Changes

===Virus Genotypes===

===Virus Genotypes===

There are two antigenically distinct⁹ 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}.

There are two antigenically distinct⁹ genotypes of BVDV, type 1 and type 2, which are most accurately characterised based on sequence variation. BVDV-1 and BVDV-2 contain 11 and 3 subtypes 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}.

In general, the genotypes differ in virulence. BVDV-1 species are found worldwide and tend to cause milder disease ¹⁴, wherease BVDV-2 isolates typically cause more severe disease which is often haemorrhagic and is associated with a high mortality rate^{11, 15}. Type 2 viruses were first reported in Canada and the USA and have a more limited distribution than type 1 isolates. The relationship between genotype and virulence is, however, not fixed: some type 2 strains cause mild or subclinical disease¹⁶, and the spectrum disease caused by type 1 viruses is broad.

In general, the genotypes differ in virulence. BVDV-1 species are found worldwide and tend to cause milder disease ¹⁴, whereas BVDV-2 isolates typically cause more severe disease which is often haemorrhagic and is associated with a high mortality rate^{11, 15}. Type 2 viruses were first reported in Canada and the USA and have a more limited distribution than type 1 isolates. The relationship between genotype and virulence is, however, not fixed: some type 2 strains cause mild or subclinical disease¹⁶, and the spectrum disease caused by type 1 viruses is broad.

===Virus Biotypes===

===Virus Biotypes===