Some people who’ve suffered through COVID-19 never quite feel 100 percent, stuck in the throes of a medical mystery centered around an impaired immune system. Long COVID isn’t fully understood yet, but scientists are closing in on crucial clues by investigating a similar phenomenon in cats.
A new study published in Stem Cells Translational Medicine explains how a relatively rare feline disease is almost like a cat version of long COVID. Similar to severe coronavirus infections in humans, feline infectious peritonitis (FIP) sends cats’ immune system off-kilter. Therapy involving mesenchymal stromal cells, however, has shown promise in restoring immune function in cats, potentially serving as a blueprint for long COVID research.
A Severe Feline Disease
FIP in cats starts out as feline coronavirus, a common viral infection that infects the cells lining a cat’s intestines and leads to mild stomach issues. But a mix of genetic and environmental circumstances can occasionally change the virus’s behavior and cause widespread infection.
This either takes the form of wet FIP (where fluid builds up in a cat’s chest or belly) or dry FIP (where fluid doesn’t build up but inflammation still impacts organs). In both cases, FIP induces fever, organ problems, and a decline in important immune cells. It ultimately affects around 2 percent of cats, and is particularly common in young cats in shelters.
FIP was mostly fatal in cats for years, but an antiviral agent called GS-441524 has now made it possible to cure cats with the disease. The medication was first developed in 2018 and was finally made available in the U.S. in 2024.
Read More: What is Long COVID and What are the Symptoms?
Similarities of FIP and Long COVID
Scientists haven’t yet been able to thoroughly study cats after they recover from FIP, but enlarged lymph nodes have been observed in some of these cats, indicating that their immune system continues to overexert itself, as if an infection were still present.
The same thing happens in people with long COVID who experience immune dysfunction, persistent immune cell activation, and autoimmune antibody production.
Scientists aren’t exactly certain why those with long COVID face lingering issues weeks, months, or even years after contracting COVID-19. A few theories have attempted to make sense of the mystery: It could be that viral antigens and viral RNA remain in the body’s tissues, or that COVID-19 awakens other dormant viruses in the body.
Cellular Therapy to the Rescue
Reversing immune dysfunction after viral infection may be possible with mesenchymal stromal cells (MSC), which are present in almost all tissues and can be used in therapeutic applications that modulate the immune system.
“Even if you treat the infection with antivirals, your immune system, oftentimes, still won’t go back to normal or where it was before infection,” said corresponding author Amir Kol, a professor at the UC Davis School of Veterinary Medicine, in a statement. “This might have long-lasting effects on your health, and this study shows that MSC may help.”
Researchers involved in the new study tested cellular therapy on cats with enlarged lymph nodes to assess how well their immune systems could recover. In a clinical trial, one group of cats received antiviral drugs along with infusions of MSCs, while a second group received antiviral drugs and placebo infusions.
According to the researchers, cats treated with MSC therapy had fewer overly active T and B cells (which are associated with immune overdrive) and more regulatory T cells (which can calm the immune system). These cats also formed long-term “memory” cells that are vital in protecting the body in the future.
In addition to helping cats with long-term issues caused by FIP, these findings could also provide insight into viruses with similar effects in humans, like COVID-19.
“It’s important to understand that many pets suffer from diseases that are similar to human diseases,” said Kol. “Veterinary medicine is a wonderful platform to conduct translational science that helps both pets and humans.”
This article is not offering medical advice and should be used for informational purposes only.
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Jack Knudson is an assistant editor at Discover with a strong interest in environmental science and history. Before joining Discover in 2023, he studied journalism at the Scripps College of Communication at Ohio University and previously interned at Recycling Today magazine
