2024 DR. PEDERSEN WINTER UPDATE

2024 has been a noteworthy period for FIP treatment and research. Although many thousands of cats have been cured of FIP over the last 5 years, antiviral drugs such as GS-441524 and Molnupiravir, were only available heretofore on the unapproved marketplace. Fortunately, both drugs are now available legally in many countries at a comparable price to non-approved sources. Full approval of Remdesivir, Molnupirvir and Paxlovid for human use against COVID-19 has also allowed veterinarians to prescribe them for cats with FIP, but at the human prescription price. The price of GS-441524, unapproved and approved, has also fallen greatly over the last few years, making it much more available to cat owners, cat rescue groups, catteries, and shelters.

Friends of SOCK FIP have continued their long-standing support of FIP research at UC Davis School of Veterinary Medicine (SVM), and ongoing studies have been quite diverse. Clinical treatment trials led by Dr. Krystle Reagan have involved GS-441524 by oral and subcutaneous routes (equal); comparison of GS-441524 vs. Molnupiravir (equally efficacious); GS-441524 vs. Remdesivir (also equal); 1, 2 and Paxlovid (extremely promising preliminary results). Ongoing trials with owned cats have also served as a critical resource for other types of studies. About 20% or so of cats with FIP succumb in the first days of treatment and the causes of these deaths have been studied by Dr. Brian Murphy and his team.3 In addition to the typical lesions of severe FIP, cats dying early often had evidence of secondary bacterial sepsis (supportive pneumonia, hepatitis) and severe heart disease (myodegeneration, myocarditis/pericarditis). Phenotypes of immune cells from blood and lymph nodes, and levels of various cytokines in body fluids, have been analyzed by Dr. Amir Kol and colleagues to determine how the immune system responds to infection. Preliminary results show that immunity is far more complex than imagined and that lymph node enlargement and cellar changes persist for a very long time after recovery. A third research team led by Drs. Patty Pesavento and Teresa Brostoff has chosen to study how vaccines might help to prevent FIP, which if effective, would be a desirable adjunct to treatment. A messenger RNA based vaccine against a major feline coronavirus protein was developed and found to be very immunogenic in mice 4 and these studies will now be extended to laboratory and field cats.

The discovery of an effective treatment for FIP, as first reported in 2018 (GC376)5 and 2019 (GS-441524)6, has led to a renaissance in clinical knowledge and research interest in FIP. Research in FIP has also greatly increased in many countries outside of the USA, such as China, Japan and countries of SE Asia, and Europe. The severity of FIP in Mediterranean countries, particularly among feral and rescue cat populations, has been recently documented and led to a new focus on cats in this region of the world. The ability to effectively cure FIP with antiviral drugs has also stimulated, not only knowledge of FIP, but interest in feline medicine by veterinarians around the world. The UC Davis SVM is proud of our contributions to this renewed interest in FIP, and hopefully SOCK FIP contributors are equally proud of the support that they have given to this effort.

On behalf of the entire SOCK FIP board, I would like to wish our supporters a joyful holiday season and a happy and productive 2025. We look forward to an even more productive 2025.

–Niels C. Pedersen

References cited
Cosaro, E.; Pires, J.; Castillo, D.; Murphy, B.G.; Reagan, K.L. Efficacy of Oral Remdesivir Compared to GS-441524 for Treatment of Cats with Naturally Occurring Effusive Feline Infectious Peritonitis: A Blinded, Non-Inferiority Study. Viruses2023, 15, 1680. https://doi.org/10.3390/v15081680
Reagan KL, Brostoff T, Pires J, Rose A, Castillo D, Murphy BG. Open label clinical trial of orally administered Molnupiravir as a first-line treatment for naturally occurring effusive feline infectious peritonitis. J Vet Intern Med. 2024; 38(6), 3087. https://doi.org/10.1111/jvim.17187
Murphy, B.G.; Castillo, D.; Neely, N.E.; Kol, A.; Brostoff, T.; Grant, C.K.; Reagan, K.L. Serologic, Virologic and Pathologic Features of Cats with Naturally Occurring Feline Infectious Peritonitis Enrolled in Antiviral Clinical Trials. Viruses2024, 16, 462. https://doi.org/10.3390/v16030462
Brostoff, T.; Savage, H.P.; Jackson, K.A.; Dutra, J.C.; Fontaine, J.H.; Hartigan-O’Connor, D.J.; Carney, R.P.; Pesavento, P.A. Feline Infectious Peritonitis mRNA Vaccine Elicits Both Humoral and Cellular Immune Responses in Mice. Vaccines2024, 12, 705. https://doi.org/10.3390/vaccines12070705
Pedersen NC, Kim Y, Liu H, Galasiti Kankanamalage AC, Eckstrand C, Groutas WC, Bannasch M, Meadows JM, Chang KO. Efficacy of a 3C-like protease inhibitor in treating various forms of acquired feline infectious peritonitis. J Feline Med Surg. 2018 20, 378. https://doi.org/10.1177/1098612X17729626.
Pedersen NC, Perron M, Bannasch M, Montgomery E, Murakami E, Liepnieks M, Liu H. Efficacy and safety of the nucleoside analog GS-441524 for treatment of cats with naturally occurring feline infectious peritonitis. J Feline Med Surg. 2019 Apr;21(4):271-281. https://doi.org/10.1177/1098612X19825701.