Genetic and In Vitro Characteristics of a Porcine Circovirus Type 3 Isolate from Northeast China

SIMPLE SUMMARY: Although several studies of porcine circovirus 3 (PCV3) have been conducted, there is little information regarding the pathogenicity of PCV3, in large part because of the small number of PCV3 isolates available. In this study, a PCV3 strain named PCV3-DB-1, belonging to the PCV3a branch, was isolated from PK-15 cells and with 24 alanine and 27 lysine in the Cap protein of this strain, which is unique. PCV-like particles were subsequently observed using electron microscopy and the RNA replication of PCV3 was confirmed in PK-15 cells using situ hybridization RNA scope. This is the first report on the isolation and in vitro characteristics of PCV3-DB-1 with 24A and 27K of the Cap protein. PCV3 was reported in 2015 on a sow farm experiencing PDNS-like and reproductive failure clinical symptoms in the United States, and was subsequently found in most swine-producing countries in Europe, Asia, and America. Although neurological disorders, as well as respiratory and enteric disease, have been described in association with PCV3 infection, multisystemic inflammation and reproductive failure are the most concerning clinical presentations. Studies reproducing and characterizing PCV3 clinical disease and pathogenesis under experimental conditions are scarce, in large part because of the difficulty of isolating PCV3. In this study, we isolated PCV3-DB-1 in PK-15 cells and characterized them in vitro. By using electron microscopy, PCV-like particles were discovered, and in situ hybridization RNA sequencing showed PCV3 replication in PK-15 cell culture. Based on phylogenetic analysis of PCV3 isolates from the Heilongjiang province of China, PCV3-DB-1 with 24 alanine and 27 lysine in the Cap protein was originally isolated and determined to belong to the clade PCV3a. ABSTRACT: Porcine circovirus 3 (PCV3) is an emerging virus first discovered in the United States in 2015, and since then, PCV3 has been found in many regions of the world, including America, Asia, and Europe. Although several PCV3 investigations have been carried out, there is a lack of knowledge regarding the pathogenicity of PCV3, mostly due to the limited number of PCV3 isolates that are readily available. In this study, PCV3-DB-1 was isolated in PK-15 cells and characterized in vitro. Electron microscopy revealed the presence of PCV-like particles, and in situ hybridization RNA analysis demonstrated the replication of PCV3 in PK-15 cell culture. Based on phylogenetic analysis of PCV3 isolates from the Heilongjiang province of China, PCV3-DB-1 with 24 alanine and 27 lysine in the Cap protein was originally isolated and determined to belong to the clade PCV3a.