M. Bublot

Genetic relationships between bovine herpesvirus 4 and the gammaherpesviruses epstein-Barr virus and herpesvirus saimiri

The overall arrangement of genes in the unique central part of the bovine herpesvirus type 4 (BHV-4) genome has been deduced by analysis of short DNA sequences. Twenty-three genes conserved in at least one of the completely sequenced herpesviruses have been identified and localized. All of these genes encoded amino acid sequences with higher similarity to proteins of the gammaherpesviruses Epstein-Barr virus (EBV) and herpesvirus saimiri (HVS) than to the homologous products of the alphaherpesviruses varicella-zoster virus and herpes simplex virus type 1 or the betaherpesvirus human cytomegalovirus. The genome organization of BHV-4 had also an overall colinearity with that of the gammaherpesviruses EBV and HVS. Furthermore, the BHV-4 genes content and arrangement were more similar to those of HVS than to those of EBV, suggesting that BHV-4 and HVS are evolutionarily more closely related to each other than either are to EBV. BHV-4 DNA sequences were generally deficient in CpG dinucleotide. This CpG deficiency is characteristic of gammaherpesvirus genomes and suggests that the BHV-4 latent genome is extensively methylated. Despite several biological features similar to those of betaherpesviruses, BHV-4 displays the molecular characteristics of the representative members of the gammaherpesvirinae subfamily.

Molecular biology of bovine herpesvirus type 4

Bovine herpesvirus type 4 (BHV-4) is a ubiquitous virus of cattle. Its genome is a 144 +/- 6 kb double-stranded DNA consisting of a unique central part (L-DNA) flanked at both ends by tandem repeats called polyrepetitive DNA (prDNA or H-DNA). The overall arrangement of genes has been obtained by the analysis of homologies between short BHV-4 DNA sequences and corresponding genes of Epstein-Barr virus (EBV) and herpesvirus saimiri (HVS). The gene expression is temporally regulated. Glycoprotein precursor p (gp10/gp17) is expressed as gamma 1 polypeptide. Glycoproteins gp1, gp8, gp11 and their precursors are gamma 2 proteins. The analysis of strain variations allows the definition of two types of strains, based on the DNA patterns: the Movar 33/63-like and the DN 599-like strains. Only the M40 strain, isolated in India, fails to fit this classification. The genomic variations have been compiled to build a dendrogram showing three levels of divergence between BHV-4 strains or isolates. The available molecular data indicate that the BHV-4 genome shares much similarity with the DNA of EBV and HVS, two representative members of the gammaherpesvirinae. BHV-4 may therefore be classified in the subfamily gammaherpesvirinae.

Experimental infection of bulls with a genital isolate of bovine herpesvirus-4 and reactivation of latent virus with dexamethasone

Five 13- to 18-month old Belgian Blue bulls were used in this experiment. Four bulls (Nos. 2, 3, 4 and 5) were inoculated intratesticularly with 10(5) plaque-forming units of bovine herpesvirus-4 (BHV-4) in each testicle (Day 0). The challenge BHV-4 strain was previously isolated from testicle cells of a bull exhibiting orchitis and azoospermia. The fifth bull (No. 1) was used as a control and received the same volume of uninfected cell culture supernatant. For 5 days, beginning on Day 51 post-infection, two bulls (Nos. 4 and 5) and the control bull (No. 1) received 0.1 mg kg-1 of dexamethasone. Unilateral castrations were then performed at regular intervals for viral examination. Treatment with dexamethasone reactivated latent BHV-4, but no clinical signs were observed in treated bulls until the end of the experiment (Day 93). Only Bull 3 showed conjunctivitis and temporary azoospermia. The virus was recovered from various samples showing that: (i) BHV-4 can be present in a latent state in the testicles and mononuclear blood cells; (ii) dexamethasone reactivates the virus; (iii) the virus is excreted by nasal and ocular routes. Each infected bull seroconverted and a booster antibody response appeared after dexamethasone treatment as shown by immunofluorescence. Neutralizing antibodies were detected in each bull by complement-dependent neutralization test with titres higher than those obtained by a classical neutralization test. No booster response of neutralizing antibodies was observed after dexamethasone treatment. The antigenically relevant envelope BHV-4 proteins were identified by Western blotting using sera samples from the animals. DNA restriction endonuclease profiles of viruses reisolated after primary infection and reactivation showed only small differences.

Bovine herpesvirus 4 (BHV-4) infections in cattle

The bovine herpesvirus-4 (BHV-4) group comprises several antigenically related herpesviruses isolated from a variety of clinical syndromes as well as from apparently healthy cattle. Except for a few isolates, they are mildly or not pathogenic for cattle. Mononuclear blood cells and lymphoid organs are the sites of acute and latent infections in cattle and rabbits. A site of latency in nervous tissue also has been described in cattle. From some of its biological characteristics, such as the morphogenesis in infected cells and a slow viral growth curve, BHV-4 was tentatively classified as cytomegalovirus. Recent molecular data have allowed BHV-4 to be classified as a group B herpesvirus. Natural and experimental infections do not induce high levels of neutralizing antibodies so that serological diagnosis is best achieved by ELISA or immunofluorescence antibody tests. BHV-4 infection has a worldwide distribution: it has been already diagnosed in Europe, America and Africa.

Reactivation of infectious bovine rhinotracheitis virus by transport.

Transport was studied as a cause of reactivation of infectious bovine rhinotracheitis virus (Bovine herpesvirus-1; BHV-1) in heifers vaccinated 2-6 months before transport, using a double dose of the thermosensitive (ts) vaccine strain (Tracherine). Eight out of 19 animals showed ts strain re-excretion over a period of 1-3 days, beginning, in 5 out of the 8 heifers, the day after transport. In 14 other heifers, only sera were examined by sero-neutralisation: only 1 out of these 14 animals showed a rise in BHV-1 neutralising antibodies. Transport can therefore be considered as a stimulus of BHV-1 reactivation.

Analysis of Bovine Herpesvirus 4 Genomic Regions Located Outside the Conserved Gammaherpesvirus Gene Blocks

Bovine herpesvirus 4 (BHV-4) DNA sequences located outside the gene blocks conserved among the gammaherpesviruses BHV-4, herpesvirus saimiri (HVS) and Epstein-Barr virus (EBV) were analysed. Twelve potential open reading frames (ORFs) were found. Protein database comparisons showed that no ORF translation products were similar to proteins encoded by alpha- or betaherpesviruses. Nevertheless, six of the ORFs were homologous in amino acid sequences to proteins encoded by HVS but apparently not to those encoded by EBV. Furthermore, the location and orientation of these six ORFs in the BHV-4 genome were similar to the corresponding ORFs in the HVS genome. No genes homologous to known cellular genes were found in the BHV-4 genome; this feature is the major difference between the BHV-4 and HVS genomes with regards to the overall gene content.

Bovine herpesvirus 4 genome: cloning, mapping and strain variation analysis.

The restriction map of the bovine herpesvirus 4 (BHV-4) genome (V. Test strain) was established for the restriction enzymes EcoRI, BamHI and HindIII by analysis of clones from a lambda library (Sau3AI partial digestion) and from a plasmid library (EcoRI fragments). One genome unit was defined as the length of the unique central part, flanked at both ends by one of the terminal tandem repeats called polyrepetitive DNA (prDNA) and was estimated to be 113 +/- 2 kbp. A restriction map of the prDNA of the V. Test strain showed internal 200 bp tandem repeats of different sequences. This region in the prDNA was highly polymorphic between BHV-4 strains, even in a viral DNA preparation from a plaque-purified strain. The right junction between the repeated and the unique sequence of the genome occurred at an almost constant site, but the left junction contained a modified prDNA and was variable between BHV-4 strains. The unique central part of the genome was very similar in the four strains under consideration, with a few variations due to the presence or absence of a restriction site and four length variations were observed, located at positions 0.006 to 0.034 (left end), 0.211 to 0.225, 0.864 to 0.881 and 0.962 to 0.984 (right end). The total length variation of 1 genome unit does not exceed 1 kbp.

Biological and biochemical comparison of bovid herpesvirus-4 strains

Bovid herpesvirus-4 (BHV-4) isolates V.Test and LVR140, isolated from genital disease, respectively, in bull and in cow, and the reference strains Movar 33/63 and DN599 were compared by several methods: cross-serological relationship studied by indirect immunofluorescence; kinetics of intracellular and extracellular viral production; comparison of the mean plaque size; restriction analysis of viral DNA with restriction enzymes EcoRI, BamHI and HindIII. BHV-4 strains were serologically identical and the kinetics of viral production were very similar. Comparison of the mean plaque size allowed classification into 3 classes (Class I, Movar33/63; Class II, LVR140; Class III, V.Test and DN599) and restriction analysis of viral DNA revealed clear differences between the electrophoretic patterns of the four BHV-4 strains. The differentiation between BHV-4 strains can therefore be achieved by a biological method (mean plaque size) and by restriction analysis. The two genital isolates are easily differentiated by the two methods.

Proteins specified by bovine herpesvirus type 4: structural proteins of the virion and identification of two major glycoproteins by using monoclonal antibodies

Bovine herpesvirus type 4 proteins were identified by PAGE of [35S]methionine- or [3H]glucosamine-labelled purified virions. Thirty-one monoclonal antibodies (MAbs) raised against the V. Test strain were used to identify 29 proteins, ten of which were glycosylated. All of these glycoproteins belonged to the viral envelope and a 140K non-glycosylated protein appeared to be the major nucleocapsid protein. The MAbs were classified into two groups. The first group precipitated three glycoproteins of Mr 150K, 120K and 51K. The 120K and 51K glycoproteins were linked by disulphide bonds and the 150K glycoprotein was linked to the others by non-covalent bonds. The second group precipitated a different 120K glycoprotein.

Production and characterization of monoclonal antibodies to bovid herpesvirus-4

Thirty-five hybridoma cell lines secreting monoclonal antibodies (Mabs) against bovid herpesvirus-4 (BHV-4) strain V. Test were produced. These hybrid cells resulted from the fusion of SP2/0 myeloma cells with splenocytes of BALB/c mice previously immunized with purified BHV-4. A modified indirect fluorescent antibody test (IFAT) was applied as a screening procedure and was compared with an indirect enzyme-linked immunosorbent assay. The selected Mabs were tested by the same IFAT against a panel of BHV-4 field isolates and against bovine herpesvirus-1, bovine herpesvirus-2 and alcelaphine herpesvirus-1 (AHV-1). Comparison of BHV-4 field isolates with Mabs confirmed their close antigenic relationships, but slight antigenic differences were observed between different isolates. One of the Mabs also reacted against AHV-1, indicating an antigenic relationship between BHV-4 and AHV-1. None of the Mabs reacting with BHV-4 possessed neutralizing activity against the strain used for immunization.