Insights from Feline Disease May Shed Light on Long COVID in Humans

Feline infectious peritonitis (FIP), caused by a coronavirus in cats, is a severe disease historically associated with high mortality. Interestingly, FIP shares many pathological features with severe COVID-19 in humans, including widespread inflammation, T cell exhaustion, and long-lasting immune dysfunction. Researchers at UC Davis have explored these parallels, uncovering potential pathways to treat long-term immune disturbances.

The study highlights that in cats, the coronavirus initially infects intestinal cells with mild effects, but in some cases—due to genetic and environmental factors—it infects immune cells, leading to systemic illness. FIP manifests mainly in two forms: wet FIP, with fluid accumulation in body cavities, and dry FIP, characterized by inflammation without fluid buildup. Both forms cause fever, multi-organ inflammation, and immune cell depletion, affecting about 2% of cats, especially young ones in shelters.

Until recent years, FIP was nearly always fatal. However, a breakthrough in 2018 involved the antiviral GS-441524, which could cure infected cats. Despite initial hurdles in approval, the drug is now accessible through compounding pharmacies in the U.S.

Long-term follow-ups indicate some recovered cats still exhibit enlarged lymph nodes and signs of ongoing immune activation, resembling the "long COVID" syndrome in humans. This suggests that even after viral clearance, immune systems may remain dysregulated.

To address persistent immune issues, scientists conducted clinical trials where cats treated with antiviral drugs received additional infusions of mesenchymal stromal cells (MSCs). Results showed that MSC therapy aided immune recovery by reducing overactive immune cells and promoting regulatory T cells, which help control inflammation. The approach was safe and showed promise in restoring immune balance, providing insights that could be relevant to human viral illnesses like COVID-19.

This research underscores the value of veterinary models in understanding complex immune responses, potentially paving the way for new treatments for long-term post-viral syndromes in humans.