Modification of PCV-2 virulence by substitution of the genogroup motif of the capsid protein

Allemandou, Aude; Grasland, Béatrice; Hernandez-Nignol, Anne-Cécile; Kéranflec'h, André; Cariolet, Roland; Jestin, André

PCV-2 are small non-enveloped viruses, belonging to the Circovirus genus of the Circoviridae family. Their genome is a circular, single-stranded DNA molecule of 1767 or 1768 bases encoding three major open reading frames (ORFs). ORF1 codes for the Rep and Rep' proteins implicated in the replication of the PCV-2 DNA [7] . ORF2 codes for the capsid protein (Cap) which is the only structural protein [8] and ORF3 for a protein possibly involved in apoptosis mechanism [9] . Molecular epidemiology studies allowed separating PCV-2 isolates into two main genogroups: PCV-2a and PCV-2b [10, 11] . PCV-2 isolates from each of the two major genogroups had a motif, located between amino acids 86 to 91, strongly specific and conserved in their capsid proteins [10] . In 2005, a PCVD outbreak occurred in North America. This event was concomitant with the emergence of isolates of PCV-2b genogroup [12] , which happened also in some European countries including Switzerland [13] and in Spain [14] . PCV-2b emergence seemed to be correlated to PMWS outbreak, giving rise to the assumption that the genogroup PCV-2b was more virulent than the PCV-2a one. Nevertheless, no link was clearly established between the genogroup and virulence of isolates, because same isolates were detected in PMWS-affected and non-affected herds in France [15] .