Porcine circovirus type 2 (PCV2) in Brazil in the past 55 years (1967-2022): Evolutionary rates and patterns

Abstract Porcine circovirus type 2 (PCV2) is a common viral agent frequently described in herds, with a marked genetic variability impacted by factors such as vaccination and commercial trade. In this study, a retrospective analysis of PCV2 was performed based on molecular characterization, Bayesian inference, and the haplotype network in tissue samples obtained from Brazilian herds from 1967 to 2018. A nested PCR targeting a 225-base pair (bp) fragment of the PCV2 capsid gene was performed followed by a bi-directional sequencing. A total of 39/178 (21.9%) samples tested positive for PCV2. Genotype 2d was the major genotype described, and this genotype was detected before the introduction of the PCV2 vaccination. The mean substitution rate was 1.54 × 10⁻ ³ substitutions per site per year (s/s/y). The haplotype diversity of PCV2 was 0.98, which shows a high mutational rate compatible with the topology found in the haplotype network. In conclusion, most of the Brazilian samples were genotyped as PCV2d, even those obtained before the introduction of the PCV2 vaccine in Brazilian herds. The PCV2 sequence from 1967 represented the oldest description in America, and the second oldest description in the world; phylogenetic analysis and haplotype network indicated the high diversity of PCV2 as well as its high evolution rate. Our results may increase knowledge about the genetic diversity, evolution, and dispersal patterns of PCV2 in Brazil.