A fatal strain of feline coronavirus isolated from a cat in eastern China has been fully characterized by a research team that sequenced its genome and tested its ability to cause disease in young cats. The strain, designated AH2023, belongs to type II feline coronavirus (FCoV-II), the less common of the two viral genotypes that infect domestic cats. According to the study published in Animal Diseases, all cats experimentally infected with the isolate died of feline infectious peritonitis within roughly two and a half weeks of exposure, underscoring the pathogenic potential of this understudied viral group.
Feline coronavirus is one of the most widespread viral pathogens of cats worldwide. In most infected animals it produces only mild, self-limiting enteritis. In some cases, however, the virus mutates into a highly virulent form that triggers feline infectious peritonitis, a fatal systemic disease marked by granulomatous inflammation and fluid accumulation in body cavities. Without appropriate treatment, feline infectious peritonitis is nearly 100 percent fatal, and cats under two years of age are particularly susceptible. The disease appears in two main forms: an effusive or wet form characterized by serositis and effusions, and a noneffusive or dry form that frequently involves the central nervous system and produces neurological and ocular signs. Recent reports have also documented the disease in nondomestic felids, including lions, tigers, and pumas.
The two genotypes of feline coronavirus differ sharply in their prevalence. Type I accounts for more than 80 percent of natural infections, while type II strains, which arise through recombination between type I virus and canine coronavirus, are far less common. Current evidence does not support a preferential association between either genotype and the development of feline infectious peritonitis under natural conditions. Type II strains, however, replicate more efficiently in laboratory cell lines such as CRFK, F81, and FCWF-4 cells, which has made them valuable models for research. Despite decades of in vitro work, sequence data for clinical type II isolates remain much more limited than those for type I, hindering comparisons between circulating field viruses and laboratory-adapted strains.
The new study began in 2023, when researchers collected ascitic fluid from a British shorthair cat diagnosed with feline infectious peritonitis at a veterinary hospital in Hefei, Anhui Province. After three blind passages in CRFK cells, the virus produced cytopathic effects, including cell rounding, shrinkage, and detachment, at 36 hours post infection. Western blotting and reverse transcription PCR confirmed the isolate as type II feline coronavirus. Following plaque purification and ultracentrifugation, transmission electron microscopy revealed typical coronavirus particles approximately 90 nanometers in diameter. The isolate was designated FCoV-II strain AH2023.
Growth kinetic analysis showed that the titer of strain AH2023 began to rise at 8 hours post infection and peaked at 10 to the power of 5.0 TCID50 per 100 microliters at 32 hours post infection. The viral nucleocapsid protein was detectable by western blotting as early as 16 hours post infection, while indirect immunofluorescence revealed signals from 8 hours onward. Whole-genome sequencing, deposited in GenBank under accession number PX471051.1, showed a genome of 29,013 nucleotides containing eleven open reading frames. These encode four structural proteins, five accessory proteins, and two nonstructural polyproteins, flanked by untranslated regions of 310 and 263 nucleotides at the 5′ and 3′ ends respectively.
Phylogenetic analyses of the complete genome and of the spike, nucleocapsid, and 3C-like protease genes consistently placed strain AH2023 within the clade of previously reported Chinese type II strains, clustering most closely with isolates SH2021 and DQ2023. The analyses also showed that, compared with type I feline coronavirus, strain AH2023 is more closely related to transmissible gastroenteritis virus and canine coronavirus. Recombination analysis using SimPlot revealed that the first 13,335 nucleotides of the genome showed the highest similarity with the type I reference strain SD, while the region spanning nucleotides 13,335 to 26,006 exhibited high homology with the canine coronavirus strain HLJ-072 and the transmissible gastroenteritis virus strain P115. The recombination breakpoint was mapped to approximately 13 kilobases and statistically confirmed.
The spike gene, which encodes the surface protein that mediates viral entry, lies within this recombinant region. It spans positions 20,436 to 24,800 of the genome, totals 4,365 nucleotides, and encodes 1,454 amino acids. Sequence homology analysis showed that the spike gene shared 91.4 to 99.9 percent nucleotide identity with other type II strains, 91.0 to 99.6 percent with canine coronavirus strains, and only 49.6 to 55.4 percent with type I strains. Comparison of the deduced spike protein with five reference type II strains revealed four amino acid substitutions at positions 387, 577, 829, and 1375. The substitutions at positions 387, 577, and 829 were shared with the Chinese isolates SH2021 and DQ2023, while the substitution at position 1375 was shared with strain DF2. The authors suggest that the S829F substitution may contribute to pathogenicity, potentially by altering protease recognition, immune evasion, or spike stability, though these mechanisms remain hypotheses requiring further study.
To assess virulence, the team inoculated eight 12-week-old specific pathogen-free cats, dividing them randomly into an infected group and a mock-inoculated control group of four animals each. All infected cats developed clinical signs consistent with feline infectious peritonitis: lethargy appeared at 3 days post challenge, anorexia at 5 days, fever ranging from 39.5 to 41 degrees Celsius, and diarrhea at 7 days. The control cats remained clinically healthy throughout the experiment. Every infected cat died between 12 and 18 days post challenge, with a mean survival of 15.2 plus or minus 2.1 days. Quantitative PCR of tissue specimens showed viral loads in all tested tissues, with the highest level in the intestine at 10 to the power of 4 copies per milligram, followed by the lung, spleen, and kidney at approximately 10 to the power of 2 copies per milligram. Viral shedding in feces was first detected at 7 days post challenge and rose to 10 to the power of 4 copies by 10 days, a pattern the authors link to the risk of fecal-oral transmission.
Necropsy of the infected cats revealed liver and kidney congestion and multifocal intestinal hemorrhage, while no gross lesions appeared in the controls. Histological examination showed marked villous atrophy in the intestine, with shortened, blunted, and fused villi accompanied by macrophage infiltration, and prominent infiltration of lymphocytes and plasma cells, vascular dilation, congestion, and focal macrophage accumulation in the liver and kidneys. Immunohistochemistry confirmed extensive distribution of viral antigen in the intestinal and liver tissues. The authors conclude that strain AH2023 is a newly isolated, recombinant, and highly pathogenic type II strain whose characterization expands knowledge of the genomic landscape of type II feline coronavirus and provides a foundation for improved diagnostics, surveillance, and control strategies against feline infectious peritonitis.
Subject of Research: Genomic characterization and pathogenicity of the feline coronavirus type II strain AH2023 isolated in China
Article Title: Genomic characterization and pathogenicity of the feline coronavirus (FCoV) type II strain AH2023
Article References: Li, S., Gao, X., Li, Y., Xu, W., Zhou, J., Wang, D., Cao, H., Hou, L., Chen, W., & Liu, J. (2026). Genomic characterization and pathogenicity of the feline coronavirus (FCoV) type II strain AH2023. Animal Diseases, 6(1), Article 44. https://doi.org/10.1186/s44149-026-00254-6
Image Credits: AI Generated
DOI: 10.1186/s44149-026-00254-6
Keywords: feline coronavirus, FCoV-II, feline infectious peritonitis, strain AH2023, recombination, spike protein, viral pathogenicity, phylogenetics, cats, China, coronavirus evolution, viral shedding
News Source: William Thompson. (October 30, 2026). Newly isolated feline coronavirus strain AH2023 proves lethal in cats. Scienmag.
