ABSTRACT
PCV is composed of two subtypes: PCV type 1 (PCV1) and PCV type 2 (PCV2). First identied in 1974,18 PCV1 frequently causes contamination in the PK15 cell line (ATCC-CCL31) and is generally considered nonpathogenic in swine. PCV2 was rst isolated from PMWS-affected pigs in the 1990s and is pathogenic in swine.19 PCV2 exhibits 68% and 66% identity to PCV1 in the full genomic and ORF2 sequences, respectively.20 The various PCV2 strains have 95%–100% sequence identity.21 According to the sequence diversity, PCV2 is further subdivided into PCV2a (with ve subclusters, 2A-2E), PCV2b (with three subclusters, 1A-1C), and PCV2c genotypes,22,23 which have been retrospectively studied and found as early as 1985, 1988, and 1980, respectively.23,24 In the past, the genotype PCV2a was the predominant virus causing PCVAD in pigs. The shift from the genotype PCV2a to PCV2b occurred between 2003 and 2006. Since 2006, the genotype PCV2b has been the predominant PCV2 subtype worldwide.24-28 The genotype PCV2c has only been found retrospectively in Denmark.23
