Emergence of canine parvovirus-2c in domestic cats and adaptive evolution of the NS1 gene: Molecular epidemiology of feline parvoviruses in Northern Vietnam (2022-2025).

Feline parvovirus (FPV) remains one of the most important viral pathogens affecting domestic cats worldwide and continues to cause substantial morbidity and mortality despite the availability of effective vaccines. Information regarding the molecular epidemiology, full-length VP2 and NS1 gene characteristics, evolutionary dynamics, and circulation of canine parvovirus (CPV) variants in cats remains limited in Vietnam. Therefore, this study investigated the epidemiological, molecular, and evolutionary characteristics of feline parvoviruses circulating in domestic cats in Northern Vietnam between 2022 and 2025. A cross-sectional molecular epidemiological study was conducted using 244 rectal swab samples collected from healthy and clinically affected domestic cats in Hanoi, Bac Ninh, Hung Yen, and Ninh Binh provinces during 2022-2025. Viral DNA was detected by conventional polymerase chain reaction targeting the VP2 gene. Nine representative positive samples were subjected to sequencing of the full-length VP2 and NS1 genes. Phylogenetic relationships, nucleotide identity, amino acid substitutions, recombination events, and natural selection profiles were analyzed using established bioinformatics tools. Associations between epidemiological variables and FPV positivity were evaluated using Fisher's exact test. Eleven of 244 samples (4.51%) were positive for parvovirus DNA. Cats younger than 12 months exhibited significantly higher infection rates than older cats (p < 0.05), whereas breed, sex, and health status were not significantly associated with viral detection. The VP2 and NS1 genes exhibited high nucleotide conservation, with identities ranging from 97.72%-100% and 98.20%-99.90%, respectively. Phylogenetic analyses demonstrated that seven isolates clustered with Asian FPV lineages, whereas two isolates grouped within the CPV-2c lineage, providing molecular evidence of CPV-2c infection in domestic cats. No recombination events were detected in either gene. Evolutionary analyses identified two positively selected sites within the NS1 protein together with numerous negatively selected sites, indicating predominantly purifying selection with localized adaptive evolution. FPV remains actively circulating among domestic cats in Northern Vietnam, with highly conserved VP2 and NS1 genes. The detection of CPV-2c in cats provides evidence of interspecies viral circulation and highlights the importance of integrated molecular surveillance. The observed adaptive evolution within the NS1 protein improves current understanding of parvovirus evolution and provides valuable baseline information for future epidemiological investigations, vaccine monitoring, and disease control strategies.