||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).|
||1.2a is the genital
subtype. 1.2b occurs predominantly in
||This encephalitic subtype has been reclassified as BHV-5 and mainly causes meningoencephalitis in young calves.|
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.