PCR studies on the potential sites for latency of BHV-4 in calves

Genome sequence and experimental infection of calves with bovine gammaherpesvirus 4 (BoHV-4)

Bovine gammaherpesvirus 4 (BoHV-4) is ubiquitous in cattle worldwide, and it has been detected in animals exhibiting broad clinical presentations. The virus has been detected in the United States since the 1970s; however, its clinical relevance remains unknown. Here, we determined the complete genome sequences of two contemporary BoHV-4 isolates obtained from respiratory (SD16-38) or reproductive (SD16-49) tract specimens and assessed clinical, virological, and pathological outcomes upon intranasal (IN) inoculation of calves with the respiratory BoHV-4 isolate SD16-38. A slight and transient increase in body temperature was observed in BoHV-4-inoculated calves. Additionally, transient viremia and virus shedding in nasal secretions were observed in all inoculated calves. BoHV-4 DNA was detected by nested PCR in the tonsil and regional lymph nodes (LNs) of calves euthanized on day 5 post-inoculation (pi) and in the lungs of calves euthanized on day 10 pi. Calves euthanized on day 35 pi harbored BoHV-4 DNA in the respiratory tract (turbinates, trachea, lungs), regional lymphoid tissues, and trigeminal ganglia. Interestingly, in situ hybridization revealed the presence of BoHV-4 DNA in nerve bundles surrounding the trigeminal ganglia and retropharyngeal lymph nodes (day 35 pi). No histological changes were observed in the respiratory tract (turbinate, trachea, and lung), lymphoid tissues (tonsil, LNs, thymus, and spleen), or central nervous tissues (olfactory bulb and trigeminal ganglia) sampled throughout the animal studies (days 5, 10, and 35 pi). This study contributes to the understanding of the infection dynamics and tissue distribution of BoHV-4 following IN infection in calves. These results suggest that BoHV-4 SD16-38 used in our study has low pathogenicity in calves upon intranasal inoculation.

Assessment of Cidofovir for Treatment of Ocular Bovine Herpesvirus-1 Infection in Cattle Using an Ex-Vivo Model

Bovine herpesvirus-1 (BoHV-1) infection contributes to keratoconjunctivitis, respiratory disease, and reproductive losses in cattle. The objective of this study was to determine the most appropriate ophthalmic antiviral agent for BoHV-1 inhibition using in-vitro culture and novel ex-vivo bovine corneal modeling. Half-maximal inhibitory concentrations of BoHV-1 were determined for cidofovir, ganciclovir, idoxuridine, and trifluridine via in-vitro plaque reduction assays. In-vitro cytotoxicity was compared amongst these compounds via luciferase assays. Trifluridine and cidofovir were the most potent BoHV-1 inhibitors in vitro, while trifluridine and idoxuridine were the most cytotoxic agents. Therefore, cidofovir was the most potent non-cytotoxic agent and was employed in the ex-vivo corneal assay. Corneoscleral rings (n = 36) from fresh cadaver bovine globes were harvested and equally divided into an uninfected, untreated control group; a BoHV-1-infected, untreated group; and a BoHV-1-infected, cidofovir-treated group. Virus isolation for BoHV-1 titers was performed from corneal tissue and liquid media. Histologic measurements of corneal thickness, epithelial cell density, and tissue organization were compared between groups. Substantial BoHV-1 replication was observed in infected, untreated corneas, but BoHV-1 titer was significantly reduced in cidofovir-treated (1.69 ± 0.08 × 10³ PFU/mL) versus untreated (8.25 ± 0.25 × 10⁵ PFU/mL, p < 0.0001) tissues by day 2 of culture. No significant differences in histologic criteria were observed between groups. In conclusion, cidofovir warrants further investigation as treatment for BoHV-1 keratoconjunctivitis, with future studies needed to assess in-vivo tolerability and efficacy.

Analysis of the anti-apoptotic v-Bcl2 and v-Flip genes and effect on in vitro programmed cell death of Argentinean isolates of bovine gammaherpesvirus 4 (BoHV-4)

Some viruses encode inhibitory factors of apoptosis during infection to prolong cell viability and then to achieve a higher production of viral progeny or facilitate persistent infections. There is evidence that some gammaherpesviruses, including BoHV-4, carry genes that can both inhibit or induce apoptosis. BoHV-4 possesses two genes (ORF16 and ORF71) that code for proteins with anti-apoptotic functions, such as v-Bcl2 and v-Flip, respectively. Thus, it is relevant to study BoHV-4 in relation to the modulation of apoptosis in infected cells as a strategy for persistence in the host. The objective of this work was to analyze whether variations in v-Flip and v- Bcl2 of six phylogenetically divergent Argentinean isolates of BoHV-4 can influence the capacity of these strains to induce apoptosis in cell cultures. In this study, variations were mainly detected in the v-Flip gene and protein of the BoHV-4 strains belonging to genotype 3. Thus, it is possible to infer that sequence variations could be associated with some BoHV-4 genotype. Induction of apoptosis was not a significant event for any of the genetically distinct local isolates of BoHV-4 and there was not an evident relationship between the variability of both genes with the apoptotic effect of the phylogenetically distinct strains.

Monitoring of the shedding and serological dynamics of Bovine gammaherpesvirus type 4 in a dairy cattle herd

Bovine gammaherpesvirus type 4 (BoHV-4) is increasingly related with reproductive disease in cattle, but its epidemiology is not fully understood. We monitored the serological response and shedding of BoHV-4 in a positive dairy cattle farm with metritis. First, we performed an ELISA to detect BoHV-4 antibodies in all the animals (n = 104). Afterwards, ten seronegative heifers introduced in the production lot and sera samples were monthly taken for four months and then 6-10 months after introduction to detect BoHV-4 antibodies by ELISA. Moreover, a vaginal swab was taken after calving to detect BoHV-4 by PCR. Concurrently, a weekly collection of vaginal and nasal swabs and milk was performed during the first month post-partum in multiparous cows with metritis (n = 14), heifers with metritis (n = 4), heifers without metritis but positive to BoHV-4 (ELISA or PCR) (n = 2) and multiparous cows without metritis (n = 3). Seropositivity was higher in older animals and in the production lot. Three heifers which shed BoHV-4 after parturition resulted seronegative at first but eventually seroconverted. In the same vein, most heifers seroconverted after 6-10 months in the production lot (8/10). Multiparous cows shed virus by various routes: 13/14 (93 %) in vaginal secretions, 7/14 (50 %) in nasal exudates and 7/14 (50 %) in milk. However, in the other groups, shedding was only detected in vaginal swabs from the first week post-partum. Our study describes BoHV-4 shedding in field conditions. Seronegative animals may become horizontally infected when moved to a contaminated environment.

Potential Pathogenetic Role of Bovine Herpesvirus 4 in Two Dairy Cows with Dermatitis-Pyrexia-Hemorrhagic Syndrome

Dermatitis, pyrexia, and hemorrhagic syndrome (DPHS) is a rare bovine syndrome of unclear etiology. We describe two DPHS cases, the first to occur in Italy, with clinicopathological findings suggesting a potential pathogenetic role of bovine herpesvirus-4 (BoHV-4).

[Bovine herpesvirus 4 (BoHV-4): general aspects of the biology and status in Argentina]

Bovine herpesvirus 4 (BoHV-4) has been isolated from cattle with respiratory infections, vulvovaginitis, mastitis, abortions, endometritis and from apparently healthy animals throughout the world. Although it has not yet been established as causal agent of a specific disease entity, it is primarily associated with reproductive disorders of cattle. This virus can infect a wide range of species, either in vivo or in vitro. Two groups of prototype strains were originated from the first isolates: the DN599-type strains (American group) and the Movar-type strains (European group). In Argentina, BoHV-4 was isolated and characterized in 2007 from vaginal discharge samples taken from cows that had aborted. So far, more than 40 isolates, mainly associated with aborting bovine females have been registered in our country.

Detection of bovine herpesvirus 2 and bovine herpesvirus 4 DNA in trigeminal ganglia of naturally infected cattle by polymerase chain reaction

Establishment of latent infection within specific tissues in the host is a common biological feature of the herpesviruses. In the case of bovine herpesvirus 2 (BoHV-2), latency is established in neuronal tissues, while bovine herpesvirus 4 (BoHV-4) and ovine herpesvirus 2 (OvHV-2) latent virus targets on cells of the monocytic lineage. This study was conducted in quest of BoHV-2, BoHV-4 and OvHV-2 DNA in two hundred trigeminal ganglia (TG) specimens, derived from one hundred clinically healthy cattle, majority of them naturally infected with bovine herpesvirus 1 (BoHV-1) and bovine herpesvirus 5 (BoHV-5). Total DNA extracted from ganglia was analyzed by polymerase chain reaction (PCR) designed to amplify part of the genes coding for BoHV-2, and BoHV-4 glycoprotein B and, for OvHV-2, the gene coding for phosphoribosylformylglycinamidine synthase-like protein. BoHV-2 DNA was detected in TG samples of two (2%) and BoHV-4 DNA in nine (9%) of the animals, whereas OvHV-2 DNA could not be detected in any of the TG DNA. The two animals in which BoHV-2 DNA was identified were also co-infected with BoHV-1 and BoHV-5. Within the nine animals in which BoHV-4 DNA was detected, six were also co-infected with BoHV-1 and BoHV-5. This report provides for the first time evidence that viral DNA from BoHV-2 and BoHV-4 can be occasionally detected in TG of naturally infected cattle. Likewise, in this report we provided for the first time evidence that the co-infection of cattle with three distinct bovine herpesviruses might be a naturally occurring phenomenon.

Impact of Bovine Herpesvirus 4 (BoHV-4) on Reproduction

Bovine herpesvirus 4 (BoHV-4) is increasingly considered as responsible for various reproductive troubles. This virus infects blood mononuclear cells and displays a specific tropism for vascular endothelia, mammary tissue, endometrium and foetal tissues. Viral multiplication can be reactivated by corticosteroids or stress, both factors present at calving. BoHV-4 has been isolated in a large variety of clinical cases, primarily metritis, vaginitis and mastitis, but also endometritis, abortion and orchitis. Its impact on reproductive performance has been suggested by several epidemiological studies: seroprevalence against BoHV-4 is higher in aborted females and in repeat breeders. Nevertheless, its intrinsic pathogenic power seems low, symptoms developing only when BoHV-4 cooperates with bacteria: within the uterus or mammary gland. BoHV-4 is rather currently considered as a cofactor for the development of an inflammatory reaction initiated by bacteria.

Transduction of the rat brain by Bovine Herpesvirus 4

Bovine herpesvirus 4 (BoHV-4) is a gamma-herpesvirus with no clear disease association. A recombinant BoHV-4 (BoHV-4EGFP Delta TK) expressing Green Fluorescent Protein (EGFP), was successfully used to infect F98 rat glioma cells. BoHV-4EGFP Delta TK was injected into the lateral ventricle of the rat brain. Histology and immunohistochemistry showed that ependymal and rostral migratory stream cells were transduced while neurons were not. Clinical scores, evaluated for 90 days, indicated that the virus was non neuropathogenic, suggesting this virus is a suitable vector for brain tumor gene therapy.

Establishment of a bovine herpesvirus 4 based vector expressing a secreted form of the bovine viral diarrhoea virus structural glycoprotein E2 for immunization purposes

Background

The biological characteristics of BoHV-4 make it a good candidate as a gene delivery vector for vaccination purposes. These characteristics include little or no pathogenicity, unlikely oncogenicity, the capability to accommodate large amounts of foreign genetic material, the ability to infect several cell types from different animal species, and the ability to maintain transgene expression in both undifferentiated and differentiated cells.

Results

A recombinant bovine herpesvirus 4 (BoHV-4CMV-IgKE2-14ΔTK) expressing an enhanced secreted form of the bovine viral diarrhea virus (BVDV) structural glycoprotein E2 (gE2-14), obtained by the removal of the putative transmembrane domain and addition of a 14 amino acids peptide at its carboxyl terminal and an immunoglobulin K signal peptide to the amino terminal, was successfully constructed using a Recombineering (recombination -mediated genetic engineering) approach on BoHV-4 cloned as bacterial artificial chromosome. The galactokinase – based recombineering system was modified by the introduction of a kanamycin expression cassette and a kanamycin selection step that allowed a significant reduction of the untargeted background clones. BoHV-4CMV-IgKE2-14ΔTK infected cell lines highly expressed gE2-14, which maintained native antigenic properties in a serum neutralization inhibition test. When rabbits and sheep were immunized with BoHV-4CMV-IgKE2-14ΔTK, high levels of serum neutralized antibodies against BVDV were generated.

Conclusion

This work highlights the engineerization of BoHV-4 genome as a vector for vaccine purposes and may provide the basis for BVDV vaccination exploiting the BoHV-4- based vector that delivers an improved secreted version of the BVDV structural glycoprotein E2.

Generation of a transposon insertion mutant library for bovine herpesvirus 4 cloned as a bacterial artificial chromosome by in vitro MuA based DNA transposition system

Bovine herpesvirus 4 (BoHV-4) is a gammaherpesvirus with no clear disease association. Although the BoHV-4 genome has been sequenced, the function of the majority of putative genes is elusive. Several features make BoHV-4 attractive as a backbone for use as a viral expression vector and/or as a model to study gamma herpesvirus biology and determining which genes are essential for its replication is a very important task. Starting from BoHV-4 genome cloned as infectious bacterial artificial chromosome (BAC-BoHV-4) in Escherichia coli. A random insertion mutant library for BoHV4 was generated by the use of MuA transposase-catalyzed in vitro transposition reaction. Viral mutant transfection and direct sequencing allow the rapid determination of which BoHV-4 genes are essential for viral growth in a permissive eukaryotic cell line. BoHV-4 functional analysis information is fundamental when the BoHV-4 genome is modified for vector purposes.

Detection of bovine herpesvirus 4 in aborted bovine placentas

Diagnostic studies on aborted placentas of cattle usually do not determine any reason for abortions. In this paper, five bovine herpesviruses (BoHVs) and some bacteriological agents were investigated by several methods in 33 aborted bovine placentas. Inclusion bodies, PCR and in situ DNA hybridization proved the presence of BoHV-4 DNA in six (18.18%) tested placentas. Positive DNA hybridization signal localized BoHV-4 DNA to placental epithelial cells macrophages and lymphocytes. By destroying epithelial cells and provoking local immune response BoHV-4 infection may inhibit physiological functions of the placenta during gestation. This finding is a further sign that BoHV-4 plays an active role in reproductive disorders of cattle.

Recombinant bovine herpesvirus 4 (BoHV-4) expressing glycoprotein D of BoHV-1 is immunogenic and elicits serum-neutralizing antibodies against BoHV-1 in a rabbit model

Several biological characteristics of bovine herpesvirus 4 (BoHV-4) make it a good candidate as a gene delivery vector for vaccination purposes. These characteristics include little or no pathogenicity, unlikely oncogenicity, the capability to accommodate large amounts of foreign genetic material, the ability to infect several cell types coming from different animal species, and the ability to maintain transgene expression in both undifferentiated and differentiated cells. Starting from BoHV-4 cloned as a bacterial artificial chromosome (BAC), we used MuA transposase-mediated in vitro transposition to generate recombinant BoHV-4 expressing the immunodominant glycoprotein D (gD) of BoHV-1, one of the most important pathogens of cattle. Although a cis-acting element from woodchuck hepatitis virus (the woodchuck hepatitis virus posttranscriptional regulatory element [WPRE]) in the 3' end of the gD expression cassette was required for maximal gD expression from plasmids in transient transfection assays, this element was not necessary for efficient expression of gD from recombinant BoHV-4 genomes. BoHV-4 recombinants containing gD expression cassettes with or without the WPRE expressed gD at similarly high levels. Several cell lines originating from different animal species expressed gD when infected with BoHV-4 recombinants. When rabbits were immunized with one of the recombinants, high levels of serum neutralizing antibodies against BoHV-1 were generated. This work is one of the first demonstrations of the use BoHV-4 as a vector for vaccine purposes and may provide the basis for BoHV-1 vaccination of cattle with recombinant BoHV-4.

Bovine herpesvirus 4 based vector interaction with liver cells in vitro and in vivo

Gene transfer into hepatocytes is highly desirable for the long-term goal of replacing deficient proteins and correcting metabolic disorders. Bovine herpesvirus 4 (BoHV-4) based vector capability to transduce rat liver cells in vitro and in vivo was assessed. For the in vitro study, a buffalo rat liver cell line was successfully transduced by BoHV-4 and although did not show toxicity, the immediate early two viral gene was transcribed and cells harboring the intact viral genome could be pharmacologically selected, but no viral replication took place. For the in vivo study, adult male rats were inoculated intraportally and intraparenchimally with a BoHV-4 expressing enhanced green fluorescent protein and liver sections were analyzed through fluorescent microscopy. Although the liver parenchyma could not be transduced, the endothelial layer of the liver vasculature showed a robust transgene expression without toxicity. Successful BoHV-4 based vector transduction of primary cultures of rat hepatocytes suggests that extrinsic factors, and not hepatocytes per se, are the cause of such lack of transducibility. The present study serves as a starting point for study of the use of BoHV-4 based vectors to target gene delivery to vascular endothelial cells.

Outcome of bovine herpesvirus 4 infection following direct viral injection in the lateral ventricle of the mouse brain

A recombinant bovine herpesvirus 4 (BoHV-4EGFPDeltaTK), obtained by the insertion of an EGFP gene into the TK locus of DN 599 BoHV-4 strain, was injected into the lateral ventricle of the brain of mice and a clinical score was evaluated for 90 days. Although BoHV-4 was not neuro-pathogenic, BoHV-4EGFPDeltaTK transduction capability was analyzed. EGFP expression was localized in close proximity to the border of the ventricles and EGFP-positive cells were found to co-localize with ependymal cells. Although most of the cells had a polarized morphology, they were not neurons. EGFP-positive cells were seen to spread in tangentially oriented rows within the rostral migratory stream (RMS). Co-localization of EGFP signal with anti-GFAP antibody showed that they were glial cells. EGFP-positive cells were observed until 31 days post-injection and then disappeared completely. Virus isolation was possible at an early post-injection time (3 days), but then virus titer was below the detection limits at later times. Viral DNA, however, could be detected until 21 days post-injection. Thus, in this report we showed that (i) BoHV-4EGFPDeltaTK did not replicate in the mouse brain, (ii) is not pathogenic and (iii) gene transfer can be obtained in long-lived cells belonging to the RMS after BoHV-4EGFPDeltaTK injection within the lateral ventricle.

Characterization of Bovine Herpesvirus Type 4 Isolated from Cattle with Mastitis and Subclinical Infection by the Virus among Cattle

An outbreak of contagious mastitis occurred among cattle on a farm, and bovine herpesviruses were isolated from the affected mammary tissues, scabs and abscess discharge of the cattle. A bovine herpesvirus type 4 (BoHV-4)-specific fragment was amplified from the isolates by polymerase chain reaction (PCR). Restriction endonuclease analyses demonstrated that the isolates were related to Movar-like European type BoHV-4. To determine the ratio of BoHV-4 subclinical infection in the cattle, a genomic survey was performed by PCR for cattle that were moved to the animal hygiene service station in Ibaraki prefecture. The BoHV-4 genome was occasionally detected in peripheral blood leukocytes, lymph nodes and nervous tissues. The rate of BoHV-4 subclinical infection was relatively high in the cattle.

Pathogenesis of gammaherpesvirus infections

Gammaherpesviruses are members of an emerging subfamily among the Herpesviridae. Two genera are discriminated: (i) lymphocryptovirus, including its type species Epstein-Barr virus (EBV), and (ii) rhadinovirus, including viruses of interest for medicine, veterinary medicine, and biomedical research, i.e. alcelaphine herpesvirus 1, bovine herpesvirus 4, equine herpesvirus 2, human herpesvirus 8, mouse herpesvirus 68, and ovine herpesvirus 2 (OvHV-2). The perception that these viruses have a narrow host range is misleading, since they cover a surprisingly wide host range, both on the cellular and the organism's level. For example, the natural range of OvHV-2 infection extends over a common animal order. While the host range determinants of EBV are well known, the corresponding features of the rhadinoviruses need still to be defined. Similarly, the gene expression patterns of the veterinary rhadinoviruses during latency require further characterization. In vivo, the gammaherpesviruses have evolved to actively protect their latently infected cells from being destroyed by immune functions of their native host. In return, those reservoir hosts have evolved to being infected and transmit the virus without overt disease symptoms. However, a balanced immune response needs to be in control over the number of infected cells. Virus excretion is usually at low level and may occur either constantly or intermittently. Animal species that are targeted by the virus but did not participate in the process of co-evolution as well as hosts with immune deficiencies are known to loose control over the amount of latently infected cells, which results in the development of lethal diseases, such as malignant catarrhal fever or Kaposi's sarcoma.

Exploiting persistent infection for selection of bovine herpesvirus 4 recombinants

Bovine herpesvirus 4 (BoHV-4) is a gamma-herpesvirus with no clear disease association, and due to its biological characteristics, has been suggested as a gene delivery vector. It was demonstrated previously that recombinant BoHV-4 carrying a neomycin-resistance gene was able to infect a human rhabdomyosarcoma cell line (RD-4), resulting in no detectable cytopathic effect (CPE) and allowing selection of G418-resistant persistently-infected cells containing circular episomal viral DNA [Donofrio, G., Cavirani, S., van Santen, V.L., 2000a. Establishment of a cell line persistently infected with recombinant BoHV-4. J. Gen. Virol. 81, 1807-1814.]. Those cells produce infectious virus and infection is predominantly non-permissive and non-cytopathic. Starting from these results, the ability of RD-4 cells to sustain persistent infection was combined with positive selection activity conferred by the neomycin-expression cassette insert, as an easier way to select recombinants of BoHV-4 following homologous recombination in permissive cells. A tool for selecting BoHV-4 recombinants was developed by drug positive selection.

Detection of bovine herpesvirus 4 in CD11b+ leukocytes of experimentally infected rabbits

The presence and numbers of bovine herpesvirus 4 (BoHV-4) infected CD11b+ leukocytes were investigated during experimental infections of New Zealand White rabbits by Fluorescence Activated Cell Sorter (FACS) analysis. Peripheral blood leukocytes (PBL) were collected every second day, and the cells were stained with phycoerythrin-labelled CD11b-specific mouse monoclonal antibody and fluorescein-conjugated bovine herpesvirus 4-specific mouse monoclonal antibody. The numbers of double-stained cells from PBLs of the control and inoculated groups were measured and compared in FACSTREK analyser. Double-stained cells were detected in the virus-inoculated group on postinoculation days (PID) 2-5 and 9-12. The results indicated that CD11b+ PBLs were permissive for BoHV-4 infection, and are probably the main reservoir of the virus during the latent period. The data did not indicate production of infectious viral particles, but virus-specific proteins were expressed on the surface of CD11b+ cells. The two waves of double-stained cells gave similar results to the PCR assays from serum samples, which showed the presence of viral DNA in the serum on the same days when virus-infected CD11b cells were also present. Productive BoHV-4 infection of mast cells or undifferentiated leukocytes in the bone marrow and the antiviral immune response might be responsible for this periodic appearance of the virus in CD11b+ PBLs and in the serum. The paper provides evidence that CD11b+ PBLs are the main target cell populations in the blood for BoHV-4.

Role of bovine herpesvirus 4 in bacterial bovine mastitis

In order to study the role played by bovine herpesvirus 4 (BoHV-4) in bovine mastitis, PCR experiments were performed on a Hungarian dairy herd of 2000 cows. Milk cells were tested with a nested PCR adjusted to detect the virus in the milk. Thirty to forty-one percentage of the udders of 101 cows with bacterial mastitis (Escherichia coli, Streptococcus uberis or Staphylococcus aureus) gave positive results, whereas less than 6% of the milk samples were positive for BoHV-4 from 118 animals with healthy udders. The mastitis status of these 118 healthy cows was followed throughout the milking period; 4.2% had clinical, and 25.42% had subclinical mastitis. By the end of the milking period, more than 90% of the cows shed the virus in their milk, regardless of the bacterial status of the udder. No correlation was found between the virus shed, the somatic cell count, and the bacterial status of the udder. Viral DNA was detected in the wall of the milk duct. These results demonstrate that BoHV-4 neither causes mastitis directly nor plays a role in the initiation of the process, but later, when bacterial infection of the udder occurs, the reactivated virus replicates in the immune cells of the udder and/or in the epithelial cells of the milk ducts and may be responsible for more severe, prolonged mastitis. As mastitis is a crucial problem of milk production, this virus may be considered a possible predisposing factor and also an agent of secondary udder infections in prolonged mastitis cases.

Activation of bovine herpesvirus 4 lytic replication in a non-permissive cell line by overexpression of BoHV-4 immediate early (IE) 2 gene

Bovine herpesvirus 4 (BoHV-4) is a gammaherpesvirus with no clear disease association, it establishes persistent infections in its natural host, the bovine, and in an experimental host, the rabbit. BoHV-4 immediate early 2 (IE2) RNA is the less abundant, spliced, 1.8 kb RNA. The predicted amino acid sequence, of the IE2 protein, reveals that it could encode a 61 kDa protein with amino acid sequence homology to the Epstein-Barr virus (EBV) transactivator R protein and its homologues including, herpesvirus saimiri (HVS), equine herpesvirus 2 (EHV-2), murine herpesvirus 68 and Kaposi's sarcoma-associated herpesvirus (KSHV). We examined recently the interaction of BoHV-4 with a human rhabdomyosarcoma cell line, RD-4, and found that although some infectious viruses can be produced, no cytopathic effect (CPE) was observed [J. Gen. Virol. 81 (2000) 1807]. Because IE2 could play a critical role in BoHV-4 productive infection and its overexpression in RD-4 cells could switch the non-permissive RD-4 status to a permissive one. RD-4 cells expressing stably BoHV-4 IE2 gene were generated. BoHV-4 IE2 induced an increased production of infectious viral particles sufficient to obtain an apparent cytopathic effect. It is concluded that BoHV-4 IE2 is a key factor in determining the outcome of BoHV-4 infection.

Detection of bovine gammaherpesviruses by a nested duplex PCR

The two bovine gammaherpesviruses (Alcelaphine herpesvirus 1, AlHV-1; Bovine herpesvirus 4, BoHV-4) are distributed worldwide in cattle populations. Since the animals are frequently infected latently with no or low seropositivity, a DNA based diagnostic method would be useful for surveys and detection of these viruses. In the present study a nested duplex PCR was established for the sensitive and specific simultaneous detection of both viruses. The primers were designed for the gene of the major capsid protein (ORF25). The assay did not amplify the capsid gene sequence of 10 related bovine herpesviruses and other gammaherpesviruses. The test was able to detect 1pfu (plaque forming unit) of AlHV-1 and BoHV-4. Among 146 clinical samples (lymph nodes and peripheral blood leukocytes, PBLs) 65 (44.52%) were found to be positives for AlHV-1 and 84 (57.53%) for BoHV-4. This nested duplex PCR assay could serve as a useful diagnostic method for rapid, sensitive, specific simultaneous detection of the two bovine gammaherpesviruses.

Latency and persistence of bovine herpesvirus type 4, strain B11-41, in bovine nervous tissues

Three cattle were experimentally infected with bovine herpesvirus type 4 (BoHV-4), strain B11-41, isolated from the spinal cord of a cow, and monitored for clinical symptoms. None of them showed any clinical signs except increases of leukocyte numbers in two of them, and the body temperature remained normal throughout the experiment. Antibody titers against BoHV-4 continuously increased for one month and were maintained at a high level for more than 1 year by enzyme-linked immunosorbent assay (ELISA). The virus was isolated only from serum and peripheral blood leukocytes (PBL) of one cow in the early stage of infection, but the viral genome was detected in PBL continuously by PCR. When they were euthanized, the viral genome was detected in the lymph nodes and nervous tissues such as medulla, spinal cord, and trigeminal ganglion. These results indicate that cattle are infected with the virus latently and persistently, and the latency site would be in the tissues of the central nervous system as well as lymphoid tissues. When a seroepidemiological survey was performed on antibodies to BoHV-4 among cattle in Japan by ELISA, the rate of antibody-positive cattle was 8.9% and they were found irregularly on certain farms.

Seroprevalence and comparison of isolates of endometriotropic bovine herpesvirus-4

Sixty-eight cases of suppurative, ulcerative endometritis associated with Bovine Herpesvirus-4 (BHV-4) in postparturient dairy cows (62 Holsteins and 6 Jerseys, mean age 4.2 years) were confirmed by a combination of histopathology, fluorescent antibody assays, electron microscopic evaluation of uterus, and polymerase chain reaction (PCR). All cases occurred in the 3- to 28-day postpartum period, and histologic lesions among various cows were consistent when compared with postpartum interval. The endometrial lining epithelium was necrotic and ulcerated from 3 to 7 days postpartum, with only mild inflammation in the lamina propria and submucosa. From 1 to 4 weeks postpartum, the ulcers were confluent to diffuse. Epithelium was replaced by fibrinonecrotic, suppurative mats, resulting in severe bacterial pyometra by day 24. Seroprevalence to BHV-4 in one dairy with a history of 18 mortality cases was 36% (107 of 296). In a random sample of 8 cows from this herd, none had serologic titers in blood sampled 2 weeks prepartum, but 3 of 8 seroconverted with significant titers of 1:8 to 1:16 at 2 weeks postpartum. By 10 weeks postpartum, all 8 cows returned to negative serologic status. Two of 6 cats from the premises also had positive titers. Random serum samples taken from 480 dairy cattle at sale barns indicated 76 (16%) were positive by serum neutralization. Clinical signs, postparturient timing, and histologic lesions were very similar to those previously reported in Belgium with BHV-4. But sequence analysis of PCR products of the glycoprotein B region of 4 separate field isolates of endometriotropic BHV-4 suggests these field isolates were more closely related to the North American nonvirulent strain DN-599 than to the endometriotropic European strain V.

Simultaneous intramammary and intranasal inoculation of lactating cows with bovine herpesvirus 4 induce subclinical mastitis

In this study, we examined whether an experimental bovine herpesvirus 4 (BHV4) infection can induce bovine mastitis, or can enhance bovine mastitis induced by Streptococcus uberis (S. uberis). Four lactating cows were inoculated intramammarily and intranasally with BHV4, and four lactating control cows were mock-inoculated. After 14 days, two of four cows from each group were inoculated intramammarily with S. uberis. No clinical signs were recorded in cows inoculated only with BHV4, and their milk samples showed no abnormal morphology, despite the fact that BHV4 replicated in inoculated quarters. Somatic cell count increased significantly in milk from three of six BHV4-inoculated quarters, compared to the non-inoculated quarters of the same cows (within-cow) and the quarters of mock-inoculated cows (control group) on days 8, 9 and 11 post-inoculation (pi). BHV4 was isolated from nasal swabs between days 2 and 9 pi. Clinical mastitis was observed in all four cows intramammarily inoculated with S. uberis. A preceding BHV4 infection did not exacerbate the clinical mastitis induced by S. uberis. S. uberis infections appeared to trigger BHV4 replication. From one quarter of each of two cows inoculated with BHV4 and S. uberis, BHV4 was isolated, and not from quarters inoculated with BHV4 only. In conclusion, BHV4 did not induce bovine clinical mastitis after simultaneous intranasal and intramammary inoculation. However, the BHV4 infection did induce subclinical mastitis in 50% of the cows and the quarters.

Potential of bovine herpesvirus 4 as a gene delivery vector

A cloning system was developed for construction of BHV-4 recombinants and recombinant virus BHV-4EGFPDeltaTK containing an enhanced green fluorescent protein (EGFP) gene was constructed. The host range of BHV-4EGFPDeltaTK was characterized in vitro. When cell lines from various species and tissues were infected, most of the non-bovine cell lines exhibited neither cytopathic effect (CPE) nor supported viral replication, but EGFP expression was clearly observed. Next, embryonic stem cells were infected and induced to either non-specific or neural differentiation to determine whether they could survive and differentiate after BHV-4EGFPDeltaTK infection. Embryonic stem cells were infected successfully, as indicated by EGFP expression prior to differentiation, and EGFP expression could be detected in many differentiated cells. No CPE was noted. Therefore, BHV-4EGFPDeltaTK infection caused neither cell death nor interfered with non-specific or neural differentiation of embryonic stem cells. Finally, to assess the capability of BHV-4EGFPDeltaTK to infect post-mitotic neurons, cultures from brains of 2-weeks old mice were infected. No death of neuronal cells due to infection was observed and EGFP expression persisted for at least 15 days. Several biological characteristics of BHV-4 demonstrated previously make it a good candidate for a gene delivery vector. These include: little or no pathogenicity, unlikely oncogenicity, ability to establish persistent infection, and capability of herpesviruses to accommodate large amounts of foreign genetic material. These findings add the ability to infect several cell types coming from different animal species, usually without CPE, lack of interference with differentiation, and ability to maintain transgene expression in both undifferentiated and differentiated cells.

Detection of feline leukaemia virus in blood and bone marrow of cats with varying suspicion of latent infection

The purpose of this study was to determine if polymerase chain reaction (PCR) could be used to detect FeLV proviral DNA in bone marrow samples of cats with varying suspicion of latent infection. Blood and bone marrow samples from 50 cats and bone marrow from one fetus were collected, including 16 cats with diseases suspected to be FeLV-associated. Serum enzyme-linked immunosorbent assay (ELISA), blood and bone marrow immunofluorescent antibody test (IFA), and blood and bone marrow PCR were performed on each cat, and IFA and PCR on bone marrow of the fetus. Forty-one cats were FeLV negative. Five cats and one fetus were persistently infected with FeLV. Four cats had discordant test results. No cats were positive on bone marrow PCR only. It appears persistent or latent FeLV infection is not always present in conditions classically associated with FeLV.

A bovine macrophage cell line supports bovine herpesvirus-4 persistent infection

Although bovine herpesvirus-4 (BHV-4), a gammaherpesvirus lacking a clear disease association, has been demonstrated in many tissues during persistent BHV-4 infection, a likely site of virus persistence is in cells of the monocyte/macrophage lineage. To establish an in vitro model of persistent infection potentially useful for examining the molecular mechanisms of BHV-4 persistence/latency, we infected the bovine macrophage cell line BOMAC. Following extensive cell death, surviving cells were found to be persistently infected, maintaining the viral genome over many passages and producing low levels of infectious virus. Although selection was unnecessary for the maintenance of the viral genome, cells persistently infected with recombinant BHV-4 containing a neomycin-resistance gene could be selected with geneticin, thus confirming that persistent BHV-4 infection was compatible with cell survival and replication. Furthermore, persistent BHV-4 infection caused no decrease in the growth rate of BOMAC cells. Sodium butyrate, which reactivates latent gammaherpesviruses in vitro, or dexamethasone, which reactivates latent BHV-4 in vivo, increased viral DNA by 10- to 15-fold in persistently infected BOMAC cells. This suggests that reactivation of latent BHV-4 by dexamethasone in vivo might involve direct action of dexamethasone on latently infected cells.

Detection of bovine herpesvirus 4 (BoHV-4) DNA in the cell fraction of milk of dairy cattle with history of BoHV-4 infection

We have demonstrated, by PCR and restriction enzyme analysis of the PCR product, the presence of bovine herpesvirus 4 (BoHV-4) DNA in the cell fraction of milk from dairy cattle with a history of BoHV-4 infection. We next evaluated the infectious nature of BoHV-4 DNA in those cells. Cocultivation of a BoHV-4-sensitive cell line with BoHV-4 DNA-positive milk cell samples produced cytopathic effects. The same result was obtained from frozen and thawed milk cell fraction coming from the cell milk fraction PCR-positive cows, ensuring that cells were killed and only infectious virus could be recovered after cocultivation with sensitive cells. This report shows that infectious BoHV-4 can be present in milk cells and that therefore nursing may be one of the transmission routes of BoHV-4.

Murine gammaherpesvirus-68 infection of and persistence in the central nervous system

Murine gammaherpesvirus-68 (MHV-68) was originally isolated from a bank vole by passage through mouse brain. Given its ability to replicate in mouse brain and its subsequent reisolation from trigeminal ganglia, it was originally considered to be an alphaherpesvirus. Molecular studies have now firmly established MHV-68 to be a gammaherpesvirus. Other gammaherpesviruses have been suggested to cause and in some cases shown to cause neurological disease. Given the isolation history of MHV-68, we have studied the ability of this virus to gain access to, to replicate in and to persist in the mouse CNS. Following intranasal inoculation the virus was not generally neuroinvasive. However, in mice with a deletion of the type-I interferon receptor gene, peripheral virus titres are higher and perivascular CNS infection was observed. There was no evidence of virus spread via olfactory routes. Direct intracerebral inoculation of virus was fatal with widespread infection and destruction predominantly of meningeal and ependymal cells. Hippocampal pyramidal neurons, oligodendrocytes, Bergmann glia cells in the cerebellar cortex and neural progenitor cells in the rostral migratory stream were also infected. A similar infection was observed in younger mice. CNS infection following virus reactivation was investigated by implantation of infected glial cells. Implantation into a brain ventricle led to widespread fatal infection, principally involving ependymal and meningeal cells. Implantation into the striatum resulted in a predominantly neuronal infection. Implantation of cells into mice transiently treated with the antiviral thionucleoside analogue 2'-deoxy-5-ethyl-beta-4'-thiouridine resulted in survival with detection of virus-infected cells in the brain 1 year later.

Malignant catarrhal fever: polymerase chain reaction survey for ovine herpesvirus 2 and other persistent herpesvirus and retrovirus infections of dairy cattle and bison

Using a polymerase chain reaction (PCR) test for sequences of ovine herpesvirus 2 (OHV2), this virus was shown to be significantly associated with sheep-associated malignant catarrhal fever (SA-MCF) in terminal cases of disease in 34 cattle and 53 bison. Ovine herpesvirus 2 was not detected in cattle (38) and bison (10) that succumbed to other diseases. Other persistent herpesviruses, retroviruses, and pestivirus, some of which have been previously isolated from cases of SA-MCF, were not associated with the disease. These included bovine herpesvirus 4 (BHV4), bovine lymphotrophic herpesvirus (BLHV), bovine syncytial virus (BSV, also known as bovine spumavirus), bovine immunodeficiency virus (BIV), and bovine viral diarrhea virus (BVDV). A PCR survey for OHV2 in DNA from individual cow's peripheral blood lymphocytes in 4 dairies showed that the 1 dairy that was in close contact to sheep had a prevalence of OHV2 of 21.3%, whereas the 3 other dairies had no OHV2. Prevalence of the other herpesviruses and retroviruses in the dairy cows was variable, ranging from 2% to 51% for BHV4, 52% to 78.7% for BLHV, and 10% to 34% for BSV. Bovine lymphotrophic herpesvirus and BSV were also found in a few (1-4 of 21 tested) cases of terminal SA-MCF, but BIV and BVDV were not found in either the dairy cows sampled, or in the cases of SA-MCE No significant correlation was found between the presence of any 2 viruses (OHV2, BHV4, BLHV, BSV) in the dairy cows or terminal cases of SA-MCE

Establishment of a cell line persistently infected with bovine herpesvirus-4 by use of a recombinant virus

Bovine herpesvirus-4 (BHV-4), a gammaherpesvirus lacking a clear disease association, productively infects multiple cell lines of various species and causes cell death. A human rhabdomyosarcoma cell line, RD-4, infected with BHV-4 produced low levels of early and late viral RNAs and infectious virus, but exhibited no cytopathic effect. Using a recombinant BHV-4 containing a neomycin-resistance gene, we established RD-4-derived cell lines persistently infected with BHV-4. The viral genome in these cells was predominantly circular. Because of drug selection, every cell contained a viral genome. In addition, all cells stained with a BHV-4-specific antiserum. Therefore, these cell lines are not carrier cultures. These cells produced infectious virus at all passages tested. Even though cells were selected and maintained at a concentration of geneticin at least 2.5 times that necessary to kill uninfected RD-4 cells, selected cells contained only approximately one viral genome per diploid host cell genome. Persistently infected cells grew more slowly than uninfected cells, even in the absence of drug. The slower growth of these cells suggests that any growth advantage conferred by multiple copies of the neomycin-gene-carrying viral genome might be offset by the detrimental effects of viral gene expression. This situation contrasts with other gammaherpesviruses, which are able to growth-transform cells.

Experimental infection with bovine herpesvirus-4 enhances atherosclerotic process in rabbits

An association of herpesvirus and atherosclerosis has been suggested by seroepidemiologic studies and detection of the virus in arterial tissues. To facilitate the studies of the pathogenic role of herpesvirus in atherosclerosis, we established a rabbit model of atherosclerosis with bovine herpesvirus type-4 (BHV-4). Forty New Zealand White rabbits were randomly divided into six groups. Groups 1, 2, and 3 were inoculated iv with BHV-4 and control Groups 4, 5, and 6 with normal saline. Groups 1 and 4 were fed a regular diet throughout the experiment; Groups 2 and 5 were fed a diet supplemented with 2% cholesterol for 3 weeks starting at 3 weeks postinoculation; and Groups 3 and 6 with a diet supplemented with 2% cholesterol for 6 weeks starting at 3 days postinoculation. Extensive atherosclerotic lesions in Groups 2, 3, and 6, and small lesions in two rabbits in Group 1 were observed, but no obvious lesions were observed in Groups 4 and 5. BHV-4 DNA was demonstrated by polymerase chain reaction and liquid hybridization in aortic sections, various tissue samples, and peripheral blood mononuclear cells of all infected rabbits. Our studies demonstrated that BHV-4 can accelerate the atherosclerotic process in rabbits, and that experimental infection of rabbits with BHV-4 can be a useful atherosclerosis model.

A sensitive and specific PCR/Southern blot assay for detection of bovine herpesvirus 4 in calves infected experimentally

A PCR/Southern blot assay for detection of bovine herpesvirus 4 (BHV-4) in the background of bovine cellular DNA was developed. A BHV-4 specific sequence within the gene coding for the glycoprotein B (gB) was selected for primer sequences to guarantee the specificity of the assay. With a detection limit of six molecules BHV-4 DNA in the background of 1 microg of cellular DNA (equals about 150,000 bovine cells) this PCR/Southern blot assay represents a highly sensitive method for detection of BHV-4 DNA. At low concentrations of BHV-4 genomes, this assay also allows to estimate the copy number of BHV-4: a distinction between fewer than 6, 6-59 and more than 60 BHV-4 genomes/100 microl DNA suspension was possible. Tissue and blood samples of two calves, infected experimentally with BHV-4 were examined for the prevalence of BHV-4 DNA 130 days post infection. Ten days before taking samples, one of the calves was immuno-suppressed with dexamethasone. In both calves, BHV-4 DNA was detected in the leucocyte fraction of the blood, and beyond that in lower quantities in the spleen and the kidney of the immuno-suppressed calf. It is assumed that a latent BHV-4 infection was activated after application of dexamethasone and that the leucocyte fraction of the blood represents one site of latency of BHV-4 in cattle.

Persistent infection of bovine herpesvirus type 4 in bovine endothelial cell cultures

Herpesviruses can establish a persistent infection in the cells and tissues of their natural hosts and thus may produce diseases due to cytolytic infections. We have isolated a herpesvirus from a bovine vascular endothelial cell culture after continuous subculturing. Typical cytopathic changes were observed in bovine endothelial cell cultures 2 days after inoculation of the virus. The virus had an icosahedral nucleocapsid of 100-150 nm in diameter and an envelope. The sequences of some DNA fragments of the virus were highly homologous to those of the bovine herpesvirus type 4 (BHV-4) strains. The DNA restriction maps of the virus and the reference strains of BHV-4, DN 599 and Movar 33/63 were very similar but not identical. Therefore, the newly isolated virus has been designated Taiwan strain. The presence of BHV-4 DNA in apparently normal bovine endothelial cell cultures was shown by Southern blot hybridization with the BamHI fragment of the newly isolated BHV-4 and was further confirmed by digestion of the DNA with BamHI plus AccI. In conclusion, we have demonstrated that BHV-4 persisted in the bovine endothelial cell cultures and continuous subcultures could lead to the production of infectious viral particles.

Periodic reappearance of bovine herpesvirus type 4 DNA in the sera of naturally and experimentally infected rabbits and calves

A BHV-4 specific nested PCR was used for the detection of viral DNA in serum samples of rabbits and calves. All animals were followed up for 62 days, blood samples were taken for PCR studies every second day. Maternal infection of calves resulted in the repeated regular reappearance (10-14 days) of the virus (DNA) in serum samples. When PCR positive five-day-old calves were infected with tissue culture adapted virus, the reappearance of the DNA in the serum was shown to be irregular, nevertheless, DNA peaks reappeared during the whole observation period. A PCR negative calf infected at the age of 60 days was found to possess viraemia until p.i.d. 32. In rabbits treated intravenously with BHV-4 the inoculum or a primary viraemia was detected at p.i.d. 2-3 and p.i.d. 14-16. Published data on human herpesviruses suggest, that the target cells might be a pluripotent stem cell population of the bone marrow and differentiated virus-infected cells destroyed by the immune system might be the source of viral DNA detected in the serum. Frequency of DNA reappearance was depended on the age of the infected animals but not on the inoculated amount of BHV-4. The described phenomenon might be part of BHV-4 infection of very young animals.