Antigenic and molecular characterization of a herpesvirus isolated from a North American elk

Pathogens at the livestock-wildlife interface in Western Alberta: does transmission route matter?

In southwestern Alberta, interactions between beef cattle and free-ranging elk (Cervus elaphus) may provide opportunities for pathogen transmission. To assess the importance of the transmission route on the potential for interspecies transmission, we conducted a cross-sectional study on four endemic livestock pathogens with three different transmission routes: Bovine Viral Diarrhea Virus and Bovine Herpesvirus 1 (predominantly direct transmission), Mycobacterium avium subsp. paratuberculosis (MAP) (indirect fecal-oral transmission), Neospora caninum (indirect transmission with definitive host). We assessed the occurrence of these pathogens in 28 cow-calf operations exposed or non-exposed to elk, and in 10 elk herds exposed or not to cattle. We characterized the effect of species commingling as a risk factor of pathogen exposure and documented the perceived risk of pathogen transmission at this wildlife-livestock interface in the rural community. Herpesviruses found in elk were elk-specific gamma-herpesviruses unrelated to cattle viruses. Pestivirus exposure in elk could not be ascertained to be of livestock origin. Evidence of MAP circulation was found in both elk and cattle, but there was no statistical effect of the species commingling. Finally, N. caninum was more frequently detected in elk exposed to cattle and this association was still significant after adjustment for herd and sampling year clustering, and individual elk age and sex. Only indirectly transmitted pathogens co-occurred in cattle and elk, indicating the potential importance of the transmission route in assessing the risk of pathogen transmission in multi-species grazing systems.

Pestivirus and alphaherpesvirus infections in Swedish reindeer (Rangifer tarandus tarandus L.)

Herding semi-domesticated reindeer has economic and social value for Sami people in the northern territories of Fennoscandia. However, with the intensification of reindeer husbandry, interspecies transmission of pathogens between reindeer and domestic animals may become a problem, especially for countries such as Sweden, Norway, and Finland where pestivirus and alphaherpesvirus have been eradicated in domestic ruminants. This study, which included 1158 Swedish reindeer, showed relatively high prevalence of antibodies against bovine viral diarrhoea virus (BVDV) (32%) and bovine herpesvirus-1 (BoHV-1) (53%). Adult animals were more often seropositive for BVDV and BoHV-1 (50% and 78%, respectively) than were calves (18 and 11%, respectively). While the seroprevalence of alphaherpesvirus was similar in different herding districts, pestivirus seropositivity was highest in the South and diminished towards the North of the Swedish reindeer herding area. High correlation of the seropositivity against both pathogens at both individual and herd levels may indicate possible mutual synergetic effects and may be explained by the immunosuppressive nature of the viruses. While alphaherpesvirus seroprevalence was probably related to putative cervid herpesvirus 2 (CvHV-2), the pestivirus infecting reindeer remains undefined. The virus neutralisation test of reindeer sera using different pestivirus strains, revealed higher titres against Border disease virus strains like 137/4 (BDV-1) and Reindeer-1 (BDV-2) than against BVDV-1. However, the virus was not identified by real time RT-PCR in any of the samples (n=276) from seronegative reindeers. The study showed that pestivirus and alphaherpesvirus infections are endemic in the Swedish reindeer population.

Cervid herpesvirus 2 infection in reindeer: a review

Herpesviruses of the genus Varicellovirus are known to infect and cause disease in a variety of ruminant species, but the impact of cervid herpesvirus 2 (CvHV2) in reindeer (Rangifer tarandus) is mostly unknown. Reindeer is a circum-polar species with a total estimated number of more than 5 million animals. Mortality may reach high values, as in northern Norway, especially in calves (37%; 2005-2006), and disease can potentially account for some of this mortality. CvHV2 has been isolated during a natural outbreak of infectious keratoconjunctivitis, indicating an etiologal link. Serological screening has shown that CvHV2 infection is prevalent in Northern Norway and experimental infection studies have demonstrated that viremia, latency and vertical transmission occur for CvHV2. The present review aims at summarizing current knowledge on the epidemiology, pathogenesis and molecular virology of CvHV2.

Alphaherpesvirus infections in semidomesticated reindeer: a cross-sectional serological study

Alphaherpesviruses infect a wide range of animal species and cause diseases. Cervid herpesvirus 2 (CvHV-2) was originally isolated from reindeer in Finland but the impact of CvHV-2 infections on reindeer remains unclear. CvHV-2 infection could be partly responsible for calf losses as there are indications that it is associated with abortions and neonatal diseases. Previous serosurveys of reindeer (Rangifer tarandus tarandus) have shown that an alphaherpesvirus is circulating among reindeer in Norway. The aim of the present study was to determine the prevalence of CvHV-2 infection among reindeer in various herding districts in Finnmark, the largest reindeer area in Norway, and to identify factors associated with becoming infected with CvHV-2. A total of 3062 serum samples were tested using an ELISA and a sub-set of samples was further tested using a seroneutralization test. The ELISA revealed that 49% of samples were positive. Extrapolation of the results to the total population (111,350 animals; 66% of the Finnmark reindeer population) showed that the seroprevalence in the population was 48%. Seroprevalence varied from 7.6% to 90.7% between districts and was affected by age, weight and population density. ELISA-positive samples neutralized CvHV-2 at serum dilutions greater than those required for neutralization of bovine herpesvirus type 1. It is concluded that CvHV-2 is endemic throughout the reindeer herding districts of northern Norway.

Isolation and characterisation of a ruminant alphaherpesvirus closely related to bovine herpesvirus 1 in a free-ranging red deer

BACKGROUND

The genus Varicellovirus of the Herpesviridae subfamily Alphaherpesvirinae includes a cluster of viruses antigenically and genetically related to bovine herpesvirus 1 (BoHV-1): namely bovine herpesvirus 5 (BoHV-5), bubaline herpesvirus 1 (BuHV-1), caprine herpesvirus 1 (CpHV-1), cervid herpesviruses 1 (CvHV-1) and 2 (CvHV-2) and elk herpesvirus 1 (ElkHV-1). Considering the serological relationship between these ruminant alphaherpesviruses, several surveys have studied the occurrence of BoHV-1 related virus infection in wild and domestic ruminant species. In this way, a recent investigation has indicated, in Belgium, a high increase in the serological prevalence of BoHV-1 related virus infection in free-ranging red deer population. In this context, it has been decided to investigate the presence of an alphaherpesvirus spreading in the Belgian free-ranging red deer population.

RESULTS

The current study reports the first isolation in a free-ranging red deer of a BoHV-1 closely related virus. The isolate was antigenically, genomically and genetically characterised by comparison with several ruminant alphaherpesvirus. Immunofluorescence assays revealed the isolate was antigenically distinct from bovine and caprine alphaherpesviruses. Similarly, BamHI and BstEII restriction analyses demonstrated the genomic difference between the isolate and the other ruminant alphaherpesviruses. Next, the sequencing of selected parts of UL27 and US8 genes showed a high degree of homologies between each BoHV-1 related ruminant alphaherpesvirus and the isolate. Besides the close relationship between all ruminant alphaherpesviruses, the phylogenetic analysis revealed that the isolate clustered with CvHV-1.

CONCLUSION

The first isolation of a virus closely related to BoHV-1 in a free-ranging red deer is reported. Data demonstrate that a CvHV-1 strain, named Anlier, circulates in wild red deer in continental Europe. Anlier strain show consistent differences with the virus isolated from Scottish farmed red deer. All together, these results improve our understanding of ruminant alphaherpesviruses.

Phylogeny and antigenic relationships of three cervid herpesviruses

Elk herpesvirus (ElkHV) from North American elk (wapiti, Cervus elaphus nelsoni) is a recently identified alphaherpesvirus related to bovine herpesvirus-1 (BHV-1). In this study, we determined its relationship with European cervid herpesviruses: cervid herpesvirus-1 (CerHV-1) from red deer and rangiferine herpesvirus (RanHV) from reindeer. For phylogenetic analysis, genes for the gC and gD proteins of these viruses were sequenced. These genes demonstrated an extremely high GC content (76-79%). Genetically, ElkHV was found to be closely related to CerHV-1 and both viruses are more closely related to BHV-1 than to RanHV. Antigenically, the same relationships were found. ElkHV shares common neutralizing epitopes with both CerHV-1 and RanHV. A total of 10 epitopes were defined on the gB, gC and gD proteins of these viruses, including a shared neutralizing epitope on gD. The results indicate that ElkHV and CerHV-1 have diverged from a common ancestor virus. Cervid herpesviruses may be useful in determination of evolutionary rates of change for alphaherpesvirus genes.

Recombination in alphaherpesviruses

Within the Herpesviridae family, Alphaherpesvirinae is an extensive subfamily which contains numerous mammalian and avian viruses. Given the low rate of herpesvirus nucleotide substitution, recombination can be seen as an essential evolutionary driving force although it is likely underestimated. Recombination in alphaherpesviruses is intimately linked to DNA replication. Both viral and cellular proteins participate in this recombination-dependent replication. The presence of inverted repeats in the alphaherpesvirus genomes allows segment inversion as a consequence of specific recombination between repeated sequences during DNA replication. High molecular weight intermediates of replication, called concatemers, are the site of early recombination events. The analysis of concatemers from cells coinfected by two distinguishable alphaherpesviruses provides an efficient tool to study recombination without the bias introduced by invisible or non-viable recombinants, and by dominance of a virus over recombinants. Intraspecific recombination frequently occurs between strains of the same alphaherpesvirus species. Interspecific recombination depends on enough sequence similarity to enable recombination between distinct alphaherpesvirus species. The most important prerequisite for successful recombination is coinfection of the individual host by different virus strains or species. Consequently the following factors affecting the distribution of different viruses to shared target cells need to be considered: dose of inoculated virus, time interval between inoculation of the first and the second virus, distance between the marker mutations, genetic homology, virulence and latency. Recombination, by exchanging genomic segments, may modify the virulence of alphaherpesviruses. It must be carefully assessed for the biosafety of antiviral therapy, alphaherpesvirus-based vectors and live attenuated vaccines.

Improved antigenic methods for differential diagnosis of bovine, caprine, and cervine alphaherpesviruses related to bovine herpesvirus 1

The control of infectious bovine rhinotracheitis induced by bovine herpesvirus 1 (BoHV-1) requires sensitive and specific diagnostic assays. As BoHV-1 is antigenically and genetically related to four other alphaherpesviruses of ruminants-namely, BoHV-5, caprine herpesvirus 1 (CpHV-1), cervine herpesvirus 1 (CvHV-1) and CvHV-2-diagnostic tests able to discriminate BoHV-1 from these related viruses are needed to avoid misdiagnosis, especially because some of these viruses are able to cross the species barrier. In this study, murine monoclonal antibodies (MAbs) specific for BoHV-1, BoHV-5, CpHV-1, CvHV-1, and CvHV-2 were produced with the aim of setting up an immunofluorescence assay able to discriminate between these related herpesviruses. Produced MAbs were selected for their viral specificity by enzyme-linked immunosorbent assay and indirect immunofluorescence staining of virus-infected cells. Radioimmunoprecipitation characterization of the selected MAbs revealed that four of them are directed against glycoprotein C (gC) and one of them is directed against gD of these related viruses. The obtained results demonstrate that the antibodies produced allow an unambiguous discrimination of each of the four alphaherpesviruses related to BoHV-1.