Feline Infectious Peritonitis (FIP) is a serious infectious disease caused by a feline coronavirus (FCoV). Coronavirus infection is quite common in cats; in most cases, however, it does not cause significant problems; generally the infection is asymptomatic or causes minor diarrhea and mostly heals spontaneously.

During the replication in the intestine, the feline coronavirus can mutate and give rise to the variants that causes FIP. There are predisposing factors to the mutation from FCoV to FIP, such as stress and breed.

Cats start to excrete the virus in the faeces (the main source of FCoV infection) from the first week following the infection.

In the event of an outbreak, FIP can take 2 forms: an effusive (moist) form characterized by thoracic and/or abdominal effusions and a non-effusive (dry) form characterized by granulomatous lesions in different organs. The first classic signs of FIP include intermittent fever, weight loss, anorexia, and weakness.

It is not easy to diagnose FIP because many symptoms are also detectable in other pathologies that are typlical of felines and no clinical test (IC, ELISA, Immunofluorescence) is conclusive by itself for the diagnosis of FIP. These clinical tests can be useful to control the spread of the virus in breeding catteries and therefore to prevent the occurence of the disease.

Diagnosis is based on anamnestic, clinical and laboratory data. The suspected diagnosis can be confirmed only through techniques that allow for the virus detection inside the macrophages present in the effusions and granulomas.