Porcine circovirus type 2 (PCV2) is generally considered to be the primary causative agent of postweaning multisystemic wasting syndrome (PMWS),which has become a serious economic problem for the swine industry worldwide.Recently,a nomenclature was proposed for PCV2 which took into account the classification of Grau et al.(2008) and identified two major genotypes of the virus (PCV2a and PCV2b) circulating worldwide and a third genotype (PCV2c) that was reported sporadically in the 1980s.A number of studies have confirmed PCV2a and PCV2b as the predominant genotypes worldwide and PCV2 has been reported to have undergone much genetic variation in recent years.