Epizootology, genetics and evolution of porcine circovirus type 2 in China

The genotypic subtype of porcine circovirus type 2 (PCV2) continues to evolve, complicating the epizootic situation. To elucidate the nature of genotype drift in the evolution of PCV2 strains in China, 2529 fully coded ORF2 genes from the NCBI database collected in China from 2004 to 2023 were classified by year of isolation. The results showed that there were two genotype drifts in PCV2 evolution in China over the past 20 years, with genotypes drifting from PCV2a before 2004. A total of 43 strains were further investigated between 2018 and 2023 from three provinces in Northeast China - Liaoning, Heilongjiang and Jilin - which are adjacent to Russia. Among them, PCV2a genotype accounted for 18.6 %, PCV2b genotype accounted for 27.9 %, and PCV2d genotype accounted for 53.4 %. This indicates that PCV2 genetic diversity increased in Northeast China, and PCV2b and PCV2d became the major genotypes prevalent during this period. Comparison of the amino acids of the ORF2 gene encoded by the sequence of virulent strains showed that there were five major regions of variation in the Cap protein among the virulent strains. These residues included amino acid sites 51-91, 121-151, 183-191, 206-217, and 232-234.