Comparative immunological and biochemical analyses of viruses in the Venezuelan equine encephalitis complex

Discriminating Tonate Virus from Dengue Virus Infection: A Matched Case-Control Study in French Guiana, 2003-2016

Tonate virus (TONV) is an arbovirus discovered in 1973 in French Guiana (FG) belonging to the Venezuelan equine encephalitis virus complex, Alphavirus genus. Only few publications and cases have been reported in FG. The objectives of the present study were to describe the clinical picture of TONV and to compare its presentation with that of dengue virus (DENV). A retrospective study was performed in Cayenne hospital from 2003 to 2016 including all patients exclusively positive for TONV IgM and not for other alphaviruses. They were classified as high probability: typical clinical picture of arbovirus infection (i.e., fever, chills, headaches, muscle, and joint pains) and IgM seroconversion; medium probability: typical clinical picture + single positive IgM on a unique serum sample without control; and low probability: atypical clinical picture of infection and single positive IgM. Only patients with high and medium probability were included in the analysis and compared with a gender- and age-matched control group of DENV diagnosed by NS1 antigen (two controls per case). During the study period, 45 cases of TONV were included and compared with 90 cases of DENV. Twenty-eight (62.2%) were men; the median age was 34 years (IQ [22–49]). In the bivariate analysis, variables significantly associated with TONV versus DENV were the presence of cough (33.3% versus 10.3%) and anemia (32.5% versus 11.1%) and the absence of nausea (4.4% versus 32.2%), rash (2.2% versus 27.4%), fatigue (17.8% versus 41.0%), anorexia (6.7% versus 30.1%), muscle pain (42.2% versus 61.4%), headache (53.3% versus 70.8%), leukopenia (9.8% versus 44.4), and lymphopenia (42.5% versus 89.9%). There were no cases with severe neurological involvement, and there were no deaths. Tonate virus may be evoked as a cause of fever in patients living or returning from the Amazonian area. Positive TONV IgM does not prove the diagnosis and should not preclude from searching for alternative infectious diagnoses.

Genetic diversity of Venezuelan alphaviruses and circulation of a Venezuelan equine encephalitis virus subtype IAB strain during an interepizootic period

Several species of alphaviruses have been previously described in the Americas, some of which are associated with encephalitis and others are associated with arthralgia. Venezuelan equine encephalitis virus (VEEV) and eastern equine encephalitis virus (EEEV) are endemic to Venezuela, with the former being responsible for major outbreaks of severe and often fatal disease in animals and humans. The aim of this study was to analyze the genetic diversity of Venezuelan alphaviruses isolated during two decades (1973-1999) of surveillance in northern Venezuela. Phylogenetic analysis indicated the circulation of a VEEV subtype IAB strain 8 years after the last reported outbreak. Thirteen strains within two subclades of South American lineage III of EEEV were also found in Venezuela. Considerable genetic variability was observed among Venezuelan Una virus strains, which were widely distributed among the clades. The first Venezuelan Mayaro sequence was also characterized.

Zoonotic encephalitides caused by arboviruses: transmission and epidemiology of alphaviruses and flaviviruses

In this review, we mainly focus on zoonotic encephalitides caused by arthropod-borne viruses (arboviruses) of the families Flaviviridae (genus Flavivirus) and Togaviridae (genus Alphavirus) that are important in both humans and domestic animals. Specifically, we will focus on alphaviruses (Eastern equine encephalitis virus, Western equine encephalitis virus, Venezuelan equine encephalitis virus) and flaviviruses (Japanese encephalitis virus and West Nile virus). Most of these viruses were originally found in tropical regions such as Africa and South America or in some regions in Asia. However, they have dispersed widely and currently cause diseases around the world. Global warming, increasing urbanization and population size in tropical regions, faster transportation and rapid spread of arthropod vectors contribute in continuous spreading of arboviruses into new geographic areas causing reemerging or resurging diseases. Most of the reemerging arboviruses also have emerged as zoonotic disease agents and created major public health issues and disease epidemics.

Microbial inactivation for safe and rapid diagnostics of infectious samples

The high risk associated with biological threat agents dictates that any suspicious sample be handled under strict surety and safety controls and processed under high-level containment in specialized laboratories. This study attempted to find a rapid, reliable, and simple method for the complete inactivation of a wide range of pathogens, including spores, vegetative bacteria, and viruses, while preserving microbial nucleic acid fragments suitable for PCRs and proteinaceous epitopes for detection by immunoassays. Formaldehyde, hydrogen peroxide, and guanidium thiocyanate did not completely inactivate high titers of bacterial spores or viruses after 30 min at 21°C. Glutaraldehyde and sodium hypochlorite showed high microbicidal activity but obliterated the PCR or enzyme-linked immunosorbent assay (ELISA) detection of bacterial spores or viruses. High-level inactivation (more than 6 log(10)) of bacterial spores (Bacillus atrophaeus), vegetative bacteria (Pseudomonas aeruginosa), an RNA virus (the alphavirus Pixuna virus), or a DNA virus (the orthopoxvirus vaccinia virus) was attained within 30 min at 21°C by treatment with either peracetic acid or cupric ascorbate with minimal hindrance of subsequent PCR tests and immunoassays. The data described here should provide the basis for quickly rendering field samples noninfectious for further analysis under lower-level containment and considerably lower cost.

Development of reverse transcription-PCR assays specific for detection of equine encephalitis viruses

Specific and sensitive reverse transcription-PCR (RT-PCR) assays were developed for the detection of eastern, western, and Venezuelan equine encephalitis viruses (EEE, WEE, and VEE, respectively). Tests for specificity included all known alphavirus species. The EEE-specific RT-PCR amplified a 464-bp region of the E2 gene exclusively from 10 different EEE strains from South and North America with a sensitivity of about 3,000 RNA molecules. In a subsequent nested PCR, the specificity was confirmed by the amplification of a 262-bp fragment, increasing the sensitivity of this assay to approximately 30 RNA molecules. The RT-PCR for WEE amplified a fragment of 354 bp from as few as 2,000 RNA molecules. Babanki virus, as well as Mucambo and Pixuna viruses (VEE subtypes IIIA and IV), were also amplified. However, the latter viruses showed slightly smaller fragments of about 290 and 310 bp, respectively. A subsequent seminested PCR amplified a 195-bp fragment only from the 10 tested strains of WEE from North and South America, rendering this assay virus specific and increasing its sensitivity to approximately 20 RNA molecules. Because the 12 VEE subtypes showed too much divergence in their 26S RNA nucleotide sequences to detect all of them by the use of nondegenerate primers, this assay was confined to the medically important and closely related VEE subtypes IAB, IC, ID, IE, and II. The RT-PCR-seminested PCR combination specifically amplified 342- and 194-bp fragments of the region covering the 6K gene in VEE. The sensitivity was 20 RNA molecules for subtype IAB virus and 70 RNA molecules for subtype IE virus. In addition to the subtypes mentioned above, three of the enzootic VEE (subtypes IIIB, IIIC, and IV) showed the specific amplicon in the seminested PCR. The practicability of the latter assay was tested with human sera gathered as part of the febrile illness surveillance in the Amazon River Basin of Peru near the city of Iquitos. All of the nine tested VEE-positive sera showed the expected 194-bp amplicon of the VEE-specific RT-PCR-seminested PCR.

Association of Tonate virus (subtype IIIB of the Venezuelan equine encephalitis complex) with encephalitis in a human

Tonate virus, subtype IIIB of the Venezuelan equine encephalitis (VEE) complex, was first isolated in 1973 in French Guiana, South America. However, very little is known about its pathogenicity; it was considered to be responsible for only mild dengue-like syndromes. In 1998, a 2-month-old boy living along the Oyapock river in French Guiana was hospitalized for fever and generalized status myoclonus, and despite treatment the patient died 72 h after admission. Testing showed the presence of IgM specific for viruses of the VEE complex. A sensitive seminested polymerase chain reaction derived from a previous study was developed to detect viruses from the VEE complex, since no virus could be recovered from clinical specimens cultured on mosquito cells or from intracerebral inoculation into newborn mice. The genome of a virus from the VEE complex was detected in postmortem brain biopsies, and Tonate virus was identified by direct sequencing. This is the first reported case of human encephalitis due to Tonate virus.

Gene gun mediated vaccination is superior to manual delivery for immunisation with DNA vaccines expressing protective antigens from Yersinia pestis or Venezuelan Equine Encephalitis virus

Plasmids expressing the V antigen of Yersinia pestis or the E2 glycoprotein of Venezuelan Equine Encephalitis (VEE) virus were used to vaccinate mice by intra-dermal or intra-muscular injection, or by particle-mediated bombardment using the Helios gene gun. After two immunizations, groups of mice which had received 4 microg doses of plasmid DNA using the gene gun had IgG levels which were higher than in other groups manually immunised with 12-fold more plasmid DNA. The immunoglobulin isotype profile was predominantly IgG1 following inoculation with either plasmid. Our results indicate that gene gun mediated vaccination can be used to increase the magnitude of the immune response to both bacterial and viral antigens expressed by plasmid DNA.

Sequencing of prototype viruses in the Venezuelan equine encephalitis antigenic complex

The 5' nontranslated region (5'NTR) and nonstructural region nucleotide sequences of nine enzootic Venezuelan equine encephalitis (VEE) virus strains were determined, thus completing the genomic RNA sequences of all prototype strains. The full-length genomes, representing VEE virus antigenic subtypes I-VI, range in size from 11.3 to 11.5 kilobases, with 48-53% overall G+C contents. Size disparities result from subtype-related differences in the number and length of direct repeats in the C-terminal nonstructural protein 3 (nsP3) domain coding sequence and the 3'NTR, while G+C content disparities are attributable to strain-specific variations in base composition at the wobble position of the polyprotein codons. Highly-conserved protein components and one nonconserved protein domain constitute the VEE virus replicase polyproteins. Approximately 80% of deduced nsP1 and nsP4 amino acid residues are invariant, compared to less than 20% of C-terminal nsP3 domain residues. In two enzootic strains, C-terminal nsP3 domain sequences degenerate into little more than repetitive serine-rich blocks. Nonstructural region sequence information drawn from a cross-section of VEE virus subtypes clarifies features of alphavirus conserved sequence elements and proteinase recognition signals. As well, whole-genome comparative analysis supports the reclassification of VEE subtype-variety IF and subtype II viruses.

TC-83 vaccine protects against airborne or subcutaneous challenge with heterologous mouse-virulent strains of Venezuelan equine encephalitis virus

Vaccination with TC-83 virus produced solid protection against subcutaneous challenge with Venezuelan equine encephalitis (VEEV) viruses from homologous and heterologous serogroups, but breakthrough infection and disease occurred after airborne challenge. Breakthrough occurred more often with time after vaccination, and was more frequent with epizootic, homologous serogroup 1A/B viruses than with enzootic, heterologous serogroup viruses. A decrease in VEEV-specific IgA levels in the respiratory tract of vaccinated mice may explain the increased frequency of breakthrough with time after vaccination. However increased breakthrough with the highly virulent homologous serogroup 1A/B viruses (compared to less virulent viruses from heterologous serogroups) may be a consequence of their greater ability to invade the brain via the olfactory neuroepithelium and olfactory nerve.

Resistance to alpha/beta interferons correlates with the epizootic and virulence potential of Venezuelan equine encephalitis viruses and is determined by the 5' noncoding region and glycoproteins

We compared the alpha/beta interferon (IFN-alpha/beta) sensitivities of the TC-83 vaccine strain and 24 enzootic and epizootic Venezuelan equine encephalitis (VEE) isolates. The IFN-resistant or -sensitive phenotype correlated well with epizootic or enzootic potential. IFN-alpha/beta resistance of Trinidad donkey (TRD) virus correlated with virulence determinants in the 5' noncoding region and glycoproteins. Infection of mice lacking a functional IFN system with the IFN-sensitive TC-83 virus resulted in disease equivalent to that produced by the virulent, IFN-resistant TRD virus, further demonstrating that IFN resistance contributes to VEE virus virulence and is a biological marker of epizootic potential.

The alphavirus 3'-nontranslated region: size heterogeneity and arrangement of repeated sequence elements

The 3'-nontranslated region (NTR) of representative strains of all known alphavirus species was amplified by reverse transcription-polymerase chain reaction. For 23 of them, the 3'-NTR sequence was determined. Together with previously published data, this allowed an analysis of the 3'-NTR of the viruses in the genus Alphavirus. The length of the 3'-NTRs varied from 77 nt for Pixuna virus to 609 nt for Bebaru virus. The 19-nt conserved sequence element directly adjacent to the poly(A) tract was found in all viruses, supporting the hypothesis that this region is a cis-acting sequence element during viral replication and essential for virus growth in vitro. Within the 3'-NTR of all alphaviruses, repeated sequence elements of various numbers and lengths were found. Their composition was very consistent in both the Venezuelan equine encephalitis (VEE) and the Sindbis-like viruses, although their number was constant only within the latter group. For the VEE viruses, our data suggested that insertion events rather than deletions from an ancestor with a long 3'-NTR created the various number of repeated sequence elements. Among the remaining viruses, both the number and the composition of repeated sequence elements varied remarkedly.

Re-emergence of epidemic Venezuelan equine encephalomyelitis in South America. VEE Study Group

BACKGROUND

Venezuelan equine encephalomyelitis (VEE) virus has caused periodic epidemics among human beings and equines in Latin America from the 1920s to the early 1970s. The first major outbreak since 1973 occurred in Venezuela and Colombia during 1995, and involved an estimated 75,000 to 100,000 people. We report an epidemiological and virological investigation of this epidemic.

METHODS

Virus isolates were made in cell culture from human serum, human throat swabs, and brain tissue from aborted and stillborn human fetuses, as well as from horse brain tissue and pooled mosquito collections. Human sera were also tested for VEE-specific antibodies. The serotypes of VEE isolates were identified by antigen assays, and viruses were characterised genetically by sequencing PCR products generated from the E3 and E2 genes. Phylogenetic analyses were done to determine evolutionary relations with respect to previous epidemic/epizootic and enzootic VEE virus isolates. Mosquito collections were made to identify possible vectors, and clinical findings were determined by direct observation of patients visiting hospitals and clinics in affected regions, and by inspecting patient records. Equine vaccination and vector control were used in an attempt to halt the spread of the outbreak.

FINDINGS

Most affected people had an acute, self-limited febrile illness of 3 to 4 days duration. However, convulsions were often seen in children, and abortions and fetal deaths occurred in pregnant women infected with VEE virus. Antigenic characterisation of 12 virus isolates spanning the temporal and spatial range of the outbreak indicated that all are VEE serotype IC. Phylogenetic analysis revealed that all of the 1995 viruses were closely related to serotype IC viruses isolated during a large VEE outbreak that occurred in the same regions of Colombia and Venezuela from 1962-1964. A 1983 mosquito isolate from north central Venezuela was also closely related to the 1995 isolates.

INTERPRETATION

This outbreak was remarkably similar to one that occurred in same regions of Venezuela and Colombia during 1962-1964. Symptoms of infected patients, estimated mortality rates, meteorological conditions preceding the epidemic, and seasonal patterns of transmission were all very similar to those reported in the previous outbreak. In addition, viruses isolated during 1995 were antigenically and genetically nearly identifical to those obtained during 1962-1964. These findings suggest that the epidemic resulted from the re-emergence of an epizootic serotype IC VEE virus. Identification of a similar virus isolate in mosquitoes in Venezuela in 1983, 10 years after epidemic/epizootic VEE activity ceased, raises the possibility of a serotype IC enzootic transmission cycle in northern Venezuela.

Emergence of a new epidemic/epizootic Venezuelan equine encephalitis virus in South America

One of the most important questions in arbovirology concerns the origin of epidemic Venezuelan equine encephalitis (VEE) viruses; these viruses caused periodic, extensive epidemics/epizootics in the Americas from 1938-1973 (reaching the United States in 1971) but had recently been presumed extinct. We have documented the 1992 emergence of a new epidemic/epizootic VEE virus in Venezuela. Phylogenetic analysis of strains isolated during two outbreaks indicated that the new epidemic/epizootic virus(es) evolved recently from an enzootic VEE virus in northern South America. These results suggest continued emergence of epizootic VEE viruses; surveillance of enzootic viruses and routine vaccination of equines should therefore be resumed.

Medically important arboviruses of the United States and Canada

Of more than 500 arboviruses recognized worldwide, 5 were first isolated in Canada and 58 were first isolated in the United States. Six of these viruses are human pathogens: western equine encephalitis (WEE) and eastern equine encephalitis (EEE) viruses (family Togaviridae, genus Alphavirus), St. Louis encephalitis (SLE) and Powassan (POW) viruses (Flaviviridae, Flavivirus), LaCrosse (LAC) virus (Bunyaviridae, Bunyavirus), and Colorado tick fever (CTF) virus (Reoviridae, Coltivirus). Their scientific histories, geographic distributions, virology, epidemiology, vectors, vertebrate hosts, transmission, pathogenesis, clinical and differential diagnoses, control, treatment, and laboratory diagnosis are reviewed. In addition, mention is made of the Venezuelan equine encephalitis (VEE) complex viruses (family Togaviridae, genus Alphavirus), which periodically cause human and equine disease in North America. WEE, EEE, and SLE viruses are transmitted by mosquitoes between birds; POW and CTF viruses, between wild mammals by ticks; LAC virus, between small mammals by mosquitoes; and VEE viruses, between small or large mammals by mosquitoes. Human infections are tangential to the natural cycle. Such infections range from rare to focal but are relatively frequent where they occur. Epidemics of WEE, EEE, VEE, and SLE viruses have been recorded at periodic intervals, but prevalence of infections with LAC and CTF viruses typically are constant, related to the degree of exposure to infected vectors. Infections with POW virus appear to be rare. Adequate diagnostic tools are available, but treatment is mainly supportive, and greater efforts at educating the public and the medical community are suggested if infections are to be prevented.

Immunogens of encephalitis viruses

The equine encephalitis viruses are members of the genus Alphavirus, in the family Togaviridae. Three main virus serogroups represented by western (WEE), eastern (EEE) and Venezuelan equine encephalitis (VEE) viruses cause epizootic and enzootic infection of horses throughout the western hemisphere. All equine encephalitis viruses are transmitted through the bite of an infected mosquito. The first equine encephalitis virus vaccines were produced by virus inactivation. Problems with inadequate inactivation, which may have caused a major epidemic/epizootic of VEE in central America and Texas in the 1970s, led to the development of a live attenuated VEE virus vaccine (TC-83) derived by cell culture passage. Inactivated vaccines are still used to prevent equine infections with WEE and EEE viruses. Alphaviruses are small single stranded, positive sense RNA viruses. The 12000 nucleotide genome is enclosed in an icosahedral nucleocapsid composed of multiple copies of the capsid (C) protein. The virion is enveloped. The membrane is modified by the insertion of heterodimers of two glycoproteins: E1 and E2. Monoclonal antibody analysis of the surface glycoproteins have provided a detailed understanding of important protective antigens. Recent studies comparing gene sequences from virulent and avirulent VEE viruses have begun to delineate mechanisms of alphavirus attenuation.

Genetic evidence that epizootic Venezuelan equine encephalitis (VEE) viruses may have evolved from enzootic VEE subtype I-D virus

An important question pertaining to the natural history of Venezuelan equine encephalitis (VEE) virus concerns the source of epizootic, equine-virulent strains. An endemic source of epizootic virus has not been identified, despite intensive surveillance. One of the theories of epizootic strain origin is that epizootic VEE viruses evolve from enzootic strains. Likely enzootic sources of VEE virus occur in Colombia and Venezuela where many of the epizootic outbreaks of VEE have occurred. We have determined the nucleotide sequences of the entire genomes of epizootic VEE subtype I-C virus, strain P676, isolated in Venezuela, and of enzootic VEE subtype I-D virus, strain 3880, isolated in Panama. VEE subtype I-D viruses are maintained in enzootic foci in Panama, Colombia, and Venezuela. The genomes of P676 and 3880 viruses differ from that of VEE subtype I-AB virus, strain Trinidad donkey (TRD), by 417 (3.6%) and 619 (5.4%) nucleotides, respectively. The translated regions of P676 and 3880 genomes differ from those of TRD virus by 54 (1.4%) and 66 (1.8%) amino acids, respectively. This study and the oligonucleotide fingerprint analyses of South American I-C and I-D viruses (Rico-Hesse, Roehrig, Trent, and Dickerman, 1988, Am. J. Trop. Med. Hyg. 38, 187-194) provide the most conclusive evidence to date suggesting that equine-virulent strains of VEE virus arise naturally from minor variants present in populations of I-D VEE virus maintained in enzootic foci in northern South America.

Synthetic peptides of Venezuelan equine encephalomyelitis virus E2 glycoprotein. III. Identification of a protective peptide derived from the carboxy-terminal extramembranal one-third of the protein

To complete our analysis of the E2 glycoprotein of Venezuelan equine encephalomyelitis (VEE) virus, we prepared six synthetic peptides corresponding to the extramembranal carboxy-terminal one-third of the protein. NIH-Swiss mice were immunized with the peptides, and antipeptide and antiviral titers were determined by enzyme-linked immunosorbent assay (ELISA). Challenge studies revealed that peptide 13 (amino acids 241-265) protected 60-70% of virus-challenged mice. Although the other peptides generally elicited antipeptide ELISA titers but no or low antiviral titers and did not protect mice, significant E2 reactivity was found in immunoblots. These results provide the first direct evidence that much of the E2 carboxy-terminal domain is cryptic in the VEE virion, even when virus was bound to polystyrene ELISA plates.

Synthetic peptides of Venezuelan equine encephalomyelitis virus E2 glycoprotein. I. Immunogenic analysis and identification of a protective peptide

Fourteen peptides representing 67% of the extramembranal domain of the Venezuelan equine encephalomyelititis (VEE) virus E2 glycoprotein were synthesized and analyzed to determine their antigenic, immunogenic, and protective capacities. Thirteen of 14 peptides elicited antibody for the homologous peptide. Thirteen peptides elicited antiviral antibody that recognized either the Trinidad (TRD) strain of VEE virus or the TC-83 vaccine derivative, or both. Two peptides, VE2pep01(TC-83) and VE2pep01(TRD), protected significant numbers of mice from TRD virus challenge. The majority of the peptides were reactive with antisera from mice immunized with the various subtypes of VEE virus. A competition assay using antipeptide antibodies to block virus binding of anti-VEE virus monoclonal antibodies corroborated previous studies on the spatial relationship of E2 epitopes and provided evidence for a spatial overlap of the E2 amino terminus with a domain composed of residues 180-210.

Recombinant vaccinia virus/Venezuelan equine encephalitis (VEE) virus protects mice from peripheral VEE virus challenge

Mice immunized with recombinant vaccinia virus (VACC) expressing Venezuelan equine encephalitis (VEE) virus capsid protein and glycoproteins E1 and E2 or with attenuated VEE TC-83 virus vaccine developed VEE-specific neutralizing antibody and survived intraperitoneal challenge with virulent VEE virus strains including Trinidad donkey (subtype 1AB), P676 (subtype 1C), 3880 (subtype 1D), and Everglades (subtype 2). However, unlike immunization with TC-83 virus, immunization with the recombinant VACC/VEE virus did not protect mice from intranasal challenge with VEE Trinidad donkey virus. These results suggest that recombinant VACC/VEE virus is a vaccine candidate for equines and humans at risk of mosquito-transmitted VEE disease but not for laboratory workers at risk of accidental exposure to aerosol infection with VEE virus.

In vitro mechanisms of monoclonal antibody neutralization of alphaviruses

We have previously identified at least eight epitopes on the E2 glycoprotein of Venezuelan equine encephalomyelitis (VEE) virus vaccine strain TC-83 by using monoclonal antibodies (MAbs). Several of these antibodies identified a critical neutralization (N) domain in competitive binding assays. Passive transfer of these MAbs protected animals from a lethal virus challenge. Using radioactive, purified virus as a marker, we have demonstrated that antibody-mediated virus N, preattachment, can be effected by one of three mechanisms. Interaction of antibody can block virus attachment to susceptible Vero or human embryonic lung cells. The MAbs that were most efficient at blocking attachment were those that defined epitopes spatially proximal to the E2c epitope. The E2c MAbs were, however, the most efficient antibodies for neutralizing virus postattachment. Other E2 MAbs were unable to efficiently block virus attachment to cells; however, resulting replication as monitored by plaque assay or intracellular viral RNA synthesis could not be detected. One novel MAb that defined the E2f epitope appeared to enhance virus attachment to Vero cells, but not BHK-21 or LLC-MK2 cells, by stabilizing virus-cell interaction. This antibody did, however, efficiently neutralize virus infectivity. Once virus had attached to cells, the ability of most MAbs to neutralize infectivity was diminished, except for E2c MAbs. On a molar basis antibody Fab fragments were less efficient than intact antibody at blocking virus attachment.

Nucleotide sequence of the 26 S mRNA of the virulent Trinidad donkey strain of Venezuelan equine encephalitis virus and deduced sequence of the encoded structural proteins

A cDNA clone containing all of the 26 S mRNA coding region of the RNA genome of Venezuelan equine encephalitis (VEE) virus, virulent strain Trinidad donkey (TRD), has been constructed and sequenced. The nucleotide and deduced amino acid sequences of the 26 S RNA of VEE virus conform to the general organization of the alphavirus subgenomic mRNA. Excluding the poly(A) tail, the VEE 26 S RNA is 3913 nucleotides long with a protein coding region of 3762 nucleotides. Codon usage in the translated region is nonrandom and correlates well with that reported for Sindbis (SIN), Semliki Forest (SF), and Ross River (RR) alphaviruses. Highly conserved sequences of 19 to 22 nucleotides representing putative replicase recognition sites occur at the 26 S RNA junction region of the 42 S genomic RNA and at the 3' terminus immediately preceding the poly(A) tail. The conserved sequence at the 26 S/42 S junction region of VEE virus differs from that of other alphaviruses in that an ochre termination codon (UAA) is substituted for a GGU (Gly) codon present in the other viruses. The 5' and 3' noncoding regions (30 and 121 nucleotides, respectively) of the VEE 26 S RNA are shorter than has been reported for several other alphaviruses. The approximate transmembrane domains of the VEE E1 and E2 envelope glycoproteins have been identified. VEE E1 contains a single asparagine-linked glycosylation site, whereas E2 has three such sites, all of which are apparently glycosylated. The deduced amino acid sequence of the VEE polyprotein shows an overall homology of 44 to 46% with the precursor polyproteins of SIN, SF, and RR viruses. VEE virus capsid, E1, and E2 structural proteins show 43 to 46%, 50 to 53%, and 36 to 41% homology, respectively, with the cognate proteins of SIN, SF, and RR viruses.

The neutralization site on the E2 glycoprotein of Venezuelan equine encephalomyelitis (TC-83) virus is composed of multiple conformationally stable epitopes

The neutralization (N) site on the gp56 (E2) surface glycoprotein of the TC-83 vaccine strain of Venezuelan equine encephalomyelitis (VEE) virus has been characterized using monoclonal antibodies. Five new epitopes (E2d-h) were identified three of which could be mapped into the critical N site by using a competitive binding assay (CBA). Antibodies reactive with these three epitopes had either N or N and hemagglutination-inhibition activity. All epitopes contained within this N site elicited monoclonal antibodies that could protect mice from peripheral virus challenge. Antibodies reactive with the N site on other subtypes of VEE virus (IC and II) bound to, but failed to neutralize, TC-83 virus. Epitopes defined by these antibodies could be located outside of the N site on TC-83 virus by CBA. Antigenic activity of all epitopes except E2d was resistant to treatment with 2% SDS, 3% beta-mercaptoethanol, or cleavage with Staphylococcus aureus V8 protease. Those antibodies which defined epitopes located within the N site of TC-83 with CBA bound the same V8 fragments in immunoblots. Those antibodies which defined epitopes not located within the N site bound a different set of fragments than neutralizing antibodies. These results indicate that there is a specific N site on the E2 of VEE virus which undergoes significant antigenic drift while maintaining structural and functional integrity.