Genetic diversity in the capsid protein gene of porcine circovirus type 3 in Vietnam from 2018 to 2019.

Porcine circovirus type 3 (PCV3) was first detected in 2016 and has been reported in many pig-producing countries around the world, including Vietnam. PCV3 has been found in complex cases with multiple clinical syndromes in swine. In this study, we investigated the genetic diversity of PCV3 strains circulating in Vietnam. A total of 249 samples were collected from swine farms located in eight provinces of Vietnam, and 11.65% (29/249) of these samples were found to contain PCV3. The ORF2 genes from the 29 PCV3-positive samples were amplified, purified, and sequenced. Phylogenetic analysis showed that 23 of these strains belonged to the PCV3b subtype, while the remaining six strains belonged to subtype c and subtype a (a-1 and a-2). Analysis of the ORF2 genes indicated that the 29 PCV3 strains had high sequence identity (96.90-100% at the genomic level and 96.19-100% at the amino acid level). Fifteen amino acid substitutions were found in predicted B-cell epitopes in the capsid proteins of the Vietnamese PCV3 strains.