Glossary
Feline infectious peritonitis
A serious disease caused when a common, usually harmless feline coronavirus mutates and triggers widespread inflammation in the body.
Also called: FIP, feline coronavirus disease, wet FIP, dry FIP
Feline infectious peritonitis, or FIP, starts with a feline coronavirus that many cats carry in the gut without any illness. In a small number of cats the virus changes, infects white blood cells and sets off severe inflammation. Young cats, often under two years old, and cats in crowded homes or shelters are affected most.
There are two main forms, and some cats show both. The wet form causes fluid to build up in the belly or chest, which can swell the abdomen or make breathing hard. The dry form involves organs such as the eyes, kidneys and brain, and can cause eye changes, wobbliness or seizures. Early signs are vague: a fever that does not respond to treatment, poor appetite, weight loss and tiredness.
No single blood test confirms FIP. A coronavirus antibody test only shows past exposure, so vets put together the history, examination, fluid or tissue samples and blood work. FIP was once almost always fatal. Antiviral drugs have since shown good results, though which drugs are legal and how they are supplied differs by country. If your cat has an unexplained fever, a swollen belly or breathing trouble, see a vet, and ask which treatment options are available where you live.
Last reviewed November 7, 2026