Feline infectious peritonitis (FIP) is a viral disease of cats. FIP is a severe form of the feline coronavirus (FCoV) and ultimately leads to death in affected cats due to the systemic immune-mediated disease that it causes. A milder form of FCoV (the enteric form of the virus) is relatively harmless and very common in multi-cat households, catteries and shelters. It is believed that cats infected with the enteric form of the virus may develop mutations of the virus that leads to FIP.