Detection and genetic evolution analysis of porcine parvovirus type 7 (PPV7) in Fujian Province

Porcine parvovirus (PPV) is an important pathogen causing reproductive disorders in sows, with clinical symptoms including stillbirth, mummified fetuses, embryonic dysplasia and death, and sow infertility. Porcine parvovirus 7 (PPV7) is a recently discovered type of PPV and its widespread distribution and rapid evolution has caused huge economic losses in the pig industry. To investigate the molecular epidemiology of PPV7 in Fujian Province, China, we collected 491 blood samples and 72 tissue samples from diseased pigs in large-scale pig farms across selected areas of Fujian Province from 2019 to 2022. PPV7 infection was determined using real-time quantitative PCR, and positive samples underwent whole-genome amplification, sequencing, and subsequent homology, phylogenetic, and recombination analyses. The PPV7 positive detection rate was 25.73% (145/563) in Fujian Province, among which the positive rate of blood and tissue samples was 26.47% (130/491) and 20.83% (15/72), respectively. The nucleotide sequence homology among the 29 PPV7 whole-genome sequences obtained in this study was 90.0%-97.2%, whereas that with 128 reference strains from China and other countries was 88.9%-98.1%. Six strains had partial nucleotide deletions or insertions. Phylogenetic analysis based on the whole-genome sequences classified the 29 PPV7 strains and 128 reference strains into eight subtypes (PPV7a-PPV7h), and PPV7h was the predominant subtype in Fujian Province. Recombination analysis revealed evidence of inferred recombination events in the genomes of four strains. This study provides significant insights into the molecular characteristics of PPV7 in Fujian Province and serves as a crucial foundation for further advancements in PPV7 prevention and control strategies.