Complete genomic RNA sequence of western equine encephalitis virus and expression of the structural genes

The impact of temperature and insect-specific viruses on the transmission of alphaviruses by Aedes japonicus japonicus

Arthropod-borne virus (arbovirus) infections are increasing globally, and invasive mosquito species are spreading. Since the end of the last century, Aedes japonicus has continued to spread in Europe as well as in North America. Aedes japonicus is known to be able to transmit several viruses, but extensive information about the vector competence of Ae. japonicus for alphaviruses is missing. Therefore, we infected field-caught Ae. japonicus mosquitoes from Germany with different alphaviruses that occur in areas with either tropical or moderate temperatures and are clustered as arthritogenic or encephalitic alphaviruses. Additionally, we studied the influence of temperature and natural infections with insect-specific viruses (ISVs) on the vector competence of Ae. japonicus. Transmission of chikungunya virus was exclusively observed at the high-temperature profile of 27° ± 5°C, with a low transmission rate of 2.9%. Transmission of Sindbis virus and western equine encephalitis virus was observed at all investigated temperature profiles with higher transmission rates of 32%-57%. We identified seven different ISVs in the investigated Ae. japonicus mosquitoes, showing that coinfections with ISVs are very common. The interplay between arbovirus infections and concurrent multiple ISV infections is highly complex, and additional research is required to fully elucidate the detailed mechanisms underlying the outcomes of this study.

IMPORTANCE

The spread of invasive mosquito species like Aedes japonicus poses a significant public health risk, particularly in the context of rising global temperatures and the growing prevalence of arbovirus infections. This study provides critical insights into the ability of Aedes japonicus to transmit alphaviruses such as chikungunya, Sindbis, and western equine encephalitis under different temperature conditions. The identification of multiple insect-specific viruses co-infecting the mosquitoes highlights the complexity of arbovirus transmission and underscores the need for further research. Understanding the interplay between environmental factors like temperature and viral coinfections is essential for predicting and mitigating future outbreaks. This work advances our knowledge of vector competence, which is helpful for developing strategies for risk assessment.

Viruses Infecting the Plant Pathogenic Fungus Rhizoctonia solani

The cosmopolitan fungus Rhizoctonia solani has a wide host range and is the causal agent of numerous crop diseases, leading to significant economic losses. To date, no cultivars showing complete resistance to R. solani have been identified and it is imperative to develop a strategy to control the spread of the disease. Fungal viruses, or mycoviruses, are widespread in all major groups of fungi and next-generation sequencing (NGS) is currently the most efficient approach for their identification. An increasing number of novel mycoviruses are being reported, including double-stranded (ds) RNA, circular single-stranded (ss) DNA, negative sense (−)ssRNA, and positive sense (+)ssRNA viruses. The majority of mycovirus infections are cryptic with no obvious symptoms on the hosts; however, some mycoviruses may alter fungal host pathogenicity resulting in hypervirulence or hypovirulence and are therefore potential biological control agents that could be used to combat fungal diseases. R. solani harbors a range of dsRNA and ssRNA viruses, either belonging to established families, such as Endornaviridae, Tymoviridae, Partitiviridae, and Narnaviridae, or unclassified, and some of them have been associated with hypervirulence or hypovirulence. Here we discuss in depth the molecular features of known viruses infecting R. solani and their potential as biological control agents.

Zoonotic Viral Diseases of Equines and Their Impact on Human and Animal Health

INTRODUCTION

Zoonotic diseases are the infectious diseases that can be transmitted to human beings and vice versa from animals either directly or indirectly. These diseases can be caused by a range of organisms including bacteria, parasites, viruses and fungi. Viral diseases are highly infectious and capable of causing pandemics as evidenced by outbreaks of diseases like Ebola, Middle East Respiratory Syndrome, West Nile, SARS-Corona, Nipah, Hendra, Avian influenza and Swine influenza.

EXPALANTION

Many viruses affecting equines are also important human pathogens. Diseases like Eastern equine encephalitis (EEE), Western equine encephalitis (WEE), and Venezuelan-equine encephalitis (VEE) are highly infectious and can be disseminated as aerosols. A large number of horses and human cases of VEE with fatal encephalitis have continuously occurred in Venezuela and Colombia. Vesicular stomatitis (VS) is prevalent in horses in North America and has zoonotic potential causing encephalitis in children. Hendra virus (HeV) causes respiratory and neurological disease and death in man and horses. Since its first outbreak in 1994, 53 disease incidents have been reported in Australia. West Nile fever has spread to many newer territories across continents during recent years.It has been described in Africa, Europe, South Asia, Oceania and North America. Japanese encephalitis has expanded horizons from Asia to western Pacific region including the eastern Indonesian archipelago, Papua New Guinea and Australia. Rabies is rare in horses but still a public health concern being a fatal disease. Equine influenza is historically not known to affect humans but many scientists have mixed opinions. Equine viral diseases of zoonotic importance and their impact on animal and human health have been elaborated in this article.

CONCLUSION

Equine viral diseases though restricted to certain geographical areas have huge impact on equine and human health. Diseases like West Nile fever, Hendra, VS, VEE, EEE, JE, Rabies have the potential for spread and ability to cause disease in human. Equine influenza is historically not known to affect humans but some experimental and observational evidence show that H3N8 influenza virus has infected man. Despite our pursuit of understanding the complexity of the vector-host-pathogen mediating disease transmission, it is not possible to make generalized predictions concerning the degree of impact of disease emergence. A targeted, multidisciplinary effort is required to understand the risk factors for zoonosis and apply the interventions necessary to control it.

Molecular determinants of alphavirus neuropathogenesis in mice

Alphaviruses are enveloped viruses with a positive-stranded RNA genome, of the family Togaviridae. In mammals and birds they are mosquito-transmitted and are of veterinary and medical importance. They cause primarily two types of disease: encephalitis and polyarthritis. Here we review attempts to understand the molecular basis of encephalitis and virulence for the central nervous system (CNS) in mouse models. Sindbis virus (SINV) was the first virus to be studied in this way. Other viruses analysed are Semliki Forest virus (SFV), Venezuelan equine encephalitis virus, Eastern equine encephalitis virus and Western equine encephalitis virus. Neurovirulence was found to be associated with damage to neurons in the CNS. It mapped mainly to the E2 region of the genome, and to the nsP3 gene. Also, avirulent natural isolates of both SINV and SFV have been found to have more rapid cleavage of nonstructural proteins due to mutations in the nsP1-nsP2 cleavage site. Immune-mediated demyelination for avirulent SFV has been shown to be associated with infection of oligodendrocytes. For Chikungunya virus, an emerging alphavirus that uncommonly causes encephalitis, analysis of the molecular basis of CNS pathogenicity is beginning. Experiments on SINV and SFV have indicated that virulence may be related to the resistance of virulent virus to interferon action. Although the E2 protein may be involved in tropism for neurons and passage across the blood-brain barrier, the role of the nsP3 protein during infection of neurons is unknown. More information in these areas may help to further explain the neurovirulence of alphaviruses.

Evolutionary genetics and vector adaptation of recombinant viruses of the western equine encephalitis antigenic complex provides new insights into alphavirus diversity and host switching

Western equine encephalitis virus (WEEV), Highlands J virus (HJV), and Fort Morgan virus (FMV) are the sole representatives of the WEE antigenic complex of the genus Alphavirus, family Togaviridae, that are endemic to North America. All three viruses have their ancestry in a recombination event involving eastern equine encephalitis virus (EEEV) and a Sindbis (SIN)-like virus that gave rise to a chimeric alphavirus that subsequently diversified into the present-day WEEV, HJV, and FMV. Here, we present a comparative analysis of the genetic, ecological, and evolutionary relationships among these recombinant-origin viruses, including the description of a nsP4 polymerase mutation in FMV that allows it to circumvent the host range barrier to Asian tiger mosquito cells, a vector species that is normally refractory to infection. Notably, we also provide evidence that the recombination event that gave rise to these three WEEV antigenic complex viruses may have occurred in North America.

Western equine encephalitis virus: evolutionary analysis of a declining alphavirus based on complete genome sequences

Western equine encephalitis virus (WEEV) is an arbovirus from the genus Alphavirus, family Togaviridae, which circulates in North America between birds and mosquitoes, occasionally causing disease in humans and equids. In recent decades, human infection has decreased dramatically; the last documented human case in North America occurred in 1994, and the virus has not been detected in mosquito pools since 2008. Because limited information exists regarding the evolution of WEEV, we analyzed the genomic sequences of 33 low-passage-number strains with diverse geographic and temporal distributions and performed comprehensive phylogenetic analyses. Our results indicated that WEEV is a highly conserved alphavirus with only approximately 5% divergence in its most variable genes. We confirmed the presence of the previously determined group A and B lineages and further resolved group B into three sublineages. We also observed an increase in relative genetic diversity during the mid-20th century, which correlates with the emergence and cocirculation of several group B sublineages. The estimated WEEV population size dropped in the 1990s, with only the group B3 lineage being sampled in the past 20 years. Structural mapping showed that the majority of substitutions in the envelope glycoproteins occurred at the E2-E2 interface. We hypothesize that an event occurred in the mid-20th century that resulted in the increased genetic diversity of WEEV in North America, followed by genetic constriction due to either competitive displacement by the B3 sublineage or stochastic events resulting from a population decline.

IMPORTANCE

Western equine encephalitis virus (WEEV) has caused several epidemics that resulted in the deaths of thousands of humans and hundreds of thousands of equids during the past century. During recent decades, human infection decreased drastically and the virus has not been found in mosquito pools since 2008. Because limited information exists regarding the evolution of WEEV, we analyzed 33 complete genome sequences and conducted comprehensive phylogenetic analyses. We confirmed the presence of two major lineages, one of which diverged into three sublineages. Currently, only one of those sublineages is found circulating in nature. Understanding the evolution of WEEV over the past century provides a unique opportunity to observe an arbovirus that is in decline and to better understand what factors can cause said decline.

The Pathogenesis of Alphaviruses

Alphaviruses are enveloped single-stranded positive sense RNA viruses of the family Togaviridae. The genus alphavirus contains nine viruses, which are of medical, theoretical, or economic importance, and which will be considered. Sindbis virus (SINV) and Semliki Forest (SFV), although of some medical importance, have largely been studied as models of viral pathogenicity. In mice, SINV and SFV infect neurons in the central nervous system and virulent strains induce lethal encephalitis, whereas avirulent strains of SFV induce demyelination. SFV infects the developing foetus and can be teratogenic. Venezuelan Equine Encephalitis virus, Eastern Equine Encephalitis virus, and Western Equine Encephalitis virus can induce encephalitis in horses and humans. They are prevalent in the Americas and are mosquito transmitted. Ross River virus, Chikungunya virus (CHIKV), and O’nyong-nyong virus (ONNV) are prevalent in Australasia, Africa and Asia, and Africa, respectively. ONNV virus is transmitted by Anopheles mosquitoes, while the other alphaviruses are transmitted by culicine mosquitoes. CHIKV has undergone adaptation to a new mosquito host which has increased its host range beyond Africa. Salmonid alphavirus is of economic importance in the farmed salmon and trout industry. It is postulated that future advances in research on alphavirus pathogenicity will come in the field of innate immunity.

Liposome-antigen-nucleic acid complexes protect mice from lethal challenge with western and eastern equine encephalitis viruses

Alphaviruses are mosquito-borne viruses that cause significant disease in animals and humans. Western equine encephalitis virus (WEEV) and eastern equine encephalitis virus (EEEV), two New World alphaviruses, can cause fatal encephalitis, and EEEV is a select agent of concern in biodefense. However, we have no antiviral therapies against alphaviral disease, and current vaccine strategies target only a single alphavirus species. In an effort to develop new tools for a broader response to outbreaks, we designed and tested a novel alphavirus vaccine comprised of cationic lipid nucleic acid complexes (CLNCs) and the ectodomain of WEEV E1 protein (E1ecto). Interestingly, we found that the CLNC component, alone, had therapeutic efficacy, as it increased survival of CD-1 mice following lethal WEEV infection. Immunization with the CLNC-WEEV E1ecto mixture (lipid-antigen-nucleic acid complexes [LANACs]) using a prime-boost regimen provided 100% protection in mice challenged with WEEV subcutaneously, intranasally, or via mosquito. Mice immunized with LANACs mounted a strong humoral immune response but did not produce neutralizing antibodies. Passive transfer of serum from LANAC E1ecto-immunized mice to nonimmune CD-1 mice conferred protection against WEEV challenge, indicating that antibody is sufficient for protection. In addition, the LANAC E1ecto immunization protocol significantly increased survival of mice following intranasal or subcutaneous challenge with EEEV. In summary, our LANAC formulation has therapeutic potential and is an effective vaccine strategy that offers protection against two distinct species of alphavirus irrespective of the route of infection. We discuss plausible mechanisms as well the potential utility of our LANAC formulation as a pan-alphavirus vaccine.

Envelope protein E1 as vaccine target for western equine encephalitis virus

Western equine encephalitis virus (WEEV) is a mosquito-borne RNA virus which causes lethal infection in humans and equines. There are no commercial vaccines or anti-WEEV drugs available for humans. We used replication-defective, human adenovirus serotype-5 (HAd5) as a delivery vector for developing WEEV vaccine. Our previous study found delivery of both E1 and E2 envelope proteins of WEEV by HAd5 vector offers complete protection against lethal challenge of WEEV. In this paper, we constructed a HAd5-vectored E1 vaccine, Ad5-E1. Mice given single-dose vaccination of Ad5-E1 were completely protected against both homologous and heterologous WEEV strains. The protection was rapid, which was achieved as early as day 7 after vaccination. In addition, Ad5-E1 induced a strong WEEV-specific T cell response. Our data suggest E1 is a potential target for developing single-dose, fast-acting, HAd5-vectored vaccine for WEEV.

Dissemination of western equine encephalomyelitis virus in the potential vector, Culex pipiens pallens

Two western equine encephalomyelitis virus (WEEV) strains have been isolated in China. Our previous studies have verified that the mosquito Culex pipiens pallens Coquillett (Diptera: Culicidae) infected with WEEV was capable of transmitting this arbovirus, but it was not clear how the sequential multiplication and spread of virus occurred within the mosquito. In this study, we observed the distribution of WEEV antigen in orally-infected Cx. p. pallens by immunohistochemistry in order to better understand the initial infection, dissemination, and transmission of WEEV in the potential vector. Orally-infected WEEV dissemination varied within the different tissues of Cx. p. pallens, with virus antigen consistently observed in the salivary glands, foregut, midgut epithelial cells, Malpighian tubules, hindgut, and ovarian follicles of some individuals after various days of extrinsic incubation. We suggest that Cx. p. pallens, the potential vector of WEEV, has the ability to harbor the virus through the alimentary system, and the midgut epithelial cell may be the initial site of WEEV replication after ingestion of a viremic blood meal.

Identification of Western equine encephalitis virus structural proteins that confer protection after DNA vaccination

DNA vaccines encoding different portions of the structural proteins of western equine encephalitis virus were tested for the efficacy of their protection in a 100% lethal mouse model of the virus. The 6K-E1 structural protein encoded by the DNA vaccine conferred complete protection against challenge with the homologous strain and limited protection against challenge with a heterologous strain.

Chimeric alphavirus vaccine candidates protect mice from intranasal challenge with western equine encephalitis virus

We developed two types of chimeric Sindbis virus (SINV)/western equine encephalitis virus (WEEV) alphaviruses to investigate their potential use as live virus vaccines against WEE. The first-generation vaccine candidate, SIN/CO92, was derived from structural protein genes of WEEV strain CO92-1356, and two second-generation candidates were derived from WEEV strain McMillan. For both first- and second-generation vaccine candidates, the nonstructural protein genes were derived from SINV strain AR339. Second-generation vaccine candidates SIN/SIN/McM and SIN/EEE/McM included the envelope glycoprotein genes from WEEV strain McMillan; however, the amino-terminal half of the capsid, which encodes the RNA-binding domain, was derived from either SINV or eastern equine encephalitis virus (EEEV) strain FL93-939. All chimeric viruses replicated efficiently in mammalian and mosquito cell cultures and were highly attenuated in 6-week-old mice. Vaccinated mice developed little or no detectable disease and showed little or no evidence of challenge virus replication; however, all developed high titers of neutralizing antibodies. Upon intranasal challenge with high doses of virulent WEEV strains, mice vaccinated with >or=10(5)PFU of SIN/CO92 or >or=10(4)PFU of SIN/SIN/McM or SIN/EEE/McM were completely protected from disease. These findings support the potential use of these live-attenuated vaccine candidates as safe and effective vaccines against WEE.

Virulence variation among isolates of western equine encephalitis virus in an outbred mouse model

Little is known about viral determinants of virulence associated with western equine encephalitis virus (WEEV). Here, we have analysed six North American WEEV isolates in an outbred CD1 mouse model. Full genome sequence analyses showed < or =2.7 % divergence among the six WEEV isolates. However, the percentage mortality and mean time to death (MTD) varied significantly when mice received subcutaneous injections of 10(3) p.f.u. of each virus. Two WEEV strains, McMillan (McM) and Imperial 181 (IMP), were the most divergent of the six in genome sequence; McM caused 100 % mortality by 5 days post-infection, whereas IMP caused no mortality. McM had significantly higher titres in the brain than IMP. Similar differences in virulence were observed when McM and IMP were administered by aerosol, intranasal or intravenous routes. McM was 100 % lethal with an MTD of 1.9 days when 10(3) p.f.u. of each virus was administered by intracerebral inoculation; in contrast, IMP caused no mortality. The presence of IMP in the brains after infection by different routes and the lack of observed mortality confirmed that IMP is neuroinvasive but not neurovirulent. Based on morbidity, mortality, MTD, severity of brain lesions, virus distribution patterns, routes of infection and differences in infection of cultured cells, McM and IMP were identified as high- and low-virulence isolates, respectively.

Immunological evaluation of Escherichia coli expressed E2 protein of Western equine encephalitis virus

The Western equine encephalitis virus (WEEV) is a potential Biological Warfare (BW) agent. The WEEV is endemic in western Canada and has caused epidemics of "sleeping sickness" with a mortality rate of 7-9%. The E2 glycoprotein is a structural component of the WEEV and elicits production of neutralizing antibodies against the virus following an infection event. The envelope glycoprotein E2 is considered as the major target protein for the development of vaccines because it includes epitopes that elicit neutralizing antibodies. This report describes the successful cloning of the E2 gene of WEEV and expression in Escherichia coli as inclusion bodies. The inclusion bodies were successfully solubilized, refolded and the immunogenicity of this non-glycosylated protein was assessed in BALB/c mice. Recombinant E2 (rE2) protein was specifically and strongly recognized by inactivated WEEV-immunized mice serum sample on ELISA, suggesting that E. coli derived rE2 protein retained at least some functional characteristics of its native conformation. The immunogenicity of the refolded rE2 protein was demonstrated by strong humoral and cell mediated immune (CMI) responses in rE2-immunized BALB/c mice. The current study also demonstrated that rE2-immunized mice could be partially protected from lethal challenge of WEEV.

Complete protection of mice against a lethal dose challenge of western equine encephalitis virus after immunization with an adenovirus-vectored vaccine

Western equine encephalitis virus (WEEV) is an important pathogen for both humans and equines. The virus is also listed as a bioterrorism agent due to its ability for aerosol transmission with high mortality. No commercial vaccines or antiviral drugs are available for the prevention and treatment of WEEV infection in humans. In this paper, we constructed a recombinant WEEV vaccine, designated as Ad5-WEEV, using a replication defective, human adenovirus serotype 5 (HAd5) as a delivery vector. Ad5-WEEV contains the E3-E2-6K-E1 structural protein gene of the 71V-1658 strain of WEEV and the E1 and E2 proteins were synthesized in cells inoculated with Ad5-WEEV. After intramuscular immunization of mice with two doses of Ad5-WEEV, neutralizing antibodies against WEEV were generated and the mice were completely protected from a lethal dose challenge of 71V-1658. In addition, we showed that passive transfer of serum from the Ad5-WEEV-immunized mice could partially control WEEV infection. These results demonstrate that HAd5 vectors are promising for WEEV vaccine development.

Infectivity variation and genetic diversity among strains of Western equine encephalitis virus

Variation in infectivity and genetic diversity in the structural proteins were compared among eight strains of Western equine encephalitis virus (WEEV) to investigate WEEV virulence at the molecular level. A lethal intranasal infectivity model of WEEV was developed in adult BALB/c mice. All eight strains examined were 100 % lethal to adult mice in this model, but they varied considerably in the time to death. Based on the time to death, the eight strains could be classified into two pathotypes: a high-virulence pathotype, consisting of strains California, Fleming and McMillan, and a low-virulence pathotype, comprising strains CBA87, Mn548, B11, Mn520 and 71V-1658. To analyse genetic diversity in the structural protein genes, 26S RNAs from these eight strains were cloned and sequenced and found to have > 96 % nucleotide and amino acid identity. A cluster diagram divided the eight WEEV strains into two genotypes that matched the pathotype grouping exactly, suggesting that variation in infectivity can be attributed to genetic diversity in the structural proteins among these eight strains. Furthermore, potential amino acid differences in some positions between the two groups were identified, suggesting that these amino acid variations contributed to the observed differences in virulence.

Initiation of viral RNA-dependent RNA polymerization

This review summarizes the combined insights from recent structural and functional studies of viral RNA-dependent RNA polymerases (RdRPs) with the primary focus on the mechanisms of initiation of RNA synthesis. Replication of RNA viruses has traditionally been approached using a combination of biochemical and genetic methods. Recently, high-resolution structures of six viral RdRPs have been determined. For three RdRPs, enzyme complexes with metal ions, single-stranded RNA and/or nucleoside triphosphates have also been solved. These advances have expanded our understanding of the molecular mechanisms of viral RNA synthesis and facilitated further RdRP studies by informed site-directed mutagenesis. What transpires is that the basic polymerase right hand shape provides the correct geometrical arrangement of substrate molecules and metal ions at the active site for the nucleotidyl transfer catalysis, while distinct structural elements have evolved in the different systems to ensure efficient initiation of RNA synthesis. These elements feed the template, NTPs and ions into the catalytic cavity, correctly position the template 3′ terminus, transfer the products out of the catalytic site and orchestrate the transition from initiation to elongation.

Sequence requirements for Sindbis virus subgenomic mRNA promoter function in cultured cells

The Sindbis virus minimal subgenomic mRNA promoter (spanning positions -19 to +5 relative to the subgenomic mRNA start site) is approximately three- to sixfold less active than the fully active -98 to +14 promoter region. We identified two elements flanking the -19 to +5 region which increase its transcription to levels comparable to the -98 to +14 region. These elements span positions -40 to -20 and +6 to +14 and act synergistically to enhance transcription. Nine different virus libraries were constructed containing blocks of five randomized nucleotides at various positions in the -40 to +14 region. On passaging these libraries in mosquito cells, a small subset of the viruses came to dominate the population. Sequence analysis at the population level and for individual clones revealed that in general, wild-type bases were preferred for positions -15 to +5 of the minimal promoter. Base mutagenesis experiments indicated that the selection of wild-type bases in this region was primarily due to requirements for subgenomic mRNA transcription. Outside of the minimal promoter, the -35 to -29 region contained four positions which also preferred wildtype bases. However, the remaining positions generally preferred non-wild-type bases. On passaging of the virus libraries on hamster cells, the -15 to +5 region again preferred the wild-type base but most of the remaining positions exhibited almost no base preference. The promoter thus consists of an essential central region from -15 to +5 and discrete flanking sites that render it fully active, depending on the host environment.

Construction and characterization of monoclonal antibodies against western equine encephalitis virus

A repertoire of mouse monoclonal antibodies (MAbs) against western equine encephalitis virus (WEE) was constructed and characterized. Anti-WEE antibodies were expressed from hybridomas and purified by protein G chromatography. Each of the antibodies was functionally assessed by indirect enzyme-linked immunosorbent assays (ELISAs), Western blotting, and immunoprecipitations. All antibodies bound to WEE antigen in ELISAs, whereas only a subgroup of antibodies was found to be active in Western blotting and immunoprecipitations. A subset of antibodies was found to cross-react with other alphaviruses, such as Sindbis virus (SIN), Venezuelan equine encephalitis (VEE), and eastern equine encephalitis (EEE). Because many of the antibodies were highly reactive to WEE antigen in one or more of the assays, these antibodies are excellent candidates for immunodetection and immunotherapy studies.