Feline Infectious Peritonitis: A Guide for Cat Owners

What is Feline Infectious Peritonitis (FIP)?

Feline Infectious Peritonitis, commonly known as FIP, is a serious and often fatal disease that affects cats. It develops when a common, usually harmless virus, the feline coronavirus (FCoV), undergoes a mutation within a cat’s body. This mutation transforms the virus into a much more dangerous pathogen that can trigger a severe inflammatory response, leading to the characteristic signs of FIP. While the initial feline coronavirus infection is widespread and often asymptomatic, the development of FIP is relatively rare. The disease is characterised by inflammation in various parts of the body, most commonly affecting the abdomen (wet FIP) or the nervous system and eyes (dry FIP), though a combination of both is also possible. Early recognition of FIP symptoms and prompt veterinary care are crucial for any cat suspected of having the disease.

How do cats get FIP?

The journey to FIP begins with the feline enteric coronavirus (FCoV). This virus is shed in the faeces of infected cats and is highly contagious. It spreads primarily through faucal-oral transmission, meaning cats ingest the virus from contaminated environments, food bowls, water, or through grooming each other after contact with faeces. Litter boxes are a significant source of infection in multi-cat households. Most cats infected with FCoV will either show no symptoms or only mild, transient gastrointestinal upset, such as vomiting or diarrhea.

In the vast majority of cases, their immune systems effectively fight off the virus, and they develop antibodies, providing some level of protection. However, in a small percentage of infected cats, the FCoV undergoes a mutation within their body. This mutated virus, now referred to as the FIP virus, triggers an overreaction of the cat’s immune system. This immune-mediated response is what causes the damaging inflammation characteristic of FIP. Factors that may increase a cat’s risk of developing FIP include stress, surgery, or the presence of other illnesses, which can weaken their immune system and potentially trigger the viral mutation.

Recognising the signs of FIP in cats

The symptoms of FIP can be varied and often mimic other common feline illnesses, making diagnosis challenging. The presentation typically depends on whether the disease manifests as ‘wet’ (effusive) FIP or ‘dry’ (non-effusive) FIP, or a combination of both.

Wet FIP symptoms

Wet FIP is characterised by the accumulation of fluid in the body cavities, most commonly the abdomen and chest. This leads to:

• A distended abdomen, which may appear swollen or bloated.
• Difficulty breathing due to fluid accumulation in the chest cavity (pleural effusion).
• Lethargy and weakness.
• Loss of appetite.
• Fever that may not respond to medication.
• Weight loss.

Dry FIP symptoms

Dry FIP does not typically involve significant fluid accumulation but causes inflammation in various organs and tissues. Symptoms can be more subtle and progressive, including:

• Neurological signs: These can include wobbliness, seizures, paralysis, or behavioural changes.
• Ocular signs: Inflammation in the eyes can manifest as redness, cloudiness, squinting, or changes in pupil size.
• Organ-specific inflammation: This can affect the kidneys, liver, spleen, or lymph nodes, leading to corresponding symptoms like increased thirst and urination (kidney), jaundice (liver), or enlarged lymph nodes.
• General malaise: Lethargy, poor coat condition, and loss of appetite are common.
• Weight loss.
• Fever.

It is important to note that a cat can present with symptoms of both wet and dry FIP simultaneously.

Diagnosing FIP in cats

Diagnosing FIP can be complex because its symptoms overlap with many other diseases, and there isn’t a single definitive test for it. Veterinarians use a combination of clinical signs, patient history, physical examination, and various diagnostic tests to reach a diagnosis.

Diagnostic tests used for FIP

• Blood tests: These can reveal general indicators of inflammation, such as an elevated white blood cell count. Specific antibody tests for feline coronavirus can indicate exposure, but a positive result does not confirm FIP, as many cats are exposed to FCoV without developing the disease. A high ratio of certain white blood cells (neutrophils) to lymphocytes, along with an elevated globulin level, can be suggestive of FIP.
• Urinalysis: Can help assess kidney function and detect abnormalities.
• Imaging: X-rays and ultrasounds are crucial for identifying fluid accumulation in the abdomen or chest (wet FIP) and can also help visualize enlarged organs or masses associated with dry FIP.
• Fluid analysis: If fluid is present, a sample is collected via abdominocentesis (abdominal fluid) or thoracentesis (chest fluid). Analysis of this fluid is key. FIP effusions typically have a high protein content and a specific cell profile. The Rivalta test, which involves dropping a sample of fluid into acetic acid and observing if it forms a precipitate, can be suggestive of FIP if a ‘cloudy string’ forms.
• Biopsy and Histopathology: In some cases, a biopsy of affected tissues may be performed. Examination of these tissues under a microscope can reveal the characteristic inflammatory patterns of FIP and detect the presence of FIP virus antigens.
• PCR (Polymerase Chain Reaction): This test can detect viral genetic material in fluid samples or tissue biopsies, helping to confirm the presence of FCoV, though distinguishing between FCoV and the mutated FIP virus can still be challenging.

Because definitive diagnosis can be difficult, experienced veterinarians often make a presumptive diagnosis based on a constellation of findings, particularly when a cat exhibits typical clinical signs and diagnostic test results consistent with FIP.

Treatment options for FIP cats

Historically, FIP was considered a death sentence for cats, with most succumbing to the disease within weeks or months of diagnosis. However, significant advancements have been made in treatment, offering hope where there was little before.

Antiviral Therapies

The most significant breakthroughs in FIP treatment have come with the development of specific antiviral medications. These drugs, such as remdesivir and GS-441524 (often referred to by various brand names), work by inhibiting the replication of the FIP virus. These treatments are typically administered via injection or oral administration for a set period, often ranging from 8 to 12 weeks, depending on the severity and type of FIP. It is crucial to understand that these treatments are often prescribed and managed by veterinarians. While some owners may seek out alternative sources for these medications, it is vital to consult with a veterinary professional to ensure the correct dosage, administration, and monitoring for side effects. The availability and legality of these specific drugs for FIP treatment can vary by region.

Supportive Care

Alongside antiviral medications, supportive care plays a vital role in managing FIP. This may include:

• Fluid therapy: For cats with significant fluid accumulation, fluid therapy can help maintain hydration and electrolyte balance. In severe cases of ascites (abdominal fluid), paracentesis (draining fluid) may be performed to alleviate breathing difficulties and discomfort, although this is a temporary measure.
• Nutritional support: Ensuring the cat receives adequate nutrition is important. This might involve appetite stimulants or a highly palatable, digestible diet.
• Medication for symptoms: Depending on the specific symptoms, a veterinarian may prescribe anti-inflammatory drugs to manage inflammation, anti-seizure medications for neurological signs, or other supportive treatments.

The success of FIP treatment depends on many factors, including the stage of the disease at diagnosis, the cat’s overall health, the specific strain of the virus, and adherence to the treatment protocol. Close monitoring by a veterinarian throughout the treatment period is essential.

Preventing FIP in cats

While FIP itself is difficult to prevent entirely due to the unpredictable mutation of the feline coronavirus, steps can be taken to minimise the risk of initial FCoV infection and to support a cat’s overall health, which may reduce the likelihood of the virus mutating into FIP.

• Hygiene: Maintaining excellent hygiene in multi-cat households is paramount. Regular cleaning and disinfection of litter boxes, food and water bowls, and living areas can help reduce the spread of FCoV.
• Stress reduction: Minimizing stress for cats is important. Overcrowding, introduction of new pets, changes in routine, or environmental stressors can weaken a cat’s immune system, potentially making them more susceptible.
• Isolation of new cats: When introducing new cats into a household, it is advisable to keep them separate for a period to monitor for any signs of illness and prevent the potential introduction of FCoV.
• Good nutrition and general care: Ensuring your cat has a balanced diet, clean water, regular veterinary check-ups, and a safe environment contributes to a strong immune system, better equipped to handle viral challenges.

Currently, there is no licensed vaccine proven to prevent FIP effectively. While some vaccines have been developed, their efficacy and safety are still debated, and they are not universally recommended or available.

The outlook for cats with FIP

The prognosis for cats diagnosed with FIP has dramatically improved in recent years, largely due to the availability of effective antiviral treatments. Previously, FIP was almost invariably fatal, with survival rates very low. With prompt diagnosis and aggressive treatment using antiviral medications, many cats can now achieve remission and go on to live healthy lives. However, it is important to be realistic. The success of treatment can vary significantly between individual cats. Some cats recover fully with no lasting effects, while others may experience relapses or require extended treatment. Cats with advanced disease at the time of diagnosis, or those with severe neurological or organ damage, may have a more guarded prognosis. Veterinarians play a critical role in discussing the individual prognosis with cat owners, considering all factors involved in the cat’s condition and response to treatment.