Feline Infectious Peritonitis in Cats

When first infected by feline coronavirus, a cat may not show any symptoms of illness, even as the cat’s body is developing an immune response. A mutation of the virus or an issue with the cat’s immune response can trigger FIP, causing the cat to become noticeably ill over time.

About five to ten percent of cats that are infected with the coronavirus develop feline infectious peritonitis. FIP occurs most often in multi-cat homes and in shelters, and most often affects cats with a weakened immune system. Cat owners and shelter owners should all know what FIP looks like so they can minimize the risk of infection.

Feline infectious peritonitis (FIP) is a viral disease caused by feline coronavirus (FCoV). Not all strains of FCoV cause illness; those that do not are called feline enteric coronavirus.

The cat becoming ill with FIP shows no symptoms at first. Soon, it displays mild symptoms, such as nasal discharge, sneezing, and watery eyes that may look like a cold. Other cats develop intestinal symptoms such as diarrhea. Only a few cats go on to develop full-blown FIP, which may not happen until weeks or years after initial exposure. Because cats are able to hide illness so well, the slow onset of illness may seem to be sudden, with symptoms becoming more severe as the days pass:

• Weight loss
• Fever
• Hair coat becomes rough
• Loss of appetite
• Depression

Types

Two types of feline infectious peritonitis affect cats, each with unique symptoms:

Effusive (wet) Form

• Swollen abdomen from accumulation of fluid
• Accumulation of fluid in chest (more rare)
• Lethargy
• Difficulty breathing
• Rapid worsening of symptoms

Non-effusive (dry) Form

• Persistent fever
• Weight loss
• Anemia
• Depression

Because each cat shows different symptoms with FIP, it can be challenging for the vet to determine the correct diagnosis. 

FCoV causes some cats to develop FIP. FCoV infection is much more common than FIP infection. It’s when the virus mutates within the exposed cat’s body that the virus develops the potential to cause the cat to develop feline infectious peritonitis. Signs of FIP can affect various areas of the cat’s body:

• Eyes
• Abdomen
• Chest cavity
• Inflammation in the brain
• Inflammation of the kidneys
• Inflammation of the eyes
• Inflammation of the liver

Because FIP looks so much like other illnesses, vets don’t have a single, definitive test that tells them when a cat has developed this disease. Instead, three blood tests let the vet know that FCoV is present as antibodies in the cat. Even knowing this, the vet doesn’t know which strain of FCoV the cat has.

If the vet is suspicious that the cat has been exposed to FCoV, they can administer the immunoperoxidase test. The polymerase chain reaction test helps to point out genetic material from viruses in body fluids and tissues. 

The only way to arrive at a definite diagnosis of FIP is through biopsy of body tissues. If the cat had FIP and died, the vet can examine its tissues during an autopsy. This means vets have to rely on the cat’s history, its symptoms and by lab examination of accumulated fluids during visits to the veterinary office. This is known as a “presumptive diagnosis” when vets tell cat owners, “It looks like FIP.”

Other blood work the vet can order may include plasma protein findings of hyperglobulinemia and hyperfibrinogenemia. Corona viral antibody titers and histopathology findings may also help the vet arrive at a presumptive diagnosis of FIP. They may also take X-rays to study fluid effusions in the chest cavity and abdomen.

At this time, no effective treatment or cure for FIP has been found or developed. Instead, vets will aim for short-term remission of symptoms in those cats whose symptoms are still fairly mild. In the end, FIP is fatal. 

Treatment is supportive, including nutritive care and nursing support. Veterinary staff works to slow down the cat’s inflammatory response to the virus.

Medications include corticosteroids, antibiotics and cytotoxic medications. The cat may undergo fluid therapy to drain accumulated fluid from its chest or abdominal cavity. It may also receive blood transfusions.

At this time, researchers are testing immunosuppressive drugs that may slow the progress of FIP. The same search is going on for effective antiviral medications to either slow down the replication of the virus itself or to completely prevent replication. One study focuses on the combination of an immunosuppressive drug and an antiviral drug to be given at the same time.

Once the cat has been diagnosed, its family should reduce the cat’s level of stress in the home. They should provide the tastiest, high-protein (all meat) diet and monitor the cat’s weight, activity level and appetite as well.

Cat owners should resist giving their cats homeopathic treatments or medications for which effectiveness and safety are unknown. 

Because FIP is known to be fatal, cat owners should work to keep their cat as comfortable as possible. Cats with “dry” FIP may live longer than those with “wet” FIP.

The best strategy in multi-cat households, catteries, and shelters is to prevent the exposure of healthy kittens and cats to FCoV-positive cats and kittens. Once the cats have finished eating, collect all food dishes and wash them thoroughly. Designate one litter box for the FCoV-positive cat only. Permit the healthy cats to share the remaining litter boxes and keep them all clean. Clean litter boxes thoroughly between cat litter changes.

Cat owners can use common household disinfectants, bleach and quaternary ammonium compounds to clean and disinfect all areas where the cats play and sleep on a daily basis. Finally, don’t allow household cats to roam outdoors, where they may come into contact with an FCoV-positive cat.