Changes

===Virus Structure===

===Virus Structure===

Donis, 1995 Dubovi, 1990

van Gennip, 2005).

The BVDV genome comprises a single strand of positive sense RNA which is around 12.3 kilobases in length³. The genome is read in one 3898-codon open reading frame that contains no non-coding sequences. BVDV polyprotein is translated directly from the ORF and is cleaved by viral and cellular proteinases to form mature viral proteins^{3, 4}. At either end of the ORF, 5’ and 3’ untranslated regions exist. These regions are long, allowing them to accomodate fuctions conferred in eukaryotic DNA by the 5’ cap and the 3' poly-A tail, such as controlling the initiation of translation, facilitating the entry of replicases, and contributing to RNA stability.  

The BVDV genome comprises a single strand of positive sense RNA which is around 12.3 kilobases in length³. The genome is read in one 3898-codon open reading frame that contains no non-coding sequences. BVDV polyprotein is translated directly from the ORF and is cleaved by viral and cellular proteinases to form mature viral proteins^{3, 4}. At either end of the ORF, 5’ and 3’ untranslated regions exist. These regions are long, allowing them to accomodate fuctions conferred in eukaryotic DNA by the 5’ cap and the 3' poly-A tail, such as controlling the initiation of translation, facilitating the entry of replicases, and contributing to RNA stability⁴.  

The first structural protein coded is Npro, which has a protease action that generates the N-terminus of the next protein, C. C packages genomic RNA and provides interactions necessary for formation of the enveloped virion. Erns, E1 and E2 are all glycoproteins. Erns has an RNase activity that is probably involved in viral replication and pathogenesis (van Gennip, 2005). E1 is membrane-anchored and initiates the translocation of E2 to the virion envelope where it is highly antigenic, causing the production of neutralising antibodies following infection or vaccination (Donis, 1995).  

BVDV's RNA genome encodes both structural and non-structural proteins. Structural proteins include ''Npro'', whose protease action generates the N-terminus of the protein ''C''. ''C'' protein packages genomic RNA and assists in the formation of the eventual enveloped virion. ''Erns'', ''E1'' and ''E2'' are all structural glycoproteins, with ''Erns'' possessing RNase activity involved in viral replication and pathogenesis<sup>5</sup. 'E1'' is membrane-anchored and initiates the translocation of the  antigenic ''E2'' to the envelope³.

The next protein is P7. Although P7 function is uncertain, studies have suggested that the C-terminal part acts as a signal sequence required for correct processing and membrane translocation of NS2 (Tautz et. al, 1999).

The next protein is P7. Although P7 function is uncertain, studies have suggested that the C-terminal part acts as a signal sequence required for correct processing and membrane translocation of NS2 (Tautz et. al, 1999).