Xue Bai

The innate immune system constitutes the host's primary defense against viral infection through the use of specific pattern recognition receptors (PRRs) for different viruses, which activate interf...

Since feline panleukopenia virus (FPV) is considered the most likely ancestor of canine parvovirus (CPV), comprehensive comparisons of nucleotide organization in corresponding viral genes between CPV and FPV may provide novel insights into the evolutionary dynamics underlying the divergence of these two viruses. Here, we characterize the evolutionary patterns of CPV and FPV genes across multiple levels of nucleotide organization. Both viruses exhibited highly conserved nucleotide usage at nonsynonymous sites, with Ka/Ks patterns consistent with strong purifying selection, whereas synonymous sites showed greater variability. CpG dinucleotides were markedly underrepresented across all four viral genes, suggesting host-associated selective pressure and/or intrinsic nucleotide compositional constraints. Extensive nonrandom biases in synonymous codon usage, codon neighboring nucleotide context, and codon pair usage further revealed fine-scale genomic optimization shaped by natural selection and nucleotide compositional constraints. Structural protein genes ( VP1 and VP2 ) displayed stronger codon usage bias and higher tRNA adaptation than nonstructural genes. Moreover, CPV genes showed greater translational adaptation to feline hosts than to canine hosts. These findings highlight how closely related parvoviruses exploit flexible nucleotide organization to facilitate host adaptation while maintaining essential protein functions.

A reverse genetics system for the feline panleukopenia virus (FPV) strain JL2280 was successfully established in this study. By optimizing the cloning strategy for the terminal hairpin structures, a full-length infectious clone, pFPV, harboring a KpnI genetic marker was constructed. The recombinant virus (rFPV) was successfully rescued in CRFK cells and exhibited replication kinetics, pathogenicity, and morphological characteristics comparable to those of the wild-type virus. To evaluate the potential of FPV as a live vector, a recombinant virus expressing enhanced green fluorescent protein (EGFP), designated rFPV–EGFP, was generated by inserting a P2A–EGFP cassette downstream of the NS1 gene. The rFPV–EGFP virus mediated efficient EGFP expression in infected cells; however, the fluorescence intensity gradually diminished with serial passages. The reverse genetics platform developed herein provides a valuable tool for investigating the genomic functions, pathogenic mechanisms, and evolution of FPV. Furthermore, the successful rescue of rFPV–EGFP demonstrates the preliminary feasibility of FPV as a live vector for foreign gene expression. Nevertheless, strategies such as optimizing insertion sites or modifying the viral backbone are required to enhance the stability of exogenous protein expression. This study lays the groundwork for the development of novel FPV-based genetically engineered vaccines and antiviral therapeutics.

Multidrug‐resistant (MDR) bacteria have reduced the effectiveness of antimicrobial agents and limited available treatment options in both human and animal settings. Antimicrobial resistance (AMR) in animal‐derived Escherichia coli ( E. coli ) has become increasingly common, with many isolates showing resistance to multiple classes of antimicrobials. However, compared with other animal sources, resistance characteristics of E. coli from mink remain less well understood, particularly in terms of genomic features. In this study, we identified a MDR E. coli strain, EC0D1, isolated from the lung tissue of a farmed mink that succumbed to hemorrhagic pneumonia (HP) in China. Antimicrobial susceptibility testing indicated that EC0D1 exhibited resistance to β‐lactams, fluoroquinolones, aminoglycosides, tetracyclines, and polymyxins but was sensitive to carbapenems and tigecycline. Whole genome sequencing showed that EC0D1 contains a single chromosome and eight plasmids. Among these, plasmid pEC0D1‐3 coharbored bla _CTX-M−55 and mcr-1.1 , while pEC0D1‐2 carried tet (A) and floR , together explaining the observed MDR phenotype. Phylogenetic analysis classified EC0D1 as sequence type ST457 and demonstrated a close genetic relationship with several human clinical isolates. Comparative genomic analysis further revealed that plasmids pEC0D1‐2 and pEC0D1‐3 shared high sequence similarity with plasmids previously identified in avian‐derived E. coli and human‐derived Klebsiella pneumoniae isolates. Conjugation assays confirmed that plasmids carrying bla _CTX-M−55 , mcr-1.1 , tet (A), and floR were transferable to different bacterial recipients. The emergence of transferable resistance determinants in mink‐associated E. coli suggests a potential role in the transmission of resistance genes between human and animal hosts.

Canine distemper virus (CDV) is a highly contagious morbillivirus that causes severe disease in carnivores, with raccoon dogs (Nyctereutes procyonoides) serving as major reservoirs for transmission. To address the limitations of current vaccines—such as virulence reversion, multiple doses, and poor efficacy in raccoon dogs—we developed a novel mRNA–lipid nanoparticle (LNP) vaccine encoding a secreted, tetrameric CDV hemagglutinin (H) protein fused to a signal peptide and Tetrabrachion domain to enhance stability and immunogenicity. The vaccine showed high purity, uniform particle size (~108 nm), and efficient in vivo expression of glycosylated H protein. In BALB/c mice, it induced strong H-specific IgG and increased splenic CD4⁺ T cells, suggesting a Th-skewed immune response. In raccoon dogs, high neutralizing antibody titers were maintained post-immunization, and all vaccinated animals survived lethal CDV challenge, whereas controls showed 100% mortality. Compared with a live-attenuated CDV vaccine, the mRNA–LNP vaccine markedly reduced clinical signs, preserved intestinal integrity, and nearly eliminated viral RNA in mucosal and systemic tissues. This study provides the first evidence that an mRNA-LNP vaccine encoding CDV hemagglutinin can confer complete protection against CDV challenge in raccoon dogs, highlighting its potential for veterinary and wildlife disease prevention.

Raccoon dog parvovirus (RDPV) is a highly contagious pathogen causing severe hemorrhagic enteritis that is fatal in young raccoon dogs. Since 2016, epidemiological investigations have documented recurrent outbreaks of RDPV, exhibiting heightened virulence; however, the molecular mechanisms driving this increased pathogenicity remain poorly understood. In this study, an alignment of 67 complete RDPV sequences identified two high-frequency amino acid mutations at positions 27 and 297 in the VP2 capsid protein that distinguish RDPV strains from before and after the 2016 outbreak. We generated a series of variant viruses with single or double amino acid substitutions using infectious cDNA clones from RDPV/CL/2016 (rRDPV-16) and RDPV/FLD/2010 (rRDPV-10) strains. In F81 cells, the mutant virus derived from rRDPV-16 exhibited reduced replication capacity and attachment than the parental strain, whereas mutants derived from rRDPV-10 showed enhanced replication and attachment. Cell-binding assay, ELISA, and biolayer interferometry (BLI) assays demonstrated a significant decrease in binding capacity to the transferrin receptor (TfR) for the rRDPV-16-derived mutant viruses. In raccoon dogs, these mutant viruses displayed reduced pathogenicity, as evidenced by clinical symptoms, viral loads in rectal swabs, and histopathological changes, compared with the parental strain. Molecular docking and dynamics simulations further suggest that the mutation at position 297 may alter the structural stability of VP2 and affect its binding affinity to raccoon dog TfR (RDTfR). This study identifies amino acid residues at positions 27 and 297 in VP2 as crucial determinants of RDPV replication and pathogenicity, providing insights for the development of therapeutic and prognostic strategies. IMPORTANCE: Raccoon dog parvovirus (RDPV), a variant of canine parvovirus 2 (CPV-2), has become an emerging threat to fur-bearing canid populations, causing severe disease outbreaks and economic losses. Despite its significance, the molecular basis underlying the enhanced pathogenicity of recent RDPV strains remains poorly understood. Our study identifies two key amino acid mutations (S27T and S297A) in the capsid protein VP2 that significantly increase viral replication, receptor binding affinity, and disease severity in raccoon dogs. These findings elucidate critical determinants of host adaptation and virulence in RDPV, highlighting the evolutionary dynamics of parvoviruses and offering a foundation for targeted antiviral strategies and disease control in fur animal farming.