FIP Symptoms in Cats: Visual Guide to All 4 Forms

If you searched for FIP symptoms in cats, you are almost certainly scared, scrolling at 2 a.m., and trying to figure out whether the strange thing your cat is doing matches what you have been reading. You deserve honest, clear answers, not vague reassurances or worst-case spirals.

Here is everything you need to know about spotting Feline Infectious Peritonitis (FIP) early, what each of the four forms actually looks like, and what works once you have a diagnosis.

FIP Symptoms in Cats: Visual Guide to All 4 Forms

What FIP Actually Is

FIP stands for Feline Infectious Peritonitis. It is caused when a common, usually harmless feline coronavirus mutates inside a cat's body and triggers a severe inflammatory disease. It is not contagious in the way the original coronavirus is, and one cat in a household getting FIP does not automatically mean the others will.

FIP has four distinct forms, and each one looks different on the outside:

1. Wet FIP (effusive)

2. Dry FIP (non-effusive)

3. Ocular FIP

4. Neurological FIP

The form your cat develops dictates the symptoms you see, the speed of progression, and the treatment plan your veterinarian will build with you. Mixing these forms up is one of the most common reasons FIP gets missed for weeks. Let's walk through each one.

The Universal Early Warning Signs (Before the Form Declares Itself)

Before FIP shows its specific form, almost every case starts with the same vague, frustrating signs that look like a dozen other illnesses:

• A fever that comes and goes and does not respond to antibiotics

• Lethargy, sleeping in unusual spots, hiding

• Loss of appetite or picky eating that gets worse

• Slow weight loss despite seeming to eat

• A dull, unkempt coat

• Stunted growth in kittens

If your cat is under two years old, recently came from a shelter, cattery, or multi-cat home, and has had a stubborn fever plus weight loss for more than a week, FIP belongs on the differential list. Push for it.

Form 1: Wet (Effusive) FIP Symptoms

Wet FIP is the form most people picture when they hear the diagnosis. It is also the fastest moving, which is both terrible and useful, because the visual cues are unmistakable.

What you will see

• A swollen, pear-shaped, or pot-bellied abdomen that feels fluid-filled, not firm

• Labored or rapid breathing if fluid accumulates in the chest instead of the belly

• Reluctance to lie flat, sitting in a hunched, sphinx-like posture to breathe

• Pale or yellow-tinged gums (jaundice)

• Rapid weight loss masked by the swollen belly, so the spine and shoulder blades feel sharp while the abdomen looks full

The visual giveaway

A kitten or young cat who looks pregnant but is not, with prominent shoulder blades and a dull coat, is the classic wet FIP silhouette. If you press gently on the belly, it may feel like a water balloon rather than firm tissue.

Wet FIP can progress in days, not weeks. If you see these signs, do not wait for a second opinion to start moving on diagnostics.

Form 2: Dry (Non-Effusive) FIP Symptoms

Dry FIP is the slow burner. There is no obvious fluid, which is exactly why it gets missed for so long. Instead of fluid, inflammatory lesions called granulomas form on internal organs.

What you will see

• Persistent low-grade fever that bounces back every time antibiotics are stopped

• Gradual, steady weight loss over weeks or months

• Enlarged abdominal lymph nodes a veterinarian can feel on exam

• Yellow-tinged gums, ears, or eye whites (jaundice) if the liver is involved

• Vomiting, diarrhea, or constipation if the intestines are affected

• Increased thirst and urination if the kidneys are involved

The visual giveaway

Dry FIP cats often just look unwell in a way that is hard to put a finger on. The coat goes flat. The eyes look tired. They are present but not quite themselves. Owners typically say, "Something is off, I just cannot prove it yet." Trust that instinct.

Form 3: Ocular FIP Symptoms

Ocular FIP is a separate form, not a subset of neurological FIP. The disease targets the eyes directly, and the signs show up in and around the eye itself.

What you will see

• A change in iris color, often a healthy green or yellow eye turning muddy brown or developing brown patches

• Cloudiness inside the eye, not just on the surface

• A visible color difference between the two eyes (one looks normal, one looks off)

• Inflammation inside the eye (uveitis), which makes the eye look red, hazy, or sore

• Pupils that are different sizes or do not respond to light evenly

• Visible debris, spots, or a film inside the eye

• Vision loss, bumping into furniture, missing jumps, hesitating in dim light

The visual giveaway

If you have phone photos of your cat from six months ago and the eye color has visibly shifted, or if one eye now looks cloudy or differently colored from the other, that is an ocular FIP red flag. Eye color change is an ocular sign, full stop. It is not a neurological sign.

Important: MolnuFIP for FIP is not indicated for ocular FIP. If you suspect this form, work directly with a veterinarian on a treatment plan suited to ocular disease.

Form 4: Neurological FIP Symptoms

Neurological FIP targets the brain, spinal cord, and surrounding tissues. The signs are about how the cat moves, balances, and behaves, not about the eyes.

What you will see

• Seizures, ranging from full convulsions to brief staring episodes with twitching

• Head tilt, holding the head consistently to one side

• Wobbly, drunken-looking walking (ataxia)

• Hind end weakness, dragging back legs, or partial paralysis

• Loss of balance, falling off familiar surfaces

• Disorientation, getting stuck in corners, forgetting the litter box location

• Behavioral changes: sudden aggression, withdrawal, excessive vocalization at night

• Hypersensitivity to touch, especially along the spine

The visual giveaway

A young cat who suddenly walks like a much older cat, with that side-to-side sway, or who has a new head tilt that was not there last week, needs neurological FIP ruled out fast. Seizures in a previously healthy cat under three years old are a major flag.

Important: MolnuFIP for FIP is not indicated for neurological FIP. The blood-brain barrier and the way neurological disease behaves require a different conversation with your veterinarian.

Mixed and Transitional FIP

Real cats do not always read the textbook. Many cases start dry and become wet, or present with both abdominal fluid and lymph node involvement at the same time. These mixed or transitional presentations are common and treatable when the dominant form is wet or dry. Your veterinarian will identify the dominant pattern and build the plan around it.

How FIP Gets Diagnosed

No single test confirms FIP on its own. Veterinarians combine:

• Bloodwork showing high globulin, low albumin, and a low A:G ratio

• Elevated bilirubin and liver enzymes

• Fluid analysis if there is effusion (the fluid is typically straw-yellow and sticky)

• PCR testing for feline coronavirus on fluid or tissue

• Imaging (ultrasound, X-ray) to find lesions or fluid pockets

• Clinical signs that match a recognized form

If your local veterinarian tells you FIP cannot be diagnosed and there is nothing to do, that information is out of date. Push for the workup or seek a second opinion from a clinic familiar with current FIP medicine.

What Actually Works for Wet and Dry FIP

The old story that FIP is untreatable is over. For wet (effusive), dry (non-effusive), and mixed presentations, antiviral therapy is now the standard of what actually works.

MolnuFIP capsules contain EIDD-1931, the active antiviral metabolite of molnupiravir, at 15 mg per capsule. EIDD-1931 is roughly 7.3 times more potent than GS-441524 in laboratory comparisons. It is an oral treatment, no injections, with veterinary guidance included.

Typical dosing reference, always confirmed by your veterinarian:

• 1 capsule every 12 hours per 2.5 kg of body weight

• Treatment course up to 60 days

• Adjustments based on response, bloodwork, and the form being treated

MolnuFIP ships directly to the United States with veterinary guidance included. Evidence and caregiver reports show many cats moving from severely ill to eating, gaining weight, and returning to normal behavior within the first one to two weeks of antiviral treatment, with full remission as the goal of the 60-day course.

MolnuFIP is indicated for wet FIP, dry FIP, and mixed or transitional presentations. It is not indicated for ocular FIP or neurological FIP, and it must not be used in pregnant, nursing, or breeding cats.

The Symptom Checklist to Take to Your Veterinarian

Print this, screenshot it, bring it in. The more specific you are, the faster the diagnosis.

1. Age, source (breeder, shelter, street), and household size

2. Date the first symptom appeared

3. Fever history (temperatures if you have them)

4. Weight changes over the last 4 to 8 weeks

5. Belly size changes, with phone photos if possible

6. Breathing rate at rest

7. Eye photos from before symptoms and now

8. Any walking, balance, or seizure events, with video

9. Appetite, water intake, litter box changes

10. Any antibiotic courses already tried and the response

FAQ

What are the symptoms of FIP in cats that show up first?

The earliest FIP symptoms are usually nonspecific: a fever that does not respond to antibiotics, lethargy, picky eating, slow weight loss, and a dull coat. These appear before any form-specific signs like a swollen belly, eye color change, or wobbly walking. A young cat with a stubborn fever and weight loss for more than a week deserves an FIP workup.

How fast do FIP symptoms progress?

Wet FIP can progress in days, with rapid belly swelling and breathing changes. Dry FIP often progresses over weeks to months, which is why it gets missed. Ocular and neurological FIP can appear suddenly even after weeks of vague illness. Speed of progression depends on the form and the cat's age and immune status.

Is eye color change a neurological FIP symptom?

No. A change in iris color, cloudiness inside the eye, or inflammation inside the eye are ocular FIP signs. Neurological FIP shows up as seizures, head tilt, wobbly walking, paralysis, and disorientation. They are two separate forms of FIP and need to be distinguished because treatment plans differ.

Can FIP be treated successfully?

Yes, for wet, dry, and mixed presentations. Modern antiviral therapy with EIDD-1931, the active ingredient in MolnuFIP, has changed the outlook dramatically. Many caregivers report cats moving from critically ill to eating and playing within the first two weeks, with remission as the goal of a 60-day course under veterinary guidance. Ocular and neurological forms require a different conversation with your veterinarian.

Where can I get MolnuFIP in the United States?

MolnuFIP ships directly to the United States with veterinary guidance included. It is an oral treatment, no injections, with clear dosing instructions and ongoing support throughout the 60-day course. Order through the official MolnuFIP site and your veterinarian will be looped in for monitoring.