Changes

===Virus Genotypes===

===Virus Genotypes===

There are two recognised genotypes of BVDV; type 1 and type 2. These differ antigenically (Paton et al., 1995), although classification based on sequence variation is more precise. Analysis of the 5’UTR has divided BVDV1 into 11 subtypes and BVDV2 into 3 subtypes (Vilcek et al., 2001). Despite large intra-genotype antigenic differences, type 1 vaccines give some degree of cross-protection against disease caused by type 2 viruses (Carman et al., 1998; Cortese et al., 1998; van Oirschot et al., 1999).

 

 

There are two antigenically distinct<sup.9</sup> genotypes of BVDV, type 1 and type 2, which are most accurately characterised based on sequence variation. 11 and 3 subtypes exist within BVDV-1 and BVDV-2 respectively, which have been demonstrated by analysis of the 5’UTR¹⁰. Despite the large antigenic differences between the genotypes, cross-protection against type 2 viruses is afforded by type 1 vaccines^{11, 12, 13}.

A split in virulence between genotypes is evident. BVDV1 species, including classical strains and common vaccine strains, tend to cause milder disease (Deregt, 2004) and are found worldwide. Alternatively, BVDV2 isolates typically cause more severe disease, characterised by fever, diarrhoea, thrombocytopaenia, haemorrhage, respiratory signs, and high abortion and mortality rates (Corapi et al., 1989; Carman et al, 1998). These viruses were first reported in Canada and the USA, although their distribution is widening. The first British case of type 2 BVDV was identified in 2002 (Drew et al., 2002).

A split in virulence between genotypes is evident. BVDV1 species, including classical strains and common vaccine strains, tend to cause milder disease (Deregt, 2004) and are found worldwide. Alternatively, BVDV2 isolates typically cause more severe disease, characterised by fever, diarrhoea, thrombocytopaenia, haemorrhage, respiratory signs, and high abortion and mortality rates (Corapi et al., 1989; Carman et al, 1998). These viruses were first reported in Canada and the USA, although their distribution is widening. The first British case of type 2 BVDV was identified in 2002 (Drew et al., 2002).