Viral Characteristics

Bovine Herpresvirus-1


Family:
Herpesviridae

Subfamily: Alphaherpesvirinae

Genus: Varicellovirus

Species: Bovine herpesvirus 1

Classification

BHV-1 is an alphaherpes virus belonging to the family of Herpesviridae which has a world-wide distribution. There are 5 known strains that affect cattle. Strains have been differentiated on the basis of DNA homology, disease patterns and antigenic properties (Engels et al. 1981; Mayfield et al. 1983; Metzler et al. 1985; Metzler et al. 1986; Engels et al. 1986; Smith et al. 1993; Rijsewijk et al. 1999). 


                                                Herpesviridae
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BHV-1 has three subtypes that have been described on the basis of endonuclease cleavage patterns of viral DNA (Wentink et al. 1993). They are as follows:

BHV-1.1
In most instances, infectious bovine rhinotracheitis (IBR) refers specifically to the BHV-1.1a subtype.  The 1.1b strain is associated with venereal disease (Wentink et al., 1993).
BHV-1.2
1.2a  is the genital subtype. 1.2b occurs predominantly in Australia, is associated with very mild respiratory disease and is not vertically transmissible between an infected dam and her fetus (Wentink et al., 1993; Edwards et al., 1991).
BHV-1.3
This encephalitic subtype has been reclassified as BHV-5 and mainly causes meningoencephalitis in young calves.


Viral structure and morphology

BHV-1 has a 136 kilobase-pair, linear, double-stranded DNA genome. The entire genome was sequenced in1997 (Schwyzer et al., 1997) and encodes structural proteins as well as proteins for nucleic acid metabolism, DNA synthesis and protein processing. The genes of greatest clinical relevance are the ones that encode the major envelope glycoproteins, gB, gC and gD, and thymidine kinase (Kit et al. 1986; van Engelenburg et al. 1994; Liang et al. 1997; Kaashoek et al. 1998).

 From the interior to exterior-most layer, the genome is enclosed in a protein capsid, followed by a tegument, and an envelope. BHV-1 glycoproteins are expressed on the surface of the viral envelope.



                                BHV-1 Virus
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ABBREVIATIONS