Cat FIP Symptoms: The Complete Guide for Cat Owners in Australia and New Zealand

Feline Infectious Peritonitis (FIP) is one of the most devastating diagnoses a cat owner can receive. It progresses fast, it mimics other diseases, and for decades it was considered a death sentence. If your cat is showing symptoms that concern you, this guide will help you understand what FIP looks like, how it differs across its four main forms, and what to do the moment you suspect it.

Cat FIP Symptoms: The Complete Guide for Cat Owners in Australia and New Zealand

Time matters. Every day without treatment reduces the chance of remission. Read this carefully, then act.

What is Feline Infectious Peritonitis (FIP)?

Feline Infectious Peritonitis (FIP) is a fatal viral disease caused by a mutated form of feline coronavirus (FCoV). Most cats carry feline coronavirus without any symptoms — it is extremely common and usually harmless. In a small percentage of cats, the virus mutates inside the body into a virulent form that attacks white blood cells and causes a systemic inflammatory response. This mutated form is what causes FIP.

FIP cannot be transmitted from cat to cat. The mutation happens spontaneously inside an individual cat. Once it occurs, the disease progresses rapidly — in wet FIP cases, this can mean days to weeks without treatment.

Since 2019, GS-441524 antiviral therapy has changed the outcome for cats with Feline Infectious Peritonitis (FIP). More than 100,000 cats have been treated globally with high remission rates across all FIP types. But early recognition of symptoms is what makes treatment successful. The earlier you start, the better the outcome.

Why FIP Symptoms Are So Difficult to Spot

FIP is notoriously difficult to diagnose because its early symptoms overlap with dozens of other feline illnesses. Lethargy, reduced appetite, and mild fever are the hallmarks of countless cat health issues. Many cats are misdiagnosed with respiratory infections, liver disease, or toxoplasmosis before FIP is confirmed.

What makes FIP distinct is the pattern and progression. The symptoms do not resolve with standard treatments. They escalate. And over time, the specific cluster of signs — combined with blood test results and, in wet FIP, fluid accumulation — points unmistakably to Feline Infectious Peritonitis (FIP).

Knowing what to look for at each stage is the difference between catching it early and losing time you cannot get back.

The Four Types of FIP and Their Symptoms

Feline Infectious Peritonitis (FIP) presents in four main forms. Understanding which type your cat has is critical because treatment protocols differ by FIP type — particularly dosing concentration and duration.

1. Wet FIP (Effusive FIP)

Wet FIP is the most common and the fastest progressing form. It is characterised by abnormal fluid accumulation in the abdomen, chest, or both. This fluid is the immune system's response to widespread blood vessel inflammation caused by the FIP virus.

Key symptoms of wet FIP:

• Visibly distended or swollen abdomen — the belly appears bloated or drum-like

• Difficulty breathing if fluid accumulates in the chest cavity

• Rapid, shallow breathing or open-mouth breathing in severe cases

• Significant and sudden weight loss despite some initial appetite

• Persistent fever that does not respond to antibiotics

• Lethargy and reluctance to move

• Pale or jaundiced (yellow-tinged) gums in advanced cases

• Loss of appetite progressing to complete food refusal

Wet FIP progresses within days to weeks without treatment. If your cat has a swollen belly combined with any of the symptoms above, this is a medical emergency. Do not wait for a follow-up appointment.

What your vet will find: Abdominal or thoracic fluid on ultrasound. The fluid is typically yellow, viscous, and high in protein — this finding, combined with a positive Rivalta test, is a strong indicator of wet FIP.

2. Dry FIP (Non-Effusive FIP)

Dry FIP is harder to diagnose because there is no fluid accumulation. Instead, inflammatory granulomas (clusters of immune cells) form in the organs — most commonly the liver, kidneys, spleen, lymph nodes, and eyes. Dry FIP progresses more slowly than wet FIP but is no less fatal without treatment.

Key symptoms of dry FIP:

• Persistent low-grade fever that fluctuates but never fully resolves

• Gradual, unexplained weight loss over weeks

• Loss of appetite

• Lethargy and reduced activity

• Enlarged lymph nodes, detectable on examination

• Jaundice (yellowing of the skin, eyes, or gums) if the liver is affected

• Increased thirst and urination if kidneys are involved

• Neurological signs in some cases as the disease advances

• Eye changes including cloudiness or inflammation

Because dry FIP mimics chronic infections, liver disease, and lymphoma, diagnosis often takes longer. Blood tests showing elevated globulins, low albumin-to-globulin ratio, and elevated bilirubin — combined with imaging findings — are the primary diagnostic tools when no fluid is present.

3. Neurological FIP

Neurological FIP occurs when the FIP virus crosses the blood-brain barrier and causes inflammation in the brain and spinal cord. It can present as a standalone form or develop as a complication of wet or dry FIP that was not treated in time.

Neurological FIP requires a higher concentration of GS-441524 to achieve adequate drug levels in the central nervous system. Recognising the neurological signs early gives the best chance of successful treatment.

Key symptoms of neurological FIP:

• Seizures — sudden and often the first alarming sign

• Loss of balance or coordination (ataxia)

• Head tilt or circling

• Wobbly, unsteady gait similar to drunkenness

• Hind limb weakness or paralysis

• Rapid, involuntary eye movement (nystagmus)

• Behavioural changes — sudden aggression, confusion, or profound personality shifts

• Hypersensitivity to touch

• Difficulty swallowing

• Persistent fever alongside neurological signs

If your cat is showing any of these neurological symptoms, consult a specialist immediately. Neurological FIP has the narrowest treatment window — delays of even a few days can result in irreversible neurological damage even if remission is achieved.

Use our Dosage Calculator to understand the concentration required for neurological FIP treatment — it is significantly higher than for wet or dry cases.

4. Ocular FIP

Ocular FIP involves inflammation of one or both eyes caused by the FIP virus attacking blood vessels within the eye. It can occur as the sole manifestation of FIP or alongside other FIP types. It is often the first visible sign that something is seriously wrong, and it is frequently misdiagnosed as a simple eye infection.

Key symptoms of ocular FIP:

• Cloudiness or haziness of one or both eyes

• Colour changes in the iris (the coloured part of the eye)

• Redness or inflammation visible within the eye

• Unequal pupil sizes (anisocoria)

• Bleeding visible within the eye (hyphema)

• Squinting, sensitivity to light, or pawing at the eye

• Visible changes to the retina on veterinary examination

• Reduced vision or apparent blindness in severe cases

Ocular FIP responds well to GS-441524 treatment in most cases, with eye clarity returning over the course of the first weeks of treatment. However, untreated ocular FIP will progress to other organ systems.

Early Warning Signs Across All FIP Types

Regardless of FIP type, there are early warning signs that appear before the disease becomes advanced. These are the signals that should prompt immediate veterinary consultation and FIP testing.

Universal early symptoms of FIP:

• Persistent fever of 39.5 degrees Celsius or higher that does not respond to antibiotics

• Gradual, unexplained weight loss over two to four weeks

• Progressive loss of appetite

• Increasing lethargy and withdrawal from normal activity

• Rough, dull, or unkempt coat

• Mild jaundice detectable in the whites of the eyes or on the gums

Cats at highest risk:

• Kittens under two years old — FIP is most common in young cats

• Cats from multi-cat households, catteries, or shelters

• Cats that have recently experienced significant stress (rehoming, surgery, illness)

• Purebred cats, particularly Bengals, Ragdolls, Birmans, and Abyssinians

What to Do When You Suspect FIP

If your cat is showing symptoms consistent with Feline Infectious Peritonitis (FIP), follow these steps immediately:

Step 1: Contact your vet and request FIP-specific testing. Ask for a complete blood panel including albumin, globulin, albumin-to-globulin ratio, bilirubin, and white blood cell differential. If your cat has a swollen abdomen, request an abdominal ultrasound. If fluid is found, request a Rivalta test and fluid analysis.

Step 2: Do not wait for symptoms to worsen. Many cat owners wait to see if their cat improves. With FIP, this window is critical. Wet FIP in particular can deteriorate within days. If the blood results are consistent with FIP, begin the treatment process immediately.

Step 3: Understand your treatment options. GS-441524 antiviral therapy is the current standard of care for Feline Infectious Peritonitis (FIP). It is available in injectable and oral capsule forms. The correct dosage is calculated based on your cat's body weight and FIP type. Visit our Dosage Calculator for an initial estimate.

Step 4: Get expert guidance before you order. FIP type and severity determine which product and which concentration is appropriate. Our veterinary support team is available to walk you through the correct protocol for your cat before you commit to any purchase.

Learn more about treatment options at GS-441524 Injectables and Dual Antiviral Oral Capsules.

What to Expect from FIP Treatment

Most cats treated with GS-441524 begin showing visible improvement within the first seven to fourteen days. Common early indicators of treatment response include:

• Return of appetite within the first three to five days

• Reduction in fever within the first week

• Increased energy and willingness to move

• In wet FIP: gradual reabsorption of abdominal or thoracic fluid

• In ocular FIP: clearing of eye cloudiness within two to four weeks

• In neurological FIP: stabilisation of neurological signs, with gradual improvement over several weeks

The standard treatment protocol is 84 days of daily GS-441524 administration, followed by an 84-day monitoring period. Consistency is critical — missed doses are the most common cause of treatment failure and relapse.

Read more about the full protocol and what to expect in our FAQ.

Frequently Asked Questions About FIP Symptoms

Can FIP symptoms come and go? In dry FIP, symptoms can fluctuate — the fever rises and falls, appetite comes and goes. This variability is part of what makes dry FIP difficult to diagnose. It does not mean the disease is resolving on its own. Without treatment, dry FIP is uniformly fatal.

My cat has a swollen belly but is still eating. Could it be FIP? Yes. In the early stages of wet FIP, cats often maintain some appetite even as fluid accumulates. The swelling itself may not cause pain initially. Do not use continued eating as a reason to delay testing.

My vet said my cat has FIP but there is nothing to do. Is that true? This was accurate until 2019. GS-441524 antiviral therapy has changed the prognosis for FIP dramatically. More than 100,000 cats have now been treated globally. We would encourage you to share our treatment documentation with your veterinarian and to reach out to our team directly.

How is FIP different from other diseases with similar symptoms? The key differentiators are the persistent fever that does not respond to antibiotics, the specific blood test pattern (high globulins, low albumin-to-globulin ratio), and in wet FIP, the characteristic fluid. A combination of clinical signs, blood results, and imaging findings is used to confirm FIP.

Is FIP contagious to my other cats? FIP itself is not transmitted between cats. The underlying feline coronavirus (FCoV) is contagious, but FIP only develops when that virus mutates inside an individual cat — which happens spontaneously and cannot be predicted.

Summary: FIP Symptoms at a Glance

FIP Type	Key Symptoms	Progression Speed
Wet FIP	Swollen belly, breathing difficulty, fever, weight loss	Days to weeks
Dry FIP	Chronic fever, organ involvement, jaundice, weight loss	Weeks to months
Neurological FIP	Seizures, wobbling, head tilt, behavioural changes	Days to weeks
Ocular FIP	Cloudy eyes, iris colour change, redness, vision loss	Weeks

You Are Not Out of Options

If you have reached this page because your cat has just been diagnosed with Feline Infectious Peritonitis (FIP), know this: treatment exists, it works, and more than 100,000 cats have recovered globally since 2019.

The symptoms are serious. The timeline is urgent. But the outcome does not have to be what it once was.

Learn more about what FIP is and how it develops, read real recovery stories from Australia and New Zealand, or go directly to treatment options to begin the process today.

CureFIP Oceania ships GS-441524 antiviral treatment directly to Australia and New Zealand via DHL and FedEx. Our veterinary support team is available to guide you through the correct protocol for your cat's FIP type before you order.