Feline Infectious Peritonitis (FIP) is a serious and often fatal viral disease affecting cats. It originates from a common virus, the feline coronavirus (FeCV). While most FeCV strains reside harmlessly in a cat’s digestive system and cause minimal illness, a mutation can transform it into the highly dangerous Feline Infectious Peritonitis Virus (FIPV) in about 10% of infected cats. This transformation leads to a severe inflammatory response, primarily around blood vessels in various organs, ultimately causing FIP. Understanding the disease, its risks, symptoms, and potential treatments is crucial for cat owners.
The disease typically presents in two main forms: the “wet” form, characterized by fluid accumulation in body cavities like the abdomen or chest, and the “dry” form, which affects the central nervous system and results in neurological symptoms. Without effective treatment, FIP is almost universally fatal. However, recent advancements have introduced therapies, including oral compounded formulations available by veterinary prescription in the US, offering new hope for affected cats.
Is Your Cat at Risk for FIP?
Any cat infected with FeCV is theoretically at risk of developing FIP, but certain groups are more susceptible. Younger cats, particularly those under 1.5 years old, account for a significant majority of cases, with a peak incidence in kittens between 7 months and 1.5 years of age. The virus is often transmitted from an infected mother cat to her kittens between five and eight weeks of age. However, adult cats can also contract FeCV through feces.
Factors that appear to increase susceptibility to FIP include living in high-density environments such as shelters or catteries, being a purebred cat, being male, or being a geriatric cat. The exact reasons for these increased risks are still under investigation, but managing stress and minimizing exposure to the virus are key preventative measures.
Recognizing the Symptoms of FIP
Initial exposure to FeCV often goes unnoticed, with some cats experiencing only mild, self-limiting symptoms like sneezing, watery eyes, nasal discharge, or brief diarrhea. The critical issue arises when the virus mutates into FIPV, which can happen weeks, months, or even years after the initial FeCV infection.
FIP manifests in two primary forms:
- Effusive (“Wet”) FIP: This form is characterized by the rapid accumulation of fluid in the abdominal (causing a pot-bellied appearance) and/or thoracic cavities. Symptoms include loss of appetite, weight loss, depression, fever, difficulty breathing due to fluid buildup, and a generally declining condition.
- Non-effusive (“Dry”) FIP: This form progresses more slowly and may include the non-specific signs of illness mentioned above, along with neurological symptoms. These can range from uncoordinated movements (ataxia) to seizures.
It’s important to note that cats can transition between the wet and dry forms, or exhibit signs of both.
Diagnosing FIP: Challenges and Approaches
Currently, there is no single definitive test to diagnose FIP. Antibody tests can detect exposure to coronaviruses but cannot reliably distinguish between the benign FeCV and the dangerous FIPV. A high antibody titer in a young cat with persistent fever unresponsive to antibiotics, especially when accompanied by characteristic fluid accumulation (yellowish, high protein, high white blood cell count), often leads to a presumptive diagnosis of FIP.
Other diagnostic methods aim to detect the virus itself. These include:
- Immunoperoxidase Test: Detects viral proteins in infected white blood cells within tissue samples (requires a biopsy).
- Immunofluorescence Test: Detects viral proteins in infected white blood cells in tissues or body fluids.
- Polymerase Chain Reaction (PCR): Detects viral genetic material in tissues or body fluids.
While these tests can be helpful, none are 100% accurate and may yield false positives or negatives. Therefore, a presumptive diagnosis of FIP is typically made by combining the cat’s history, physical examination findings, and the results of various laboratory tests.
Treatment Options for FIP
Historically, FIP was considered untreatable and invariably fatal. However, significant progress has been made with the development of antiviral drugs. The drug GS-441524 has shown considerable promise in laboratory and clinical studies, appearing to be a safe and effective treatment for FIP. This medication has been available in Australia and the UK for some time and is now accessible as an oral compounded formulation in the US, requiring a veterinary prescription.
While the long-term effectiveness, optimal dosage, and potential for drug resistance are still being studied, the availability of reliable FIP therapies marks a major advancement in veterinary medicine. Discussing the risks and benefits with your veterinarian is essential if your cat has been diagnosed with FIP. Supportive care, such as fluid therapy, draining accumulated fluid, and blood transfusions, may also be necessary in some cases.
Preventing FIP in Your Cat
Preventing FIP ultimately means preventing FeCV infection, which can be challenging due to its widespread nature. Minimizing stress is key, especially for cats in high-density environments. Maintaining living spaces with no more than three cats per room is recommended. While FeCV is highly contagious and spreads through feces and saliva, FIPV itself is not believed to be transmitted directly between cats, but rather develops through mutation after FeCV infection in an individual cat.
Keeping cats healthy through appropriate vaccinations against other common feline viruses like feline leukemia virus and calicivirus may reduce the overall risk of FIP. Maintaining excellent hygiene, including clean litter boxes located away from food and water, is also important.
There is one licensed FIP vaccine, but its effectiveness is questionable, and it is not routinely recommended by major veterinary associations. Cat owners should consult their veterinarian to weigh the potential risks and benefits before considering vaccination.
