Feline Infectious Peritonitis (FIP) begins as an upper respiratory infection that can progress to a widely distributed inflammation of tissues and organs, including peritonitis (inflammation of the abdominal cavity). Although not always present, a classic sign of FIP is abdominal swelling with fluid as a result of inflammation. FIP is caused by a coronavirus that is transmitted by contact with cats. Once signs of FIP appear, death loss approaches 100%. Cats 2 years of age and younger and elderly cats are most often affected.