β-Catenin-Specific Inhibitor, iCRT14, Promotes BoHV-1 Infection-Induced DNA Damage in Human A549 Lung Adenocarcinoma Cells by Enhancing Viral Protein Expression

Oncolytic bovine herpesvirus type 1 (BoHV-1) infection induces DNA damage in human lung adenocarcinoma cell line A549. However, the underlying mechanisms are not fully understood. We found that BoHV-1 infection decreased the steady-state protein levels of p53-binding protein 1 (53BP1), which plays a central role in dictating DNA damage repair and maintaining genomic stability. Furthermore, BoHV-1 impaired the formation of 53BP1 foci, suggesting that BoHV-1 inhibits 53BP1-mediated DNA damage repair. Interestingly, BoHV-1 infection redistributed intracellular β-catenin, and iCRT14 (5-[[2,5-Dimethyl-1-(3-pyridinyl)-1H-pyrrol-3-yl]methylene]-3-phenyl-2,4-thiazolidinedione), a β-catenin-specific inhibitor, enhanced certain viral protein expression, such as the envelope glycoproteins gC and gD, and enhanced virus infection-induced DNA damage. Therefore, for the first time, we provide evidence showing that BoHV-1 infection disrupts 53BP1-mediated DNA damage repair and suggest β-catenin as a potential host factor restricting both virus replication and DNA damage in A549 cells.

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.

Natto extract, a Japanese fermented soybean food, directly inhibits viral infections including SARS-CoV-2 in vitro

Natto, a traditional Japanese fermented soybean food, is well known to be nutritious and beneficial for health. In this study, we examined whether natto impairs infection by viruses, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as well as bovine herpesvirus 1 (BHV-1). Interestingly, our results show that both SARS-CoV-2 and BHV-1 treated with a natto extract were fully inhibited infection to the cells. We also found that the glycoprotein D of BHV-1 was shown to be degraded by Western blot analysis and that a recombinant SARS-CoV-2 receptor-binding domain (RBD) was proteolytically degraded when incubated with the natto extract. In addition, RBD protein carrying a point mutation (UK variant N501Y) was also degraded by the natto extract. When the natto extract was heated at 100 °C for 10 min, the ability of both SARS-CoV-2 and BHV-1 to infect to the cells was restored. Consistent with the results of the heat inactivation, a serine protease inhibitor inhibited anti-BHV-1 activity caused by the natto extract. Thus, our findings provide the first evidence that the natto extract contains a protease(s) that inhibits viral infection through the proteolysis of the viral proteins.

MG-132 interferes with iron cellular homeostasis and alters virulence of bovine herpesvirus 1

Bovine herpesvirus 1 (BoHV-1) requires an iron-replete cell host to replicate efficiently. BoHV-1 infection provokes an increase in ferritin levels and a decrease of transferrin receptor 1 (TfR-1) expression, ultimately lowering iron pool extent. Thus, cells try to limit iron availability for virus spread. It has been demonstrated that MG-132, a proteasome inhibitor, reduces BoHV-1 release. Since ferritin, the major iron storage protein in mammalian cells, undergoes proteasome-mediated degradation, herein, the influence of MG-132 on iron metabolism during BoHV-1 infection was examined. Following infection in bovine cells (MDBK), MG-132 reduced cell death and viral yield. Western blot analysis showed a significant ferritin accumulation, likely due to the inhibition of its proteasome-mediated degradation pathway. In addition, the concomitant down-regulation of TfR-1 expression, observed during infection, was counteracted by proteasome inhibitor. This trend may be explained by enhanced acidic vesicular organelles, detected by acridine orange staining, determining a reduction of intracellular pH, that promotes new synthesis of TfR-1 degraded in a recycling pathway. In addition, MG-132 influences cellular iron distribution during BoHV-1 infection, as revealed by Perls' Prussian blue staining. However, cellular iron content, evaluated by Atomic Absorption Spectrophotometry, resulted essentially unaltered. These findings reveal that MG-132 may contribute to limit cellular iron availability for virus replication thereby enhancing cell survival.

Fluorescent TAP as a Platform for Virus-Induced Degradation of the Antigenic Peptide Transporter

Transporter associated with antigen processing (TAP), a key player in the major histocompatibility complex class I-restricted antigen presentation, makes an attractive target for viruses that aim to escape the immune system. Mechanisms of TAP inhibition vary among virus species. Bovine herpesvirus 1 (BoHV-1) is unique in its ability to target TAP for proteasomal degradation following conformational arrest by the UL49.5 gene product. The exact mechanism of TAP removal still requires elucidation. For this purpose, a TAP-GFP (green fluorescent protein) fusion protein is instrumental, yet GFP-tagging may affect UL49.5-induced degradation. Therefore, we constructed a series of TAP-GFP variants using various linkers to obtain an optimal cellular fluorescent TAP platform. Mel JuSo (MJS) cells with CRISPR/Cas9 TAP1 or TAP2 knockouts were reconstituted with TAP-GFP constructs. Our results point towards a critical role of GFP localization on fluorescent properties of the fusion proteins and, in concert with the type of a linker, on the susceptibility to virally-induced inhibition and degradation. The fluorescent TAP platform was also used to re-evaluate TAP stability in the presence of other known viral TAP inhibitors, among which only UL49.5 was able to reduce TAP levels. Finally, we provide evidence that BoHV-1 UL49.5-induced TAP removal is p97-dependent, which indicates its degradation via endoplasmic reticulum-associated degradation (ERAD).

Bovine herpesvirus 1 can cross the intact zona pellucida of bovine oocytes after artificial infection

Bovine herpesvirus 1 (BHV1) is an important bovine pathogen, responsible for respiratory diseases and reproductive problems. This study investigated the penetration capacity of BHV1 into oocytes after co-incubation for either 1 h or 24 h. Immunofluorescence assays in cumulus-oocyte complexes (COCs) and denuded oocytes (without the presence of cumulus cells) were performed and evaluated using confocal laser scanning microscopy. Blood samples and ovaries from BHV1 seronegative cows were used. The oocytes recovered were divided into two groups. Group I comprised COCs (n = 312) and denuded oocytes (n = 296), which were experimentally infected with BHV1 and incubated for 1 h at 38.5°C and 5% CO₂. Group II comprised COCs (n = 425) and denuded oocytes (n = 405), which were co-incubated with BHV1 under the same conditions for 24 h. The negative control of these two groups was respectively subjected to the same protocol, except for exposure to BHV1. To our knowledge, this study provides the first evidence of BHV1 detection within COCs and denuded oocytes exhibiting intact zona pellucida when co-incubated with the virus for 24 h. Immunolocalization also confirmed the presence of BHV1 in the cytoplasm of the cumulus cells of all COCs exposed to the virus after both incubation periods. In conclusion, detection of BHV1 inside oocytes has a great meaning for the field of animal reproduction. The detection of BHV1 in different layers of cumulus cells also demonstrates that these cells are sources of viral infection.

Does porphyrin suppres the apoptotic and necrotic effects of bovine herpes virus type-1(BoHV-1) and herpes simplex virus type-1(HSV-1)?

In this study, antiviral effect of porphyrin was investigated. Cooper strain of Bovine Herpes Virus type 1(BoHV-1) and Kos strain of Herpes Simplex Virus type-1 (HSV-1) were used to determine the potential of porphyrins to inhibit infection in vitro (with morphological and cytopathological criteria). Apoptotic and necrotic changes were determined by using DAPI and propidium staining. The non-cytotoxic dose of porphyrin (NCD-p) was initially calculated as 312.50µg/mL on MDBK and Vero cells. The apoptotic cell (APC) count was found 10% with BoHV-1 while it was 5.3% with BoHV-1 treated with porphyrin on MDBK cells between 6th to 24th hours post infection (hpi). Necrotic cell (NEC) count was 51% with BoHV-1 and 37.8% BoHV-1 treated with porphyrin on MDBK cells at 24th hpi. On the other hand, the APC count was found 23% with HSV-1, while 22% with the HSV-1 treated with porphyrin on Vero cells between 6th to 24th hpi. NEC count was 49% with HSV-1 and 34% HSV-1 treated with porphyrin on MDBK cells at 24th hpi. The results show that BoHV-1 was inhibited by porphyrin resulting in decreased apoptotic and necrotic changes in MDBK cells. On the contrary, porphyrine was not effective in the inhibition of HSV-1 in terms of apoptosis but it caused necrotic changes in Vero cells.

Environmental Factors Influencing White-Tailed Deer (Odocoileus virginianus) Exposure to Livestock Pathogens in Wisconsin

White-tailed deer (Odocoileus virginianus) are commonly exposed to disease agents that affect livestock but environmental factors that predispose deer to exposure are unknown for many pathogens. We trapped deer during winter months on two study areas (Northern Forest and Eastern Farmland) in Wisconsin from 2010 to 2013. Deer were tested for exposure to six serovars of Leptospira interrogans (grippotyphosa, icterohaemorrhagiae, canicola, bratislava, pomona, and hardjo), bovine viral diarrhea virus (BVDV-1 and BVDV-2), infectious bovine rhinotracheitis virus (IBR), and parainfluenza 3 virus (PI3). We used logistic regression to model potential intrinsic (e.g., age, sex) and extrinsic (e.g., land type, study site, year, exposure to multiple pathogens) variables we considered biologically meaningful to exposure of deer to livestock pathogens. Deer sampled in 2010–2011 did not demonstrate exposure to BVDV, so we did not test for BVDV in subsequent years. Deer had evidence of exposure to PI3 (24.7%), IBR (7.9%), Leptospira interrogans serovar pomona (11.7%), L. i. bratislava (1.0%), L. i. grippotyphosa (2.5%) and L. i. hardjo (0.3%). Deer did not demonstrate exposure to L. interrogans serovars canicola and icterohaemorrhagiae. For PI3, we found that capture site and year influenced exposure. Fawns (n = 119) were not exposed to L. i. pomona, but land type was an important predictor of exposure to L. i. pomona for older deer. Our results serve as baseline exposure levels of Wisconsin white-tailed deer to livestock pathogens, and helped to identify important factors that explain deer exposure to livestock pathogens.

ICP27 protein encoded by bovine herpesvirus type 1 (bICP27) interferes with promoter activity of the bovine genes encoding beta interferon 1 (IFN-β1) and IFN-β3

Bovine herpes virus 1 (BHV-1) infection leads to upper respiratory tract infections, conjunctivitis, and the infection predisposes cattle to secondary bacterial infections. The infected cell protein 0 (bICP0) encoded by BHV-1 suppresses antiviral innate immune signaling by interfering with expression of interferon beta (IFN-β). In contrast to humans or mice, cattle contain three IFN-β genes that have distinct transcriptional promoters. We previously cloned and characterized all three bovine IFN-β promoters. In this study, we provide evidence that bICP27; a viral early protein that shuttles between the nucleus and cytoplasm inhibits transcriptional activity of two bovine IFN-β gene promoters (IFN-β1 and IFN-β3). Conversely, the BHV-1 infected cell protein 0 (bICP0) early promoter was not inhibited by bICP27. C-terminal mutants lacking the bICP27 zinc RING finger-like motif did not efficiently inhibit IFN-β3 promoter activity but inhibited IFN-β1 promoter activity as efficiently as wild type bICP27. An N-terminal mutant lacking the nuclear localization signal (NLS) and nucleolar localization signal (NoLS) was localized to the cytoplasm and this mutant had no effect on IFN-β promoter activity. In summary, these studies provided evidence that bICP27 inhibited IFN-β1 and IFN-β3 promoter activity in transiently transfected cells.

Eicosanoids mediate cellular immune response and phenoloxidase reaction to viral infection in adult Pimpla turionellae

Nodulation is the predominant insect cellular immune response to microbial infections. We posed the hypothesis that parasitoid insects in their adulthood express melanotic nodulation reactions to viral challenge and that eicosanoids mediate nodulation reactions and phenoloxidase (PO) activation in response to viral challenge. To test this idea, we injected Pimpla turionellae adults with indomethacin, a nonsteroidal anti-inflammatory drug, immediately prior to intrahemocoelic injection of Bovine herpes simplex virus-1 (BHSV-1). Treating newly emerged adults of P. turionellae with BHSV-1 induced nodulation reactions, and decreased PO activity at high viral doses. Relative to vehicle-treated controls, indomethacin-treated adults produced significantly reduced numbers of nodules following viral infection (down from approximately 21 nodules per adult to less than six nodules per adult). In addition to injection treatments, increasing dietary indomethacin dosages (from 0.01% to 0.1%) were associated with decreasing nodulation (by six-fold) and PO (by about three-fold) reactions to BHSV-1 injection. Wasp adults orally fed with the lowest dietary indomethacin concentration (0.001%) expressed significantly increased PO activity (1.45 unit/min/mg protein) while nodulation reaction was not affected in response to viral challenge compared to control adults. We infer from these findings that cyclooxygenase (COX) products, at least prostaglandins, mediate nodulation response and PO action to viral infection in adults of these highly specialized insects.

Respiratory disease caused by Mycoplasma bovis is enhanced by exposure to bovine herpes virus 1 (BHV-1) but not to bovine viral diarrhea virus (BVDV) type 2

To determine if previous exposure to bovine viral diarrhea virus (BVDV) and bovine herpes virus 1 (BHV-1) type 2 affects the onset of disease caused by Mycoplasma bovis, 6- to 8-month-old beef calves were exposed to BVDV or BHV-1 4 d prior to challenge with a suspension of 3 clinical isolates of M. bovis. Animals were observed for clinical signs of disease and at necropsy, percent abnormal lung tissue and presence of M. bovis were determined. Most animals pre-exposed to BHV-1 type 2 but not BVDV developed M. bovis-related respiratory illness. In a second trial, we determined that a 100-fold reduction in the number of M. bovis bacteria administered to BHV-1 exposed animals reduced the percentage of abnormal lung tissue but not the severity of clinical signs. We conclude that previous exposure to BHV-1 but not BVDV type 2 was a necessary cause of M. bovis-related respiratory diseases in our disease model.

Bovine herpesvirus type 1 (BHV-1) UL49.5 luminal domain residues 30 to 32 are critical for MHC-I down-regulation in virus-infected cells

Bovine herpesvirus type 1 (BHV-1) U_L49.5 inhibits transporter associated with antigen processing (TAP) and down-regulates cell-surface expression of major histocompatibility complex (MHC) class I molecules to promote immune evasion. We have constructed a BHV-1 U_L49.5 cytoplasmic tail (CT) null and several U_L49.5 luminal domain mutants in the backbone of wild-type BHV-1 or BHV-1 U_L49.5 CT- null viruses and determined their relative TAP mediated peptide transport inhibition and MHC-1 down-regulation properties compared with BHV-1 wt. Based on our results, the U_L49.5 luminal domain residues 30–32 and U_L49.5 CT residues, together, promote efficient TAP inhibition and MHC-I down-regulation functions. In vitro, BHV-1 U_L49.5 Δ30–32 CT-null virus growth property was similar to that of BHV-1 wt and like the wt U_L49.5, the mutant U_L49.5 was incorporated in the virion envelope and it formed a complex with gM in the infected cells.

A protein (ORF2) encoded by the latency-related gene of bovine herpesvirus 1 interacts with Notch1 and Notch3

Like other Alphaherpesvirinae subfamily members, bovine herpesvirus 1 (BHV-1) establishes latency in sensory neurons. The latency-related RNA (LR-RNA) is abundantly expressed in latently infected sensory neurons. An LR mutant virus with stop codons at the amino terminus of the first open reading frame (ORF) in the LR gene (ORF2) does not reactivate from latency, in part because it induces higher levels of apoptosis in infected neurons. ORF2 is not the only viral product expressed during latency, but it is important for the latency reactivation cycle because it inhibits apoptosis. In this study, a yeast 2-hybrid screen revealed that ORF2 interacted with two cellular transcription factors, Notch1 and Notch3. These interactions were confirmed in mouse neuroblastoma cells by confocal microscopy and in an in vitro "pulldown" assay. During reactivation from latency, Notch3 RNA levels in trigeminal ganglia were higher than those during latency, suggesting that Notch family members promote reactivation from latency or that reactivation promotes Notch expression. A plasmid expressing the Notch1 intercellular domain (ICD) stimulated productive infection and promoters that encode the viral transcription factor bICP0. The Notch3 ICD did not stimulate productive infection as efficiently as the Notch1 ICD and had no effect on bICP0 promoter activity. Plasmids expressing the Notch1 ICD or the Notch3 ICD trans-activated a late promoter encoding glycoprotein C. ORF2 reduced the trans-activation potential of Notch1 and Notch3, suggesting that ORF2 interfered with the trans-activation potential of Notch. These studies provide evidence that ORF2, in addition to inhibiting apoptosis, has the potential to promote establishment and maintenance of latency by sequestering cellular transcription factors.

Envelope protein Us9 is required for the anterograde transport of bovine herpesvirus type 1 from trigeminal ganglia to nose and eye upon reactivation

In this study, the authors examined the role of bovine herpesvirus type 1 (BHV-1) Us9 in the anterograde transport of the virus from trigeminal ganglia (TG) to nose and eye upon reactivation from latency. During primary infection, both BHV-1 Us9-deleted and BHV-1 Us9-rescued viruses replicated efficiently in the nasal and ocular epithelium. However, upon reactivation from latency, only the BHV-1 Us9-rescued virus could be isolated in the nasal and ocular shedding. By real-time polymerase chain reaction, comparable DNA copy numbers were detected in the TGs during latency and reactivation for both the viruses. Therefore, Us9 is essential for reactivation of the virus in the TG and anterograde axonal transport from TG to nose and eye.

Molecular and antigenic characterization of Brazilian bovine herpesvirus type 1 isolates recovered from the brain of cattle with neurological disease

Bovine herpesviruses type 1 and 5 (BoHV-1 and BoHV-5) are closely related yet differ markedly in their neuropathogenic potential. BoHV-1 isolates have been associated with respiratory and genital disease whereas BoHV-5 has been consistently isolated from neurological infection. We report the characterization of five Brazilian BoHV-1 isolates associated with neurological disease, an unusual finding. All five viruses were isolated from the brain of cattle presenting neurological disease, yet prominent histological encephalitis was not observed in three cases. The isolated viruses were identified as BoHV-1 by a glycoprotein C gene-based PCR able to differentiate BoHV-1 from BoHV-5. The identity of the isolates was confirmed by nucleotide sequencing of the amplicons and by restriction analysis of PCR products from another gC region. Monoclonal antibody binding and cross-neutralization assays with BoHV-1 and BoHV-5 antisera showed a typical BoHV-1 antigenic profile. Lastly, inoculation of rabbits with these five BoHV-1 isolates did not result in neurological disease, contrasting with fatal meningoencephalitis produced by BoHV-5. Thus, the involvement of BoHV-1 in neurological disease of cattle is more frequent than previously reported, indicating the need for fast and precise means of differentiating it from BoHV-5. Likewise, the potential role of BoHV-1 in neurological infection in cattle should be further investigated.

Microscopical Lesions and Antigen Distribution in Bovine Fetal Tissues and Placentae Following Experimental Infection with Bovine Herpesvirus-1 during Pregnancy

As part of a larger investigation, gross and histopathological examinations were carried out on six aborted and one non-viable calf born to heifers inoculated with bovine herpesvirus-1 (BHV-1) early in the third trimester of pregnancy. Antibody titres in sera collected from the dams confirmed seroconversion following inoculation. Samples of liver, lung, kidney, brain, heart, spleen, hepatic lymph node and placenta were subjected to histopathological examination. Immunohistochemistry for the detection of BHV-1 antigen was performed on liver and placenta from each calf, and on the full range of tissue from three of the six calves. Six dams aborted between 15 and 50 days post-inoculation (dpi) whilst one produced a live but non-viable calf at 51dpi. Consistent microscopical findings in tissues from the six aborted calves were multifocal coagulative necrosis in the liver and necrotic placentitis. The latter was characterized by villous necrosis, necrosis of vascular endothelium and infiltration of necrotic villi by mixed inflammatory cells. Other findings included multifocal necrosis in kidney, spleen and hepatic lymph node as well as haemorrhage in the lung and kidney. Immunohistochemistry confirmed the presence of BHV-1 antigen in association with these lesions and also revealed focal labelling of the endothelium of small blood vessels and surrounding glial processes in the brains of three calves. Virus isolation confirmed the presence of BHV-1 in the placentae from the six aborted calves and in pooled tissues of three of the fetuses. It is concluded that the pathogenesis of BHV-1 abortion involves infection of vascular endothelial cells in multiple tissues including placenta and brain. Furthermore, histopathological examination in suspected cases of BHV-1 abortion should include placenta as well as fetal viscera, and immunohistochemistry is a valuable tool for confirming a diagnosis of infection with the virus.

Bovine herpesvirus 1 infection and infectious bovine rhinotracheitis

Bovine herpesvirus 1 (BoHV-1), classified as an alphaherpesvirus, is a major pathogen of cattle. Primary infection is accompanied by various clinical manifestations such as infectious bovine rhinotracheitis, abortion, infectious pustular vulvovaginitis, and systemic infection in neonates. When animals survive, a life-long latent infection is established in nervous sensory ganglia. Several reactivation stimuli can lead to viral re-excretion, which is responsible for the maintenance of BoHV-1 within a cattle herd. This paper focuses on an updated pathogenesis based on a molecular characterization of BoHV-1 and the description of the virus cycle. Special emphasis is accorded to the impact of the latency and reactivation cycle on the epidemiology and the control of BoHV-1. Several European countries have initiated BoHV-1 eradication schemes because of the significant losses incurred by disease and trading restrictions. The vaccines used against BoHV-1 are described in this context where the differentiation of infected from vaccinated animals is of critical importance to achieve BoHV-1 eradication.

Quantification of the contact structure in a feral cattle population and its hypothetical effect on the transmission of bovine herpesvirus 1

The organisation of animal populations in social groupings may play a crucial role in the transmission of any infectious disease that requires close contact. The objective of this study was to quantify the contact structure of part of the Heck cattle population in a Dutch nature reserve and its hypothetical effect on the transmission of bovine herpesvirus 1 (BHV1). The contact structure was quantified by observing the number of different animals with whom contact was made (i.e. the number of contactees) within a fixed time period. Two types of behaviour sampling methods, namely focal sampling and scan sampling were used to observe the contact structure. In this study only those contacts between individuals were observed that were assumed to be a proxy measure of an at-risk event for BHV1-infection. Two reproduction ratios (R), i.e. the average number of new cases caused by a typical infected individual, were estimated, one for the observed contact structure and another for a random mixing contact structure. The two reproduction ratios were then compared to study the hypothetical effect on BHV1 transmission. The overall number of contactees was highest during summer and lowest during winter-spring. The contact structure of the homogeneous population did differ significantly from a random mixing contact structure, resulting in that the variation in the number of contactees was higher than under random mixing. Bulls, young bulls and cows had the highest number of contactees during, respectively, summer, autumn and winter-spring. From the analysis of the contingency tables it was clear that contacts between animal types did not occur at random during summer and autumn. For example, during summer more contacts than expected occurred between bulls and cows. This heterogeneity at animal type level was taken into account in the calculation for R, which resulted for the observed contact structure in higher estimates for R than for the homogeneous population. When looking at heterogeneity at individual level it was found that during summer almost all individuals were observed together direct or indirect in the same group except for certain bull groups. During autumn and winter-spring almost all individuals were seen together in the same group when considering a long contact period of 14 days but the groups were fallen apart in smaller groups and solitary individuals for a short contact period of 5 days. It could be concluded that based on the observed contact structure transmission would be favoured most during summer.

Intraspecific bovine herpesvirus 1 recombinants carrying glycoprotein E deletion as a vaccine marker are virulent in cattle

Vaccines used in control programmes of Bovine herpesvirus 1 (BoHV-1) utilize highly attenuated BoHV-1 strains marked by a deletion of the glycoprotein E (gE) gene. Since BoHV-1 recombinants are obtained at high frequency in experimentally coinfected cattle, the consequences of recombination on the virulence of gE-negative BoHV-1 were investigated. Thus, gE-negative BoHV-1 recombinants were generated in vitro from several virulent BoHV-1 and one mutant BoHV-1 deleted in the gC and gE genes. Four gE-negative recombinants were tested in the natural host. All the recombinants were more virulent than the gE-negative BoHV-1 vaccine and the gC- and gE-negative parental BoHV-1. The gE-negative recombinant isolated from a BoHV-1 field strain induced the highest severe clinical score. Latency and reactivation studies showed that three of the recombinants were reexcreted. Recombination can therefore restore virulence of gE-negative BoHV-1 by introducing the gE deletion into a different virulence background.

Bovine herpesvirus 1 immediate-early protein (bICP0) interacts with the histone acetyltransferase p300, which stimulates productive infection and gC promoter activity

The immediate-early protein, bICP0, ofBovine herpesvirus 1(BHV-1) transactivates viral promoters and stimulates productive infection. bICP0 is expressed constitutively during productive infection, as its gene contains an immediate-early and an early promoter. Like other ICP0 homologues encoded by members of the subfamilyAlphaherpesvirinae, bICP0 contains a zinc RING finger located near its N terminus. Mutations that disrupt the bICP0 zinc RING finger impair its ability to activate transcription, stimulate productive infection, inhibit interferon-dependent transcription in certain cell types and regulate subnuclear localization. bICP0 also interacts with a cellular chromatin-remodelling enzyme, histone deacetylase 1 (HDAC1), and can relieve HDAC1-mediated transcriptional repression, suggesting that bICP0 inhibits silencing of the viral genome. In this study, it was shown that bICP0 interacted with the histone acetyltransferase p300 during productive infection and in transiently transfected cells. In addition, p300 enhanced BHV-1 productive infection and transactivated a late viral promoter (gC). In contrast, a CH3-domain deletion mutant of p300, which is a dominant-negative mutant, did not activate the gC promoter. bICP0 and p300 cooperated to activate the gC promoter, suggesting that there is a synergistic effect on promoter activation. As p300 can activate certain antiviral signalling pathways (for example, interferon), it was hypothesized that interactions between p300 and bICP0 may dampen the antiviral response following infection.

The Us9 gene of bovine herpesvirus 1 (BHV-1) effectively complements a Us9-null strain of BHV-5 for anterograde transport, neurovirulence, and neuroinvasiveness in a rabbit model

The alphaherpesvirus envelope protein Us9 is a type II viral membrane protein that is required for anterograde spread of bovine herpesvirus 5 (BHV-5) infection from the olfactory receptor neurons to the brain. In a rabbit seizure model, Us9-deleted BHV-5 failed to invade the central nervous system (CNS) following intranasal infection. However, when injected directly into the olfactory bulb, retrograde-spread infection from the olfactory bulb (OB) to the piriform cortex and other areas connected to the OB was not affected. In contrast to BHV-5, wild-type BHV-1 failed to invade the CNS following intranasal infection. In this study, we show that mature BHV-1 Us9 is a 30- to 32-kDa protein, whereas mature BHV-5 Us9 is an 18- to 20-kDa protein. In vitro, BHV-1 Us9 is expressed at 3 h postinfection (hpi), whereas BHV-5 Us9 is expressed at 6 hpi. Despite these differences, BHV-1 Us9 not only complemented for BHV-5 Us9 and rescued the anterograde-spread defect of the BHV-5 Us9-deleted virus but conferred increased neurovirulence and neuroinvasiveness in our rabbit seizure model. Rabbits infected with BHV-5 expressing BHV-1 Us9 showed severe neurological signs at 5 days postinfection, which was 1 to 2 days earlier than BHV-5 wild-type or Us9-reverted BHV-5 virus. The data underscore the importance of both Us9 genes for virion anterograde transport and neuroinvasiveness. However, Us9 is not the determinant of the differential neuropathogenesis of BHV-1 and BHV-5.

Ruminant alphaherpesviruses related to bovine herpesvirus 1

Herpesviruses have mainly co-evolved with their hosts for millions of years. Consequently, different related host species may have been infected by various genetically related herpesviruses. Illustrating this concept, several ruminant alphaherpesviruses have been shown to form a cluster of viruses closely related to bovine herpesvirus 1 (BoHV-1): namely bovine herpesvirus 5, bubaline herpesvirus 1, caprine herpesvirus 1, cervid herpesviruses 1 and 2 and elk herpesvirus 1. These viruses share common antigenic properties and the serological relationships between them can be considered as a threat to BoHV-1 eradication programmes. BoHV-1 is a herpesvirus responsible for infectious bovine rhinotracheitis, which is a disease of major economic concern. In this article, the genetic properties of these ruminant alphaherpesviruses are reviewed on a comparative basis and the issue of interspecific recombination is assessed. The pathogenesis of these infections is described with emphasis on the host range and crossing of the host species barrier. Indeed, the non bovine ruminant species susceptible to these ruminant alphaherpesviruses may be potential BoHV-1 reservoirs. The differential diagnosis of these related infections is also discussed. In addition, available epidemiological data are used to assess the potential of cross-infection in ruminant populations. A better knowledge of these ruminant alphaherpesvirus infections is essential to successfully control infectious bovine rhinotracheitis.

Recombination in the alphaherpesvirus bovine herpesvirus 1

Herpesviruses are DNA viruses characterized by a low rate of nucleotide substitution. Therefore, other mechanisms must be involved to their evolution, like recombination that can be seen as an essential evolutionary driving force of these viruses. Recombination contributes to the long-term evolution of alphaherpesviruses. It acts also to continuously create new alphaherpesvirus strains. We have used bovine herpesvirus 1 to investigate recombination both within DNA concatemers in infected cells and in vitro and in vivo at the end of the lytic cycle. The following results have been obtained: (i) intramolecular recombination occurs at the level of concatemers and gives rise to genomic segment inversions; (ii) intraspecific recombination occurs frequently both in vitro and in vivo; (iii) interspecific recombination is possible and requires two highly genetically related viruses; (iv) only simultaneous or closely separated infections lead to the production of recombinant viruses; (v) recombination between wild-type and glycoprotein defective vaccine virus can produce a glycoprotein defective virus keeping part of the virulence of parental wild-type virus. 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.

Functional analysis of bovine herpesvirus 1 (BHV-1) genes expressed during latency

Bovine herpes virus 1 (BHV-1) establishes latency in sensory neurons of trigeminal ganglia (TG), and germinal centers of pharyngeal tonsil. Periodically BHV-1 reactivates from latency, virus is shed, and consequently virus transmission occurs. Two transcripts, the latency related (LR) RNA and ORF-E, are abundantly expressed in TG of latently infected cattle. A LR mutant strain of BHV-1 was constructed that contains stop codons near the beginning of the LR-RNA. The LR mutant virus does not express two proteins encoded by the LR gene, or reactivate from latency suggesting that LR protein expression regulates the latency-reactivation cycle. Higher levels of apoptosis occur in TG of calves infected with the LR mutant versus wild type BHV-1 indicating that the anti-apoptotic properties of the LR gene regulate the latency-reactivation cycle. The LR gene also inhibits bICP0 expression and mammalian cell growth, but these functions do not require LR protein expression. In contrast, the ability of the LR gene to inhibit apoptosis appears to require LR protein expression. A small open reading frame (ORF-E) that is located within the LR promoter is expressed in the nucleus of neuroblastoma cells. We predict that the LR gene and ORF-E regulate the BHV-1 latency-reactivation cycle.

Quantification of the transmission of bovine herpesvirus 1 among red deer (Cervus elaphus) under experimental conditions

Bovine herpesvirus 1 (BHV1) is endemically present in a cattle population that lives in a nature reserve in the Netherlands. Red deer (Cervus elaphus), living in the same nature reserve, can come into contact with the BHV1-infected cattle and could then become infected with BHV1. For the eradication of BHV1 in cattle, it is, therefore, important to know whether red deer alone can play a role in the transmission of BHV1. For that reason, we quantified the transmission of BHV1 among farmed red deer under experimental conditions. Two groups of ten animals were formed. In each group, five of these animals were inoculated with BHV1 and the other five served as contact animals. Three inoculated animals in each transmission experiment became infected and none of the contact animals became infected. The one-sided 95% confidence interval for R [0.0-0.94] showed that limited transmission might occur among red deer. Based on these results, we would expect only minor outbreaks of BHV1 to occur in red deer populations. We concluded that BHV1 will probably not survive longer than a few decades (several times the mean deer lifetime) in red deer populations. Consequently, it is not necessary for the eradication of BHV1 in cattle to eradicate BHV1 in red deer populations as well.

Characterization of the nuclear localization and nuclear export signals of bovine herpesvirus 1 VP22

The bovine herpesvirus 1 (BHV-1) tegument protein VP22 is predominantly localized in the nucleus after viral infection. To analyze subcellular localization in the absence of other viral proteins, a plasmid expressing BHV-1 VP22 fused to enhanced yellow fluorescent protein (EYFP) was constructed. The transient expression of VP22 fused to EYFP in COS-7 cells confirmed the predominant nuclear localization of VP22. Analysis of the amino acid sequence of VP22 revealed that it does not have a classical nuclear localization signal (NLS). However, by constructing a series of deletion derivatives, we mapped the nuclear targeting domain of BHV-1 VP22 to amino acids (aa) 121 to 139. Furthermore, a 4-aa motif, 130PRPR133, was able to direct EYFP and an EYFP dimer (dEYFP) or trimer (tEYFP) predominantly into the nucleus, whereas a deletion or mutation of this arginine-rich motif abrogated the nuclear localization property of VP22. Thus, 130PRPR133 is a functional nonclassical NLS. Since we observed that the C-terminal 68 aa of VP22 mediated the cytoplasmic localization of EYFP, an analysis was performed on these C-terminal amino acid sequences, and a leucine-rich motif, 204LDRMLKSAAIRIL216, was detected. Replacement of the leucines in this putative nuclear export signal (NES) with neutral amino acids resulted in an exclusive nuclear localization of VP22. Furthermore, this motif was able to localize EYFP and dEYFP in the cytoplasm, and the nuclear export function of this NES could be blocked by leptomycin B. This demonstrates that this leucine-rich motif is a functional NES. These data represent the first identification of a functional NLS and NES in a herpesvirus VP22 homologue.

Analysis of a bovine herpesvirus 1 recombinant virus that does not express the bICP0 protein

Bovine herpesvirus 1 (BHV-1) infected-cell protein 0 (bICP0) stimulates productive infection by activating viral gene expression. In this study, an attempt was made to construct a recombinant virus with point mutations in the C3HC4zinc RING finger of bICP0, as this domain is necessary for activating viral transcription and productive infection. A virus was identified in bovine cells that induced small clusters of infected cells resembling a small plaque. Instead of the expected mutations within the zinc RING finger, this virus contained a point mutation within the initiating ATG of bICP0, a point mutation two bases downstream from the ATG mutation and deletion of flanking plasmid sequences used for homologous recombination. The bICP0 mutant was rescued with wild-type (wt) bICP0 sequences and the bICP0-rescued virus produced wt plaques. The bICP0-rescued virus and wt BHV-1, but not the mutant, expressed the bICP0 protein during productive infection of bovine cells, suggesting that the mutant virus was a null mutant. Consequently, the mutant was designated the bICP0 null mutant. Infection of bovine cells with the bICP0 null mutant resulted in at least 100-fold lower virus titres, indicating that bICP0 protein expression is important, but not required, for virus production. When bovine cells infected with the bICP0 null mutant virus were subcultured, the cells continued to divide, but viral DNA could be detected after more than 35 passages, suggesting that the bICP0 null mutant induced a persistent-like infection in bovine cells and that it may be useful for generating additional bICP0 mutants.

The latency-related gene encoded by bovine herpesvirus 1 can suppress caspase 3 and caspase 9 cleavage during productive infection

When the bovine herpesvirus 1 (BHV-1) latency-related (LR) gene is inserted into the latency-associated transcript (LAT) locus of a herpes simplex virus type 1 (HSV-1) LAT deletion mutant, high levels of spontaneous reactivation from latency and enhanced pathogenesis occur. The LR gene, but not LAT, inhibits caspase 3 cleavage during productive infection. Plasmids containing LAT or the LR gene inhibit caspase 3 activation in transiently transfected cells, suggesting productive infection blocks certain antiapoptotic properties of LAT. These studies demonstrate a correlation between the enhanced pathogenic potential of CJLAT and the LR gene inhibiting caspase 3 cleavage during productive infection.

A mutation in the latency-related gene of bovine herpesvirus 1 inhibits protein expression from open reading frame 2 and an adjacent reading frame during productive infection

The latency-related (LR) gene of bovine herpesvirus 1 (BHV-1) is abundantly expressed during latency. A mutant BHV-1 strain that contains three stop codons at the 5' terminus of the LR gene (LR mutant) does not reactivate from latency. This study demonstrates that the LR mutant does not express open reading frame 2 or an adjacent reading frame that lacks an initiating ATG (reading frame C). Since the LR mutant and wild-type BHV-1 express similar levels of LR RNA, we conclude that LR protein expression plays an important role in regulating the latency reactivation cycle in cattle.

Both viral and host factors contribute to neurovirulence of bovine herpesviruses 1 and 5 in interferon receptor-deficient mice

Herpes simplex virus (HSV) type 1 and bovine herpesviruses 1 and 5 (BHV-1 and BHV-5) can use the same cellular receptor for entry, but only HSV is known to cause disease in mice. We hypothesized that components of either the innate or the adaptive immune system, or a combination of both, were responsible for curbing replication of BHVs in mice. Therefore, wild-type mice as well as mice with various combined genetic deficiencies in the alpha/beta interferon receptor or gamma interferon receptor and in the ability to produce mature B and T lymphocytes (RAG-2 deletion) were infected with BHV-1 and BHV-5 and monitored clinically, serologically, histopathologically, and virologically. A functional immune system protected the mice from disease and death due to BHV infection, and the immune response was Th1 like. BHV-5 was transported to the central nervous system by the axonal pathway, whereas viremia was required for this outcome with BHV-1. The alpha/beta interferon system was able to obstruct quantitative spread of the viruses in the infected organism. The gamma interferon system had a protective effect against BHV-1, even in mice with the RAG-2 deletion. In contrast, the same mice succumbed to neurological disease and death upon infection with BHV-5. Productively infected neurons were detected only in BHV-5-infected mice with an intact gamma interferon system. We conclude that the alpha/beta interferon system had a protective effect, while an intact gamma interferon system was required for efficient replication of BHV-5 in mouse neurons and for the development of neurological disease.

Resistance to pseudorabies virus infection in transformed cell lines expressing a soluble form of porcine herpesvirus entry mediator C

Porcine herpesvirus entry mediator C (HveC) is an alphaherpesvirus receptor that binds to virion glycoprotein D (gD). Porcine HveC mediates entry of pseudorabies virus (PRV), herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) and bovine herpesvirus type 1 (BHV-1). In order to assess the antiviral potential of a soluble form of porcine HveC, Vero cells were transformed with the chimeric gene expressing a fusion protein (PHveCIg) consisting of an extracellular domain of porcine HveC and the Fc portion of human IgG1. The transformed cell lines expressing PHveCIg showed marked resistance to PRV infection. Resistance to infection by other alphaherpesviruses (HSV-1 and BHV-1) was also observed in the transformed cell line. The present results demonstrate that a soluble form of porcine HveC is able to exert a significant antiviral effect against pseudorabies virus and other alphaherpesvirus infection in vitro.

Bovine herpesvirus-1 associated with single, trypsin-treated embryos was not infective for uterine tubal cells

It has been reported that bovine herpesvirus-1 (BHV-1) remains associated with in vitro-produced (IVP) bovine embryos after exposure to the virus and either washing or trypsin treatment. However, it is not known if the quantity of virus associated with an exposed IVP embryo is likely to infect a recipient cow after transfer. The specific objective of this study was to determine if IVP embryos that were exposed to BHV-1 would infect uterine tubal cells (UTC) in a co-culture system. In vitro-produced Day 7 embryos were exposed to BHV-1 and then washed or trypsin treated according to the IETS guidelines. These embryos were then co-cultured individually or in groups with UTC in microdrops of tissue culture medium 199 (TCM 199) supplemented with 10% equine serum. Following co-culture for 48 h, virus isolation was attempted on the embryos and the UTC from each drop. Virus was detected in washed individual embryos, groups of washed embryos, groups of trypsin-treated embryos and the UTC co-cultured with each of these treatments. However, BHV-1 was not detected in the individual, trypsin-treated embryos or the UTC co-cultured with them. It is concluded that trypsin treatment might effectively prevent infection of recipients if individual, Day 7, exposed embryos were transferred into the uterus.

Bovine herpesvirus 1 interferes with TAP-dependent peptide transport and intracellular trafficking of MHC class I molecules in human cells

Bovine herpesvirus 1 (BoHV-1), the cause of infectious bovine rhinotracheitis and infectious pustular vulvovaginitis in cattle, establishes a lifelong infection, despite the presence of antiviral immunity in the host. BoHV-1 has been shown to elude the host immune system, but the viral gene products responsible for this interference have not yet been identified. Studies aiming at the identification of BoHV-1-encoded immune evasion genes have been hampered by the lack of bovine-specific immunological reagents. Some of the immune evasion molecules identified for other herpesviruses are host species specific; others can act across the species barrier. In this study, experiments were performed to investigate whether BoHV-1 can infect human cells and interfere with antigen processing and presentation in these cells. A human melanoma cell line, Mel JuSo, appeared to be permissive for BoHV-1 infection. BoHV-1 induced expression of major viral glycoproteins at the surface of these cells and produced progeny virus up to 10(5) plaque forming units per ml. BoHV-1 infection resulted in impaired intracellular transport of human MHC class I molecules and inhibition of human TAP. These data indicate that the BoHV-1-encoded molecule(s) that block antigen presentation in bovine cells are able to interact with homologous components of the human MHC class I presentation pathway. The fact that immune evasion by BoHV-1 can be studied in human cells will facilitate the identification of the BoHV-1 gene products involved in this process. Moreover, the data presented here suggest that the BoHV-1 encoded inhibitors of antigen presentation represent potential immune suppressive agents for use in humans.

Infection of cattle with a bovine herpesvirus 1 strain that contains a mutation in the latency-related gene leads to increased apoptosis in trigeminal ganglia during the transition from acute infection to latency

Bovine herpesvirus 1 (BHV-1) is an important pathogen of cattle and infection is usually initiated via the ocular or nasal cavity. After acute infection, the primary site for BHV-1 latency is sensory neurons in the trigeminal ganglia (TG). Reactivation from latency occurs sporadically, resulting in virus shedding and transmission to uninfected cattle. The only abundant viral transcript expressed during latency is the latency-related (LR) RNA. An LR mutant was constructed by inserting three stop codons near the beginning of the LR RNA. This mutant grows to wild-type (wt) efficiency in bovine kidney cells and in the nasal cavity of acutely infected calves. However, shedding of infectious virus from the eye and TG was dramatically reduced in calves infected with the LR mutant. Calves latently infected with the LR mutant do not reactivate after dexamethasone treatment. In contrast, all calves latently infected with wt BHV-1 or the LR rescued mutant reactivate from latency after dexamethasone treatment. In the present study, we compared the frequency of apoptosis in calves infected with the LR mutant to calves infected with wt BHV-1 because LR gene products inhibit apoptosis in transiently transfected cells. A sensitive TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling) assay and an antibody that detects cleaved caspase-3 were used to identify apoptotic cells in TG. Both assays demonstrated that calves infected with the LR mutant for 14 days had higher levels of apoptosis in TG compared to calves infected with wt BHV-1 or to mock-infected calves. Viral gene expression, except for the LR gene, is extinguished by 14 days after infection, and thus this time frame is operationally defined as the establishment of latency. Real-time PCR analysis indicated that lower levels of viral DNA were present in the TG of calves infected with the LR mutant throughout acute infection. Taken together, these results suggest that the antiapoptotic properties of the LR gene play an important role during the establishment of latency.

Stimulation of bovine herpesvirus-1 productive infection by the adenovirus E1A gene and a cell cycle regulatory gene, E2F-4

Identifying cellular genes that promote bovine herpesvirus-1 (BHV-1) productive infection is important, as BHV-1 is a significant bovine pathogen. Previous studies demonstrated that BHV-1 DNA is not very infectious unless cotransfected with a plasmid expressing bICP0, a viral protein that stimulates expression of all classes of viral promoters. Based on these and other studies, we hypothesize that the ability of bICP0 to interact with and modify the function of cellular proteins stimulates virus transcription. If this prediction is correct, cellular proteins that activate virus transcription could, in part, substitute for bICP0 functions. The adenovirus E1A gene and bICP0 encode proteins that are potent activators of viral gene expression, they do not specifically bind DNA and both proteins interact with chromatin-remodelling enzymes. Because of these functional similarities, E1A was tested initially to see if it could stimulate BHV-1 productive infection. E1A consistently stimulates BHV-1 productive infection, but not as efficiently as bICP0. The ability of E1A to bind Rb family members plays a role in stimulating productive infection, suggesting that E2F family members activate productive infection. E2F-4, but not E2F-1, E2F-2 or E2F-5, activates productive infection with similar efficiency as E1A. Next, E2F family members were examined for their ability to activate the BHV-1 immediate-early (IE) transcription unit 1 (IEtu1) promoter, as it regulates IE expression of bICP0 and bICP4. E2F-1 and E2F-2 strongly activate the IEtu1 promoter, but not a BHV-1 IEtu2 promoter or a herpes simplex virus type 1 ICP0 promoter construct. These studies suggest that E2F family members can stimulate BHV-1 productive infection.

Effects of virion host shut-off activity of bovine herpesvirus 1 on MHC class I expression

Previously, we have shown that bovine herpesvirus 1 (BHV-1) down-regulates the expression of major histocompatibility complex class I molecules by interfering with transport of peptides by the transporter associated with antigen processing (TAP). Further studies revealed that BHV-1 down-regulates the expression of mRNA for class I molecules and other cellular proteins. To further elucidate the mechanisms of down-regulation of class I molecules, a virion host shut-off (vhs) deletion mutant was generated. The mutant, like the wildtype (wt) virus, interfered with transport of peptides by the TAP, and down-regulated cell surface expression of class I molecules. However, unlike the wt virus, the mutant did not impair the synthesis of class I molecules. These results indicate that down-regulation of class I molecules by BHV-1 is mediated by vhs activity of the virus, as well as mechanisms specifically directed at the class I pathway. Absence of vhs activity should result in decreased pathogenicity and enhanced immunogenicity of BHV-1 vhs deletion mutant, making it a better vaccine candidate.

Rapid and efficient construction of recombinant bovine herpesvirus 1 genomes

Bovine herpesvirus 1 (BoHV-1) is an important pathogen of cattle. Recombinant bovine herpesvirus 1 viruses (rBoHV) have been studied extensively as potential vaccines for BoHV-1 associated diseases. A method is described which advances protocols used currently for constructing rBoHV by producing recombinant viruses free of parent virus. The method, restriction endonuclease mediated recombination (REMR), utilises a unique NsiI site in the BoHV-1 genome. Following NsiI digestion the two genomic fragments are prevented from recombining by dephosphorylation. However, when the genomic fragments are co-transfected into a susceptible cell-line with a third DNA fragment (DNA bridge), which encodes DNA homologous to the digested viral termini, the three DNA molecules are able to undergo homologous recombination and produce infectious BoHV-1. During the recombination process foreign DNA within the DNA bridge is incorporated into the BoHV-1 genome, producing rBoHV. In the absence of the DNA bridge virus reconstitution does not occur thus eliminating contamination by the nonrecombinant parent virus. As REMR used an NsiI site occurring naturally in the BoHV-1 genome it can be used for the insertion of foreign DNA into the genome without any prior modifications. REMR could also be applied to any herpesvirus for which the genome sequence is known.

Herpes simplex virus type 1 and bovine herpesvirus 1 latency

Primary infection by herpes simplex virus type 1 (HSV-1) can cause clinical symptoms in the peripheral and central nervous system, upper respiratory tract, and gastrointestinal tract. Recurrent ocular shedding leads to corneal scarring that can progress to vision loss. Consequently, HSV-1 is the leading cause of corneal blindness due to an infectious agent. Bovine herpesvirus 1 (BHV-1) has similar biological properties to HSV-1 and is a significant health concern to the cattle industry. Latency of BHV-1 and HSV-1 is established in sensory neurons of trigeminal ganglia, but latency can be interrupted periodically, leading to reactivation from latency and spread of infectious virus. The ability of HSV-1 and BHV-1 to reactivate from latency leads to virus transmission and can lead to recurrent disease in individuals latently infected with HSV-1. During latency, the only abundant HSV-1 RNA expressed is the latency-associated transcript (LAT). In latently infected cattle, the latency-related (LR) RNA is the only abundant transcript that is expressed. LAT and LR RNA are antisense to ICP0 or bICP0, viral genes that are crucial for productive infection, suggesting that LAT and LR RNA interfere with productive infection by inhibiting ICP0 or bICP0 expression. Numerous studies have concluded that LAT expression is important for the latency-reactivation cycle in animal models. The LR gene has recently been demonstrated to be required for the latency-reactivation cycle in cattle. Several recent studies have demonstrated that LAT and the LR gene inhibit apoptosis (programmed cell death) in trigeminal ganglia of infected animals and transiently transfected cells. The antiapoptotic properties of LAT map to the same sequences that are necessary for promoting reactivation from latency. This review summarizes our current knowledge of factors regulating the latency-reactivation cycle of HSV-1 and BHV-1.

The latency-related gene of bovine herpesvirus-1 can inhibit the ability of bICP0 to activate productive infection

Transfection of bovine cells with bovine herpesvirus-1 genomic DNA yields low levels of infectious virus. Cotransfection with the bICP0 gene enhances productive infection and virus yield because bICP0 can activate viral gene expression. Since the latency-related (LR) gene overlaps and is antisense to bICP0, the effects of LR gene products on productive infection were tested. The intact LR gene inhibited productive infection in a dose-dependent fashion but LR protein expression was not required. Further studies indicated that LR gene sequences near the 3' terminus of the LR RNA are necessary for inhibiting productive infection. When cotransfected with the bICP0 gene, the LR gene inhibited bICP0 RNA and protein expression in transiently transfected cells. Taken together, these results suggest that abundant LR RNA expression in sensory neurons is one factor that has the potential to inhibit productive infection and consequently promote the establishment and maintenance of latency.

Amino acid substitutions in the V domain of nectin-1 (HveC) that impair entry activity for herpes simplex virus types 1 and 2 but not for Pseudorabies virus or bovine herpesvirus 1

The entry of herpes simplex virus (HSV) into cells requires the interaction of viral glycoprotein D (gD) with a cellular gD receptor to trigger the fusion of viral and cellular membranes. Nectin-1, a member of the immunoglobulin superfamily, can serve as a gD receptor for HSV types 1 and 2 (HSV-1 and HSV-2, respectively) as well as for the animal herpesviruses porcine pseudorabies virus (PRV) and bovine herpesvirus 1 (BHV-1). The HSV-1 gD binding domain of nectin-1 is hypothesized to overlap amino acids 64 to 104 of the N-terminal variable domain-like immunoglobulin domain. Moreover, the HSV-1 and PRV gDs compete for binding to nectin-1. Here we report that two amino acids within this region, at positions 77 and 85, are critical for HSV-1 and HSV-2 entry but not for the entry of PRV or BHV-1. Replacement of either amino acid 77 or amino acid 85 reduced HSV-1 and HSV-2 gD binding but had a lesser effect on HSV entry activity, suggesting that weak interactions between gD and nectin-1 are sufficient to trigger the mechanism of HSV entry. Substitution of both amino acid 77 and amino acid 85 in nectin-1 significantly impaired entry activity for HSV-1 and HSV-2 and eliminated binding to soluble forms of HSV-1 and HSV-2 gDs but did not impair the entry of PRV and BHV-1. Thus, amino acids 77 and 85 of nectin-1 form part of the interface with HSV gD or influence the conformation of that interface. Moreover, the binding sites for HSV and PRV or BHV-1 gDs on nectin-1 may overlap but are not identical.

Construction and manipulation of an infectious clone of the bovine herpesvirus 1 genome maintained as a bacterial artificial chromosome

The complete genome of bovine herpesvirus 1 (BoHV-1) strain V155 has been cloned as a bacterial artificial chromosome (BAC). Following electroporation into Escherichia coli strain DH10B, the BoHV-1 BAC was stably propagated over multiple generations of its host. BAC DNA recovered from DH10B cells and transfected into bovine cells produced a cytopathic effect which was indistinguishable from that of the parent virus. Analysis of the replication kinetics of the viral progeny indicated that insertion of the BAC vector into the thymidine kinase gene did not affect viral replication. Specific manipulation of the BAC was demonstrated by deleting the gene encoding glycoprotein E by homologous recombination in DH10B cells facilitated by GET recombination. These studies illustrate that the propagation and manipulation of herpesviruses in bacterial systems will allow for rapid and accurate characterization of BoHV-1 genes. In turn, this will allow for the full utilization of BoHV-1 as a vaccine vector.

Bovine herpesvirus 1 glycoprotein G is necessary for maintaining cell-to-cell junctional adherence among infected cells

Glycoproteins gE and gG of bovine herpesvirus 1 (BHV-1) are involved in viral cell-to-cell transmission. We have compared the subcellular localizations of gE and gG and examined the cell-to-cell adherence of bovine kidney (MDBK) cells infected with BHV-1 mutants lacking gE or gG. In BHV-1-infected MDBK cells, gE was observed at cell junctions but did not localize at apical or basal plasma membranes. BHV-1 gG was primarily found in the cytoplasm and was also observed at boundaries among infected cells. During the infection with wild-type or gE-negative BHV-1, the filamentous actin and the adherent junctional proteins accumulated at the cell junctions. In contrast, cell junctions of MDBK cells infected with gG-negative BHV-1 were loosened, and the junctional proteins and BHV-1 gE were distributed in the cytoplasm. These data indicate that BHV-1 gG facilitates viral cell-to-cell spread by maintaining the cell-to-cell junctions among the infected cells.

Oral DNA vaccination in utero induces mucosal immunity and immune memory in the neonate

Infectious diseases are responsible for a significant number of deaths during the first weeks of life. Some of the salient pathogens include HSV, HIV, hepatitis B virus, group B streptococcus, Haemophilus sp., and Chlamydia sp. The vertical transmission of many of these pathogens significantly increases the risk of neonatal infection. We recently reported that oral DNA immunization in utero induced high serum Ab titers and cell-mediated immunity in fetal lambs. In this study, we demonstrate immune memory and mucosal immunity in newborn lambs following oral DNA immunization of the fetus. A single oral exposure in utero to plasmid DNA encoding a truncated form of glycoprotein D of bovine herpesvirus-1 induced detectable immune responses in 80% (12 of 15) of newborn lambs. There was no evidence for the induction of immune tolerance in nonresponding lambs. Responding lambs displayed both systemic and mucosal immune responses and reduced virus shedding following intranasal challenge. Furthermore, strong anamnestic responses were evident for at least 3 mo after birth. The efficacy of in utero oral DNA immunization was further demonstrated with the hepatitis B surface Ag, and protective serum Ab titers occurred in 75% of immunized lambs. Thus, the present investigation confirms that oral DNA immunization in utero can induce both mucosal and systemic immune responses in the neonate and that this immunity has the potential to prevent vertical disease transmission.

The bovine herpesvirus 1 immediate-early protein (bICP0) associates with histone deacetylase 1 to activate transcription

Infected-cell protein 0 encoded by bovine herpesvirus 1 (BHV-1) (bICP0) is necessary for efficient productive infection, in large part, because it activates all 3 classes of BHV-1 genes (U. V. Wirth, C. Fraefel, B. Vogt, C. Vlcek, V. Paces, and M. Schwyzer, J. Virol. 66:2763-2772, 1992). Although bICP0 is believed to be a functional homologue of herpes simplex virus type 1-encoded ICP0, the only well-conserved domain between the proteins is a zinc ring finger located near the amino terminus of both proteins. Our previous studies demonstrated that bICP0 is toxic to transfected cells but does not appear to directly induce apoptosis (Inman, M., Y. Zhang, V. Geiser, and C. Jones, J. Gen. Virol. 82:483-492, 2001). C-terminal sequences in the last 320 amino acids of bICP0 mediate subcellular localization. Mutagenesis of the zinc ring finger within bICP0 revealed that this domain was important for transcriptional activation. In this study, we demonstrate that bICP0 interacts with histone deacetylase 1 (HDAC1), which results in activation of a simple promoter containing four consensus Myc-Max binding sites. The interaction between bICP0 and HDAC1 correlated with inhibition of Mad-dependent transcriptional repression. In resting CV-1 cells, bICP0 relieved HDAC1-mediated transcriptional repression. The zinc ring finger was required for relieving HDAC1-induced repression but not for interacting with HDAC1. In fetal bovine lung cells but not in a human epithelial cell line, bICP0 expression correlated with reduced steady-state levels of HDAC1 in crude cytoplasmic extracts. We hypothesize that the ability of bICP0 to overcome HDAC1-induced repression plays a role in promoting productive infection in highly differentiated cell types.

[The preparation phosprenyl suppresses diarrhea and cattle infectious rhinotracheitis virus multiplication in sensitive cell cultures]

Fosprenil suppressed the multiplication of cattle diarrhea virus in calf coronary vessel cell culture. Added to the culture of infected cells in a dose of 200 mg, the drug decreased the virus titer 30-fold in comparison with infected control cultures. Antiviral activity of fosprenil towards infective rhinotracheitis virus multiplication was still higher: in a dose of 100 mg it decreased the virus titer in fetal calf lung culture 100-fold in comparison with the control. Moreover, the cytopathogenic effects of the viruses in infected cultures were 24-48 h delayed under the effect of fosprenil in comparison with infected control cultures. These results recommend fosprenil for the treatment of cattle viral diseases.

Comparative pathogenesis of acute and latent infections of calves with bovine herpesvirus types 1 and 5

This study was conducted to compare the pathogenesis of acute and latent infections with closely related bovine herpesvirus types 1 (BHV-1) and 5 (BHV-5) in their natural host. Two groups of eight calves were inoculated intranasally with BHV-1 or BHV-5. Although BHV-1 and BHV-5 similarly replicate in the nasal mucosa after inoculation, both viruses differ markedly in their ability to cause disease, BHV-5 being responsible of some fatal encephalitis while BHV-1 inducing rhinotracheitis. Virus isolation and immunohistochemistry demonstrated that BHV-5 replicates extensively in neurons of the central nervous system (CNS) and in respiratory cells of lungs, tracheal and nasal mucosae. Invasion of the CNS likely occurs through the trigeminal and olfactory pathways. Both groups developed cross-neutralising antibodies during this experiment suggesting partial clinical cross-protection afforded by the two infections. Three months after primary infection, experimental reactivation showed that BHV-5 was able to establish latency in the trigeminal ganglia but also the CNS of surviving calves. Moreover, laboratory findings suggested that BHV-5 could also persist in the tracheal and nasal mucosae. These results indicate that, after primary infection, BHV-1 and BHV-5 displayed similar biological features and consequently need to be considered together for the control of BHV-1 infection.

[The effect of a high dose bovine herpes virus 1 marker vaccine in pregnant heifers: virological, bacteriological, immunological, and pathological findings]

To determine a possible relationship between the compulsory vaccination against bovine herpesvirus 1 (BHV1) and cattle wasting disease, the effects of BHV1 vaccination on heifers were investigated. Twenty heifers in the third trimester of pregnancy were randomly allotted to a vaccine and a control group. The vaccine group was vaccinated twice with a 50-fold dose of BHV1 vaccine and the control group was inoculated with the diluent. The experiment was performed double blind. After vaccination, the cows were examined daily and condition scores were determined weekly. Blood, milk, and faeces samples were collected weekly for virological, bacteriological, and immunological investigation. The heifers were euthanized either 9 or 13 weeks after the first inoculation and pathological, virological, and bacteriological examination was performed. No differences were detected between the vaccine group and the control group. No concurrent infections were detected and there were no indications of immunosuppression after vaccination. No relationship between the BHV1 vaccination and wasting disease in cattle was detected.

A vhs-like activity of bovine herpesvirus-1

Bovine herpesvirus 1 (BHV-1) is a major pathogen of cattle, causing significant disease including immunosuppression in infected animals. In vitro, the surface expression of major histocompatibility complex (MHC) class I molecules, crucial for an appropriate anti-viral immune response of the host, is down-regulated by BHV-1 infection. Northern blot analyses revealed that the mRNAs for MHC class I and class II molecules were significantly down-regulated in BHV-1 infected cells, starting as early as 2 h after infection. Furthermore, mRNA expression of the two house keeping genes actin and glyceraldehyde-6-phosphate dehydrogenase (GAPDH) was also repressed after infection. This BHV-1 induced effect on cellular metabolism resembled the virion host shutoff (vhs) activity of herpes simplex virus (HSV). Similar to the HSV vhs activity, the putative BHV-1 vhs activity was not abrogated in cells infected in the presence of actinomycin D (ActD) which suggested that no viral gene expression is required for the vhs function and the putative vhs protein is associated with the virion. Sequence comparison indicated a BHV-1 open reading frame having a 60% similarity to the HSV vhs sequence. This putative BHV-1 open reading frame contained the four conserved regions of the alphaherpesvirus vhs protein. Since an HSV vhs-mutant exhibited less virulence and good immunogenicity, we suggest that a BHV-1 vhs- mutant may hold promising potential as a candidate vaccine.

Genomic and pathogenic studies on a glycoprotein E variant field isolate of bovine herpesvirus 1

Glycoprotein E-negative (gE-) laboratory strains of bovine herpesvirus 1 (BHV-1) were recently introduced as novel marker vaccines, allowing serological discrimination between vaccinated and naturally infected animals on the basis of lack or presence of antibodies against gE epitopes. The applicability pf this approach is based on the genetic stability of the gE. However, mutant field variants of BHV-1 with a variable response in anti-gE ELISA have been isolated. The molecular characterization of a gE variant field isolate (Salwa strain) is presented here. By comparing the gE nucleotide and amino acid sequences of the Salwa strain with those of the wild strain Jura, ten mutated bases were found in the gE strain of Salwa, six of which alter the amino acid sequence, leading to changes in five amino acids. Both strains caused respiratory disease in experimentally infected calves, but Salwa generated slightly milder signs. Both viruses were excreted in nasal and ocular discharges, and were reactivated by dexamethasone treatment. In conclusion, the rather close similarities observed in the gE gene structure and pathogenicity features of the gE mutant and of the wild strain of BHV-1 confirm the genetic stability of gE. The findings indicate that the Salwa isolate is virulent, but less virulent than wild strains. Our data support the use of gE-negative marker vaccines in eradication programmes.