What FIP actually is
FIP, or feline infectious peritonitis, is a disease that develops when a common feline coronavirus mutates inside an individual cat. It is important to know that FIP itself is not passed directly from cat to cat like an ordinary cold. Instead, the harmless intestinal coronavirus that many cats carry occasionally changes form in one particular cat and triggers the disease. This is why FIP can appear even in a home where the other cats stay perfectly healthy. If you ever hear the word FIP, it helps to remember that it is uncommon, even though the underlying coronavirus is very widespread.
From common coronavirus to FIP
Feline coronavirus is extremely common, especially where several cats live together, and for most cats it causes little more than mild or no symptoms. The virus usually lives quietly in the gut and spreads through litter boxes and shared spaces. In a small number of cats the virus mutates and the immune system reacts in a way that leads to FIP. Exactly why this happens in one cat and not another is still not fully understood, and stress or a young immune system may play a role. Carrying the ordinary coronavirus does not mean your cat will develop FIP.
Signs to watch for
FIP is often described as having a wet form and a dry form, and both can look vague at first. In the wet form, fluid builds up in the abdomen or chest, which can cause a swollen belly or laboured breathing. The dry form is subtler and may show up as a cat that is losing weight, running a fever that does not respond to treatment, seeming tired, or developing eye or neurological changes. Because these signs overlap with many other conditions, only a vet can work toward a diagnosis. If your cat seems persistently unwell or off in ways you cannot explain, it is always worth a check-up.
Treatment and hope today
For many years FIP was considered untreatable, but that picture has changed dramatically. Modern antiviral medicines, often based on a compound called GS-441524, have helped a great many cats recover from what was once a fatal diagnosis. Treatment is demanding and needs to be guided closely by a vet, and outcomes still vary from cat to cat, so it is not right to think of it as a guaranteed cure. Even so, a diagnosis of FIP today carries far more hope than it did just a few years ago. If FIP is ever suspected, ask your vet about current treatment options as early as you can.