Feline Panleukopenia Virus ZZ202303 Strain: Molecular Characterization and Structural Implications of the VP2 Gene Phylogenetic Divergence

Abstract

Feline panleukopenia virus (FPV), the etiological agent of a highly contagious multispecies disease, demonstrates concerning phylogenetic divergence that compromises vaccine cross-protection. This study aimed to characterize a novel FPV strain through integrated virological and molecular analyses to assess epidemiological implications. From seven clinical specimens obtained from feline hosts with panleukopenia in Henan Province, China, we isolated FPV ZZ202303 using an F81 cell culture coupled with PCR verification, demonstrating potent cytopathic effects (TCID₅₀: 10^-5.72/0.1 mL) and rapid replication kinetics (viral peak at 12-24 h post-infection). Comparative virulence assessments revealed a 1.8- to 2.3-fold greater pathogenicity versus contemporary field strains (2021-2023). Phylogenetic reconstruction based on complete VP2 gene sequences positioned FPV ZZ202303 within an emerging clade sharing 97.5-98.2% identity with canine parvovirus strains versus 98.8-99.7% with FPV references, forming a distinct cluster (bootstrap = 94%) diverging from vaccine lineages. Critical structural analysis identified a prevalent I101T mutation (89.13% prevalence) in the VP2 capsid protein's antigenic determinant region, with molecular modeling predicting altered surface charge distribution potentially affecting host receptor binding. Our findings substantiate FPV ZZ202303 as an evolutionarily divergent strain exhibiting enhanced virulence and unique genetic signatures that may underlie vaccine evasion mechanisms, providing critical data for updating prophylactic strategies against this economically impactful pathogen.

Keywords: FPV; analysis of phylogenetic divergence; biological properties; identification of isolates.

Figure 1

PCR detection of the pathological samples. (A) FCV identification of the disease samples; (B) FCoV identification of the disease samples; (C) FHV identification of the disease samples; (D) FPV identification of the disease samples. Note: M: DL1,000 DNA marker; 1–7: sample to be tested; 8: the template was a negative control of sterile water; 9: positive control.

Figure 2

Isolation and identification of FPV. (A) Normal F81 cell morphology; (B) F81 cell morphology after FPV infection; (C) PCR detection of the samples after continuous passage; (D) Westen blotting identification of FPV. Bar: 100 μm. M: DL1000 DNA marker; 1–5: five successive generations of the disease venom; 6: positive control; 7: the template was a negative control of sterile water.

Figure 3

IFA identification of FPV ZZ202303. (A) Normal F81 cell; (B) F81 cell after FPV infection, the green fluorescence observed in the cells indicates infection with FPV. Bar: 100 μm.

Figure 4

Determination of TCID₅₀ of FPV ZZ202303.

Figure 5

Proliferation kinetics analysis of FPV ZZ202303. (A) Standard curve of the FPV-VP2 recombinant plasmid; (B) one-step growth curve of FPV ZZ202303.

Figure 6

Nucleotide Sequence similarity analysis of the FPV ZZ202303-VP2 gene. Analysis of nucleotide similarity of the VP2 gene of FPV ZZ202303. Note: FPV ZZ202303 is the isolate from this study. *** This is the diagonal, with the upper part and the lower part separated.

Figure 7

Phylogenetic analysis of the FPV ZZ202303-VP2 gene. FPV ZZ202303 phylogenetic divergence tree of the VP2 genes. Note: FPV ZZ202303 is the isolate from this study. Different colors represent different hosts of parvovirus. Yellow, blue, green, and gray represent FPV, MEV, FCV, and RDPV, respectively. The values on the branches of the phylogenetic tree are bootstrap values. The higher the value, the higher the credibility of the corresponding branch.