getah virus (GETV) and sagiyama virus (SAGV)

Getah virus (GETV), which was first isolated in Malaysia in 1955, and Sagiyama virus (SAGV), isolated in Japan in 1956, are members of the genus Alphavirus in the family Togaviridae. It is a consensus view that SAGV is a variant of GETV. In the present study, we determined the complete sequences of the prototype GETV MM2021 and SAGV M6-Mag132 genomic RNA extracted from plaque-purified viruses. The MM2021 genome was 11,692 nucleotides (nt) in length in the absence of 3' poly(A) tail, and the length of M6-Mag132 genome was 11,698 nt. Through sequence alignment of MM2021 and M6-Mag132, we located all the amino acid differences between these two strains, which were scattered in all the encoded proteins. Subsequently, we validated the close evolutionary relationship between GETV and SAGV by constructing phylogenetic trees based on either complete genomes or structural genomes. We eventually analyzed the growth kinetics of GETV and SAGV as well as other representative alphaviruses in various mammalian and insect cell lines. It was shown that human-oriented cell lines such as HEK-293T and Hela cells were relatively resistant to GETV and SAGV infection due to absence of proviral factors or species-specific barrier. On the other hand, both GETV and SAGV replicated efficiently in non-human cell lines. Our results provide essential genetic information for future epidemiological surveillance on Alphaviruses and lay the foundation for developing effective interventions against GETV and SAGV.

Monitoring Mosquito-Borne Arbovirus in Various Insect Regions in China in 2018

Background

Increases in global travel and trade are changing arbovirus distributions worldwide. Arboviruses can be introduced by travelers, migratory birds, or vectors transported via international trade. Arbovirus surveillance in field-collected mosquitoes may provide early evidence for mosquito-borne disease transmission.

Methods

During the seasons of high mosquito activity of 2018, 29,285 mosquitoes were sampled from seven sentinel sites in various insect regions. The mosquitoes were analyzed by RT-PCR for alphaviruses, flaviviruses, and orthobunyaviruses.

Results

We detected three strains of Japanese encephalitis virus (JEV), five strains of Getah virus (GETV), and 45 strains of insect-specific flaviviruses including Aedes flavivirus (AeFV, 1), Chaoyang virus (CHAOV, 1), Culex flavivirus (CxFV, 17), Hanko virus (HANKV, 2), QuangBinh virus (QBV, 22), and Yunnan Culex flavivirus (YNCxFV, 2). Whole genomes of one strain each of GETV, CxFV, CHAOV, and AeFV were successfully amplified. Phylogenetic analysis revealed that the new JEV strains detected in the Shanghai and Hubei Provinces belong to the GI-b strain and are phylogenetically close to the NX1889 strain (MT134112) isolated from a patient during a JE outbreak in Ningxia in 2018. GETVs were found in Inner Mongolia, Hubei, and Hainan and belonged to Group III. They were closely related to strains isolated from swine. HANKV was recorded for the first time in China and other ISFVs were newly detected at several sentinel sites. The bias-corrected maximum likelihood estimation value for JEV in Jinshan, Shanghai was 4.52/1,000 (range 0.80-14.64). Hence, there is a potential risk of a JEV epidemic in that region.

Conclusion

GI-b is the dominant circulating JEV genotype in nature and poses a health risk to animals and humans. The potential threat of widespread GETV distribution as a zoonosis is gradually increasing. The present study also disclosed the dispersion and host range of ISFVs. These findings highlight the importance of tracing the movements of the vectors and hosts of mosquito-borne pathogens in order to prevent and control arbovirus outbreaks in China.

A serological survey and characterization of Getah virus in domestic pigs in Thailand, 2017-2018

Getah virus (GETV) is a mosquito-borne RNA virus belonging to the family Togaviridae, genus Alphavirus. GETV infection causes diarrhoea and death in piglets, and reproductive failure and abortion in sows. This study conducted a serological survey of GETV infection among domestic pig populations in Thailand. ELISA was used to analyse 1,188 pig serum samples collected from 11 provinces of Thailand during 2017-2018, with 23.1% of the samples being positive for anti-GETV antibodies. The positive ratio of anti-GETV antibodies was significantly higher in nursery (67.9%) and older stages (84.5%) of pigs than in finishing stage (14.2%). Furthermore, we successfully isolated GETV from one pig serum, designated as GETV strain GETV/SW/Thailand/2017, and determined the complete genome sequence (11,689 nt). Phylogenetic analysis demonstrated that our isolate was different from the recent GETV group spreading among pig populations in East Asia and formed a cluster with two GETV strains, namely YN12031 (China, 2015) and LEIV16275Mar (Far-East Russia, 2007). We concluded that two different GETV groups are currently spreading among pig populations in Asian countries.

Emergence and Phylogenetic Analysis of a Getah Virus Isolated in Southern China

Getah virus (GETV) has caused many outbreaks in animals in recent years. Monitoring of the virus and its related diseases is crucial to control the transmission of the virus. In the summer of 2018, we conducted routine tests on clinical samples from different pig farms in Guangxi province, South China, and isolated and characterized a GETV strain, named GX201808. Cytopathic effects were observed in BHK-21 cells inoculated with GX201808. The expression of E2 protein of GETV could be detected in virus-infected cells by indirect immunofluorescence assays. Electron microscopic analysis showed that the virus particles were spherical and ~70 nm in diameter with featured surface fibers. The multistep growth curves showed the virus propagated well in the BHK-21 cells. Molecular genetic analysis revealed that GX201808 belongs to Group 3, represented by Kochi-01-2005 isolated in Japan in 2005, and it clustered closely with the recently reported Chinese strains isolated from pigs, cattle, and foxes. A comparison of the identities of nucleotides and amino acids in the coding regions demonstrated that the GX201808 showed the highest amino acid identity (99.6%) with the HuN1 strain, a highly pathogenic isolate resulting in an outbreak of GETV infection in swine herds in Hunan province in 2017. In the present study, GETV was identified and isolated for the first time in Guangxi province of southern China, suggesting that future surveillance of this virus should be strengthened.

Sequencing of Historical Isolates, K-mer Mining and High Serological Cross-Reactivity with Ross River Virus Argue against the Presence of Getah Virus in Australia

Getah virus (GETV) is a mosquito-transmitted alphavirus primarily associated with disease in horses and pigs in Asia. GETV was also reported to have been isolated from mosquitoes in Australia in 1961; however, retrieval and sequencing of the original isolates (N544 and N554), illustrated that these viruses were virtually identical to the 1955 GETV_MM2021 isolate from Malaysia. K-mer mining of the >40,000 terabases of sequence data in the Sequence Read Archive followed by BLASTn confirmation identified multiple GETV sequences in biosamples from Asia (often as contaminants), but not in biosamples from Australia. In contrast, sequence reads aligning to the Australian Ross River virus (RRV) were readily identified in Australian biosamples. To explore the serological relationship between GETV and other alphaviruses, an adult wild-type mouse model of GETV was established. High levels of cross-reactivity and cross-protection were evident for convalescent sera from mice infected with GETV or RRV, highlighting the difficulties associated with the interpretation of early serosurveys reporting GETV antibodies in Australian cattle and pigs. The evidence that GETV circulates in Australia is thus not compelling.

Isolation and characterization of Getah virus from pigs in Guangdong province of China

Getah virus (GETV) is a mosquito-borne virus that is widely distributed in Asian countries including China, in which the first case of equine GETV infection was reported in Guangdong province in August 2018. In this study, GETVs were detected in two classical swine fever virus-positive samples collected from swine herds in Foshan city, Guangdong province, 2018. Infection of porcine PK-15 cells produced rapid cytopathic effects (CPEs), including shrinking, rounding and detaching, and peak titre of 109.3 TCID50 /ml occurred at 24 hr post-infection. Electron microscopy and ultra-thin sectioning revealed spherical GETV particles of 70 nm diameter with an isometric interior and are found to be lining the outer membrane of infected cells. Whole-genome analysis showed that the two GETV isolates are identical to each other and cluster with Group III strains of GETV, sharing 96.1%-99.7% nucleotide sequence identity with all available reference strains. The most closely relative of the obtained GETV isolates was porcine strain HNJZ-S2 from Henan province (99.7%), with 98.6% sequence identity shared with equine GETV strain GZ201808 first identified in Guangdong province, indicating different sources for porcine and equine GETV infections in this region. No evidence of GETV infection was found in 497 archived porcine samples collected between 1990 and 2018 in Guangdong province.

First isolation and characterization of Getah virus from cattle in northeastern China

Background

Getah virus (GETV) is a neglected mosquito-borne Alphavirus that causes pyrexia, body rash, and leg oedema in horses and foetal death and reproductive disorders in pigs. Infected animals may play a critical role in the amplification and circulation of the virus. The present study aimed to investigate GETV infection in clinically infected cattle and vector mosquito species in northeastern China.

Results

Serum samples were collected from beef cattle that presented sudden onset of fever in forest grazing areas, and metagenomic sequencing was conducted, revealing 29 contigs from ten serum samples matching the GETV genome. Quantitative RT-PCR (RT-qPCR) was performed with GETV RNA from 48 beef cattle serum samples, showing that the overall prevalence of GETV in the beef cattle samples was 6.25% (3/48). Serological investigation indicated that GETV neutralizing antibodies were detected in 83.3% (40/48, 95% CI 67–100) of samples from the study region. The GETV JL1808 strain was isolated from clinically infected cattle showing fever. Sequence comparisons showed high identity with the HuN1 strain, a highly pathogenic swine epidemic isolate obtained in Hunan province in 2017, at the nucleotide level (99.5%) and at the deduced amino acid level (99.7–99.9%). The phylogenetic analysis of JL1808 clustered in Group III, and also revealed a close genetic relationship with the HuN1 strain. Additionally, about 12,000 mosquitoes were trapped in this region. The presence of GETV infection was detected in mosquitoes, suggesting that the minimum infection rate (MIR) was 1.50‰, with MIRs of 1.67‰ in Culex pseudovishnui, 1.60‰ in Culex tritaeniorhynchus, and 1.21‰ in Anopheles sinensis.

Conclusions

To the best of our knowledge, this is the first report of GETV infection in cattle. These results demonstrated that a highly pathogenic, mosquito-borne swine GETV can infect and circulate in cattle, implying that it is necessary to conduct surveillance of GETV infection in animals in northeastern China.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-2061-z) contains supplementary material, which is available to authorized users.