Comparison of immediate-early transcripts among bovine herpesvirus type 1 and type 5 strains differing in neurovirulent potential

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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Pathogenesis of meningoencephalitis in rabbits by bovine herpesvirus type-5 (BHV-5)

This article describes the main aspects of bovine herpesvirus type-5 (BHV-5) neurologic infection and disease in rabbits, a candidate animal model for studying BHV-5 neuropathogenesis. Intranasal inoculation of weanling rabbits with a Brazilian BHV-5 isolate produced neurological disease and death in 78.8% (26/33) of the animals. Neurological signs started as early as 5 days post-inoculation and lasted from 10-12 hours up to several days. Most animals evolved to a moribund state or death within 24 (69.2%) to 48 hours (88.5%). Neurological disease was characterized by excitability or depression, tremors, bruxism, walking or running in circles, backward arching of the head and body, incoordination, backward and sideways falling, paddling, profound depression and death. Moderate levels of infectivity were detected in several areas of the brain, most consistently in the ventro-lateral hemisphere (in 16 out of 20 animals), anterior cerebrum (15/20), midbrain (11/20), dorso-lateral hemisphere (10/20) and pons (12/26). Infectious virus was also recovered from the olfactory bulb (9/20), medulla oblongata (10/26), cerebellum (7/20), posterior cerebrum (5/20) and trigeminal ganglia (4/20). No gross lesions were observed. Microscopic lesions were mild and consisted of non-suppurative meningitis, mononuclear perivascular cuffing and focal gliosis. These changes were observed most consistently in the ventro-lateral hemisphere and anterior cerebrum. Passive immunity partially protected rabbits from BHV-5-induced encephalitis. Rabbits born to immunized dams showed a significative delay in the onset of clinical disease and reduced morbidity and mortality rates compared to rabbits born to unvaccinated dams. These results demonstrate that BHV-5-induced neurological disease can consistently be reproduced in rabbits and point towards the use of this species as an animal model to study BHV-5 neuropathogenesis.

Molecular virology of ruminant herpesviruses

Molecular virology has served to establish bovine herpesvirus 1 (BHV-1) as the prototype member of ruminant herpesviruses. Based on the genomic sequence of the virus, we aim to identify and characterize virus-specified components, to explain their concerted action, and to predict how the chain of events during the lytic and latent phases of the viral life cycle may be interrupted. The nucleotide sequence of the BHV-1 genome (136 kb) has just been completed by international cooperation (July 1995; except for a small gap in UL36). It comprises 67 unique genes and 2 genes, both duplicated, in the inverted repeats. In general, these genes exhibit strong homology at the amino acid sequence level to those of other alphaherpesviruses (HSV-1, VZV, EHV-1) and are arranged in similar order. A few genes are peculiar to only one or two herpesviruses, e.g. in BHV-1 the circ, UL0.5, UL3.5 and US1.5 genes. Not long ago, the repertoire of BHV-1 proteins under study was restricted to the three major glycoproteins (gB, gC, and gD) and thymidine kinase. The repertoire is now growing rapidly and includes 7 additional glycoproteins (gE, gI, gH, gL, gG, gK and gM), a number of enzymes (e.g. ribonucleotide reductase, DNA Polymerase, dUTPase), and a group of regulatory proteins (BICPO, 4, 22, and 27, alpha TIF). Investigations into the functions of these proteins and comparison with their counterparts in other herpesviruses should reveal which are useful targets for diagnosis, prevention or antiviral treatment. Recombinant viruses containing deletions or replacements of individual genes are being created, aiming at vaccine development and insights into pathogenesis, notably latency, neurotropism, and interference with host functions. Molecular analysis of other ruminant herpesviruses is much less advanced. Over a dozen virus species have been described; most share basic properties with BHV-1 and may be classified as alphaherpesviruses. The gammaherpesviruses are represented by the proposed agent of malignant catarrhal fever, alcelaphine herpesvirus 1, and by bovine herpesvirus 4, whose partial sequences exhibit similarity to herpesvirus saimiri.

Immediate-early gene expression and gene mapping comparisons among isolates of bovine herpesvirus 1 and 5

Bovine herpesviruses (BHV) are associated with a variety of clinical syndromes. Bovine herpesvirus 1 isolates were placed into three genome subtypes based on restriction endonuclease analyses, which were loosely associated by clinical manifestation as BHV1.1 (respiratory), BHV1.2 (genital), and BHV1.3 (encephalitic). More recently the encephalitic isolate has been classified BHV5. A comparison of the cytopathic effect (CPE) in fetal bovine lung cell cultures in the presence of cycloheximide showed that BHV1.1 and 1.2 isolates produced elongated, spindle-shaped CPE, whereas BHV5 produced more syncytial-like CPE. Each BHV-1 subtype synthesized four immediate-early transcripts. The sizes in kb were: 1.6, 3.4, 5.8, 7.5 (BHV1.1); 1.8, 3.6, 5.8, 7.5 (BHV1.2); and 1.8, 3.6, 5.8, 8.6 (BHV5). These transcripts were mapped to the inverted repeat region of each isolate by Southern blot hybridization using cDNA prepared from cycloheximide-treated BHV1-infected cellular polyA RNA. A possible unique immediate-early RNA may be produced by the BHV5 encephalitic isolate from an area of the internal repeat region unique to this isolate. Hybridization analysis using BHV1.1 cloned probes of the immediate-early protein gene, thymidine kinase gene, DNA binding/DNA polymerase gene, and glycoprotein III gene provided information for mapping of these genes to the BHV5 encephalitic isolate.