Genotypic change and phylogenetic analysis of porcine circovirus type 2 in Taiwanese pig herds.

Porcine circovirus type 2 (PCV2) is the primary causative agent of postweaning multisystemic wasting syndrome. Two major PCV2 genotypes, PCV2a and PCV2b, have been identified. To explore the prevalence of different subgroups of PCV2 in Taiwan, 37 PCV2 isolates collected during 2002-2011 were analyzed. The genotypes of the PCV2 isolates collected before 2007 belonged to either PCV2a or PCV2b. However, all of the isolates collected after 2008 were PCV2b. Most of the isolates obtained since 2008 have been classified into a novel genotype within a subgroup of PCV2b based on complete ORF2 sequence analysis. Moreover, analysis of the PCV2 isolates from the same pig farm but from different years revealed that the viruses shifted from a PCV2b genotype to a novel subgroup of the PCV2b genotype. Collectively, PCV2b was the dominant PCV2 genotype in Taiwan currently, and the viruses have shifted into a new emerging subgroup of the PCV2b genotype.