Feline infectious peritonitis (FIP) is a fatal disease that affects cats. It is caused by a mutation of the feline coronavirus (FeCV), which is a common virus that infects most cats at some point in their lives — and is typically harmless. However, only a small percentage of cats that are infected with FeCV will go on to develop FIP, which is 100% fatal if left untreated. The FIP virus itself is not usually contagious. Although horizontal transmission of FIP is possible, it is rare.
FeCV is spread through contact with the feces of an infected cat. This can happen through direct contact, such as when one cat grooms another, or through indirect contact, such as when cats share a litter box. However, this does not guarantee that your cat will develop FIP from exposure to FeCV/FCoV. In fact, only 5% to 10% of cats who are exposed to FeCV develop FIP.
FeCV can also be transmitted from mother to kitten during pregnancy or nursing.
Once a cat is infected with FeCV, it may take months or even years for the virus to mutate and cause FIP. This is why not all cats that are infected with FeCV will develop the disease.
If you are concerned that your cat may have FIP, please contact your veterinarian to assess the likelihood of FIP. Because the only test that can diagnose FIP with 100% requires a tissue sample and laboratory testing that can take weeks, it is best to treat your cat at first suspicion of FIP.