FIP Cats Symptoms: Stage-by-Stage Guide for Pawrents
Key takeaway: Feline Infectious Peritonitis (FIP) often starts quietly, with a fever that will not go away, low energy, poor appetite and weight loss, before moving into one of four distinct forms: wet (effusive), dry (non-effusive), ocular or neurological. The faster you recognize these FIP symptoms and get a clear diagnosis with your veterinarian, the sooner your cat's recovery journey can begin. You are not the first Pawrent to face this, and your cat's odds are better than they have ever been.
Feline Infectious Peritonitis (FIP) can feel frightening, especially when the signs come on slowly and change over time. This guide walks you through the fip cats symptoms stage by stage, in plain language, so you know what to watch for and when to call your veterinarian.
A cat resting comfortably at home.
What is Feline Infectious Peritonitis (FIP) and what causes it?
Feline Infectious Peritonitis (FIP) is a serious viral disease caused by a mutated form of the common feline coronavirus (FCoV). Many cats carry the harmless coronavirus in their gut, but in a small number it mutates and triggers FIP.
The virus can affect young cats, senior cats, and everyone in between. Stress, a recent move, or a multi-cat home can play a role in how it shows up.
FIP used to be seen as hopeless. That is no longer true. Across our network, more than 100,000 cats have been helped since 2019, and there is now a clear path forward that starts with the right diagnosis. For a fuller overview, our complete FIP guide for Filipino caregivers is a good companion to this symptom checklist.
What are the early symptoms of FIP in cats?
The early symptoms of FIP in cats are usually vague: a fever that does not respond to antibiotics, tiredness, reduced appetite, and slow weight loss or stunted growth in kittens. These signs are easy to miss because they look like many other illnesses.
The tricky part is that early Feline Infectious Peritonitis (FIP) rarely announces itself. Your cat may simply seem "off" for a week or two.
Here is what many families notice first:
A recurring or persistent fever that antibiotics do not fix
Low energy, sleeping more, hiding away
Eating less, or losing interest in favourite food
Gradual weight loss, or a kitten that stops growing well
A dull, rough coat
Write down when the fever started and how high it is.
Note any change in appetite, weight, or litter box habits.
Bring these notes to your veterinarian, because the pattern over time matters as much as any single sign.
Early action gives your cat the best start. If your gut tells you something is wrong, trust it.
What are the four forms of Feline Infectious Peritonitis (FIP)?
Feline Infectious Peritonitis (FIP) has four distinct forms: wet (effusive), dry (non-effusive), ocular, and neurological. Ocular and neurological FIP are separate forms in their own right, not simply branches of the dry form.
A cat can show signs of more than one form, and the picture can shift as the disease progresses. This is why your veterinarian looks at the whole cat, not just one symptom.
FIP form | Where it shows | Common signs |
Wet (effusive) | Belly or chest fluid | Swollen belly, trouble breathing, fluid build-up |
Dry (non-effusive) | Internal organs | Weight loss, fever, organ changes, no fluid |
Ocular | The eyes | Colour change in the iris, cloudiness, inflammation inside the eye |
Neurological | Brain and spine | Seizures, head tilt, loss of balance, disorientation |
What are the signs of wet FIP in cats?
Wet FIP signs center on fluid build-up: a swollen, rounded belly, or fluid in the chest that makes breathing fast and difficult. Wet (effusive) Feline Infectious Peritonitis (FIP) is often the fastest-moving form.
You may notice your cat's tummy looking bloated even as the rest of the body grows thin. That fluid is the hallmark of the effusive form.
Watch for these wet FIP signs:
A belly that looks swollen or pear-shaped
Breathing that is rapid, shallow, or laboured
Reluctance to move, lying low, tiring quickly
Ongoing fever and weight loss underneath the swelling
Pale or yellow-tinged gums in some cats
If your cat is struggling to breathe, treat it as urgent and contact your veterinarian right away. Fluid in the chest needs prompt attention.
What are the dry FIP signs in the Philippines?
Dry FIP signs in the Philippines, and everywhere, are harder to spot because there is little or no fluid build-up. Dry (non-effusive) Feline Infectious Peritonitis (FIP) works inside the organs, so the clues are weight loss, a stubborn fever, poor appetite, and a cat that slowly fades in energy.
Because there is no dramatic swelling, dry FIP can go undiagnosed longer. Many Pawrents describe a cat that just keeps losing condition despite eating.
Signs to watch for:
Steady weight loss with no clear reason
A fever that comes and goes
Poor appetite and low energy
Enlarged organs your veterinarian may feel on exam
A generally unwell, "not themselves" appearance
Dry FIP sometimes overlaps with ocular or neurological signs, so tell your veterinarian about any eye or balance changes too.
What are the signs of ocular FIP in cats?
Ocular Feline Infectious Peritonitis (FIP) shows up in the eyes: a change in the colour of the iris, cloudiness, inflammation inside the eye (uveitis), or vision loss from lesions in the eye. A sudden colour change in your cat's eye is an ocular sign and should never be ignored.
The eye can be a window into FIP. Changes here are real red flags, even when the rest of the cat seems stable.
Look for:
One or both irises changing colour
A cloudy or hazy look to the eye
Redness or visible inflammation inside the eye
Bumping into things or other signs of reduced vision
Eye changes can have other causes too, including Feline Herpesvirus (FHV-1). If you are unsure whether an eye problem is viral and from a different source, our guide on cat eye ulcers and FHV-1 explains how those signs differ. Either way, your veterinarian is the one to make the call.
What are the signs of neurological FIP in cats?
Neurological Feline Infectious Peritonitis (FIP) affects the brain and spinal cord, causing seizures, head tilt, loss of balance, wobbliness, paralysis, or disorientation. These signs mean the virus is affecting the nervous system and need urgent veterinary attention.
Neurological FIP is a separate form from ocular FIP, though a cat can sometimes show both. Changes in coordination or behaviour are the key clues.
Signs include:
Seizures or sudden collapse
A tilted head or walking in circles
Loss of balance, wobbling, or falling
Weakness or partial paralysis in the legs
Confusion or unusual behaviour
Remember, a change in eye colour is an ocular sign, not a neurological one. Describe exactly what you see to your veterinarian so the form can be identified correctly.
How is Feline Infectious Peritonitis (FIP) diagnosed?
Feline Infectious Peritonitis (FIP) is diagnosed by your veterinarian using the full picture: your cat's symptoms, a physical exam, blood tests, and fluid analysis when fluid is present. There is no single at-home test, which is why professional diagnosis matters so much.
Your notes help a lot here. The timeline of the fever, the weight loss, and any eye or balance changes all guide your veterinarian toward the right answer.
Share your symptom diary and photos of any eye changes.
Allow blood work and, if needed, a sample of any belly or chest fluid.
Work with your veterinarian to confirm the form, because the form guides the treatment plan.
Can FIP be treated once you see the symptoms?
Yes. Feline Infectious Peritonitis (FIP) is now a treatable disease, and the main antiviral used worldwide is GS-441524. Many families across our network have walked this road since 2019, and the results speak for themselves.
Treatment is a journey you take together with your veterinarian. A common path starts with GS-441524 subcutaneous injections at the standard dose for the form, then switches to oral capsules after 2 to 4 weeks.
The standard GS-441524 injectable doses by form are:
FIP form | Standard GS-441524 dose |
Wet (effusive) | 6 mg/kg |
Dry (non-effusive) | 8 mg/kg |
Ocular | 10 mg/kg |
Neurological | 10 mg/kg |
These doses sit within the 5 to 10 mg/kg range linked with the best outcomes in the systematic review by Gokalsing et al. 2025. A full injectable course runs 12 weeks (84 days).
For the oral phase, the dual capsule (GS-441524 + EIDD-1931) keeps things simple: one capsule a day for your cat's weight class, with no mg calculation and no counting capsules.
Weight class | Dual capsule dose |
0 to 2.5 kg (0 to 5.5 lb) | 1 capsule per day |
2.5 to 5 kg (5.5 to 11 lb) | 1 capsule per day |
Over 5 kg (over 11 lb) | 1 capsule per day |
One capsule matches one weight class, so dosing is easy to get right at home. The dual capsule is used after the injection phase, or once your cat is stable, always under your veterinarian's guidance.
A few important safety notes during FIP care: avoid fluoroquinolone antibiotics, spot-on flea medications, lysine, and immune boosters, as these can work against treatment. Any product containing EIDD-1931, including the dual capsule and FipX, is not for pregnant, nursing, or breeding cats. And cost is a real concern for many Pawrents, so our 84-day FIP treatment budget guide can help you plan ahead.
Success rates are statistics, not promises, and every cat is different. There are no guarantees in medicine. The one guarantee we do offer is simple: you can cancel any time before your order ships for a full refund.
FAQ: Feline Infectious Peritonitis (FIP) Symptoms
What are the first symptoms of Feline Infectious Peritonitis (FIP) in cats?
The first symptoms of Feline Infectious Peritonitis (FIP) are usually a fever that does not respond to antibiotics, low energy, reduced appetite, and gradual weight loss or stunted growth in kittens. These early signs are vague, so keep a simple diary and share it with your veterinarian.
How do I tell wet FIP from dry FIP?
Wet (effusive) Feline Infectious Peritonitis (FIP) causes fluid build-up, seen as a swollen belly or fast, difficult breathing, while dry (non-effusive) FIP has little or no fluid and shows mainly as weight loss, fever, and low energy. Your veterinarian confirms the form with an exam and tests, including fluid analysis when fluid is present.
Is a change in my cat's eye colour a sign of FIP?
A change in the iris colour, cloudiness, or inflammation inside the eye can be a sign of ocular Feline Infectious Peritonitis (FIP). Eye changes also have other causes, so have your veterinarian examine your cat promptly to find the reason.
Are ocular and neurological FIP the same thing?
No. Ocular Feline Infectious Peritonitis (FIP) affects the eyes, while neurological FIP affects the brain and spinal cord with signs like seizures, head tilt, and loss of balance. They are two separate forms, though a cat can sometimes show both.
Can FIP be cured if I catch the symptoms early?
Feline Infectious Peritonitis (FIP) is now treatable, and catching the symptoms early gives your cat the best start on the recovery journey. Treatment with GS-441524 is guided by your veterinarian, and while results are never guaranteed, many families across our network have seen their cats return to eating, playing, and coming home well.
You do not have to face this alone, Pawrent. If you have spotted any of these signs, the next step is a clear diagnosis with your veterinarian and a treatment plan you can trust and afford. Learn more about the available options and reach out to our team through BasmiFIP Philippines, and take that first hopeful step forward today.
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