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J F Hedges

Publications and source records attributed to J F Hedges.

15 recordsLinked to original sources
PubMed2003

Lateral transmission of equine arteritis virus among Lipizzaner stallions in South Africa.

REASONS FOR PERFORMING STUDY: A serological study conducted in 1995 revealed that 7 stallions at the Lipizzaner Centre, Gauteng, South Africa, were seropositive for antibody to equine arteritis virus (EAV). A Lipizzaner stallion imported into South Africa from Yugoslavia in 1981 had previously (1988) been confirmed to be an EAV carrier. Despite being placed under life-long breeding quarantine, EAV had been transmitted between stallions at the Lipizzaner Centre. OBJECTIVES: To investigate the phylogenetic relationships between the strain of EAV shed in the semen of the original carrier stallion and strains recovered from the semen of 5 other stallions; and to investigate the means whereby lateral transmission of EAV occurred among 7 in-contact, nonbreeding stallions at the Centre. METHODS: EAV was isolated from semen collected from the seropositive stallions using RK-13 cells. Viral RNA was reverse transcribed and amplified by polymerase chain reaction using ORF 5-specific primers, subjected to sequence and phylogenetic analysis. RESULTS: Phylogenetic analysis of strains of EAV recovered from the semen of 6 persistently infected stallions confirmed that all viruses were closely related and probably derived from a common ancestor, i.e. the stallion imported from Yugoslavia. Lateral transmission subsequently occurred among 7 in-contact, nonbreeding stallions at the Centre. It is speculated that these stallions may have been exposed to virus from bedding or fomites contaminated with semen. CONCLUSIONS: These data confirm that lateral transmission of EAV can occur from shedding stallions to susceptible, in-contact horses, including other stallions, which may become persistently infected with the virus. POTENTIAL RELEVANCE: The findings are consistent with lateral spread of a single, unique strain of EAV among a group; and suggest that transmission of EAV may be initiated by infection of one or more stallions with virus on bedding or other fomites contaminated with EAV- infected semen.

Animals↗
PubMed2003

West Nile virus infection of Thoroughbred horses in South Africa (2000-2001).

REASONS FOR PERFORMING STUDY: West Nile virus (WNV) infection is endemic in southern Africa. With the recent emergence of WNV infection of horses in Europe and the USA the present study was performed to estimate the risk of seroconversion to WNV in a cohort of 488 young Thoroughbred (TB) horses. OBJECTIVES: To estimate the risk of seroconversion to WNV among a cohort of South African TB yearlings sold at the 2001 National Yearling Sales (NYS) and to determine whether the risk varied geographically. Two horses were also infected with a recent South African isolate of WNV to evaluate its virulence in horses. METHODS: Serum samples were collected from the cohort of 488 TB yearlings at the 2001 NYS. Serum samples that were collected from the same horses at the time that they were identified were sourced from our serum bank. Sera from 243 of the dams that were collected at the time that the foals were identified were also sourced from our serum bank. These sera were subjected to serum neutralisation (SN) tests for antibody to WNV. RESULTS: Approximately 11% of yearlings seroconverted to WNV on paired serum samples collected from each animal approximately 12 months apart. Studfarms with WNV-seropositive yearlings were widely distributed throughout South Africa and SN tests on sera from their dams indicated that exposure to WNV was even more prevalent (75%) in this population. Neurological disease was not described in any of the horses included in this study and 2 horses inoculated with a recent lineage 2 South African isolate of WNV showed no clinical signs of disease after infection and virus was not detected in their blood. CONCLUSIONS: Infection of horses with WNV is common in South Africa, but infection is not associated with neurological disease. POTENTIAL RELEVANCE: In contrast to recent reports from Europe, North Africa, Asia and North America, the results of our field and experimental studies indicated that exposure of horses to the endemic southern African strains of WNV was not associated with neurological disease.

Animals↗
PubMed2001

Characterization of equine E-selectin.

Expression of E-selectin on activated endothelium is a critical initial step that leads to extravasation of leucocytes during inflammation, yet E-selectin is largely uncharacterized in several animal species including the horse. We have sequenced and compared E-selectin genes derived from activated cultures of purified equine (horse), cervid (black-tailed deer) and ovine (sheep) pulmonary artery endothelial cells (ECs). Phylogenetic and amino acid sequence comparisons indicate that bovine, cervid and ovine E-selectin are similar, whereas human and equine E-selectin are more closely related to each other than to the ruminant molecules. Human E- and P-selectin-specific monoclonal antibodies that also recognize equine E-selectin were identified and used to characterize its expression. Expression of E-selectin was more readily induced by lipopolysaccharide treatment in equine ECs than in human ECs and supported adhesion and activation of neutrophils, consistent with the extreme sensitivity of horses to endotoxaemia and septic shock.

Amino Acid Sequence↗
PubMed2000

Expression of the two major envelope proteins of equine arteritis virus as a heterodimer is necessary for induction of neutralizing antibodies in mice immunized with recombinant Venezuelan equine encephalitis virus replicon particles.

RNA replicon particles derived from a vaccine strain of Venezuelan equine encephalitis virus (VEE) were used as a vector for expression of the major envelope proteins (G(L) and M) of equine arteritis virus (EAV), both individually and in heterodimer form (G(L)/M). Open reading frame 5 (ORF5) encodes the G(L) protein, which expresses the known neutralizing determinants of EAV (U. B. R. Balasuriya, J. F. Patton, P. V. Rossitto, P. J. Timoney, W. H. McCollum, and N. J. MacLachlan, Virology 232:114-128, 1997). ORF5 and ORF6 (which encodes the M protein) of EAV were cloned into two different VEE replicon vectors that contained either one or two 26S subgenomic mRNA promoters. These replicon RNAs were packaged into VEE replicon particles by VEE capsid protein and glycoproteins supplied in trans in cells that were coelectroporated with replicon and helper RNAs. The immunogenicity of individual replicon particle preparations (pVR21-G(L), pVR21-M, and pVR100-G(L)/M) in BALB/c mice was determined. All mice developed antibodies against the recombinant proteins with which they were immunized, but only the mice inoculated with replicon particles expressing the G(L)/M heterodimer developed antibodies that neutralize EAV. The data further confirmed that authentic posttranslational modification and conformational maturation of the recombinant G(L) protein occur only in the presence of the M protein and that this interaction is necessary for induction of neutralizing antibodies.

Animals↗
PubMed1999

The open reading frame 3 of equine arteritis virus encodes an immunogenic glycosylated, integral membrane protein.

Open reading frame 3 (ORF 3) of equine arteritis virus (EAV) is predicted to encode a glycosylated membrane protein (GP3) that is uncharacterized. ORF 3 of the American Type Culture Collection strain of EAV was in vitro transcribed and the encoded GP3 protein was in vitro translated with and without canine microsomal membranes. The GP3 protein was approximately 17 kDa after in vitro translation without canine microsomal membranes whereas the glycosylated form, after translation with microsomal membranes, was a diffuse band of 36-42 kDa, indicating that the GP3 protein is extensively glycosylated. Deglycosylation reduced the GP3 protein to approximately 17 kDa, the same size as that translated without microsomal membranes, indicating that the signal sequence was not cleaved. The EAV GP3 protein was membrane associated and not released as a soluble protein, in marked contrast to the ORF 3-encoded proteins of some other arteriviruses. The GP3 protein was protected from protease digestion in closed membrane vesicles, suggesting that the protein extends into the membrane vesicles and is anchored by the N-terminal signal sequence, a C-terminal hydrophobic domain, or both, but does not span the membrane three times. A GP3 protein lacking the C-terminal transmembrane domain remained membrane associated, indicating that this terminus is not a necessary membrane anchor. Sera from stallions persistently infected with EAV and horses immunized repeatedly with the modified live EAV vaccine contained antibodies specific for the GP3 protein. The data indicate that the GP3 protein is an extensively glycosylated membrane protein that is immunogenic during some EAV infections.

Animals↗
PubMed1999

Equine arteritis virus derived from an infectious cDNA clone is attenuated and genetically stable in infected stallions.

Virus derived from an infectious cDNA clone of equine arteritis virus (EAV030H) was intranasally inoculated into two stallions, neither of which subsequently developed clinical manifestations of equine viral arteritis (EVA). Virus was isolated from nasal swabs and mononuclear cells collected from both stallions </=14 days p.i. and from the semen of one stallion only at 7 days p.i. Similarly, viral RNA was detected by RT nested-PCR in nasal swabs and mononuclear cells for </=14 days p.i. and at 7 days p.i. in the semen of the one stallion. Both stallions seroconverted to EAV by 10 days p.i. and maintained high neutralizing antibody titers thereafter. Sequence and restriction digestion analysis demonstrated that the recombinant virus present in nasal swabs, mononuclear cells, and semen from the two stallions was identical to the infectious clone-derived virus that was used to inoculate them. Furthermore analysis of multiple clones derived by RT nested-PCR amplification from several samples indicated that the recombinant EAV030H virus was stable during replication in horses. These studies document for the first time that a recombinant virus derived from an infectious cDNA clone of a member of the order Nidovirales is replication competent in animals, and the genetic stability of the recombinant virus during in vivo replication indicates that it will be useful for the characterization of genetic determinants of virulence and persistence of EAV. The genetic conservation of the cloned recombinant virus during in vivo infection is similar to that which occurs during natural horizontal and vertical transmission of EAV in horses and contrasts with the heterogeneous virus population (quasispecies) that occurs in the semen of carrier stallions.

Animals↗
PubMed1999

The adenovirus that causes hemorrhagic disease of black-tailed deer is closely related to bovine adenovirus-3.

DNA sequence data was obtained from an adenovirus previously shown to be the cause of a distinctive, fatal hemorrhagic disease of black-tailed deer in California. A 256 base fragment of the viral hexon gene was amplified by PCR from purified adenovirus preparations. The amplicon then was cloned and sequenced. Phylogenetic relationships with other mammalian adenoviruses were also determined. Although sequence analysis of this portion of the hexon gene indicates that the black-tailed deer adenovirus is closely related to bovine adenovirus-3, the biologic properties of the two viruses are clearly distinct.

Adenoviridae Infections↗
PubMed1999

Phylogenetic characterization of a highly attenuated strain of equine arteritis virus from the semen of a persistently infected standardbred stallion.

An avirulent, novel variant of equine arteritis virus (EAV; CA95G) was isolated from the semen of a persistently infected Standardbred stallion. The CA95G virus caused subclinical infection and seroconversion in susceptible horses, and virus was isolated only once from blood and nasal secretions collected from 6 experimentally infected horses. Sequence analysis of genes encoding the known EAV structural proteins shows that this highly attenuated strain of EAV is genetically similar to virulent field strains of EAV and, in particular, to a strain of EAV that was isolated during an outbreak of equine viral arteritis in western Canada in 1986. Not only is the carrier stallion the critical natural reservoir of EAV, but genetic diversity of the virus is generated in the course of persistent infection of carrier stallions. The subtle genetic changes that facilitate and maintain persistent EAV infection of the stallion's reproductive tract likely influence phenotypic properties of the virus such as virulence.

Animals↗
PubMed1999

Genetic divergence with emergence of novel phenotypic variants of equine arteritis virus during persistent infection of stallions.

The persistently infected carrier stallion is the critical natural reservoir of equine arteritis virus (EAV), as venereal infection of mares frequently occurs after breeding to such stallions. Two Thoroughbred stallions that were infected during the 1984 outbreak of equine viral arteritis in central Kentucky subsequently became long-term EAV carriers. EAV genomes amplified from the semen of these two stallions were compared by sequence analysis of the six 3' open reading frames (ORFs 2 through 7), which encode the four known structural proteins and two uncharacterized glycoproteins. The major variants of the EAV population that sequentially arose within the reproductive tract of each carrier stallion varied by approximately 1% per year, and the heterogeneity of the viral quasispecies increased during the course of long-term persistent infection. The various ORFs of the dominant EAV variants evolved independently, and there was apparently strong selective pressure on the uncharacterized GP3 protein during persistent infection. Amino acid changes also occurred in the V1 variable region of the GL protein. This region has been previously identified as a crucial neutralization domain, and selective pressures exerted on the V1 region during persistent EAV infection led to the emergence of virus variants with distinct neutralization properties. Thus, evolution of the EAV quasispecies that occurs during persistent infection of the stallion clearly can influence viral phenotypic properties such as neutralization and perhaps virulence.

Amino Acid Sequence↗
PubMed1998

Serologic and molecular characterization of an abortigenic strain of equine arteritis virus isolated from infective frozen semen and an aborted equine fetus.

A virus isolated from an aborted equine fetus was determined to be antigenically distinct from several other strains of equine arteritis virus (EAV) by use of a neutralization assay with a large panel of neutralizing monoclonal antibodies. The virus was readily neutralized by polyclonal equine anti-EAV serum. Comparative nucleotide and amino acid sequence analyses indicated that the virus (WA97) isolated from the aborted fetus was virtually identical to a virus (S1971) isolated from imported semen used to inseminate another mare on the farm. Phylogenetic analysis indicated that the WA97/S1971 virus was more related to European than to North American strains of EAV. These sensitive molecular procedures may be useful for epidemiologic investigations of EAV infections. Screening and certification of stallions and frozen equine semen would prevent dissemination of pathogenic strains of EAV.

Abortion, Veterinary↗
PubMed1998

Detection of antibodies to equine arteritis virus by enzyme linked immunosorbant assays utilizing G(L), M and N proteins expressed from recombinant baculoviruses.

Indirect enzyme linked immunosorbant assays (ELISAs) utilizing the three major structural proteins (M, N, and G(L)) of equine arteritis virus (EAV) expressed from recombinant baculoviruses were developed. A large panel of sera collected from uninfected horses, and from animals experimentally and naturally infected with EAV or vaccinated with the modified live virus vaccine against equine viral arteritis, were used to characterize the humoral immune response of horses to the three major EAV structural proteins. The data suggest that the M protein was the major target of the equine antibody response to EAV. The responses of individual animals varied and ELISAs that utilized individual EAV structural proteins were not reliable for detecting antibodies in all sera that contained neutralizing antibodies to EAV. An ELISA based on a cocktail of all three EAV structural proteins, however, was used successfully to detect antibodies in most equine sera that were positive in the standard serum neutralization assay following natural or experimental EAV infection (100% specificity, 92.3% sensitivity). In contrast, this ELISA did not reliably detect antibodies in the sera of vaccinated horses. EAV frequently causes a persistent infection in stallions and all sera from carrier stallions evaluated in this study had obvious reactivity with the N protein, whereas seropositive non-carrier stallions, mares and geldings did not respond consistently to the N protein.

Animals↗
PubMed1998

Serologic response of horses to the structural proteins of equine arteritis virus.

Equine arteritis virus (EAV) is the causative agent of equine viral arteritis, an apparently emerging disease of equids. In this study, the antibody response of horses to the structural proteins of EAV was evaluated using gradient-purified EAV virions and baculovirus-expressed recombinant EAV structural proteins (G(L), G(S), M, N) as antigens in a Western immunoblotting assay. Thirty-three sera from horses that previously had been naturally or experimentally infected with EAV were evaluated, including samples from mares, geldings, and both persistently and nonpersistently infected stallions. Sera also were evaluated from 4 horses that had been vaccinated with the commercial modified live EAV vaccine. The data suggest that the serologic response of individual horses to EAV may vary with the infecting virus strain and duration of infection. The M protein was most consistently recognized by the various serum samples, whereas the response to the N and G(L) proteins was variable and the G(S) protein was bound by only 1 serum sample. The immunoblotting assay definitively established the protein specificity of the humoral response of horses to EAV; however, it clearly is less sensitive than the standard serum neutralization (SN) test--2 of the 37 sera that were seropositive by the SN test failed to react in the immunoblot assay with any EAV structural protein. Furthermore, the G(L) protein expresses the known neutralization determinants of EAV, yet only 22 of the 37 sera that had SN antibodies bound the G(L) protein in the immunoblotting assay. Information from this study will assist ongoing efforts to develop improved methods for the serologic diagnosis of EAV infection of horses.

Animals↗
PubMed1996

Genetic variation in open reading frame 2 of field isolates and laboratory strains of equine arteritis virus.

The open reading frame 2 (ORF2) of three laboratory strains, the live attenuated vaccine virus, and 18 field isolates of equine arteritis virus (EAV) from Europe and North America was sequenced. The ORF2 of EAV encodes the Gs protein that is abundantly expressed in infected cells but constitutes less than 2% of the virion protein mass. Variation of ORF2 among the isolates facilitated phylogenetic analysis that largely confirmed results of an earlier study based on sequence divergence of ORF5 of the same isolates of EAV, despite exposure of the proteins encoded by ORF2 (Gs) and ORF5 (GL) to potentially different selective pressures in vivo. The data indicate that the Gs protein is highly conserved between isolates, considerably more so than the GL protein, consistent with an important role of the Gs protein in virus replication.

Amino Acid Sequence↗