Infectious Feline Peritonitis

What precisely is feline infectious peritonitis?

Feline infectious peritonitis (FIP) is a serious disease that affects domestic cats. It affects cats of all ages worldwide, but it is more common in young cats under the age of two. Although FIP is not a common disease, it is significant because once a cat has the condition, it is nearly always deadly.

What is the origin of FIP?

FIP is linked to a viral illness known as feline coronavirus. There are numerous strains of feline coronavirus, each with a different potential to produce disease. Previously, these strains were classified as feline infectious peritonitis virus strains (capable of producing FIP disease) or feline enteric coronavirus strains (basically innocuous strains found primarily in the digestive tract). It is now known that feline enteric coronavirus strains can evolve (transform) into a more dangerous virus and cause FIP.

FIP diagnosis is difficult for a variety of reasons. Unfortunately, there are no scientific assays that can differentiate between enteric coronavirus and FIP-causing strains. Many cats do not develop FIP disease even when infected with known FIP-causing strains. The variables that cause one cat to get ill while another remains healthy are unknown. FIP is still one of the least understood cat diseases.

In comparison to FIP disease, how common is feline coronavirus infection?

Many cats become infected with one or more strains of feline coronavirus at some point in their lives (up to 50% in single-cat households and as high as 80-90% in multi-cat situations). The vast majority of cats infected with feline enteric coronavirus (approximately 90% or more) survive. Only 5 to 10% of diseased cats and less than 1% of cats admitted to veterinary facilities have feline infectious peritonitis illness.

Is FIP more common in certain cat breeds?

FIP tends to be more common in multi-cat households, shelters, and catteries. Cats who are agitated as a result of re-homing, have recently undergone surgery, or have concurrent infections (more than one infection at the same time) may be more prone to acquiring FIP. Genetic factors may potentially play a role in the development of FIP. Male cats are more commonly affected than females. Purebred cats such as Abyssinian, Bengal, Birman, Himalayan, Ragdoll, and Devon Rex may be prone to FIP.

How does a feline coronavirus infection occur?

The fecal-oral route (oral contact with infected feces) is the most common way for cats to become infected with feline coronavirus. One-third of these cats are thought to shed the virus in their feces. Most cats shed the virus for a few months, but a tiny number will shed the virus indefinitely. Although the virus is highly delicate and does not survive for more than 24-36 hours in normal conditions, low temperatures are thought to retain the virus for months. Transmission on clothing or other things is unlikely to occur for several hours after contact.

"The virus can remain dormant or inactive in the body for months to years"

As previously stated, the majority of infections are caused by very harmless types of feline coronavirus. Unfortunately, in some cats, this initially innocuous illness can evolve and produce FIP. Even with the most dangerous strains, apparently, healthy cats can be carriers of the virus and shed it without ever showing indications of sickness. Many cats that get FIP have no history of contact with other FIP-positive cats. The virus might remain dormant or inactive in the cat's body for months or years before causing sickness.

When is a cat most likely to develop FIP?

Most cats are thought to be exposed to feline coronavirus at an early age, possibly during their first few weeks of life. The condition affects cats of all ages, although most get it between the ages of three months and two years.

What clinical indications does a FIP-infected cat exhibit?

The early signs of disease in cats with FIP might be quite ambiguous. Clinical symptoms typically reported include listlessness, lethargy, decreased or nonexistent appetite, weight loss, and a fluctuating temperature. Other symptoms usually begin to appear after a few days to a few weeks.

Most cats will acquire the 'wet' or effusive type of FIP at this stage, which refers to the buildup of fluid in body cavities; fluid may accumulate in the abdomen, causing a bloated abdomen, or in the chest cavity, causing difficulties breathing.

Some cats get 'dry' or non-effusive FIP, which means that little to no fluid collects. The dry type frequently causes significant inflammation in one or more organs, such as the eyes, brain, liver, intestine, or other organs, resulting in a variety of clinical symptoms. The only clinical sign in many cats with non-effusive FIP is ocular (eye) symptoms.

Without therapy, most individuals deteriorate quickly after sickness occurs, however, some cats remain normal for several weeks. Unfortunately, practically every occurrence of the disease will lead to death.

Most cats exposed to feline coronavirus, even possibly FIP-inducing strains, are able to generate an immune response that protects them, thus only a tiny fraction of infected cats acquire clinical illness. However, as previously indicated, those who contract the sickness almost always die.

How is FIP diagnosed?

Many of the clinical indications of FIP are ambiguous and overlap with other feline disorders, making FIP extremely difficult to diagnose. Standard blood analysis may reveal anomalies, although none are specific to FIP. X-rays can help identify whether there is fluid in the abdomen or chest. If there is fluid present, it can be evacuated by tapping the chest or abdomen. The analysis of this fluid in a veterinary laboratory can be especially beneficial because few other diseases produce the same type of fluid that FIP does. Nonetheless, fluid analysis can not always offer a definitive illness diagnosis.

FIP is sometimes a diagnosis of exclusion, which means that a number of comparable disorders have been ruled out. The diagnosis may be complicated further since FIP can coexist with other disorders such as feline leukemia virus infections. For more information on diagnosing FIP, see the "Feline Infectious Peritonitis Testing" handout.

Currently, the only approach to confirm a positive diagnosis of FIP is to have a pathologist examine damaged tissue (or perform a post-mortem study) in a laboratory. If there is any doubt about the diagnosis, your veterinarian may recommend that a biopsy be performed on your cat in order to differentiate FIP from other conditions.

I'm aware that there are particular blood testing. How trustworthy are these?

Although veterinary laboratories offer assays to detect antibodies to feline coronavirus in the blood, these tests are non-specific and cannot be used to diagnose FIP on their own. Although some laboratories offer polymerase-chain-reaction (PCR) assays that can detect very minute levels of the virus, no unique genetic sequence associated with FIP has been established. Although some of these tests claim to be able to differentiate between strains and find strains that are more likely to be connected with FIP, many independent specialists disagree. As a result, a positive test in a healthy cat is not a good predictor of FIP disease.

"FIP is one of the most difficult diagnoses to make for your veterinarian."

If a cat displays clinical indications associated with FIP, a positive test is supportive but not proof of the diagnosis. Similarly, a negative test in the context of advanced symptoms does not rule out FIP.

As you can see, FIP is one of the most difficult diagnoses for your veterinarian to make due to the disease's intricacy and the limitations of current diagnostics.

Is it possible to treat FIP?

FIP is almost always deadly. Although supportive therapy may increase longevity and quality of life, there is no definitive cure. Corticosteroids (e.g., prednisolone) in combination with immune-suppressing medicines (e.g., cyclophosphamide) may temporarily reduce inflammation and enhance the cat's quality of life. While experimental treatments are being researched, there are currently no commercially accessible or legally approved drugs in the United States to treat FIP. Once FIP has been detected in a clinically ill cat, euthanasia may be the most humane and acceptable course of action.

Remdesivir, a novel anti-viral medicine, was approved for the treatment of FIP in the United Kingdom in 2021. This medicine, which is administered in a series of injections over several weeks, has proven to be more effective than traditional treatment thus far. Other drugs for FIP treatment are actively being developed. Consult your veterinarian about the most recent FIP treatment options.

Is there a FIP vaccine?

Some firms have developed vaccinations to aid in the prevention of FIP in recent years. Because the route of transmission and the sequence of events leading to clinical FIP disease are unknown, and infection may have occurred prior to vaccination, vaccination success is uncertain. Currently, FIP vaccinations are not recommended for widespread usage. You and your veterinarian can decide whether or not immunization is necessary for your cat.

Are the other cats in the house in danger?

If your cat has FIP, other cats in your home may be at a higher risk of contracting feline coronavirus. Fortunately, only a small percentage of cats will develop this lethal condition as a result of infection. To reduce the risk of viral exposure, many veterinarians recommend waiting about a month after an infected cat dies before introducing a new cat into the family. It is advisable to wait at least three months after an infected cat has died in a multi-cat home to determine if any other cats acquire clinical illness. However, these previously exposed cats may be disease carriers and could infect any new animals.

The virus can be killed by cleaning with weak bleach (1:32). Having an adequate number of litter boxes can also help to reduce exposure to the excrement of other cats.