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What Is Feline Infectious Peritonitis (FIP) in Cats?

Feline infectious peritonitis is a disease caused by a viral infection with a coronavirus that is specific to cats. This type of coronavirus cannot infect people or other species.  

FIP can be very difficult to diagnose because it can infect many organ systems, ranging from the abdomen to the eyes to the central nervous system. FIP symptoms also resemble symptoms from several other conditions, and the exact nature of your cat’s symptoms will depend on what form of the disease your cat has and which organs are affected.

Symptoms of Feline Infectious Peritonitis

A variety of symptoms can be seen in cats with FIP, depending on which organ system is affected. FIP can affect the liver, kidneys, pancreas, or other organ systems. 

Most cats will start showing symptoms of simply not feeling well—eating poorly, running a fever, or acting lethargic. Some animals will develop other diseases, depending on the type of the disease present. There are two main forms of FIP: 

  • Wet (or effusive) form: Causes bloating and swelling in the abdomen (ascites) and may affect the heart and lungs. Cats with this form may pant and act sleepy or lethargic. 

  • Dry (or non-effusive) form: Usually affects the eyes and may have neurological symptoms such as trouble with balance and seizures. 

These forms are mainly used for diagnostic purposes, and one cat may show symptoms from both forms. 

Because the symptoms associated with FIP are extremely varied and variable, it can be very hard to diagnose FIP based on clinical signs alone. Conditions that have similar symptoms include abdominal tumors, toxoplasmosis, infection with mycobacterium, and other conditions.

Causes of FIP in Cats

Feline infectious peritonitis is caused by a coronavirus that is unique to cats—it is not contagious to people, dogs, or other species of animal. This virus typically lives in the cat’s intestinal system. It’s spread through contact with feces in most cases, as infected cats shed the virus into litter boxes. Respiratory transmission is possible but less common. Because the most common route of infection is contact with feces, cats living in multi-cat households that share litter boxes are most likely to get infected.  

Infection with feline coronavirus is very common among cats, but it’s estimated that less than 5% of cats infected with feline coronavirus will go on to develop FIP. Cats with compromised immune systems are at higher risk of developing FIP, including kittens and cats with chronic diseases.

How Veterinarians Diagnose FIP in Cats

Diagnosis of FIP can be very challenging. The “wet form” that presents with abdominal swelling is relatively straightforward to diagnose by drawing a sample of fluid from the abdomen for analysis. For other cats, additional testing may be required to piece together the puzzle and suggest FIP.  

There is no completely reliable FIP test available to run on living cats. A conclusive diagnosis sometimes comes with a necropsy (the animal version of an autopsy) after the cat passes away. In most cases, many tests need to be run to rule out other diseases, leaving FIP as the most likely possibility.

Recovery and Management of FIP in Cats

Traditionally, FIP has been considered universally fatal. Many cats cannot be conclusively diagnosed with FIP until they pass away. 

Only in recent times has a promising medication come to light, but it is not legally available in the United States at this time. Some owners have purchased it on the black market, but unfortunately, this comes with significant risks, including: 

  • No quality control of the medication  

  • No way to know if you are getting the active compound  

  • Medication is sold at exorbitant prices  

Hopefully, there will soon be research to substantiate this medication’s use, but until then, it’s not recommended that cat parents try to self-treat their animals.  

Conventional treatment for FIP focuses on minimizing the clinical symptoms that are interfering with the cat’s quality of life—but FIP is inevitably fatal without definitive treatment, and supportive care is the best we can offer most cats. 

FIP in Cats FAQs

What are the first signs of FIP in cats?

Typically, the first signs of FIP in cats are simply signs that the cat is not feeling well—excessive tiredness, poor appetite/weight loss, and fever.

Are cats with FIP in pain?

Cats with FIP do not appear to be in any pain. However, they seem to feel much like we do with a case of the flu—tired and wiped out.

How is FIP transmitted in cats?

Most cats are exposed early in their lives to the organism that causes FIP—sometimes even from their mother. Cats almost universally carry the organism responsible for the infection—however, the development of disease requires a specific interaction between the immune system of the cat and a mutated form of the organism. Therefore, although many cats carry the organism, the vast majority never develop disease. This is also the primary reason we do not have a diagnostic test for the disease—there are more factors at play than simply carrying the organism.

Is FIP in cats contagious to other cats?

We don’t consider FIP too contagious in the way so many other diseases are, primarily because almost all cats are exposed to the organism early in life and carry it long-term without symptoms. The development of disease requires a specific interaction between the virus and the immune system. It is not uncommon to see one cat in a household die of FIP while the other cats remain perfectly healthy.

Can FIP cause blindness in cats?

Yes, it can. In fact, in some infected cats, changes associated with the eyes may be the only symptoms seen, although for most animals, multiple signs are present.

Is there a vaccine for FIP in cats?

There is a vaccine for feline coronavirus, but it has some drawbacks. Unfortunately, vaccinating cats in multi-cat households may not be effective, since infection with feline coronavirus is so common that most cats will already have been infected by the time they are old enough to receive the vaccine. The vaccine is only approved for kitten older than 16 weeks of age. Because of these limitations, the American Association of Feline Practitioners does not recommend routine use of the FIP vaccine.

Featured Image: iStock.com/Iva Vagnerova

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