Epidemiology and Genetic Characterization of Porcine Parvovirus 7 Recovered from Swine in Hunan, China

Abstract

Porcine parvovirus 7 (PPV7) was first discovered in swine in 2016, and PPV7 infection has been detected in aborted pig fetuses and in sows that experienced reproductive failure. The objective of this study was to report the prevalence and genetic characterization of PPV7 in Hunan, China. Seventy of the four hundred and twenty-two (16.6%) serum, semen, and tissue samples collected from pigs were positive for PPV7. One complete PPV7 strain and eighteen complete cap gene sequences were obtained; nucleotide and amino acid identity among the nineteen Cap sequences were 88.1-99.4% and 88.1-100%, respectively. They shared identity with previously discovered sequences ranging from 86.6 to 98.9% and 83.7 to 99.8% at the nucleotide- and amino acid-level, respectively. The phylogenetic tree analysis exhibited that PPV7 strains had two major groups based on the presence or absence of five amino acid (181-185) insertions on the Cap protein. Analysis of the Cap protein demonstrated that PPV7 Cap had significant variability, implying that PPV7 evolved at high substitution rates. Substantial variations of that PPV7 Cap may enable the emergence of newly mutated capsid profiles due to its viral adaptation to host responses. Furthermore, antigenic alteration owing to PPV7 Cap protein amino acid mutations at immune epitopes may enable viruses to escape from the host's immune system. This study determined the prevalence and genetic characteristics of PPV7 circulating in swine in Hunan, China, and provided the impetus and basis to further investigate the pathogenicity and epidemiology of PPV7.

Keywords: PPV7; cap; epidemiology; genetic characterization.

Figure 1

Geographical distribution of PPV7 in Hunan Province. Blue regions represent locations of swine with samples that were positive for PPV7.

Figure 2

Phylogenetic trees of the Parvovirinae subfamily and PPV7 strains. The phylogenetic trees were reconstructed based on Cap amino acid sequences using p-distance-based neighbor-joining (NJ) method (A) and using the Maximum-likelihood (ML) method (B) with Jones-Taylor-Thornton (JTT) model of MEGA 7.0 with 1000 bootstrap replicates, respectively. Red solid circles indicate the strains obtained in this study.

Figure 3

Ratio of high-frequency amino acid mutations in the Cap protein of all PPV7 isolates. Red solid circles indicate ratio of high-frequency amino acid mutations in Cap protein in our PPV7 isolates obtained in this study.