Feline Infectious Peritonitis (FIP) in Cats

FIP presents in ‘wet’ and ‘dry’ forms.

Wet FIP is more common and accounts for 80% of cases. Cases of wet FIP present with fluid accumulation in the abdomen and chest. These cats often experience difficulty breathing and abdominal swelling.

Dry FIP causes inflammatory nodules to form throughout the body, including in the abdomen, chest, brain, and spinal cord. These cats typically present with symptoms such as palpable abdominal masses, seizures, uncoordinated movement, weakness, or unusual behavior.

Wet and dry FIP overlap and some cats present with symptoms of both forms.

Cats showing symptoms of FIP require urgent veterinary treatment.

FIP is a severe viral disease in cats which is usually fatal. Nearly all cats are exposed to FCoV in their lifetime, but only 5 - 10% of cases mutate and develop into FIP. The condition is rare in the general cat population, but more common in multicat households and breeding facilities, where cats are more likely to be exposed to FCoV.

Young cats are most likely to develop FIP, particularly cats between 3 months and 2 years of age. Cats that are immunosuppressed, such as those with feline leukemia virus or feline immunodeficiency virus, are also more susceptible to developing FIP.

A diagnosis of FIP in a multicat household increases the risk of further infections, particularly in young cats and sibling groups. The mutated forms of FCoV themselves have an extremely low transmission rate to other cats.

FIP results from mutation of the FCoV virus in an infected cat. Most cases of FCoV infection do not result in FIP. While some specific mutations have been recognized, it is thought that there are many different mutations which transform FCoV into FIP.

Symptoms of FIP vary and are often non-specific.

Diagnosis is challenging, as there are no reliable tests to confirm FIP. Diagnosis involves several tests, such as:

• Physical examination
• Blood work
• Diagnostic imaging, such as X-rays or ultrasound, to identify fluid accumulations or inflammatory nodules
• Specific lab work to identify evidence of FCoV in the system
• Exploratory surgery to examine the abdominal organs for inflammatory nodules or other signs of FIP

Confirmation of FCoV antibodies in the blood is not diagnostic for FIP in and of itself, since the vast majority of cats test positive due to previous exposure to the virus. Confirmation of FCoV in fluid or tissue samples, in combination with appropriate symptoms, is considered diagnostic for FIP.

FIP is almost always fatal, and has no specific treatment available at this time. Intensive supportive care can extend duration and quality of life, however most cats only survive a few days to months before they are euthanized due to a poor prognosis.

Recently, experimental antiviral treatments have achieved remission in some cats. The overall efficacy of these medications has not been thoroughly examined to date, and the medications are not licensed for use against FIP infections in many countries. Additionally, long-term follow-up is not yet available, so it is not possible to determine if these cats have been truly cured.

FIP remains a severe disease with a poor prognosis in most cats.

Prevention of FIP is challenging. Vaccination is possible, but is not recommended due to low efficacy. Additionally, the vaccine cannot be used in cats under 4 months of age, by which time many cats have already been exposed to the virus.

Outbreaks of FIP can occur in multi cat households or breeding facilities. Once there is a highly mutagenic strain in the population, it is more likely to mutate in more of the individual in-contact cats and develop into FIP, even though the mutated form is not being transmitted between individuals.

Strategies to reduce FCoV infection risk include:

• Not introducing new cats into the household for 12 months
• Avoiding stressful events, including travel or boarding in a cattery
• Regular blood testing for FCoV to identify ‘carrier’ cats in multicat households, which may be persistently shedding the virus
• Separating cats into small groups of 2-3 cats to reduce spread between groups
• Not breeding from cats that have had FIP in previous litters, as there may be a heritable susceptibility to FIP-causing forms of FCoV
• Routine disinfection of cages, water and food dishes, and surfaces

Ultimately, elimination of FCoV in breeding units may not be possible, and consideration should be given to not breeding that group of cats.

Infection with FCoV is very common in cats, but is normally asymptomatic. FCoV infection results in FIP in 5-10% of cases.

• Supportive treatment
• Immunosuppression with medications such as steroids
• Experimental antiviral treatments