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a difficult diagnosis: feline infectious peritonitis

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Siamese cat on bench outside | a difficult diagnosis: feline infectious peritonitis | Petplan
Posted by Dr. Rebecca Jackson on Nov 10 2016


Unlike a discussion about diabetes or feline leukemia, FIP (feline infectious peritonitis) can be difficult to explain. As a veterinary community, there is a lot we know about the disease, however, there is still a great deal that we don’t yet understand. Here is what we do know.

Feline infectious peritonitis develops in cats from a mutated coronavirus. Many cats (upwards of 40% of the cat population) have been infected with feline coronavirus. Usually, it causes mild gastrointestinal disease (if any clinical signs) and the cat recovers uneventfully.

However, in cats that have a genetic predisposition, have a high level of stress, live in overcrowded or multi-cat households, or are immunocompromised (such as those infected with FIV or FeLV, Feline Leukemia Virus), this virus can mutate into an incredibly virulent form resulting in the disease we call FIP. There is no single factor that guarantees a cat will develop FIP, and cats with any combination of the above mentioned characteristics may never develop FIP. As you can see, the picture is as clear as mud.

Feline infectious peritonitis is a disease that we generally see in young purebred cats (less than 3 years of age) that live in multiple cat households (such as catteries, where large numbers of cats are housed). It is a progressive, fatal disease that cannot be treated or cured. We can symptomatically treat it for a period of time to improve a cat’s quality of life, but the disease will inevitably take the cats life. There is a vaccine for FIP, but its effectiveness and use is controversial within the veterinary community (if you have further questions about the vaccine, please contact your veterinarian).

Signs of feline infectious peritonitis in cats


So, what exactly does FIP look like in a cat? The clinical signs are vague and nonspecific. Many cats will have lethargy, weight loss, vomiting, diarrhea, fever, pale mucous membranes, a bloated abdomen and/or anorexia. Some cats present with neurologic signs (funny eye movement, seizures and walking unsteadily, to name a few), or inflammation within their eyes. There is no indication that a cat with FIP can transmit the disease to another cat.

How is FIP diagnosed?

Not easily. It is a VERY difficult disease to diagnose, because there is no single test that is conclusive. Diagnosis is made based on the cat’s history, clinical signs, response to therapy, and a combination of various laboratory tests (bloodwork, ultrasound, radiographs, cytology of body fluids and histopathology of tissue samples). This is a very frustrating disease for pet parents and veterinarians alike. It is difficult to diagnose, and as I mentioned previously, inevitably fatal.

As you can see, the question of why cats get FIP is not an easy one to answer. Feline infectious peritonitis is a complex and frustrating disease. The good news? It is NOT that common. Many veterinarians will go years without ever seeing a case in their clinic. Hopefully, yours will be one of them.