Feline infectious peritonitis (FIP) is a complicated viral disease of cats that is seen worldwide. The disease can affect the immune system and organs. Cats can be infected with the virus without any symptoms or problems and few will develop the disease and become fatally ill. There are two forms of the disease with symptoms that often overlap and they are equally tricky to diagnose.

What Is FIP?

FIP is a complex disease that is a result of infection with the feline coronavirus. While large numbers of cats are infected with feline coronavirus, few will ever develop FIP. The fatal disease is thought to result from a mutation of the virus within the body that combines with an incorrect response of the immune system. This combination leads to inflammation in various organ systems.

Symptoms of FIP in Cats

The two main categories of FIP, the wet form and the dry form, have different characteristics. These broad forms are not necessarily completely distinct and some cats will have some of both.

Distention of Abdomen

If a cat has the wet form of FIP, it will have fluid build-up in its abdomen and chest area. Fluid may become concentrated directly around the heart, as well.

Difficulty Breathing

If a cat has wet form FIP, it will have difficulty breathing as the lungs are inflamed.

Fever

A cat with FIP may have a minor long-term fever that is unresponsive to treatment. Fevers are often vague symptoms that can accompany many other problems in cats.

Loss of appetite and weight loss

A cat with FIP may or may not lose its appetite or lose weight. In some cases, it's noted that a cat's appetite and weight may slightly increase if it has FIP.

Depression

A cat with FIP may or may not seem depressed and listless. However, if it has nervous system problems, the cat's personality and behaviors may change.

Organ Failure

Cats with the dry form of FIP are usually seen with inflamed cells invading various organs, such as the kidneys, liver, pancreas, or spleen. As a result, jaundice may become apparent as the disease progresses.

Eye Problems

Inflamed eyes may show signs of pus accumulation or tinges of blood, leading to possible blindness.

Poor Muscle Coordination

A cat's nervous system will show signs of distress if it has FIP. It will begin to lose muscle coordination resulting in minor limb paralysis. This can further lead to seizures and tremors.

Causes of FIP

FIP is most often seen in young cats less than 12 months old, but it can be seen at any age. It's still unknown why some cats develop FIP while others do not. Most cats that develop FIP have been recently exposed to some sort of stressful experience such as boarding, rehoming, or surgery.

The common coronavirus is spread through direct contact via the nose and mouth with infected feces, usually while sharing litter boxes. It is thought that a mutation in the virus directly affects cells and leads to FIP which causes a poor immune response in cats with immature or weakened immune systems. In addition, it appears that purebred cats, such as Abyssinian, Bengal, Birman, Himalayan, Persian, ragdoll, and all types of rex breeds, are prone to developing the disease.

Diagnosing FIP in Cats

Confirming a diagnosis of FIP can be very difficult. The best method to confirm a diagnosis of FIP requires a veterinarian to take a biopsy. The tissue samples from the biopsy are examined microscopically and often include special tests to mark the presence of the virus in tissue samples. If these tests are not possible, the diagnosis must be made on a combination of other factors, including clinical signs and laboratory tests which can include blood tests and analysis of fluid sampled from the abdomen if the wet form is present.

Testing for antibodies to coronavirus is not helpful in the diagnosis of FIP but is useful in screening healthy cats before introducing them to a coronavirus-free cat or group. A positive result only indicates exposure to coronavirus and possible shedding of coronavirus but does not mean a cat has or will develop FIP.

Treatment

There is no treatment for FIP. Some supportive measures, including draining excessive fluid build-ups, can provide temporary relief. A variety of medications designed to reduce the abnormal immune response to the virus or reduce the ability of the virus to reproduce have been tried. They may provide some relief from the disease and prolong survival.

Prognosis for Cats With FIP

Most cats infected with the virus that causes FIP may never become ill. But the cats who do develop signs of FIP will always succumb to the disease. Generally, cats showing signs of the wet form succumb to FIP sooner (within days to weeks) than those with symptoms of the dry form (up to a few months), though survival for several months may be possible.

How to Prevent FIP

Preventing exposure to coronavirus is the best way to prevent FIP. This is very difficult to do as well over half of all cats in a single-cat or multi-cat household may be infected with the virus. A majority of those cats will remain healthy, however. FIP only develops in a very low percentage of cats who are infected with the coronavirus, so exposure does not automatically mean cats will get FIP.

There is a vaccine available, although its use is controversial. The vaccine is given in the nose and is designed to produce just a local response to prevent the virus from gaining access to the body. The efficacy of the vaccine is questionable and it must be given before natural exposure to coronavirus to be effective. Because FIP is uncommon in the general cat population, the need for routine use of FIP vaccines is generally not recommended, although it can sometimes be used in shelters where the risk is highest. Your vet can discuss the use of FIP vaccines for your cat.

Is FIP Contagious to Other Animals?

The benign feline coronavirus is contagious to other cats because felines shed the virus in the feces. Another cat can become infected with the benign feline coronavirus through oral contact with the infected feces. However, if the virus mutates in an infected cat leading to FIP, the animal may not shed the mutated virus because it becomes cell-associated (the cells become directly infected). This means that FIP is not technically contagious to animals.

With that said, housemates of a cat diagnosed with FIP may not have a greater risk of developing FIP unless they are litter mates that share a genetic predisposition. They have also likely been exposed to coronavirus already, so no special precautions are usually necessary. Your vet can provide further advice regarding home care.