The widespread distribution and genetic diversity of porcine circovirus type 2 (PCV2) seriously threatens the swine industry worldwide. This study investigates the molecular epidemiology of PCV2 in Henan Province (2020–2023) through PCR screening (385 samples) and whole-genome sequencing (34 strains). The overall detection rate was 71.17% (274/385), with annual rates of 81.16% (112/138) in 2020, 72.41% (84/116) in 2021, 62.50% (55/88) in 2022, and 53.49% (23/43) in 2023, indicating a declining trend. Phylogenetic analysis revealed the dominance of the PCV2d genotype, comprising 82.4% (28/34) of sequenced strains. Evolutionary analysis identified strong negative selection pressure on ORF2, with an elevated substitution rate of 1.098 × 10⁻³ ssy. These findings provide critical insights into the predominance and adaptive evolution of PCV2d, and significantly improve our understanding of its genetic diversity and evolutionary dynamics.

Aeromonas veronii (A. veronii) is a ubiquitous bacterium in terrestrial and aquatic environments. It has a significant impact on animal and human health, with it becoming an emerging crucial pathogen worldwide. However, there have been no reports of mute swan infections. In the present study, after an observation of pathological changes, one bacterial strain isolated from a dead migratory mute swan was identified as A. veronii HNZZ-1/2022 based on its morphology, matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS), and sequence analysis of the 16S rRNA and gyrB genes. To explore its pathogenicity, virulence gene detection and a gosling infection experiment were subsequently carried out, respectively. Six virulence genes for cytotonic enterotoxins (alt), lateral elastase (ela), lipase (lip), cytotoxic enterotoxin (act), aerolysin (aerA), and polar flagellin (fla) were present in the template DNA of A. veronii HNZZ-1/2022. Experimentally infected goslings exhibited hemorrhages of various different degrees in multiple organs. The half-maximal lethal dose (LD₅₀) value of A. veronii strain HNZZ-1/2022 was estimated to be 3.48 × 10⁸ colony forming units (CFUs) per mL for goslings. An antimicrobial susceptibility test showed that the A. veronii HNZZ-1/2022 strain was resistant to meropenem, ampicillin, and enrofloxacin. To date, this is the first report of A. veronii in migratory mute swans, thus expanding the currently known host spectrum. These results suggest that the migratory mute swan is a new host for A. veronii and demonstrate the need for extensive surveillance and research of A. veronii to minimize its transmission between animals, the environment, and humans.