Porcine circovirus type 2 characteristics

Genetic characteristics of porcine circovirus

The PCV2 genome is all very simple in structure, with circular single-stranded DNA that is only 1.7 kb in length. of the seven predicted ORFs, ORF1 encodes replication-associated proteins (Rep and Rep'), ORF2 encodes coat protein (Cap), and ORF3 and ORF4 encode proteins involved in apoptosis and anti-apoptosis, respectively.

REP genes are highly conserved, while CAP genes evolve at a higher rate than the PCV2 genome as a whole. A single amino acid mutation in the PCV2b Cap protein prevents the neutralization of PCV2b monoclonal antibodies, and these studies suggest that even small mutations in the Cap protein may lead to the production of antigenically different viruses.

The immune epitopes of the Cap protein that can be recognized by antibodies are divided into four regions, ABCD, corresponding to amino acids 65-87, 113-139, 169-183 and some C-terminal amino acids, where the C region is considered a decoy epitope that induces the production of antibodies without neutralizing activity and is commonly used for serological analysis of the protective efficacy of antibodies. most of the differences between the PCV2d and PCV2a Cap proteins concentrated on the A and C regions, and bioinformatic analysis of the changes in the A region may be responsible for the altered antigenic structure that leads to enhanced binding of PCV2d antigen to the host and immune evasion.

Porcine circovirus prevalence
Porcine circovirus type 3 was found in the United States, and the homology between PCV3 and PCV2 genomes was only 37%, and PCV3 had a higher homology with bat circovirus. In China, PCV3 was also found in 11 provinces, and the homology of this strain with the US PCV3 strain was 97.4%-98.5%. The national center collected 189 clinical samples for PCV3 antigen testing from onset pig farms in eight provinces, and the positivity was 12.7%. Among them, the mixed infection rate of PCV3/PCV2 was 45.8%; the mixed infection rate of PCV3/PRRSV was 62.5%; and the mixed infection rate of PCV3/PCV2/PRRSV was 33.3%.