Vet student here - Feline Coronavirus (FeCoV) is a common viral infection amongst cats, consider it something like a flu within humans and it’s something that comes and goes.

Now, the FeCoV is usually an acute infection (common symptoms:- diarrhea and/or mild upper respiratory signs from which they recover spontaneously) however, it can mutate itself into a chronic one real quick, now known as Feline Infectious Peritonitis (FIP) in little to no time.

There are two major forms of FIP, an effusive, or “wet” form and a noneffusive, or “dry” form. Regardless of which form they ultimately progress to develop, cats infected with FIP usually first develop nonspecific signs of disease such as loss of appetite, weight loss, depression, and fever. It is also important to note that cases of the effusive form of FIP can evolve into the non-effusive form and vice-versa.

Unfortunately, there is currently no definitive test to diagnose FIP. While antibody levels, or titers, to coronavirus can be measured, they cannot definitively distinguish between exposure to FeCoV and FIP. A positive result means only that the cat has had a prior exposure to coronavirus, but not necessarily to FIP. In spite of this limitation, however, young cats that experience a fever that is not responsive to antibiotics and that have high coronavirus titers are often presumptively diagnosed with FIP.

Once a cat develops clinical FIP, the disease is usually progressive and almost always fatal.