Wet FIP vs Dry FIP: How to Spot Both Forms Early

Wet Feline Infectious Peritonitis (FIP) and dry FIP are two clinical presentations of the same virus, and the fastest way to tell them apart is fluid. Wet (effusive) FIP produces fluid build-up in the abdomen or chest, often causing a swollen belly or laboured breathing, while dry (non-effusive) FIP produces little or no fluid and instead causes weight loss, fever, and organ or nervous system signs. Recognising which form your cat has early matters because FIP progresses quickly, and the form guides the treatment plan.

FIP was once considered untreatable, but the antiviral GS-441524 has changed the outlook completely. Below, you will find a clear breakdown of wet FIP vs dry FIP, the four recognised forms of the disease, the early signs to watch for, and how treatment is structured under veterinary supervision.

A cat resting comfortably at home.

What is the difference between wet FIP and dry FIP?

The difference between wet FIP and dry FIP is the presence or absence of inflammatory fluid. Wet (effusive) FIP causes fluid to accumulate in body cavities, most often the abdomen or chest, producing visible swelling or breathing difficulty. Dry (non-effusive) FIP causes little to no fluid and instead damages internal organs, eyes, or the nervous system, which can make it harder to spot early.

Both forms come from the same feline coronavirus that has mutated inside the cat. A cat can also shift from one presentation to another, or show mixed features, which is one reason a prompt veterinary assessment matters so much.

Here is a side-by-side comparison of the two most common forms.

Feature	Wet (effusive) FIP	Dry (non-effusive) FIP
Fluid build-up	Yes, abdomen or chest	Minimal or none
Typical early sign	Swollen belly, laboured breathing	Gradual weight loss, persistent fever
Speed of onset	Often faster and more obvious	Often slower and subtler
Common overlap	Can progress from dry	Can develop ocular or neurological signs

Because dry FIP can be mistaken for other illnesses, it helps to understand common misdiagnoses every cat owner should know before assuming the cause.

What are the four forms of Feline Infectious Peritonitis (FIP)?

Feline Infectious Peritonitis (FIP) takes four forms: wet (effusive), dry (non-effusive), ocular, and neurological. Each form shapes the symptoms you will notice and the dosing your veterinarian will recommend. Presenting them as four distinct forms keeps the picture clear, because ocular and neurological FIP each carry their own signs and dosing needs.

Wet / Effusive Feline Infectious Peritonitis (FIP)

Wet FIP is the effusive form, defined by fluid that collects in the abdomen or chest. The most recognisable early sign is a rounded, fluid-filled belly, sometimes described as a pot-bellied appearance, even as the cat loses condition elsewhere.

When fluid gathers in the chest, cats may breathe rapidly or with visible effort, and may sit with their elbows out. Wet FIP often moves quickly, so laboured breathing or a fast-growing belly is a reason to see your veterinarian without delay.

Other wet FIP signs include a fever that does not respond to standard antibiotics, lethargy, and reduced appetite.

Dry / Non-effusive Feline Infectious Peritonitis (FIP)

Dry FIP is the non-effusive form, producing little or no fluid and instead causing inflammatory lesions in organs such as the liver, kidneys, or lymph nodes. Because there is no obvious swelling, dry FIP is often subtler and slower to reveal itself.

Common dry FIP signs include steady weight loss, a persistent fluctuating fever, poor appetite, and a dull coat. Jaundice, a yellow tinge to the gums, eyes, or skin, can also appear as the liver is affected.

Dry FIP can quietly develop ocular or neurological involvement over time, which is why close monitoring matters. For a broader picture of how signs emerge, our guide to cat FIP symptoms walks through the full range.

Ocular Feline Infectious Peritonitis (FIP)

Ocular FIP affects the eyes and is often linked to the dry form. The signs are visible in the eye itself: colour changes to the iris, cloudiness, an uneven or irregular pupil, or inflammation inside the eye.

You may notice one or both eyes looking different, or your cat becoming sensitive to light. Because ocular FIP reflects viral activity that can reach the eye and beyond, it is treated as its own form with its own dosing.

Any sudden change in a cat's eye colour or clarity warrants a prompt veterinary examination.

Neurological Feline Infectious Peritonitis (FIP)

Neurological FIP affects the brain and spinal cord and is considered the most challenging form to treat. Signs can include wobbliness or loss of balance, tremors, unusual behaviour, seizures, or partial paralysis.

Neurological FIP requires higher antiviral dosing because the medicine must cross into the central nervous system. If you see stumbling, head tilting, or seizures in a cat suspected of FIP, treat it as urgent and contact your veterinarian immediately.

Understanding how FIP progresses from infection to symptoms can help you catch these shifts between forms earlier.

How can you recognise Feline Infectious Peritonitis (FIP) early?

You can recognise FIP early by watching for a cluster of signs rather than a single symptom, especially a persistent fever that does not respond to antibiotics combined with weight loss or a swollen belly. Early recognition gives treatment the best possible starting point, because FIP tends to advance quickly once symptoms appear.

Watch for these early warning signs:

• A fluctuating fever that antibiotics do not resolve

• Gradual or sudden weight loss and muscle wasting

• A swollen, fluid-filled abdomen (wet FIP)

• Laboured or rapid breathing (wet FIP in the chest)

• Loss of appetite and lethargy that does not improve

• Yellowing of the gums or eyes (jaundice)

• Changes in eye colour or clarity (ocular FIP)

• Wobbliness, tremors, or seizures (neurological FIP)

If you notice several of these together, take these steps:

1. Book a veterinary appointment as soon as possible and describe every sign you have observed.

2. Ask your veterinarian about diagnostic testing, which may include bloodwork, fluid analysis, and imaging.

3. Note when symptoms started and how they have changed, since the timeline helps identify the form.

4. Discuss treatment options and next steps promptly, because time matters with FIP.

Young cats and kittens are at higher risk, though FIP can affect cats of any age. Our practical FIP survival strategies for Australian and New Zealand cat owners offer more guidance for those first anxious days.

How is Feline Infectious Peritonitis (FIP) treated once you know the form?

FIP is treated with GS-441524, the antiviral at the core of modern FIP treatment, delivered over a standard 84-day protocol under veterinary supervision. The form of FIP determines the dose, which is why identifying wet, dry, ocular, or neurological FIP is a practical first step, not just a label.

GS-441524 monotherapy delivered by injection has a 92% success rate reported by UC Davis (Pedersen, 2019). Across the CureFIP network, 100,000+ cats have been treated since 2019.

The injectable dosing is matched to the form of FIP. The figures below are taken directly from the CureFIP catalog for the GS-441524 Antiviral Injectable products.

Form of FIP	GS-441524 injectable dose	Schedule	Duration
Wet / Effusive	6 mg/kg	1 subcutaneous injection per day	84 days (12 weeks)
Dry / Non-effusive	8 mg/kg	1 subcutaneous injection per day	84 days (12 weeks)
Ocular	10 mg/kg	1 subcutaneous injection per day	84 days (12 weeks)
Neurological	10 mg/kg	1 subcutaneous injection per day	84 days (12 weeks)

The GS-441524 Antiviral Injectable is available as 20mg/ml, 8ml at AU$79.00 and as GS-441524 Antiviral Injectables, 30mg/ml, 8ml at AU$99.00, both with a With B12 or Without B12 option. Your veterinarian will confirm which strength and volume suit your cat's weight and form of FIP.

What about oral treatment options?

For caregivers who prefer an oral route, CureFIP Oral Capsules - Dual-Action Formula are available at AU$139.00, combining GS-441524 and EIDD-1931. This dual antiviral approach is associated with a 78.3% remission rate (Li and Cheah, 2025), and the oral route is positioned for wet and dry FIP.

The dual-action capsules are dosed by weight: under 2.5 kg uses GS-441524 25 mg + EIDD-1931 5 mg, 2.5 to 5 kg uses GS-441524 35 mg + EIDD-1931 8 mg, and over 5 kg uses GS-441524 50 mg + EIDD-1931 12 mg, taken as 1 capsule per day for a recommended 12 weeks. Some regions note the oral dual formula is not recommended once ocular or neurological signs are present, or if the cat cannot eat or defecate, so ocular and neurological cases are typically managed with injectable dosing under veterinary guidance.

Many caregivers in the region are learning why vets and cat owners are choosing dual antiviral therapy for FIP, and it is a conversation worth having with your own veterinarian.

What happens after treatment starts?

Most cats begin to show improvement within the first days to weeks, though the full 84-day protocol should always be completed. Knowing what to expect during your cat's first week on GS-441524 treatment can ease the early uncertainty, and steady appetite is a reassuring early sign.

We are clear about what the data shows and what it does not. Success rates are strong, but every cat is an individual, and outcomes depend on the form, the timing, and consistent veterinary care throughout.

Frequently Asked Questions About Feline Infectious Peritonitis (FIP)

Is wet FIP or dry FIP more serious?

Both forms of FIP are serious and were historically fatal without treatment, but they differ in how they present. Wet FIP often progresses faster and is easier to spot because of fluid build-up, while dry FIP can be subtler and may quietly develop ocular or neurological signs, so neither should be considered mild.

Can dry FIP turn into wet FIP?

Yes, FIP can shift between forms, and a cat may show features of more than one form at once. This is why ongoing veterinary monitoring throughout the 84-day protocol is important, so the treatment plan can be adjusted if the presentation changes.

How is the form of FIP diagnosed?

Your veterinarian diagnoses the form of FIP using a combination of clinical signs, bloodwork, fluid analysis where fluid is present, and imaging. Fluid in the abdomen or chest points toward wet FIP, while its absence alongside organ, eye, or nervous system signs points toward dry, ocular, or neurological FIP.

Does the form of FIP change the treatment dose?

Yes, the form directly determines the GS-441524 injectable dose. Wet FIP is dosed at 6 mg/kg, dry FIP at 8 mg/kg, and both ocular and neurological FIP at 10 mg/kg, each given once daily for 84 days under veterinary supervision.

What should I do if I think my cat has FIP?

Contact your veterinarian as soon as possible and describe every sign you have noticed, including when it started. Early recognition and prompt diagnosis give treatment the strongest starting point, and reading real-life cases of cats overcoming FIP can help you understand what recovery can look like.

If your cat is showing any of the signs described here, you do not have to face the next steps alone. Learn more about the FIP treatment options available across Australia and New Zealand and talk with our team or your own veterinarian about the plan that fits your cat. Every FIP journey is unique, and the right decisions are always made together with your veterinarian.