WHAT CATS MAY TEACH US ABOUT LONG COVID

Feline infectious peritonitis (FIP) is a severe, often fatal disease in cats caused by a coronavirus. Similar to serious coronavirus infections in humans, FIP triggers widespread inflammation, T cell exhaustion, and chronic immune dysfunction. Researchers at the University of California, Davis, have discovered that combining mesenchymal stromal cell (MSC) therapy with antiviral drugs helps cats’ immune systems recover and reduces systemic inflammation. Their findings were published in STEM CELLS Translational Medicine.

“FIP in cats serves as a valuable model for understanding long-term immune complications following viral infections—much like what some people experience after COVID-19,” said Amir Kol, associate professor at UC Davis School of Veterinary Medicine and lead author of the study. “Our results suggest MSC therapy not only reduces immediate inflammation but also helps restore lasting immune balance.”

What Is FIP?

Feline coronavirus usually causes mild intestinal issues. However, in about 2% of cats—mostly young cats in shelters or catteries—the virus mutates, infecting immune cells and spreading throughout the body. This can lead to:

• Wet FIP: fluid accumulation in the chest or abdomen
• Dry FIP: inflammation affecting organs without fluid buildup

Both forms cause fever, organ damage, and a decline in critical immune cells.

Until recently, FIP was almost always fatal. In 2018, UC Davis researchers reported that the antiviral drug GS-441524 could cure FIP. However, it wasn’t widely available in the U.S. until recently, when a veterinary compounding pharmacy began offering it.

Long-Term Effects of FIP

Some cats that recover from FIP still show enlarged lymph nodes, indicating ongoing immune activity. This is reminiscent of “long COVID” in humans, where the immune system remains overactive even after the virus is gone. Kol refers to this as a potential “long-FIP” syndrome.

“Treating the virus with antivirals doesn’t always return the immune system to normal,” Kol explained. “MSC therapy might help fix that.”

Clinical Trial Results

In the study, cats with FIP and enlarged lymph nodes were treated either with antivirals plus MSC infusions or antivirals plus placebo. All cats survived thanks to the antiviral treatment, but those receiving MSC therapy showed better immune recovery.

Treated cats had fewer overactive T and B cells—which can cause immune damage—and more regulatory T cells that calm the immune response. The therapy also helped rejuvenate exhausted immune cells and supported the development of protective memory cells.

Importantly, the treatment was safe with no serious side effects.

Broader Implications

These results could not only improve FIP treatment for cats but also provide insights into similar immune challenges in humans recovering from viral infections like COVID-19.

“Many pet diseases mirror human conditions,” Kol said. “Veterinary medicine offers a unique opportunity for translational research benefiting both animals and people.”