Cat Disease FIP: What Every UK Owner Needs to Know

Key takeaway: Feline Infectious Peritonitis (FIP) is a serious viral disease of cats that was once considered fatal, but antiviral treatment with GS-441524 has changed that outlook, with a 92% success rate reported by UC Davis (Pedersen, 2019). FIP takes four forms (wet, dry, ocular, and neurological), and early recognition plus a confirmed diagnosis from your veterinarian gives your cat the best chance at remission. A standard course runs 84 days under veterinary supervision.

A cat resting comfortably at home.

What is FIP in cats?

FIP is a disease caused when a common feline coronavirus mutates inside a cat and triggers an aggressive immune reaction. Most cats carry the harmless enteric form of the coronavirus without any problem, but in a small percentage the virus changes and spreads through the body, causing the illness we call FIP.

FIP is not the same as the intestinal coronavirus that many cats shed and clear on their own. The dangerous version develops when that virus mutates within an individual cat, which is why FIP itself is not considered highly contagious between cats in the way a simple cold might be.

In the UK, FIP is seen most often in younger cats, particularly those under two years old, and in multi-cat households, rescues, and pedigree lines. Stress, a still-developing immune system, and high-density living all raise the risk.

What are the symptoms of FIP in cats?

The early symptoms of FIP in cats are often vague and easy to miss: a fluctuating fever that does not respond to antibiotics, reduced appetite, weight loss, and low energy. As the disease progresses, the signs become more specific and depend on which of the four forms is present.

Because the first signals are subtle, many owners only recognise the pattern in hindsight. Our guide to the 12 early warning symptoms of FIP walks through the changes that most often prompt a vet visit.

FIP presents in four distinct forms, and each one shapes both the symptoms you will notice and the treatment plan your veterinarian builds. Below, each form is set out on its own so you can match what you are seeing to what happens next.

Wet (Effusive) FIP

Wet FIP causes fluid to build up in the abdomen or chest. You may notice a swollen, rounded belly, laboured breathing if fluid collects around the lungs, and rapid deterioration in overall condition.

This is often the fastest-moving form, so a suspected wet FIP case deserves urgent veterinary attention. The fluid itself is frequently straw-coloured and thick, which can help your veterinarian point toward a diagnosis.

Dry (Non-effusive) FIP

Dry FIP produces little or no fluid and instead causes inflammatory lesions in organs such as the liver, kidneys, intestines, and lymph nodes. Symptoms tend to be slower and harder to read, including persistent fever, weight loss, and vague malaise.

Because there is no obvious fluid swelling, dry FIP is often harder to diagnose and can be mistaken for other chronic conditions. Careful bloodwork and imaging usually guide the picture.

Ocular FIP

Ocular FIP affects the eyes and can appear on its own or alongside other forms. Watch for colour changes in the iris, cloudiness, a visibly inflamed eye, or changes in the pupil and vision.

Eye involvement signals that the disease has reached tissues protected by the blood-eye barrier, which is an important factor in dosing. This is why ocular cases are treated at a higher dose than wet FIP.

Neurological FIP

Neurological FIP affects the brain and spinal cord and produces signs such as wobbliness, loss of balance, tremors, seizures, behavioural change, and partial paralysis. It reflects the virus crossing into the central nervous system.

Like ocular FIP, this form sits behind a protective barrier that antiviral treatment must reach, so it is dosed at the highest level. Prompt veterinary assessment matters because neurological signs can escalate quickly.

How is FIP diagnosed in cats?

FIP diagnosis is made by your veterinarian using a combination of clinical signs, blood tests, fluid analysis where fluid is present, and imaging, because no single test confirms FIP on its own. The picture is built from several results rather than one definitive number.

Common findings include a raised globulin level, a low albumin to globulin ratio, anaemia, and elevated markers of inflammation. Where there is effusion, analysing that fluid is one of the most useful steps.

Bloodwork is also central to monitoring once treatment begins, not just to reaching the diagnosis. Our guide to cat bloodwork during FIP treatment explains what each result means as your cat progresses.

If you are researching diagnosis while comparing providers, our FIP treatment FAQ for Europe covers many of the practical questions UK and European owners raise before starting.

Can FIP in cats be treated?

Yes. FIP is now treatable with the antiviral GS-441524, which is the medicine at the core of modern FIP treatment and the hero ingredient behind CureFIP. Before 2019 the disease was almost always fatal, and evidence shows that outcomes have transformed since antiviral therapy became available.

GS-441524 monotherapy delivered a 92% success rate in the UC Davis study (Pedersen, 2019), which remains the reference point for injectable treatment. Since 2019, more than 100,000 cats have been treated across the CureFIP network.

A more recent approach pairs GS-441524 with a second antiviral, EIDD-1931. In cats that had already relapsed, this combination reported 78.3% remission (Li and Cheah, 2025), and you can read the detail in our overview of how dual antiviral therapy is changing FIP treatment.

How is FIP treated with GS-441524?

FIP is treated with a daily course of GS-441524 given under veterinary supervision, typically as a subcutaneous injection once per day for 84 days (12 weeks). The exact dose depends on which of the four forms of FIP your cat has, because ocular and neurological disease sit behind protective barriers and need higher dosing.

The CureFIP injectable range shares the same dosing structure across strengths, so your veterinarian can match concentration to your cat's size and comfort. The table below sets out the dose by form, exactly as listed for the injectable products.

FIP form	GS-441524 injectable dose	Schedule	Duration
Wet / Effusive	6 mg/kg	1 subcutaneous injection per day	84 days
Dry / Non-effusive	8 mg/kg	1 subcutaneous injection per day	84 days
Ocular	10 mg/kg	1 subcutaneous injection per day	84 days
Neurological	10 mg/kg	1 subcutaneous injection per day	84 days

Reference: Pedersen et al., UC Davis (PMC6435921). Your veterinarian will confirm the correct dose for your individual cat.

The steps of a typical treatment journey look like this:

1. Get a working diagnosis from your veterinarian based on signs, bloodwork, and fluid analysis where relevant.

2. Confirm your cat's weight and FIP form so the correct dose is set.

3. Begin the daily protocol and keep to the same time each day for 84 days.

4. Recheck bloodwork at intervals your veterinarian recommends to track progress.

5. Complete the full course, then enter an observation period to confirm remission.

For a week-by-week view of what happens over the 12 weeks, see our GS-441524 treatment timeline.

Which CureFIP treatment options are available?

CureFIP offers three GS-441524 injectable strengths and an oral dual antiviral option, so the route can be matched to your cat's form of FIP and your veterinarian's guidance. Injectables follow the four-form dosing table above; the oral dual capsule is dosed by weight.

Product	Strength	Price	Notes
CureFIP™ GS-441524 Injectable 20mg/ml	20 mg/ml	€79.00	Available in 8ml and 10ml
CureFIP™ GS-441524 Injectable 30mg/ml	30 mg/ml	€89.00	Available in 8ml and 10ml
Cure FIP Antiviral 40mg/ml	40 mg/ml	€119.00	Available in 8ml and 10ml
CURE FIP™ Dual Antiviral Oral Capsules	GS-441524 + EIDD-1931	€179.00	Dosed by weight band

The dual antiviral oral capsules are dosed by body weight: under 2.5 kg receives GS-441524 25 mg + EIDD-1931 5 mg; 2.5 to 5 kg receives GS-441524 35 mg + EIDD-1931 8 mg; and over 5 kg receives GS-441524 50 mg + EIDD-1931 12 mg. The recommended duration is 12 weeks, taken as one capsule per day.

The oral dual route is positioned for wet and dry FIP. In some regions it is not recommended once ocular or neurological signs are present, or if a cat cannot eat or defecate, so this is a decision to make with your veterinarian.

If you want the scientific reasoning behind combining two antivirals, our article on dual nucleoside analogue therapy for FIP sets out the rationale and evidence in depth.

How can UK owners improve the odds for a cat with FIP?

The biggest factors are catching FIP early, confirming the diagnosis with your veterinarian, starting the full 84-day protocol promptly, and completing the course without gaps. Consistent daily dosing and regular bloodwork monitoring give your cat the strongest footing.

Supportive care alongside antiviral treatment can help, including good nutrition, hydration, a low-stress environment, and managing any secondary issues your vet identifies. Our FIP survival tips collect practical strategies used by families through treatment.

We are clear about what the data shows and what it does not. FIP treatment has strong reported outcomes, but every cat is different, and your veterinarian remains the right person to guide dose, monitoring, and decisions throughout.

FAQ

Is FIP in cats always fatal?

No. FIP was once considered fatal, but antiviral treatment with GS-441524 has changed this, with a 92% success rate reported by UC Davis (Pedersen, 2019). Early diagnosis and completing the full 84-day protocol under veterinary supervision matter most.

What are the first signs of FIP I should watch for?

The earliest FIP signs are usually a persistent fluctuating fever that does not respond to antibiotics, reduced appetite, weight loss, and low energy. As the disease develops you may also see a swollen abdomen, breathing difficulty, eye changes, or neurological signs such as wobbliness, depending on the form.

How is FIP diagnosed in the UK?

FIP is diagnosed by your veterinarian using clinical signs together with bloodwork, fluid analysis where fluid is present, and imaging, because no single test confirms FIP alone. Typical findings include raised globulin, a low albumin to globulin ratio, and markers of inflammation.

How long does FIP treatment take?

A standard course of GS-441524 runs 84 days (12 weeks), given as one daily dose under veterinary supervision. Your cat then enters an observation period so your veterinarian can confirm remission.

Is FIP contagious to other cats?

The underlying feline coronavirus is common and can pass between cats, but FIP itself develops when that virus mutates inside an individual cat, so FIP is not considered highly contagious in the usual sense. Reducing stress and overcrowding in multi-cat homes is still sensible.

If your cat has been diagnosed with FIP, or you suspect it, the next step is to understand your options and act quickly. You can explore treatment routes and dosing in more detail and speak with the team at CureFIP's FIP treatment centre, then work with your own veterinarian to decide the right plan for your cat.