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David W C Beasley

Publications and source records attributed to David W C Beasley.

At least 19 recordsLinked to original sources
PubMed2006

A mutation in the envelope protein fusion loop attenuates mouse neuroinvasiveness of the NY99 strain of West Nile virus.

Substitutions were engineered individually and in combinations at the fusion loop, receptor-binding domain and a stem-helix structure of the envelope protein of a West Nile virus strain, NY99, and their effects on mouse virulence and presentation of epitopes recognized by monoclonal antibodies (MAbs) were assessed. A single substitution within the fusion loop (L107F) attenuated mouse neuroinvasiveness of NY99. No substitutions attenuated NY99 neurovirulence. The L107F mutation also abolished binding of a non-neutralizing MAb, 3D9, whose epitope had not been previously identified. MAb 3D9 was subsequently shown to be broadly cross-reactive with other flaviviruses, consistent with binding near the highly conserved fusion loop.

Animals↗
PubMed2006

Structure of the envelope protein domain III of Omsk hemorrhagic fever virus.

We have solved the NMR solution structure of domain III from the Omsk hemorrhagic fever virus envelope protein and report the first sequencing of the Guriev strain of this virus. Important structural differences between tick-borne flaviviruses, such as OHFV and TBE, and mosquito-borne flaviviruses, such as West Nile virus, are discussed.

Amino Acid Sequence↗
PubMed2006

A single amino acid substitution in the central portion of the West Nile virus NS4B protein confers a highly attenuated phenotype in mice.

West Nile virus (WNV) NS4B is a small hydrophobic nonstructural protein that is hypothesized to participate both in viral replication and evasion of host innate immune defenses. The protein has four cysteine residues (residues 102, 120, 227, and 237). Since cysteines are often critical for the function of proteins, each of the four cysteine residues found in WNV NS4B was mutated to serine by site-directed mutagenesis. While three of these substitutions had little effect on replication or mouse virulence phenotypes, the C102S mutation was associated with a temperature-sensitive phenotype at 41 degrees C as well as attenuation of the neuroinvasive and neurovirulence phenotypes in mice.

Amino Acid Sequence↗
PubMed2006

Selection of thioaptamers for diagnostics and therapeutics.

Thioaptamers offer advantages over normal phosphate ester backbone aptamers due to their enhanced affinity, specificity, and higher stability, largely due to the properties of the sulfur backbone modifications. Over the past several years, in vitro thioaptamer selection and bead-based thioaptamer selection techniques have been developed in our laboratory. Furthermore, several thioaptamers targeting specific proteins such as transcription factor NF-kappaB and AP-1 proteins have been identified. Selected thioaptamers have been shown diagnostic promise in proteome screens. Moreover, some promising thioaptamers have been shown in preliminary animal therapeutic dosing to increase survival in animal models of infection with West Nile virus.

Animals↗
PubMed2006

Introductions of West Nile virus strains to Mexico.

Complete genome sequencing of 22 West Nile virus isolates suggested 2 independent introductions into Mexico. A previously identified mouse-attenuated glycosylation variant was introduced into southern Mexico through the southeastern United States, while a common US genotype appears to have been introduced incrementally into northern Mexico through the southwestern United States.

Animals↗
PubMed2005

Phylogenetic analysis of North American West Nile virus isolates, 2001-2004: evidence for the emergence of a dominant genotype.

The distribution of West Nile virus has expanded in the past 6 years to include the 48 contiguous United States and seven Canadian provinces, as well as Mexico, the Caribbean islands, and Colombia. The suggestion of the emergence of a dominant genetic variant has led to an intensive analysis of isolates made across North America. We have sequenced the pre-membrane and envelope genes of 74 isolates and the complete genomes of 25 isolates in order to determine if a dominant genotype has arisen and to better understand how the virus has evolved as its distribution has expanded. Phylogenetic analyses revealed the continued presence of genetic variants that group in a temporally and geographically dependent manner and provide evidence that a dominant variant has emerged across much of North America. The implications of these findings are discussed as they relate to transmission and spread of the virus in the Western Hemisphere.

Genes, Viral↗
PubMed2005

Differential expression of domain III neutralizing epitopes on the envelope proteins of West Nile virus strains.

Neutralization of flaviviruses by antibody is primarily mediated via epitopes in the viral envelope (E) protein. Comparative studies using neutralizing monoclonal antibodies revealed differential expression of epitopes within the E protein domain III of ten naturally occurring West Nile virus strains representing major subtypes of genetic lineages 1 and 2. Residues that defined these subtype-specific determinants were identified by mutational studies and found to be surface exposed in the domain III structure. Mutations of residue 332 had the most significant effects on variation of domain III neutralizing epitopes among strains.

Amino Acid Sequence↗
PubMed2005

Envelope protein glycosylation status influences mouse neuroinvasion phenotype of genetic lineage 1 West Nile virus strains.

The introduction of West Nile virus (WNV) into North America has been associated with relatively high rates of neurological disease and death in humans, birds, horses, and some other animals. Previous studies identified strains in both genetic lineage 1 and genetic lineage 2, including North American isolates of lineage 1, that were highly virulent in a mouse neuroinvasion model, while other strains were avirulent or significantly attenuated (D. W. C. Beasley, L. Li, M. T. Suderman, and A. D. T. Barrett, Virology 296:17-23, 2002). To begin to elucidate the basis for these differences, we compared a highly virulent New York 1999 (NY99) isolate with a related Old World lineage 1 strain, An4766 (ETH76a), which is attenuated for mouse neuroinvasion. Genomic sequencing of ETH76a revealed a relatively small number of nucleotide (5.1%) and amino acid (0.6%) differences compared with NY99. These differences were located throughout the genome and included five amino acid differences in the envelope protein gene. Substitution of premembrane and envelope genes of ETH76a into a NY99 infectious clone backbone yielded a virus with altered in vitro growth characteristics and a mouse virulence phenotype comparable to ETH76a. Further site-specific mutagenesis studies revealed that the altered phenotype was primarily mediated via loss of envelope protein glycosylation and that this was associated with altered stability of the virion at mildly acidic pH. Therefore, the enhanced virulence of North American WNV strains compared with other Old World lineage 1 strains is at least partly mediated by envelope protein glycosylation.

Animals↗
PubMed2005

Recent advances in the molecular biology of west nile virus.

Since the mid-1990s, West Nile virus (WNV) has emerged as a significant agent of arboviral encephalitis in several regions of the world. In 1999, WNV was introduced into the northeastern United States and was associated with an outbreak of encephalitis affecting humans, birds and horses. Subsequently, the virus has spread across the country, and across southern Canada, and in 2002 and 2003 was associated with the largest outbreaks of arboviral encephalitis recorded in the Western hemisphere. Interestingly, the more recent spread of WNV into Mexico, Central America and the Caribbean has not been associated with the high levels of clinical disease observed in North America. This review addresses the most recent results from studies investigating the molecular biology and evolution of WNV, as well as progress in the development of diagnostic and therapeutic reagents.

Animals↗
PubMed2005

Short report: serological evidence of West Nile virus activity in El Salvador.

Epizootics of encephalitis in El Salvador killed 203 equines between November 2001 and April 2003. During an investigation of the outbreaks, 18 (25%) of 73 serum samples collected from stablemates of deceased animals in 2003 had antibodies to West Nile virus. Ten of these infections were confirmed by plaque reduction neutralization tests, suggesting West Nile virus has extended its range and spread to Central America.

Animals↗
PubMed2004

Emergence of attenuated West Nile virus variants in Texas, 2003.

In order to understand how West Nile virus (WNV) has evolved since its introduction into North America, we have studied the genetic and phenotypic variation among WNV isolates collected in various areas during consecutive transmission seasons. The present report describes for the first time phenotypic changes occurring in the North American WNV population. Several isolates collected in Texas during 2003 display a small plaque (sp) and temperature sensitive (ts) phenotype, as well as reduced replication in cell culture, in comparison to isolates collected in 2002 and New York in 1999. Studies of mouse neuroinvasiveness/neurovirulence also indicate that several of these isolates were attenuated in neuroinvasiveness, but not for neurovirulence. The complete genome and deduced amino acid sequences of several of these isolates have been determined in order to map the mutations responsible for this phenotypic variation. These data indicate microevolution of WNV and the emergence of isolates exhibiting phenotypic variation.

Animals↗
PubMed2004

Protection against Japanese encephalitis virus strains representing four genotypes by passive transfer of sera raised against ChimeriVax-JE experimental vaccine.

The ability of antisera raised against a candidate Japanese encephalitis virus (JEV) vaccine, ChimeriVax-JE, and the currently licensed vaccine, JE-VAX, to protect against strains of JEV representing the four major genotypes was assessed. Neutralization assays and passive protection studies in mice showed that greatest protection was provided against strains of genotypes II and III, although some protection was also afforded against genotypes I and IV strains. ChimeriVax-JE stimulated protection that was comparable or superior to the JE-VAX control.

Animals↗
PubMed2004

Solution structure and antibody binding studies of the envelope protein domain III from the New York strain of West Nile virus.

The solution structure of domain III from the New York West Nile virus strain 385-99 (WN-rED3) has been determined by NMR methods. The West Nile domain III structure is a beta-barrel structure formed from seven anti-parallel beta-strands in two beta-sheets. One anti-parallel beta-sheet consists of beta-strands beta1 (Phe(299)-Asp(307)), beta2 (Val(313)-Tyr(319)), beta4 (Arg(354)-Leu(355)), and beta5 (Lys(370)-Glu(376)) arranged so that beta2 is flanked on either side by beta1 and beta5. The short beta4 flanks the end of the remaining side of beta5. The remaining anti-parallel beta-sheet is formed from strands beta3 (Ile(340)-Val(343)), beta6 (Gly(380)-Arg(388)), and beta7 (Gln(391)-Lys(399)) arranged with beta6 at the center. Residues implicated in antigenic differences between different West Nile virus strains (and other flaviviruses) and neutralization are located on the outer surface of the protein. Characterization of the binding of monoclonal antibodies to WN-rED3 mutants, which were identified through neutralization escape experiments, indicate that antibody neutralization directly correlates with binding affinities. These studies provide an insight into theoretical virus-receptor interaction points, structure of immunogenic determinants, and potential targets for antiviral agents against West Nile virus and highlight differences between West Nile virus and other flavivirus structures that may represent critical determinants of virulence.

Antibodies, Monoclonal↗
PubMed2004

Experimental infection of rhesus macaques with West Nile virus: level and duration of viremia and kinetics of the antibody response after infection.

Reports of transfusion-associated cases of West Nile virus (WNV) infection indicate the need for sensitive screening methods to identify WNV-infected blood products. We experimentally infected 5 rhesus macaques with WNV, to determine the level and duration of viremia, the kinetics of the humoral immune response, and the sensitivity of various assay systems for detecting WNV in blood. All macaques developed subclinical infections with low levels of viremia; nested reverse-transcription polymerase chain reaction was the most sensitive method for detecting virus or viral RNA in blood. Specific WNV antibodies appeared during the second week of infection; the results of an IgM enzyme-linked immunosorbent assay became positive on the ninth or tenth day after infection, followed in 1-2 days by hemagglutination-inhibiting and neutralizing antibodies. Our results suggest that both nucleic acid and serological testing may be needed to determine exposure to WNV and to identify potentially infected blood donors.

Animals↗
PubMed2004

Characterization of a West Nile virus isolate from a human on the Gulf Coast of Texas.

Genetic characterization of a human cerebrospinal fluid West Nile virus isolate from Beaumont, Texas, revealed several nucleotide changes and amino acid substitutions that differentiated it from all other North American strains isolated to date, suggesting that isolates from the Texas Gulf Coast may form a unique genetic group among North American strains.

Amino Acid Substitution↗
PubMed2004

Use of a recombinant envelope protein subunit antigen for specific serological diagnosis of West Nile virus infection.

Serological diagnosis of West Nile virus (WNV) infection is complicated by extensive antigenic cross-reactivity with other closely related flaviviruses, such as St. Louis encephalitis virus. Here we describe a recombinant, bacterially expressed antigen equivalent to structural domain III of the WNV envelope protein that has allowed clear discrimination of antibody responses to WNV from those against other related flaviviruses in indirect enzyme-linked immunosorbent assays using standardized control antisera and field-collected samples.

Animals↗
PubMed2004

Genome sequence and attenuating mutations in West Nile virus isolate from Mexico.

The complete genome sequence of a Mexican West Nile virus isolate, TM171-03, included 46 nucleotide (0.42%) and 4 amino acid (0.11%) differences from the NY99 prototype. Mouse virulence differences between plaque-purified variants of TM171-03 with mutations at the E protein glycosylation motif suggest the emergence of an attenuating mutation.

Animals↗