What is FIP?
Feline Infectious Peritonitis (FIP) is a severe, often fatal, immune-mediated disease caused by feline coronavirus (FCoV)(1). While most FCoV infections produce mild or no symptoms, a small percentage of viruses mutate within the cat, gaining the ability to infect macrophages and spread throughout the body, leading to the systemic inflammation that defines FIP(2,3).
Clinical Forms of FIP
• Effusive (Wet) FIP: Characterized by the accumulation of fluid (effusions) in body cavities or organs.
• Non-Effusive (Dry) / Neurological FIP: Marked by neurological or ocular signs, often with few or no effusions.(4)
FIP is heartbreaking for both cats and their caregivers, as it can affect multiple organ systems and present with a wide range of clinical signs. Although effective antivirals now exist, outbreaks still occur. The most notable recent example was in Cyprus, where the emergent strain “FCoV-23” led to an estimated 10,000+ feline deaths(5).
What We Know
FIP arises when FCoV acquires internal mutations that alter its cellular tropism, enabling systemic infection. Despite major progress, FIP remains a challenging “rule-out” diagnosis in veterinary medicine, underscoring the need for faster, more definitive diagnostic tools(4).
Advances in FIP Research
• Improved diagnostic assays
• Development of effective antiviral therapies(6)
• Greater epidemiological insight into FCoV transmission
• Genetic and molecular characterization of FCoV(7,8)
• Cryo-EM structures of the spike (S) protein, offering deeper understanding of viral entry and pathogenicity(9)
The Whittaker Lab is committed to advancing FIP research through:
• Expanded surveillance studies
• Antiviral research that supports antimicrobial-resistance (AMR) stewardship
• Structural and functional studies of the S protein
• Genomic identification of viral mutations associated with the shift to pathogenic FIP-causing variants
Together, with collaborative global efforts, we will continue to FIGHT FIP by carrying out ongoing research, in hopes of paving the way toward improved outcomes for cats affected by FIP.
- Hartmann K. Feline infectious peritonitis. Vet Clin North Am Small Anim Pract. 2005 Jan;35(1):39–79, vi.
- Hora AS, Asano KM, Guerra JM, Mesquita RG, Maiorka P, Richtzenhain LJ, et al. Intrahost Diversity of Feline Coronavirus: A Consensus between the Circulating Virulent/Avirulent Strains and the Internal Mutation Hypotheses? ScientificWorldJournal. 2013 Mar 27;2013:572325.
- Jaimes JA, Millet JK, Stout AE, André NM, Whittaker GR. A Tale of Two Viruses: The Distinct Spike Glycoproteins of Feline Coronaviruses. Viruses. 2020 Jan 10;12(1):83.
- 2022 AAFP/EveryCat Feline Infectious Peritonitis Diagnosis Guidelines – Vicki Thayer, Susan Gogolski, Sandra Felten, Katrin Hartmann, Melissa Kennedy, Glenn A Olah, 2022 [Internet]. [cited 2025 Oct 5]. Available from: https://journals.sagepub.com/doi/full/10.1177/1098612X221118761
- Attipa C, Warr AS, Epaminondas D, O’Shea M, Hanton AJ, Fletcher S, et al. Feline infectious peritonitis epizootic caused by a recombinant coronavirus. Nature. 2025 Sept;645(8079):228–34.
- Mir S, Peters M, Penny G, Agsaoa A, Mir M. From Challenge to Cure: A Look at Feline Infectious Peritonitis and Emerging Treatment Strategies and Breakthroughs. Veterinary Sciences. 2025 July;12(7):650.
- Tortorici MA, Choi A, Gibson CA, Lee J, Brown JT, Stewart C, et al. Loss of FCoV-23 spike domain 0 enhances fusogenicity and entry kinetics. Nature. 2025 Sept;645(8079):235–43.
- Jaimes JA, Whittaker GR. Feline coronavirus: Insights into viral pathogenesis based on the spike protein structure and function. Virology. 2018 Apr;517:108–21.
- Yang TJ, Chang YC, Ko TP, Draczkowski P, Chien YC, Chang YC, et al. Cryo-EM analysis of a feline coronavirus spike protein reveals a unique structure and camouflaging glycans. Proc Natl Acad Sci U S A. 2020 Jan 21;117(3):1438–46.
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Sweet AN, André NM, Stout AE, Licitra BN, Whittaker GR. Clinical and Molecular Relationships between COVID-19 and Feline Infectious Peritonitis (FIP). Viruses. 2022 Feb 26;14(3):481.