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00.073.0.01.027.00.001. Western equine encephalitis virus, strain 5614

Cite this publication as: ICTVdB Management (2006). 00.073.0.01.027.00.001. Western equine encephalitis virus, strain 5614. In: ICTVdB - The Universal Virus Database, version 4. Büchen-Osmond, C. (Ed), Columbia University, New York, USA

Cite this site as: ICTVdB - The Universal Virus Database, version 4. http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/

Table of Contents

Isolate Description

Isolate designation: 5614.
Isolation date: not specified.

Host of Isolate and Habitat Details
Source of isolate: not specified.
Virus was isolated from adults.

Natural hosts and symptoms WEEV.natural.host.range.doc.

Collection and Isolation Details
Virus was isolated by unknown.

Biocontainment Level

Distribution of this virus falls under quarantine restrictions. It is recommended to handle this virus at the biocontainment level BSL-2.

Classification

This is a description of an invertebrate and vertebrate virus at the strain level with data on all virus properties from morphology to genome, replication, antigenicity and biological properties.

ICTVdB Virus Code: 00.073.0.01.027.00.001. Virus accession number: 73001127.
NCBI Taxonomy Identifier Taxon ID: 11039.

Name, Synonyms and Lineage

Virus is assigned to the genus 00.073.0.01. Alphavirus in the family 00.073. Togaviridae; not assigned to an order.

Virion Properties

Symptoms in the host are well established and the causative agent is determined.

Distinct viral structures are visible in thin sections of infected tissue. Particles contain nucleic acid which is encapsidated. Size and shape of virus has been determined by electron microscopy.

Virion Properties

Morphology

Virions consist of an envelope and a nucleocapsid. During their life cycle, virions have a cell-associated cycle and occur in one phenotype only. Virus capsid is surrounded by a single layer envelope and virions mature naturally by budding through the membrane of the host cell. Virions are spherical and measure 70 nm in diameter. The envelope surrounds one nucleocapsid. Envelope has surface projections. Surface projections are distinctive spikes covering evenly the surface. They are evenly dispersed and embedded in a lipid bilayer which is comprises hemagglutinin. Surface projections are composed of different types of proteins. Projections are formed by glycosylated and antigenic proteins, designated E1 and E2 which exhibit hemagglutinin activity. Host ribosomes are not seen inside the envelope. A regular capsid structure is present. Capsid/nucleocapsid is round and exhibits icosahedral symmetry (T=4). The nucleocapsid is isometric and has a diameter of 40 nm. The capsid shells of virions are composed of a single layer. Capsids appear round. Nucleocapsid contains a nucleoprotein complex.

Virion populations are comprised of particles of uniform size. Capsids all have the same appearance and only one species is recovered in preparations.

Physicochemical and Physical Properties

The molecular mass (Mr) of virions is 52 x 106. Virions have a buoyant density in sucrose of 1.22 g cm-3. The sedimentation coefficient is 280 S20w. Virion infectivity is inactivated and destroyed by heating for 10 min above 56°C. Extent of effect on virion infectivity is reduced by heat. Under in vitro conditions virions are stable when stored at -70°C; relatively stable when stored at -40°C, not stable at -20°C or above, or 37°C (half-life about 7 hours). Virions are inactivated in acid environment of pH 1-3, but are stable in alkaline environment of pH 7-9. Virions are sensitive to treatment with lipid solvents, detergents, ether, trypsin, chloroform, formaldehyde, heat, and ß-propiolactone. The infectivity is reduced after exposure to irradiation.

Nucleic Acid

The genome is monomeric; not segmented and contains a single molecule of linear, positive-sense, single-stranded RNA. The genome is infectious. Minor species of genomic nucleic acid are not found. The complete genome is 11000 nucleotides long. Sequence can be accessed from GenBank. The RNA is partially sequenced, sequenced region is 4498 nucleotides long, or 4471 nucleotides long and encodes C, E1, E2, nsP1, nsP2, nsP3, nsP4. Sequenced genome has the accession number(s)
[X74892]; [U01065]. Nucleotide sequences at the 3'-terminus are identical (polyadenylated), or unrelated to the 5'-terminus. The 3'-terminus has no long non-coding region; conserved nucleotide sequences. The 3'-terminus has a poly (A) tract. Each virion contains a single copy of the genome; a full length copy.

Reference to nucleotide sequence in PubMed: reference(s). GenBank records for nucleotide sequences; complete genome sequences.

Proteins

Proteins have been characterized and functions are assigned to them. Particles are made up of 3 proteins.

The viral genome encodes structural proteins and non-structural proteins. Virions consist of 3 structural protein(s) located in the envelope (E1, E2), nucleocapsid (CP).

Structural Proteins: Nucleocapsid protein CP has a molecular mass of 30000-33000 Da; is the product of the polyprotein encoded on the 3’ end of the genome by the S-ORF, as are the other structural proteins.

Non-Structural Proteins: Virus-coded non-structural proteins have been identified by sequence analysis and 4 non-structural protein(s) are found (nsP1, nsP2, nsP3, nsP4). The virus codes for enzymes and replication-associated proteins; an RNA-dependent RNA polymerase. In addition to the polymerase, the virus codes for enzymes such as helicase, protease, synthetase, and replicase. The non-structural proteins are thought to be involved in capping of viral RNAs, initiation of negative strand RNA synthesis, processing of non-structural proteins, in RNA replication, the formation of a replicase complex for the minus strand synthesis, and the synthesis of the plus strand; function in the cytoplasm of infected cells. Non-structural protein nsP1 has a function assigned. The protein is coded from NS-ORF; a replication-associated protein (capping of viral RNAs and initiating negative strand RNA synthesis) possesses methyltransferase activity. Non-structural protein nsP2 has a function assigned. The protein is coded from NS-ORF. The protein is a replication-associated protein (functions as a protease to process the nonstructural proteins, and as a helicase for RNA replication). Non-structural protein nsP3has a function assigned and iscoded from NS-ORF.

Lipids

Lipids are present in significant amounts and are located in the envelope. Virions are composed of 30% lipids by weight. The lipids are of host origin and composition depends on the cell in which the virus replicates. Lipids are derived from host cell membranes. Viral membranes include phosphatidyl ethanolamine, phosphatidyl choline, phosphatidyl serine, cholesterol, and sphingomyelin. Lipids are essential for infectivity.

Carbohydrates

Carbohydrates are glycoproteins and N-linked glycans that contain mannose. Carbohydrate composition in the virion is virus-dependent.

Genome Organization and Replication

Virions attach to receptors located on the surface of cell membrane to enter host cells.

By itself, genomic nucleic acid is infectious.

Infection and Replication: Virus replication is initiated by the insect host; occurs in the midgut and proceeds to salivary glands. In the vertebrate host virus replication occurs in various organs. Replication is not restricted to a particular tissue or organ of the host. Although severity of illness depends on route and dose, the majority of infections are subclinical, or mild. Infection involves a noncytocidal productive infectious cycle (in the invertebrate host), or does not involve a noncytocidal productive infectious cycle (in the mammalian host). Infected cells continue to grow slowly (cells from arthropods), or do not continue to grow (cells from vertebrates).

Transcription: The 5' ends of mRNAs are capped. The 3' ends of mRNAs possess a poly (A) tract.

Antigenicity

The virus is serologically related to all viruses in the genus Alphavirus. Antigenic determinants may be found on envelopes, spikes, and nucleocapsids and correspond to each of the major structural proteins, structural glycoproteins, and non-structural proteins; correspond to each of the major virion proteins CP, E1, E2, nsP1, nsP2, nsP3, nsP4. The type-specific antigenic determinants are involved in antibody mediated neutralization and hemagglutination inhibition. Antigenic determinants that possess serogroup-specific reactivity are found on the nucleocapsids. The serogroup-specific antigenic determinants are involved in antibody mediated neutralization, hemagglutination inhibition, and complement fixation. Antigenic specificity of the virion can be determined by neutralization tests, hemagglutination inhibition tests, complement fixation tests, ELISA tests, and immunofluorescence assays. In gel-diffusion tests antisera display cross-reactivities among different members of the taxon.

Serological relationships between different members are very close (but relationships depend on antigenic complex membership;). Cross-reactivity is found. Cross-reactivity between isolates of the same species and species, but not genera. Protective immunity is induced in the form of neutralizing antibodies. Virions are usually satisfactorily stabilized for use as antigens or immunogens by fixation with glutaraldehyde (or any of many other fixatives). The virus is immunogenic. The virus serves as an efficient immunogen when animals are infected with whole virus particle preparations, disrupted virus particle preparations and denatured virus particle preparations. These preparations produce antibodies. The virus induces antibodies with distinct reactivities to the subtype-specific determinants, type-specific determinants, serogroup-specific determinants, complex-specific determinants, and genus-specific determinants. The virus induces the formation of neutralizing antibodies, hemagglutination inhibiting antibodies, and complement-fixing antibodies. Antibody response that is protective against infection is usually directed against virion glycoproteins and virion surface proteins. The serotype is defined by E proteins. The virus serotype is determined by a serum neutralization test; using polyclonal antibodies. Antigenic distances between individual species, expressed as serological indices, are correlated with the degree of sequence difference in their coat protein (E1 and E2). Species that are serologically interrelated have antigenic homologies with different isolates of the same virus species. Although the degree of antigenic specificity varies with the degree of relatedness, the antigenicity is considerable between isolates of the same virus species and species of the same serogroup. Some species in the genus are related antigenically. They are sharing some epitopes in the structural proteins (40% homology between species), or in the non-structural proteins (60% homology between species). The virus is closely related to other viruses of the WEEV complex and related to all other alphaviruses. Classification of members of this taxon is based on their sequence homologies. Minor biological differences have been recognized between WEE virus isolates. Most closely homologous to other viruses of the WEEV complex.

Diagnostics and Reference Collections

The best tests for diagnosis are PCR, neutralization, IgM and IgG ELISA, Hi, CF, IFA. Antisera are commercially available from American Type Culture Collection and W.H.O. regional reference centers.

Vaccines are restricted for use in humans.

Vaccines

Vaccines are commercially available but not licensed for use in humans. Vaccines are not licensed for experimental use in humans.

Biological Properties

Natural Host

Virus infects during its life cycle arthropod and vertebrate hosts. Virus has an enzootic cycle and is transmitted from arthropod vector to birds and arthropod vector to an incidental incompetent host (dead end host). Domain
Viral hosts belong to the Domain Eucarya.

Domain Eucarya
Kingdom Animalia.

Kingdom Animalia
Phylum Arthropoda and Chordata.

Phylum Arthropoda
Subphylum Hexapoda; Class Insecta; Subclass Pterygota (winged insects), Order Diptera.

Phylum Vertebrata
Subphylum Vertebrata; Class Mammalia.

Class Mammalia Order Primates;
Family Hominidae.
Virus infects Homo sapiens (human).

General Symptoms in Animals Infection can affect the nervous system and dermis, mucosa or epithelium. General symptoms include headache, or malaise, or photophobia, or prostration, or pyrexia, or retardation, or stiff neck, or tremor, or uncoordination. Lesions are found in nerve tissue. Signs and symptoms include meningitis, paralysis, sequelae, seizures, encephalitis.

Severity and Occurrence of Disease

Host: Signs and symptoms may vary, but are usually mild and disappear soon after infection. Prevalence of viral infection is seasonally dependent, and incidences of virus infection are usually observed in summer, or autumn and during a wet season followed by a dry season. Contagiousness is not observed.

Transmission and Vector Relationships

Virus is transmitted by a vector in a direct manner. Virus is transmitted by mechanical inoculation (usually only under laboratory conditions, through an injection; not transmitted by contact between hosts. Vector Transmission: Viral transmission by vectors is frequent.

Virus is transmitted by arthropods, by insects of the order Diptera, family Culicidae, Culicinae (culicine mosquitoes). Virus is transmitted in a persistent manner; retained when the vector moults; circulates in hemolymph; replicates in the vector; does not require a helper virus for vector transmission.

Non-Vector Transmission: The likelihood of viral transmission by respiratory route (air-borne) is nil; faecal-oral route (water and food-borne) is nil; direct contact is nil; through sexual contact is nil; through parenteral transmission is nil; through blood or blood products is nil; through congenital (germ line) transmission is nil; through transplacental transmission is nil; through perinatal transmission is nil.

Experimental Hosts and Symptoms

Under experimental conditions susceptibility to infection by virus is found in many families.

Host:
Experimentally infected hosts mainly show symptoms of WEEV.Vert.Susc.TBL.doc. Cell lines or tissue cultures susceptible to infection are WEEV.Suscept.cell.cultures.doc. Symptoms include cytopathic effects, plaques.

Diagnostic Hosts

For virus isolation the most commonly used test animals are suckling mice; cell lines or tissue cultures are chicken embryo, duck embryo, Vero cells. Virus has been propagated in experimental animals, cell culture, and developing embryo.

Maintenance and Propagation Hosts

Most commonly used maintenance and propagation host species are suckling mice, Vero cells. Virus is propagated in embryonated eggs of chicken and duck. Virus is propagated in embryonated eggs by inoculating the amnion.

Assay Hosts

Host: Most commonly used species for assaying the virus are suckling mice, Vero cells.

Pathology

Virus can be best detected in nervous system; brain tissue, or liver.

Histopathology: Histopathologic lesions are found in brain. Virions are found in the cytoplasm. Primary histological changes include inflammation and necrosis.

Geographical Distribution

The virus is known to occur in temperate regions, subtropical regions, and tropical regions; viral host lives in the atmosphere. The viral host is found in a pristine environment with no signs of human interference and a undisturbed environment yet with signs of human disturbance; an agricultural environment, or an aquatic environment; a populated environment. The virus occurs in Argentina, Belize, Brazil, Canada, Cuba, Ecuador, Mexico, the United States of America, and Uruguay.

Ecology, Epidemiology and Control

Studies reported by Reeves WC (1990) Calif. Mosq. and Vector Control Assoc., Inc., Sacramento, CA; 508 pages. Epidemiological surveillance activities are overseen by Centers for Disease Control and Prevention (CDC) (various state and national laboratories throughout the western hemisphere). A fact sheet on this virus is available from the Centers for Disease Control and Prevention (CDC), National Center for Infectious Diseases (NCID) ().

References

Weaver SC, Hagenbaugh A, Bellew L, Netesov SV, Volchkov VE, Chang GJ, Clarke DK, Gousset L, Scott TW, Trent DW and Holland JJ (1993). A comparison of the nucleotide sequences of eastern and western equine encephalomyelitis viruses with those of other alphaviruses and related RNA viruses. Virology 197 (1), 375-390.

PubMed References.



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DELTA - DEscription Language for TAxonomy developed by Dr Mike Dallwitz, Toni Paine and Eric Zurcher, CSIRO Entomology, Canberra, Australia. ICTVdB - The Universal Virus Database, developed for the International Committee on Taxonomy of Viruses by Dr Cornelia Büchen-Osmond is written in DELTA. The virus descriptions in ICTVdB are coded by, or using data from experts in the field of virology or members ICTV. The character list is the underlying code. All virus descriptions are based on the character list and natural language translations are automatically generated and formatted for display on the Web from the descriptions in DELTA-format. The description has been generated automatically from DELTA files. DELTA - DEscription Language for TAxonomy developed by Dr Mike Dallwitz, Toni Paine and Eric Zurcher, CSIRO Entomology, Canberra, Australia.

ICTVdB - The Universal Virus Database, developed for the International Committee on Taxonomy of Viruses (ICTV) by Dr Cornelia Büchen-Osmond, is written in DELTA. The virus descriptions in ICTVdB are coded by ICTV members and experts, or by the ICTVdB Management using data provided by the experts, the literature or the latest ICTV Report. The character list is the underlying code. All virus descriptions are based on the character list and natural language translations from the encoded descriptions are automatically generated and formatted for display on the Web.

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