Feline Infectious Peritonitis (FIP) is a rare and serious condition, particularly for younger or more vulnerable cats.
It can cause a variety of symptoms, making it difficult to diagnosis. Until recently, FIP was usually considered fatal, but recent developments in treatment options have improved the outcome for affected cats.
How does FIP develop in cats?
The origins of feline infectious peritonitis can be traced to a generally harmless virus known as feline coronavirus. Most cats are exposed to this virus at some point, particularly in multi-cat households or shelters. While initial infection usually results in mild or no symptoms, complications arise when, on rare occasions, the virus undergoes a mutation within the body.
This mutated coronavirus provokes an aggressive immune response that eventually causes severe damage to internal organs. Not every cat infected with feline coronavirus will develop FIP, however, those that do face a significant risk to their health.
What is the difference between feline coronavirus and FIP?
Feline coronavirus typically resides benignly in the intestines, sometimes causing mild digestive issues or going completely unnoticed.
The crucial difference between feline coronavirus and FIP stems from genetic changes that can occur. If the feline coronavirus mutates after infecting a cat, it gains the ability to invade immune cells. This mutated form leads to infectious peritonitis, triggering inflammation and significant tissue damage driven by the immune system.
Transmission pathways and risk factors
Feline coronavirus spreads mainly through fecal-oral transmission. Cats become exposed by contact with contaminated litter boxes, food bowls or during self-grooming, after coming into contact with infected surfaces. Young kittens, purebred cats and those living in crowded environments are more susceptible, though FIP can develop in any age group.
While FIP presents a serious health risk, most cats never progress to FIP, even if they are carriers of the original coronavirus.
Symptoms of FIP in cats
The symptoms of FIP vary widely, which can make early diagnosis challenging. FIP is typically seen in two forms, the "wet" (effusive) form and the "dry" (non-effusive) form.
Common symptoms include a fever, pronounced weight loss, lethargy and reduced appeitite. These signs tend to worsen, even when treatment for other conditions is provided.
The wet (effusive) form of FIP is characterised by fluid accumulation in the abdomen or chest. Affected cats may develop a pot-bellied appearance, or difficulty breathing due to fluid on the lungs. Draining the fluid may provided temporary relief, but the systemic illness will unfortunately persist.
Dry (non-effusive) FIP involves less fluid, but leads to the formation of hard nodules or lesions on organs such as the kidneys, liver, eyes or brain. Neurological symptoms can include vision disturbances or personality changes.
Diagnosing FIP
Diagnosing FIP is complex and nuanced. There is currently no single test capable of conclusively confirming FIP. Instead, veterinarians combine clinical observations, laboratory results, imaging, and evaluation of risk factors.
Bloodwork can reveal indicators consistent with a viral disease, such as elevated protein levels or specific inflammatory markers. If fluid is present in the chest or abdomen, analysing this liquid can provide important diagnostic clues. Ultimately, diagnosis usually comes down to consistent monitoring, repeat testing when necessary, and close communication between caregivers and veterinarians.
Is there a cure for FIP?
While FIP was once considered almost always fatal, recent advances in antiviral medication have opened up new possibilities for affected cats.
Treatment plans focus on suppressing viral activity, reducing inflammation, and offering supportive care tailored to each cat’s needs. In addition to direct medication, support prioritises hydration, nutrition, and pain management.
Appetite stimulants, fluid replacement, and therapies to control fever or nausea all help keep cats feeling as comfortable as possible during recovery attempts. Cats battling FIP often require environmental modifications, such as minimising stress and ensuring easy access to preferred resting spots.
Preventative steps can also be taken among high-risk groups and where cats live in crowded environments:
- Maintaining strict hygiene standards, regularly cleaning litter trays, food bowls and bedding
- Limiting over-crowding in multi-cat facilities
- Monitoring regularly for early signs of any clinical changes to each cat's health
Living with a cat diagnosed with FIP
A confirmed diagnosis of feline infectious peritonitis brings both emotional and practical challenges for any caregiver.
Ultimately, while FIP remains one of the most formidable viral diseases facing cats, growing awareness, ongoing research, and shared commitment to early detection are gradually improving outcomes for feline health.
