Isolation, characterization, and phylogenetic analysis of two new porcine parvovirus 1 isolates from Northern China

Porcine parvovirus (PPV) is a pathogen of infectious reproductive disease, which can cause stillbirth, mummification, embryo death, and infertility (SMEDI) syndrome in pigs. The objective of this study was to gain new insights into the evolution and phylogeny of the PPV1 genome. In this study, we isolated two new PPV1 (HLJ202108-Y and SDLC202109) from northern China and sequenced their whole genomes. The new isolates were found to have three amino acid substitutions (K195R, K562R, and S578P) in nonstructural protein 1. The VP2 amino acid site contained nine nonsynonymous substitutions, including six substitutions of the Kresse strain corresponding to the NADL-2 strain and three substitutions of A414S, S436T, and N555K. Genetic evolution analysis was conducted on 107 reference sequences available in the GenBank database, and 4-5 PPV1 taxa were defined. The new isolates were in the same phylogenetic cluster as strain 27a. The changes in the cluster, specifically marker amino acids, and their potential role in enhancing pathogenicity are discussed in this study. Furthermore, the evolutionary tree map results showed that the strains in China were evolving in two directions: one was becoming increasingly similar to early NADL-2 strains, while the other was evolving toward 27a-like strains. We also compared the proliferation ability of the isolated strains in susceptible cells by analyzing the multistep growth curves. The results showed that the virulence titer of the mutant strain was high. In summary, this study introduced the latest changes in PPV and discussed the virus characteristics that were considered to affect virulence.