Abstract: To investigate molecular epidemiology and genetic variation of porcine circovirus type 2 (PCV2) in Zhejiang province,a total of 329 clinical samples collected in 2018 were subjected to PCR, and the whole genome of PCV2 from 7 positive samples were sequenced. The results demonstrated that the total positive rate of PCV2 was 27.4% (90/329), and the highest positive rate (52%) was in Ningbo district. By age, the highest positive rates were from fattening pigs and growing pigs (38.8% and 68.8%). Three or four clones of each of the seven randomly selected positive samples were sequenced, and genetic variation were analyzed with MEGA 6.0. Sequence comparison showed that the nucleotide sequence homologies among the 22 PCV2 strains were up to 93.3%~99.8%; and were up to 93.5%~99.8% compared with the 16 reference strains. The phylogenetic analysis revealed that these 22 strains belonged to 3 subtypes: PCV2a(6/22)、PCV2b(6/22) and PCV2d(10/22). It was indicated that PCV2d was the dominant subtype in Zhejiang province. The genetic variation analysis of ORF2 gene showed lower homology than the whole genome. The phylogenetic tree analysis of ORF2 showed that the strains were located in subtype of PCV2b, PCV2d and PCV2e respectively, indicating that the prevalent strains in Zhejiang may be shifting to PCV2e. This study explored the molecular epidemiology of PCV2 in Zhejiang province, and provided the basis for screening the candidate strain for the development of PCV2 vaccine.

Key words: porcine circovirus type 2, whole genome, ORF2 gene, epidemiological investigation, genetic variation analysis