Molecular basis of antigenic variation between the glycoproteins C of respiratory bovine herpesvirus 1 (BHV-1) and neurovirulent BHV-5

Synthetic antimicrobial peptides Bac-5, BMAP-28, and Syn-1 can inhibit bovine respiratory disease pathogens in vitro

Mass treatment with antibiotics at arrival has been the mainstay for bovine respiratory disease (BRD) control but there is an increase in antimicrobial-resistant bacteria being shed from treated cattle. BRD is a disease complex that results from the interaction of viruses or bacteria and susceptible animals with inappropriate immunity. With bacteria being the only feasibly treatable agent and the emergence of antimicrobial resistance, decreased efficacy of commonly used antibiotics could threaten livestock health. There is a need for new antimicrobial alternatives that could be used to control disease. Naturally occurring antimicrobial peptides (AMP) have been proposed to address this need. Here we tested the effect of bovine myeloid antimicrobial peptide-28 (BMAP-28), a synthetic BMAP-28 analog Syn-1, and bactenecin 5 (Bac-5) on Mannheimia haemolytica (Mh) using a quantitative culture method and the broth microdilution method to determine minimum inhibitory and bactericidal concentrations (MIC and MBC). We also tested the antiviral effect of these AMP against bovine herpes-1 (BHV-1) and bovine respiratory syncytial virus (BRSV) using the Reed and Muench method to calculate the viral titers after treatment. We demonstrated that BMAP-28 and Syn-1 can inhibit Mh growth and BMAP-28 can inhibit replication of BHV-1 and BRSV. Moreover, we showed that BMAP-28 and Bac-5 can be used together to inhibit Mh growth. When used alone, the MIC of BMAP-28 and Bac-5 was 64 and 128 μg/mL respectively, but when applied together, their MIC ranged from 0.25-16 for BMAP-28 and 8-64 μg/mL for Bac-5, resulting in a decrease in concentration of up to 256 and 16-fold, respectively. The synergistic interaction between those peptides resulted in concentrations that could be well tolerated by cells. Our results demonstrate that bovine cathelicidins could be used as alternatives to antimicrobials against BRD pathogens. These findings introduce a path to discovering new antimicrobials and determining how these peptides could be tailored to improve cattle health.

Preliminary molecular study for DIVA trial of antigenically characterized circulating bovine herpesvirus subtype 1.1 in Egypt

Using marker vaccines to control bovine alphaherpesvirus-1 (BoHV-1) is a novel strategy for differentiation between infected and vaccinated animals (DIVA). In this study, multiplex real-time PCR targeting gD and gE genes was applied for BoHV-1 screening on 60 clinical samples from cattle with a history of vaccination, in some cases by US2-deleted marker vaccines, that were suffering from severe respiratory symptoms. Conventional PCR targeting the gC and US2 flanking region was done for molecular characterization and identification of the US2-deleted vaccine strain. Six samples were positive for BoHV-1 by both RT-PCR and conventional PCR. Surprisingly, a conventional PCR DIVA trial based on the US2 gene revealed that only one sample that exhibited the US2 gene was a wild virus, while others that did not exhibit the US2 gene were vaccine viruses. Phylogenetic characterization classifies the samples as BoHV-1.1. This finding reveals the circulation of vaccine virus in field-diseased animals, which threatens the eradication program.

An indirect ELISA to detect antibodies to the gC of bovine alphaherpesvirus 1 (BoAHV1) displaying no crossreactivity with antibodies induced by bovine alphaherpesvirus 5 (BoAHV5)

Seroprevalence of bovine alphaherpesvirus type 1 (BoAHV1) infections may be contaminated by crossreactive antibodies to bovine alphaherpesvirus type 5 (BoAHV5). To avoid such crossreactivity, an indirect enzyme-linked immunosorbent assay prepared with a recombinant glycoprotein C (gC) antigen (ELISA-gC1) was developed, aiming the detection of antibodies to BoAHV1, with no crossreactivity with BoAHV5 antibodies. The antigen for the ELISA-gC1 was the product of the expression of 219 bp from the N-terminal portion of the BoAHV1 gC gene, which bears low homology between the two virus types. The test was validated on 131 bovine serum samples, including 26 sera from BoAHV1-experimentally immunized, 38 sera from BoAHV5-experimentally infected or immunized calves, and 67 sera from calves seronegative for both BoAHV1 and BoAHV5, as determined by serum neutralization (SN). When compared to SN for BoAHV1, the ELISA-gC1 presented 100% sensitivity, 95.5 % specificity, 100 % negative predictive value, 89.6 % positive predictive value, 98.8 % precision, and a kappa correlation coefficient (κ) 0.95. None of the 38 BoAHV5-seropositive calves was detected by the ELISA-gC1. The ELISA-gC1 proved highly effective for the identification of BoAHV1-positive sera, with no crossreactivity with anti-BoAHV5 antibodies, thus able to distinguish serological responses from BoAHV1- and BoAHV5-seropositive cattle. Its capacity to detect BoAHV1-specific antibodies should allow the determination of the actual BoAHV1 prevalence in herds, which cannot be serologically determined in countries where BoAHV5 is also prevalent due to antibody crossreactivity. Apart from recognizing exclusively BoAHV1-infected cattle, the ELISA-gC1 may also be used in support of BoAHV5 epidemiological studies by allowing the exclusion of BoAHV1-seropositive animals.

The full-genome characterization and phylogenetic analysis of bovine herpesvirus type 1.2 isolated in China

Bovine herpesvirus type 1 (BHV-1) causes bovine respiratory disease that poses a significant threat to the cattle industry. The prevalence of BHV-1 has recently increased in China. However, the lack of information about the prevalent isolates limits the control of the disease. In this study, a novel strain of BHV-1 was isolated from nasal swabs of Holstein cows in 2020 in China, designated as BHV SHJS. The genome of BHV strain SHJS is 135, 102 bp in length and highly similar to strain SP1777 (KM258883.1) with an identity of 99.64%. Mutations, insertions, or deletions mainly occur in UL27, UL44, and US8, etc., relative to the different genomic coordinates. Phylogenetic tree of UL44 (gC) showed that BHV strain SHJS belongs to BHV-1.2b cluster. The result showed that the strain had a different evolutionary origin from those prevalent in China. This study will enrich our knowledge regarding BHV outbreak strains in China and contribute to the prevention and pathogenic studies of BHV-1.2.

Phylogenetic analysis and characterization of bovine herpesvirus-1 in cattle of China, 2016-2019

Bovine herpesvirus type 1 (BoHV-1) is one of the most critical pathogens in cattle and is prevalent in China. BoHV-1 is divided into two gene types, BoHV-1.1 and 1.2, which are further differentiated into two subtypes, BoHV-1.2a and 1.2b. However, the phylogenetic analysis of BoHV-1 isolates has not been reported in China. To perform a molecular epidemiological survey based on isolates from cattle in China, 102 lung tissue samples of calves under ten months of age with respiratory disease (BRD) that died from 2016 to 2019 in China were used to isolate BoHV-1 with Madin-Darby bovine kidney (MDBK) cells. Part of the BoHV-1 isolates were applied to the phylogenetic analysis based on the region of the glycoprotein C (gC) gene of BoHV-1. Thirty BoHV-1 isolates were obtained, and the gC gene of 13 isolates was amplified by polymerase chain reaction (PCR) methods and sequenced. The result of the phylogenetic analysis according to the 451-nucleotide portion of the gC gene found that all of 13 isolates belonged to the BoHV-1.2b gene subtype, but these isolates had located two different phylogenetic tree branches. The gC gene sequence homology of isolates in group1 was higher with a reference strain of BoHV-1.2b EVI14 up to 98.0-100%, while in group 2, this was higher with reference strain BoHV-1.2b B589 up to 97.8-99.8%. The deduced amino acid sequence of gC from isolates in group 2 had two amino acid mutations with interference strain BoHV-1.2b K22 or BoHV-1.1 COOPER. The cytopathic effects (CPEs) of BoHV-1 isolates in group 2 were ulcered on the centration like a volcano on MDBK cell, and different from traditional CPEs of BoHV-1. Overall, BoHV-1.2b seems to be the primary strain of BoHV-1 in cattle in China and is also a critical cause of BRD. These BoHV-1.2b isolates had significant genetic variations.

Sequence analysis of the 5' third of glycoprotein C gene of South American bovine herpesviruses 1 and 5

Bovine herpesviruses 1 (BoHV-1) and 5 (BoHV-5) share high genetic and antigenic similarities, but exhibit marked differences in tissue tropism and neurovirulence. The amino-terminal region of glycoprotein C (gC), which is markedly different in each of the viruses, is involved in virus binding to cellular receptors and in interactions with the immune system. This study investigated the genetic and antigenic differences of the 5′ region of the gC (5′ gC) gene (amino-terminal) of South American BoHV-1 (n=19) and BoHV-5 (n=25) isolates. Sequence alignments of 374 nucleotides (104 amino acids) revealed mean similarity levels of 97.3 and 94.2% among BoHV-1 gC (gC1), respectively, 96.8 and 95.6% among BoHV-5 gC (gC5), and 62 and 53.3% between gC1 and gC5. Differences included the absence of 40 amino acid residues (27 encompassing predicted linear epitopes) scattered throughout 5′ gC1 compared to 5′ gC5. Virus neutralizing assays testing BoHV-1 and BoHV-5 antisera against each isolate revealed a high degree of cross-neutralization between the viruses, yet some isolates were neutralized at very low titers by heterologous sera, and a few BoHV-5 isolates reacted weakly with either sera. The virus neutralization differences observed within the same viral species, and more pronounced between BoHV-1 and BoHV-5, likely reflect sequence differences in neutralizing epitopes. These results demonstrate that the 5′ gC region is well conserved within each viral species but is divergent between BoHV-1 and BoHV-5, likely contributing to their biological and antigenic differences.

Nucleotide sequencing and phylogenetic analysis of the 3' region of glycoprotein C gene of South American bovine herpesviruses 1 and 5

We herein describe a molecular analysis based on the 3' region of the glycoprotein C gene of 45 bovine herpesvirus (BoHV) isolates from Brazil (n=41), Uruguay (n=2) and Argentina (n=2). Nucleotide (nt) sequencing and alignment of 333 nt revealed levels of similarity ranging from 99.1% to 100% among BoHV-1 sequences (n=12); 96.2-100% among BoHV-5 sequences (n=32); and 77.7-90.3% between BoHV-1 and BoHV-5 sequences. The phylogenetic tree reconstruction provided a clear distinction between BoHV-1 and BoHV-5, and BoHV-1 into subtypes BoHV-1.1 and BoHV-1.2. The isolate SV 453/93 (BoHV-1 associated with genital disease) could not be included within BoHV-1 subtypes since it presented a markedly distinct nt and amino acid (aa) deduced sequences. A transmembrane domain of 24 aa and the putative cytoplasmic tail of 8 aa were identified and mapped. These results indicate that this genome region represents a suitable target for phylogenetic subgrouping of BoHV-1 and BoHV-5 isolates and, perhaps, for understanding evolutionary relationships.

Attenuation of bovine herpesvirus type 1 by deletion of its glycoprotein G and tk genes and protection against virulent viral challenge

To develop a novel vaccine against infectious bovine rhinotracheitis (IBR), a bovine herpesvirus-1 (BoHV-1) mutant was constructed by deleting the genes for glycoprotein G (gG) and thymidine kinase (tk) through homologous recombination. The resulting sequences for both genes were shown to be correct and a gG expression defect was also confirmed. A parallel study of the BoHV-1 gG(-)/tk(-), gE(-)/tk(-) mutants and wild type (wt) in 31 calves was performed at three different doses, 4×10(5)PFU, 4×10(6)PFU and 4×10(7)PFU. Compared to wt BoHV-1, inoculation of BoHV-1 gG(-)/tk(-) and gE(-)/tk(-) produced no clinical signs and the virus was not reactivated by dexamethasone (dex). Inoculation of BoHV-1 gG(-)/tk(-) at the doses of 4×10(6) and 4×10(7)PFU provided full clinical protection for the cattle against wt BoHV-1 challenge at 4×10(7)PFU/calf. Although the mutants were associated with significantly lower levels of serum neutralizing antibody, interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α) than wt BoHV-1 on days 3, 5 and 7 after immunization, stimulation of IFN-β by BoHV-1 gG(-)/tk(-) was significantly higher than that of wt BoHV-1 and gE(-)/tk(-) on days 3 and 5. We conclude that BoHV-1 gG(-)/tk(-) was attenuated adequately and that it maintains the ability to stimulate immune protection. Therefore, it may be a promising candidate for a marker vaccine against IBR.

The bovine herpesvirus type 1 envelope protein Us9 acidic domain is crucial for anterograde axonal transport

In this study, we examined the functional role of bovine herpesvirus type 1 (BHV-1) Us9 acidic domain residues 83-90 in the anterograde axonal transport of the virus in calves (natural host), rabbits, and in cultured neurons. A mutant virus strain lacking Us9 residues 83-90 (BHV-1 Us9 Δ83-90) and the rescued virus (BHV-1 Us9 R83-90) replicated efficiently in the nasal and ocular epithelium during primary infection and established latency in the trigeminal ganglia (TG). However, upon reactivation from latency, only the BHV-1 Us9 R83-90 virus was detected in nasal and ocular swabs of animals. In compartmentalized, rabbit primary dorsal root ganglia (DRG) neuron cultures, the Us9-deleted BHV-1, BHV-1 Us9 Δ83-90 and BHV-1 Us9 R83-90 viruses were transported efficiently in the retrograde direction. However, only the BHV-1 Us9 R83-90 virus was transported in an anterograde direction. These studies suggested that the Us9 acidic domain residues located between 83 and 90 were required for axonal anterograde transport.

Effects of bovine Herpesvirus Type 5 on development of in vitro-produced bovine embryos

Bovine (Bos indicus) herpesviruses have been associated with reproductive disease. Type 1, the most studied species, is best known for its reproductive and respiratory effects. Type 5 (BoHV-5) has been detected in bull semen and aborted fetuses but not in oocytes and embryos. This study consisted of three experiments that evaluated (1) BoHV-5-infected oocytes matured in medium with fetal bovine serum (BoHV-FBS) or polyvinyl alcohol (BoHV-PVA) and fertilized by noninfected sperm; (2) noninfected oocytes fertilized by BoHV-5-infected sperm; and (3) infection of presumptive zygotes by BoHV-5. Each treatment involved nine drops of 15 to 20 oocytes. Infection with BoHV-5 was detected by polymerase chain reaction and in situ hybridization assay, and fertilization capacity and embryonic development were assessed using in vitro culture. Experimentally induced infection was obtained in all experiments, and vertical transmission of BoHV-5 by gametes was confirmed. The cleavage rate was reduced (P=0.0201) in BoHV-FBS (80.4+/-8.9%; mean+/-SD) compared with that of noninfected oocytes (89.9+/-6.5%); neither differed from BoHV-PVA (87.3+/-7.1%), and the resulting embryo production rate was not significantly different among groups. Rates of cleavage (87.5+/-7.5% vs. 92.2+/-5.5%, control vs. infected) and development of embryos (41.7+/-9.9% vs. 44.3+/-7.7% to morula/blastocyst/expanded blastocyst [M/B/EB] and 39.6+/-10.3% vs. 40.8+/-9.2% to blastocyst/expanded blastocyst/hatching blastocyst [B/EB/HB] stages) were not compromised by infected sperm (P=0.1462, P=0.5402, and P=0.8074, respectively). However, presumptive zygotes directly infected 1 d after fertilization produced a lower number (P=0.0140 to M/B/EB and P=0.002 to B/EB/HB stages) of in vitro-produced embryos (31.6+/-4.6 vs. 25.0+/-5.5 and 31.6+/-4.6 vs. 20.2+/-5.4; control vs. infected). In conclusion, BoHV-5 infected gametes and was transmissible to the embryo during in vitro development. As zygotes infected 1 d after fertilization had compromised development, BoHV-5 has the potential to be a pathogen with economic consequences.

Encephalitis in aborted bovine fetuses associated with Bovine herpesvirus 1 infection

Brain tissue from 12 aborted bovine fetuses submitted to the Wisconsin Veterinary Diagnostic Laboratory revealed histologic lesions that consisted of glial nodules and variable degrees of mononuclear inflammation, microhemorrhage, neuronal necrosis, and cerebral cortical cavitation. A diagnosis of Bovine herpesvirus 1 (BHV-1) abortion had been made in all of these cases through multiple testing modalities. Brain tissue from 8 of the 12 fetuses was immunohistochemically stained with a monoclonal antibody specific to BHV-1, and, in 5 fetuses, there was positive intralesional staining of neurons, glial cells, and endothelial cells. This preliminary data suggested that herpesviral infection of brain tissue led to the described neurologic lesions. BHV-1 was then amplified from brain tissue in all 12 of the fetuses and was confirmed by partial sequencing of the thymidine kinase and glycoprotein C genes. To the authors' knowledge, neurologic lesions have not previously been described in BHV-1-infected fetuses, nor has BHV-1 previously been identified in bovine fetal brain tissue. The neurologic histopathology attributed to BHV-1 infection in these cases overlaps with the neurologic lesions produced by Neospora caninum, a common etiologic agent of bovine abortion. Therefore, when bovine fetal neurologic lesions are found, both etiologies should be considered and then distinguished by using additional diagnostic tools.

A bovine herpesvirus type 1 mutant virus specifying a carboxyl-terminal truncation of glycoprotein E is defective in anterograde neuronal transport in rabbits and calves

Bovine herpesvirus type 1 (BHV-1) is an important component of the bovine respiratory disease complex (BRDC) in cattle. The ability of BHV-1 to transport anterogradely from neuronal cell bodies in trigeminal ganglia (TG) to nerve ending in the noses and corneas of infected cattle following reactivation from latency plays a significant role in the pathogenesis of BRDC and maintenance of BHV-1 in the cattle population. We have constructed a BHV-1 bacterial artificial chromosome (BAC) clone by inserting an excisable BAC plasmid sequence in the long intergenic region between the glycoprotein B (gB) and UL26 genes. A BAC-excised, reconstituted BHV-1 containing only the 34-bp loxP sequence within the gB-UL26 intergenic region was highly infectious in calves, retained wild-type virulence properties, and reactivated from latency following treatment with dexamethasone. Using a two-step Red-mediated mutagenesis system in Escherichia coli, we constructed a gE cytoplasmic tail-truncated BHV-1 and a gE-rescued BHV-1. Following primary infection, the gE cytoplasmic tail-truncated virus was efficiently transported retrogradely from the nerve endings in the nose and eye to cell bodies in the TG of calves and rabbits. However, following dexamethasone-induced reactivation from latency, the gE mutant virus was not isolated from nasal and ocular sheddings. Reverse transcriptase PCR assays detected VP5 transcription in the TG of rabbits infected with gE-rescued and gE cytoplasmic tail-truncated viruses during primary infection and after dexamethasone treatment but not during latency. Therefore, the BHV-1gE cytoplasmic tail-truncated virus reactivated in the TG; however, it had defective anterograde transport from TG to nose and eye in calves and rabbits.

Phylogenetic comparison of the carboxy-terminal region of glycoprotein C (gC) of bovine herpesviruses (BoHV) 1.1, 1.2 and 5 from South America (SA)

Different types and subtypes of bovine herpesvirus 1 and 5 (BoHV-1 and BoHV-5) have been associated to different clinical conditions of cattle, in such a way that type/subtype differentiation has become an essential tool for understanding the pathogenesis and epidemiology of BoHV infections. In search for a genomic region that would allow a clear distinction between BoHV-1 and BoHV-5, the carboxy-terminal portion of glycoprotein C (gC), corresponding to residues 321-450 (BoHV-1) and 301-429 (BoHV-5) of 23 South American (SA) isolates (Brazil mostly) was amplified and sequenced. The nucleotide sequence alignments revealed levels of genomic similarity ranging from 98.7 to 99.8% among BoHV-1 isolates, 88.3 to 92% between BoHV-1/BoHV-5 and 96 to 99.7% among BoHV-5 isolates. At the amino acid level, sequence similarity varied ranging from 97.5 to 99.5% among BoHV-1, 77.5 to 84.4% between BoHV-1/BoHV-5 and 92.1 to 99.5% (BoHV-5/BoHV-5). The isolates could be clearly separated into BoHV-1.1, BoHV-1.2 and BoHV-5 after phylogenetic analysis. The results suggest that the phylogenetic analysis performed here can be used as a potential molecular epidemiological tool for herpesviruses.

Identificação e diferenciação de herpesvírus bovino tipos 1 e 5 isolados de amostras clínicas no Centro-Sul do Brasil, Argentina e Uruguai (1987-2006)

Os herpesvírus bovino tipos 1 e 5 (BoHV-1; BoHV-5) são genética e antigenicamente muito semelhantes e por isso são indistinguíveis pela maioria dos testes diagnósticos. Como o BoHV-1 tem sido classicamente associado com doença respiratória e genital, os herpesvírus isolados dessas enfermidades têm sido provisoriamente - e às vezes definitivamente - identificados como BoHV-1. Da mesma forma, os casos de infecção neurológica por herpesvírus em bovinos têm sido atribuídos em sua totalidade ao BoHV-5. Este trabalho relata a identificação de 40 amostras de herpesvírus isoladas de diferentes casos clínicos na região Centro-Sul do Brasil, Argentina e Uruguai entre 1987 e 2006, pelo uso de um PCR capaz de diferenciar esses vírus. As amostras identificadas como BoHV-1 (n=16) foram isoladas de doença respiratória (n=3), balanopostite e/ou vulvovaginite (n=3), do sêmen de touros saudáveis (n=5) e de casos doença neurológica (n=5). As amostras virais identificadas como BoHV-5 (n=24) foram em sua maioria isoladas de doença neurológica (n=21), mas também do sêmen de touros saudáveis (n=2) e do baço de um bezerro com doença sistêmica (n=1). Esses resultados demonstram que tanto o BoHV-1 como o BoHV-5 não estão estritamente associados às suas respectivas síndromes clínicas e que podem estar freqüentemente envolvidos em casos clínicos classicamente atribuídos ao outro vírus. Esses achados também reforçam a necessidade de se identificar corretamente os isolados de herpesvírus para um melhor conhecimento da sua patogenia e epidemiologia.

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.

Glycoprotein E (gE) specified by bovine herpesvirus type 5 (BHV-5) enables trans-neuronal virus spread and neurovirulence without being a structural component of enveloped virions

Bovine herpesvirus 5 (BHV-5) is a neurovirulent alpha-herpesvirus that causes fatal encephalitis in calves. We previously demonstrated that deletion of a glycine-rich epitope in the gE ectodomain dramatically reduced BHV-5 neurovirulence. To investigate the role of gE cytoplasmic tail sequences in the neuropathogenesis of BHV-5 in rabbits, we constructed a BHV-5gE recombinant virus with a short residual cytoplasmic domain lacking the YXXL motifs and the acidic (BHV-5gEAm480). In vitro, BHV-5gEAm480 produced on the average smaller plaques, compared with wild-type BHV-5, but it produced on the average substantially larger plaques than the gE ORF-deleted BHV-5. The truncated gE was not phosphorylated, and was not endocytosed from the cell surface. Importantly, the truncated gE was not incorporated into enveloped infectious virions, but its glycosylation and interaction with gI were not affected. In a rabbit model of infection, the BHV-5gEAm480 remained highly virulent, while the gE-null virus was avirulent. The gEAm480 mutant virus invaded most of the central nervous system (CNS) structures that are invaded by the wild-type BHV-5. The number of neurons infected by BHV-5gEAm480 was very similar to the number infected by BHV-5 wild-type and gEAm480-rescued viruses. Collectively, the results suggest that gE functions in transsynaptic transmission of BHV-5 and neurovirulence without being a structural component of the virion particle.

BHV-1 vaccine induces cross-protection against BHV-5 disease in cattle

Protection against BHV-5 disease induced by inactivated BHV-1 or BHV-5 based vaccines was analysed. Two groups of calves were subcutaneously immunized with an inactivated BHV-1 or BHV-5 based vaccine. A third group was not vaccinated and used as control. In the post-vaccination period, we studied the humoral and cellular immune response resulting similar to both groups. The efficacy of the vaccines was tested after intranasal challenge of the calves with a virulent Argentinean BHV-5 isolate (A-663). All control animals developed neurological signs associated with BHV-5 infection and high levels of virus shedding. Calves immunized with the BHV-1 and BHV-5 inactivated vaccines were protected against BHV-5 disease. Our study provides evidence that strongly support the existence of cross-protection between BHV-1 and BHV-5 in calves. Even though this has already been suggested by previous works, this is the first time an exhaustive study of the immune response is performed and typical clinical BHV-5 meningoencephalitis signs are reproduced in an experimental BHV-5 challenge trial.

Rapid detection and differentiation of bovine herpesvirus 1 and 5 glycoprotein C gene in clinical specimens by multiplex-PCR

A multiplex polymerase chain reaction (multiplex-PCR) to detect and differentiate bovine herpesvirus 1 (BoHV-1) and 5 (BoHV-5) was developed using primers for the gene sequence that encodes the glycoprotein C. The technique was assessed against the BoHV-1 and BoHV-5 cell culture adapted strains, and clinical samples collected from animals with clinical signs of BoHV-1 (n = 10) or BoHV-5 (n = 7) infection and with diagnosis confirmed by virus isolation in cell culture and semi-nested PCR. Fifteen clinical samples from asymptomatic animals were included as control group. For the evaluation of the amplifiability of the extracted nucleic acid from clinical specimens was included a bovine internal control that amplified a 626 bp fragment of the ND5 gene present in the bovine mitochondrial DNA. For DNA extraction, a combination of the phenol/chloroform/isoamyl alcohol and silica/guanidine isothiocyanate methods was used. The specificity of the BoHV-1 and BoHV-5 amplicons from standard strains were confirmed by sequence analysis. All the positive clinical samples for BoHV included in this study were characterized as BoHV-1 or BoHV-5 by the difference in length of the amplified product visualized in a agarose gel (354 bp size for BoHV-1, and 159 bp for BoHV-5). The internal control was amplified in all clinical specimens. Non-specific reactions were not observed when the multiplex-PCR was assessed with other viruses (bovine viral diarrhea virus and rabies virus) and BoHV-negative clinical samples from fetuses and adult cattle obtained from a slaughterhouse.

In the absence of glycoprotein I (gI), gE determines bovine herpesvirus type 5 neuroinvasiveness and neurovirulence

Bovine herpesvirus type 5 (BHV-5) is an alphaherpesvirus that causes fatal encephalitis in calves. Envelope glycoproteins E (gE) and gI of alphaherpesviruses are important for the pathogenesis in vivo. Previously the authors determined that BHV-5 gE is important for BHV-5 neurovirulence. To determine the role of gI in BHV-5 neurovirulence, the authors have constructed gI-deleted and gI-revertant BHV-5 and analyzed their neuropathogenic properties in a rabbit seizure model. Following intranasal infection, 40% of the rabbits infected with the gI-deleted virus showed severe neurological signs. gI-deleted BHV-5 invaded all the central nervous system (CNS) structures invaded by the gI-revertant BHV-5; however, the number of neurons infected by the gI-deleted virus was similar or slightly reduced (two to four fold). Thus, the gI-deleted virus retained significant neurovirulence and/or neuroinvasive properties when compared with the gE-deleted BHV-5. Pulse-chase analysis revealed that the gE of gI-deleted virus was processed to a larger and a diffused 94- to 100-kDa protein (instead of 94 kDa). The 94- to 100-kDa protein was processed in the Golgi with delayed kinetics but it was endoglycosidase H (EndoH) resistant. In cells infected with gI-deleted virus, there was a reduction in cell-surface gE expression compared to wild-type, which correlated to reduced amount of gE processed in the Golgi. The authors believe that in the absence of gI, BHV-5 gE is sufficient for BHV-5 neurovirulence.

Detection of equine herpesvirus 3 in equine skin lesions by polymerase chain reaction

During a recent breeding season, ulcerative, pustular skin lesions were observed on the external genitalia of 2 mares and 1 stallion within a small herd. Based on the location and description of the skin lesions plus the clinical history, equine coital exanthema, caused by equine herpesvirus 3 (EHV3), was the primary differential diagnosis. Scrapings of skin lesions from the perineum of 2 mares were submitted for diagnostic evaluation. Virus isolation was attempted by inoculation of several cell lines of equine origin, but no cytopathic agent was detected. The skin scrapings were processed for DNA extraction, and polymerase chain reaction (PCR) amplification was performed for herpesvirus DNA polymerase and DNA-packaging protein (terminase) genes using nested, degenerate primers targeted to conserved regions of the herpesvirus genome. Products of the expected sizes were generated for both assays, and subsequent nucleotide sequencing of the amplification products established that EHV3 had been detected in DNA extracted from the skin lesions. Detection of EHV3 was confirmed using an EHV3-specific PCR assay targeted to the gC gene. Using the novel EHV3 nucleotide sequence identified in this report, a sensitive and specific PCR assay targeted to the highly conserved DNA polymerase gene was developed.

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

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

Production and characterization of monoclonal antibodies to a Brazilian bovine herpesvirus type 5

Antigens of a bovine herpesvirus type 5 (BHV-5), isolated from a cow with a neurological infection in Rio Grande do Sul State, Brazil, were used to immunize BALB/c mice to produce monoclonal antibodies (mAbs). Eleven hybridomas secreting mAbs directed at BHV-5 antigens were obtained after two fusions and screening of 356 hypoxanthine-aminopterin-thymidine-resistant clones. The mAbs reacted at dilutions up to 1:500 (hybridoma culture supernatant) and up to >1:10,000 (ascitic fluid) in an indirect fluorescent antibody assay (IFA) and in immunoperoxidase staining of BHV-5-infected cells. Four mAbs (1D12, 2E2, 2G10 and 4E4) showed virus-neutralizing activity against the parental BHV-5 isolate. Five mAbs (1F3, 2A6, 2F9, 2G10 and HB24L) reacted in Western immunoblotting with a protein of approximately 90 kDa. Three other mAbs (2E2, 3D6 and 4E4) reacted in IFA with antigens of a BHV-1 mutant glycoprotein C- negative strain, demonstrating that they are directed at a viral antigen other than glycoprotein C. The eleven mAbs tested reacted with 20 BHV-5 field isolates and nine mAbs reacted with 10 BHV-1 isolates. Two mAbs (1F3 and 2F9) failed to react with BHV-1 field isolates, although they displayed a weak and nonreproducible reaction with the BHV-1 reference strain Los Angeles. These mAbs may be very useful in distinguishing between BHV-1 and BHV-5 infections since most of the traditional reagents and techniques are unable to do so. One mAb (2F9) was shown to bind to viral antigens by immunohistochemistry of histological sections of the brain of a BHV-5-infected calf. These results demonstrate that the mAbs produced here are suitable for use in a variety of immunological techniques and therefore may be useful for diagnostic and research purposes.

Bovine herpesvirus 5 (BoHV-5) in bull semen: amplification and sequence analysis of the US4 gene

Bovine herpesvirus type 5 (BoHV-5), which is potentially neuropathogenic, was detected in clinical samples of bovine semen, both directly and after isolation in cell culture, using a nested PCR system for amplifying the US4 gene. Nucleotide sequences generated from the amplicons were analysed and deposited at GenBank (NCBI, Bethesda, MD, USA) under the accession numbers AF298174 and AF330157. Alignment of these sequences and previously deposited sequences of BoHV-1 and BoHV-5 showed 82% and 98% similarity, respectively. The bulls, which were maintained at an artificial insemination centre, had presented no clinical signs, indicating that bovine semen should be screened for BoHV-5 to prevent transmission of the virus.

Genome of bovine herpesvirus 5

Here we present the complete genomic sequence of bovine herpesvirus 5 (BHV-5), an alphaherpesvirus responsible for fatal meningoencephalitis in cattle. The 138390-bp genome encodes 70 putative proteins and resembles the alpha2 subgroup of herpesviruses in genomic organization and gene content. BHV-5 is very similar to BHV-1, the etiological agent of infectious bovine rhinotracheitis, as reflected by the high level of amino acid identity in their protein repertoires (average, 82%). The highest similarity to BHV-1 products (>or=95% amino acid identity) is found in proteins involved in viral DNA replication and processing (UL5, UL15, UL29, and UL39) and in virion proteins (UL14, UL19, UL48, and US6). Among the least conserved ( Collapse

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MESH Headings

• Amino Acid Sequence
• Base Sequence
• Genes, Immediate-Early
• Genome, Viral
• Herpesvirus 5, Bovine/genetics
• Molecular Sequence Data
• Promoter Regions, Genetic
• Repetitive Sequences, Nucleic Acid
• Virus Latency/genetics

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Affiliation(s)

G Delhon Plum Island Animal Disease Center, Agricultural Research Service, U.S. Department of Agriculture, Greenport, New York 11944, USA
M P Moraes
Z Lu
C L Afonso
E F Flores
R Weiblen
G F Kutish
D L Rock

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Bovine herpesvirus 5 (BHV-5) Us9 is essential for BHV-5 neuropathogenesis

Bovine herpesvirus 5 (BHV-5) is a neurovirulent alphaherpesvirus that causes fatal encephalitis in calves. In a rabbit model, the virus invades the central nervous system (CNS) anterogradely from the olfactory mucosa following intranasal infection. In addition to glycoproteins E and I (gE and gI, respectively), Us9 and its homologue in alphaherpesviruses are necessary for the viral anterograde spread from the presynaptic to postsynaptic neurons. The BHV-5 Us9 gene sequence was determined, and the predicted amino acid sequence of BHV-5 Us9 was compared with the corresponding Us9 sequences of BHV-1.1. Alignment results showed that they share 77% identity and 83% similarity. BHV-5 Us9 peptide-specific antibody recognized a doublet of 17- and 19-kDa protein bands in BHV-5-infected cell lysates and in purified virions. To determine the role of the BHV-5 Us9 gene in BHV-5 neuropathogenesis, a BHV-5 Us9 deletion recombinant was generated and its neurovirulence and neuroinvasive properties were compared with those of a Us9 rescue mutant of BHV-5 in a rabbit model. Following intranasal infection, the Us9 rescue mutant of BHV-5 displayed a wild-type level of neurovirulence and neural spread in the olfactory pathway, but the Us9 deletion mutant of BHV-5 was virtually avirulent and failed to invade the CNS. In the olfactory mucosa containing the olfactory receptor neurons, the Us9 deletion mutant virus replicated with an efficiency similar to that of the Us9 rescue mutant of BHV-5. However, the Us9 deletion mutant virus was not transported to the bulb. Confocal microscopy of the olfactory epithelium detected similar amounts of virus-specific antigens in the cell bodies of olfactory receptor neuron for both the viruses, but only the Us9 rescue mutant viral proteins were detected in the processes of the olfactory receptor neurons. When injected directly into the bulb, both viruses were equally neurovirulent, and they were transported retrogradely to areas connected to the bulb. Taken together, these results indicate that Us9 is essential for the anterograde spread of the virus from the olfactory mucosa to the bulb.

Sequence analysis of the alpha trans-inducing factor of bovine herpesvirus type 5 (BHV-5)

Bovine herpesvirus (BHV), a member of the subfamily Alphaherpesvirinae, is classified into neurovirulent and non-neurovirulent subtypes on a basis of differential neuropathogenicities. Transcription of viral immediate early (IE) genes during alphaherpesvirus gene expression, is mediated by a multi-component immediate early complex (IEC) integrated by the viral tegument protein alpha trans-inducing factor (alpha-tif), a host cell protein (HCF), and a host Octamer protein (Oct). In this paper, we present a sequence analysis of the alpha-tif of the encephalitic BHV subtype, bovine herpesvirus type 5 (BHV-5). Bovine herpesvirus type 1 (BHV-1) and BHV-5 alpha-tifs share 98% amino acid sequence homology. However, BHV-5 alpha-tif is 23 residues shorter at the amino terminus than BHV-1 alpha-tif. Amino acid alignment of the alpha-tifs of BHV-1 and BHV-5 with other alphaherpesviruses indicates areas of conserved motifs but also important differences located mainly at the amino and carboxyl termini.

Bovine herpesvirus 5 glycoprotein E is important for neuroinvasiveness and neurovirulence in the olfactory pathway of the rabbit

Glycoprotein E (gE) is important for full virulence potential of the alphaherpesviruses in both natural and laboratory hosts. The gE sequence of the neurovirulent bovine herpesvirus 5 (BHV-5) was determined and compared with that of the nonneurovirulent BHV-1. Alignment of the predicted amino acid sequences of BHV-1 and BHV-5 gE open reading frames showed that they had 72% identity and 77% similarity. To determine the role of gE in the differential neuropathogenesis of BHV-1 and BHV-5, we have constructed BHV-1 and BHV-5 recombinants: gE-deleted BHV-5 (BHV-5gEDelta), BHV-5 expressing BHV-1 gE (BHV-5gE1), and BHV-1 expressing BHV-5 gE (BHV-1gE5). Neurovirulence properties of these recombinant viruses were analyzed using a rabbit seizure model (S. I. Chowdhury et al., J. Comp. Pathol. 117:295-310, 1997) that distinguished wild-type BHV-1 and -5 based on their differential neuropathogenesis. Intranasal inoculation of BHV-5 gEDelta and BHV-5gE1 produced significantly reduced neurological signs that affected only 10% of the infected rabbits. The recombinant BHV-1gE5 did not invade the central nervous system (CNS). Virus isolation and immunohistochemistry data suggest that these recombinants replicate and spread significantly less efficiently in the brain than BHV-5 gE revertant or wild-type BHV-5, which produced severe neurological signs in 70 to 80% rabbits. Taken together, the results of neurological signs, brain lesions, virus isolation, and immunohistochemistry indicate that BHV-5 gE is important for efficient neural spread and neurovirulence within the CNS and could not be replaced by BHV-1 gE. However, BHV-5 gE is not required for initial viral entry into olfactory pathway.

Improved detection of five closely related ruminant alphaherpesviruses by specific amplification of viral genomic sequences

The detection and discrimination of five closely related ruminant alphaherpesviruses, bovine herpesvirus 1 (BHV-1), bovine herpesvirus 5 (BHV-5), caprine herpesvirus 1 (CapHV-1), cervine herpesvirus 1 (CerHV-1), and rangiferine herpesvirus 1 (RanHV-1), were achieved by the development of specific PCR systems. The highly variable N-terminal of the glycoprotein C was chosen to select the diagnostic primers, except for the CerHV-1 primers, which targeted the glycoprotein D region. All the assays proved specific since no heterologous virus was amplified. BHV-1 and BHV-5 were detected by using the same PCR assay and the different sizes of the amplification products allowed their identification on agarose gels. The practical diagnostic applicability of the novel PCR assays, with special regard to the BHV-1 system, has been evaluated on clinical samples from experimentally infected animals.

Identification and characterization of bovine herpesvirus type 5 glycoprotein H gene and gene products

Bovine herpesvirus type 5 (BHV-5) is the causative agent of a fatal meningo-encephalitis in calves and is closely related to BHV-1 which causes infectious bovine rhinotracheitis. The gene encoding BHV-5 glycoprotein gH was sequenced. A high degree of conservation was found between BHV-1 and BHV-5 deduced gH amino acid sequences (86. 4%), which is also observed for all alphaherpesvirus gH sequences. Transcriptional analysis revealed a 3.1 kb mRNA as the specific gH transcript which was detected 2 h post-infection (p.i.). Twelve out of twenty-one MAbs directed against BHV-1 gH immunoprecipitated a 108-110 kDa glycoprotein, which was then designated BHV-5 gH. Synthesis and intracellular processing of BHV- 5 gH was analysed in infected MDBK cells using gH cross-reacting MAbs. Glycoprotein gH was expressed as a beta-gamma protein, detected by radioimmunoprecipitation as early as 3 h p.i. Glycosylation studies indicated that BHV-5 gH contains N-linked carbohydrates which are essential for the recognition of the protein by the MAbs. This suggests that N-linked glycans are involved in protein folding or are targets for the gH cross-reacting MAbs. Plaque- reduction neutralization assays showed that at least one BHV-1 gH antigenic domain is lacking in BHV-5 which may possibly relate to in vivo differences in virus tropism.

Comparison of PCR, virus isolation, and indirect fluorescent antibody staining in the detection of naturally occurring feline herpesvirus infections

Cats with clinical signs suggestive of ocular infection with feline herpesvirus type 1 (FHV 1) and cats without such signs were assayed by 3 methods to detect FHV. Comparison of polymerase chain reaction (PCR), virus isolation, and indirect fluorescent antibody staining techniques for the detection of FHV demonstrated higher sensitivity of PCR in detecting this common infectious agent of cats. Compared with PCR, sensitivity and specificity for virus isolation was 49% and 100%, respectively, and those of indirect immunofluorescence were 29% and 96%, respectively. FHV was detected in 13.7% of client-owned cats with conjunctivitis and in 31% of shelter cats with no ocular signs. The use of FHV PCR as a diagnostic test for FHV-associated disease is limited because of the occurrence of healthy carriers.

The renal afferent pathways in the rat: a pseudorabies virus study

Retrograde tract tracing studies have indicated that dorsal root ganglion cells from T8 to L2 innervate the rat's left kidney. Electrophysiology studies have indicated that putative second-order sympathetic afferents are found in the dorsal horn at spinal segments T10 to L1 in laminae V-VII. Here, the spread of pseudorabies virus through renal sensory pathways was examined following 2-5 days post-infection (PI) and the virus was located immunocytochemically using a rabbit polyclonal antibody. Two days PI, dorsal root ganglion neurons (first-order sympathetic afferents) were infected with PRV. An average of 1.2, 0.8, 2.1 and 4.4% of the infected dorsal root ganglion neurons were contralateral to the injected kidney at spinal segments T10, T11, T12 and T13, respectively. Four days PI, infected neurons were detected within laminae I and II of the dorsal horn of the caudal thoracic and upper lumbar spinal cord segments. The labeling patterns in the spinal cord are consistent with previous work indicating the location of renal sympathetic sensory pathways. The nodose ganglia were labeled starting 4 days PI, suggesting the involvement of parasympathetic sensory pathways. Five days PI, infected neurons were found in the nucleus tractus solitarius. In the present study, it was unclear whether the infected neurons in the nucleus tractus solitarius are part of sympathetic or parasympathetic afferent pathways or represent a convergence of sensory information. Renal denervation prevented the spread of the virus into the dorsal root ganglia and spinal cord. Sectioning the dorsal roots from T10-L3 blocked viral spread into the spinal cord dorsal horn, but did not prevent infection of neurons in dorsal root ganglion nor did it prevent infection of putative preganglionic neurons in the intermediolateral cell column. The present results indicated that renal afferent pathways can be identified after pseudorabies virus infection of the kidney. Our results suggest that renal afferents travel in sympathetic and parasympathetic nerves and that this information may converge at the NTS.

Neuropathology of bovine herpesvirus type 5 (BHV-5) meningo-encephalitis in a rabbit seizure model

The suitability of a rabbit seizure model for studying the neuropathogenesis of bovine herpesvirus type 5 (BHV-5) encephalitis was evaluated. Intranasal administration of BHV-5 (strain TX89) together with intramuscular administration of dexamethasone produced seizures in 70% of rabbits tested and meningo-encephalitis in 100%. Infectious BHV-5 was consistently isolated from the following sites: olfactory bulb; anterior cortex, containing the frontal cortex, olfactory tract and anterior portion of the olfactory cortex; posterior cortex, containing the temporal, parietal, piriform, entorhinal and occipital cortices; amygdala; hippocampus. Less frequently, BHV-5 was isolated from the midbrain and diencephalon, the pons and medulla, the cerebellum, and the trigeminal ganglia. Rabbits similarly infected with the Cooper strain of bovine herpesvirus type 1 showed no neurological signs or meningo-encephalitis, and virus was not recovered from the brain. The brains of BHV-5-infected rabbits showed neuronal degeneration, leptomeningitis, gliosis and perivascular cuffing, predominantly in the olfactory cortex (piriform and entorhinal cortices), amygdala and hippocampus. Mild lymphocytic meningitis was seen in the olfactory bulb and focal lymphocytic infiltration was sometimes present in the medulla and cerebellum. BHV-5, specific antigens and nucleic acids were detected in the olfactory cortex, amygdala and hippocampus by immunohistochemical methods and in-situ hybridization. The results suggested that, after intranasal BHV-5 inoculation, the virus spread to the central nervous system via the olfactory and trigeminal pathways. The olfactory pathway was more susceptible than the trigeminal pathway to neuropathogenic effects.

Fine mapping of bovine herpesvirus 1 (BHV-1) glycoprotein C neutralizing epitopes by type-specific monoclonal antibodies and synthetic peptides

Bovine herpesvirus glycoprotein C (gC) functions as a major virus attachment protein. Here, two BHV-1 gC-specific epitopes that are specified by complement-dependent neutralizing MAbs are mapped. The BHV-1 gC-specific peptides and MAbs were used to specifically localize continuous epitopes by direct binding to the MAbs and by blocking the Mab reactivity (competitive ELISA) to authentic viral antigen. The results of competitive ELISA indicated that the complement-dependent neutralizing epitopes recognized by MAbs F2 and 24 were located between BHV-1 gC amino acids (aa) 47-69 and (aa) 109-119, respectively.

Specific detection of shedding and latency of bovine herpesvirus 1 and 5 using a nested polymerase chain reaction

A sensitive method for simultaneously detecting and discriminating between bovine herpesviruses types 1 and 5 (BHV-1 and BHV-5) was developed using a nested polymerase chain reaction (PCR) technique. Following amplification using type-common primers derived from gC sequences, amplification using type-specific nesting primers produced different-sized bands specific to the corresponding types, as demonstrated by blot hybridization. Less than 0.1 plaque-forming units (PFU) of each virus and 75 fg or less of viral DNA were routinely detected. The PCR technique amplified correct product from 4 BHV-5 isolates and from 48 BHV-1 isolates, all from the United States, and did not amplify heterologous herpesviruses. The PCR technique was more sensitive than virus isolation in detection of BHV-1 or BHV-5 in nasal secretions from experimentally and naturally infected calves, and it detected BHV-1 or BHV-5 in trigeminal ganglia from these calves.

Construction and characterization of an attenuated bovine herpesvirus type 1 (BHV-1) recombinant virus

A recombinant bovine herpesvirus type 1 (BHV-1) virus (Gal-TK) has been constructed. The Gal-TK virus contains a chimeric reporter/marker gene coding for bacterial beta-galactosidase (beta-gal gene) that was inserted stably within the viral TK gene. This resulted in inactivation of the TK gene. The beta-gal gene is under the regulation of a strong, human cytomegalovirus-immediate early (HCMV-IE) promoter and is expressed as an authentic viral-coded gene. Even though the one-step growth kinetics of the recombinant and parent viruses were similar, the recombinant virus yielded less than the parent virus on Madin-Darby bovine kidney cells. After intranasal inoculation, the engineered virus was virtually avirulent for colostrum-deprived new-born calves. Similar to the parent virus, the recombinant virus replicated in the upper respiratory tract of calves, but the amount of progeny viruses produced was reduced significantly. The progeny viruses recovered from nasal swabs of animals inoculated with the recombinant and the Cooper strains of BHV-1 were easily distinguishable based on the beta-gal marker.