Complete FIP Symptoms Guide: 12 Signs Every Cat Owner Must Know

Feline Infectious Peritonitis is one of the most feared diagnoses in cat medicine and for good reason. FIP progresses rapidly, its symptoms are easy to confuse with other illnesses, and without the right treatment, it is almost always fatal.

However, the earlier you recognise FIP symptoms, the better your cat's chances of making a full recovery. With GS-441524 treatment now available, cats diagnosed early consistently show better outcomes than those who begin treatment in the advanced stages of the disease.

In this complete guide, you will learn the 12 key symptoms of FIP in cats, understand the difference between wet FIP and dry FIP symptoms, and know exactly what to do the moment you suspect your cat may have FIP.

 

 

What Is FIP and Why Do Symptoms Vary So Much?

Before looking at specific symptoms, it helps to understand why FIP can be so difficult to spot.

FIP is caused by a mutation of the feline coronavirus (FCoV). In most cats, feline coronavirus causes no symptoms or only mild digestive upset. However, in a small percentage of cats roughly 1 to 2 percent the virus mutates into a far more aggressive form known as FIPV. This mutated virus spreads through white blood cells and triggers severe inflammation throughout the body.

Because FIPV can affect multiple organ systems simultaneously, FIP does not present the same way in every cat. The symptoms your cat shows depend largely on which form of FIP has developed and which organs are affected.

There are two main forms of FIP:

Wet FIP (effusive FIP) causes fluid to accumulate in the abdomen or chest cavity. It progresses quickly — often within days to weeks — and tends to produce more visible, dramatic symptoms. For a full breakdown of this form, read our detailed guide on wet FIP in cats.

Dry FIP (non-effusive FIP) does not cause fluid buildup. Instead, it causes inflammatory lesions to form on internal organs, the brain, or the eyes. Dry FIP tends to progress more slowly but is significantly harder to diagnose. Read more in our guide on dry FIP in cats.

Some cats develop both forms simultaneously, which makes early recognition of the shared warning signs even more critical.

 

 

The 12 Key Symptoms of FIP in Cats

Symptom 1 — Persistent fever that does not respond to antibiotics

Fever is one of the earliest and most consistent symptoms of FIP across all forms of the disease. A cat with FIP will typically develop a persistent, fluctuating fever that keeps returning even after antibiotic treatment.

This is an important distinguishing feature. Because the fever in FIP is caused by a viral infection not a bacterial one antibiotics will have no lasting effect. If your cat has been on antibiotics for a fever that keeps coming back, FIP should be considered a possible cause.

A normal cat temperature ranges from 38.1°C to 39.2°C (100.5°F to 102.5°F). Cats with FIP often run temperatures of 39.5°C to 40.5°C (103°F to 105°F) or higher.

Symptom 2 — Significant and rapid weight loss

Weight loss is another early and consistent symptom of FIP. Because the FIP virus affects the body's ability to absorb nutrients and causes chronic inflammation, cats lose weight rapidly even when they appear to be eating.

In many cases, the weight loss in FIP is strikingly fast. Cat owners frequently report that their cat lost a noticeable amount of weight within one to two weeks. Additionally, muscle wasting is common the cat's spine and hip bones may become visibly prominent even under a thick coat.

If your cat is losing weight rapidly without an obvious dietary change, this warrants immediate veterinary attention.

Symptom 3 — Loss of appetite and refusal to eat

Closely related to weight loss is a marked decrease in appetite. Most cats with FIP gradually lose interest in food, and in advanced cases may refuse to eat entirely.

This symptom is particularly concerning in cats that were previously enthusiastic eaters. A sudden and sustained change in eating behaviour, combined with weight loss and lethargy, is one of the classic early FIP warning clusters that should prompt a vet visit without delay.

Symptom 4 — Extreme lethargy and weakness

Cats with FIP typically become progressively less active. In the early stages, you may notice your cat sleeping more than usual or being less interested in play. As the disease progresses, however, the lethargy becomes severe, the cat may spend most of the day lying in one spot, struggling to find the energy to move.

This is not normal tiredness. The lethargy in FIP is a direct result of the body's immune system fighting a losing battle against the virus, along with the metabolic impact of chronic inflammation and, in wet FIP, the physical discomfort of fluid accumulation.

Symptom 5 — Swollen or distended abdomen

A visibly distended, fluid-filled abdomen is the hallmark symptom of wet FIP. When fluid accumulates in the peritoneal cavity a condition known as ascites the belly becomes noticeably swollen and feels like a water balloon when gently pressed.

This symptom can develop surprisingly quickly. Some cat owners report noticing their cat's belly swell within days. Furthermore, the fluid in wet FIP is not just water it is a high-protein, inflammatory exudate that is very characteristic of the disease. A vet can draw a small sample of this fluid for analysis, which is one of the most useful diagnostic steps for wet FIP.

It is important to note, however, that not all swollen bellies indicate FIP. Other conditions including heart disease, liver disease, and cancer can also cause ascites. Proper veterinary diagnosis is always essential.

Symptom 6 — Difficulty breathing or laboured breathing

In some cats, wet FIP causes fluid to accumulate in the chest cavity (pleural effusion) rather than or in addition to the abdomen. When fluid compresses the lungs, the cat struggles to breathe normally.

Signs of breathing difficulty in cats with chest FIP include:

  • Open-mouth breathing or panting at rest

  • Rapid, shallow breathing

  • Sitting in an unusual position with elbows pushed outward, cats do this to maximise lung space

  • Visible effort in the chest when breathing

  • Reluctance to lie flat

If your cat is showing any signs of breathing difficulty, this is a medical emergency. Seek veterinary attention immediately, do not wait.

cats with jaundice

Symptom 7 — Jaundice — yellowing of eyes, gums, or skin

Jaundice, or icterus, occurs when the body accumulates too much bilirubin a yellow pigment produced when red blood cells are broken down. In cats with FIP, jaundice typically appears because the virus has affected the liver.

The most visible sign of jaundice is a yellow tint to the whites of the eyes (the sclera), the gums, or the skin inside the ears. In cats with white or light-coloured fur, the yellowing may also be visible on the skin itself.

Jaundice in a cat with other FIP symptoms particularly fever and weight loss is a serious warning sign that the disease has progressed. If you notice yellowing in your cat's eyes or gums, contact your vet the same day.

Symptom 8 — Rough, dull coat condition

A cat's coat condition is a reliable indicator of overall health. In healthy cats, the coat should be smooth, shiny, and well-groomed. In cats with FIP, the coat often becomes rough, dull, and unkempt as the disease progresses.

This happens for several reasons. First, the systemic inflammation and nutritional depletion caused by FIP directly affects the quality of new hair growth. Second, cats with FIP often feel too unwell to groom themselves properly, leading to a matted or dishevelled appearance.

While a dull coat alone is not diagnostic of FIP, when combined with other symptoms on this list, it is an important supporting indicator.

Symptom 9 — Neurological signs — seizures, wobbling, or behavioural changes

Neurological symptoms are characteristic of neurological FIP — a form of dry FIP where the virus infiltrates the central nervous system. These symptoms are among the most alarming and can include:

  • Seizures or convulsions

  • Loss of coordination — the cat staggers, wobbles, or falls over when walking

  • Hind limb weakness or paralysis

  • Head tilt or abnormal eye movements (nystagmus)

  • Sudden and unexplained behavioural changes — aggression, confusion, or disorientation

  • Difficulty swallowing or vocalising abnormally

Neurological FIP requires a higher dose of GS-441524 than standard wet or dry FIP because the medication needs to penetrate the blood-brain barrier. Therefore, early identification of neurological symptoms is critical for ensuring the correct treatment protocol is prescribed. Learn more in our guide on neurological FIP treatment.

cats with jaundice with real image

Symptom 10 — Eye changes — cloudiness, redness, or unequal pupils

Ocular FIP affects the eyes and can produce a range of visible changes including:

  • Cloudiness or haziness within the eye (uveitis)

  • Redness or visible inflammation in or around the eye

  • Unequal pupil sizes (anisocoria)

  • A colour change within the iris

  • Visible deposits or bleeding inside the eye

Eye changes in FIP are caused by inflammatory cells infiltrating the ocular tissues. While ocular symptoms alone may sometimes be the only early sign of FIP, they more commonly appear alongside other symptoms such as fever and weight loss.

If you notice any sudden changes in your cat's eyes, have them examined by a vet promptly. Eye symptoms in FIP can cause permanent damage if not addressed quickly.

Symptom 11 — Enlarged lymph nodes

In cats with dry FIP, enlarged lymph nodes also called lymphadenopathy are commonly found during veterinary examination. The lymph nodes most frequently affected include those in the abdomen, chest, and neck.

Your vet will check for enlarged lymph nodes during a physical examination. While this symptom is not always visible to the naked eye, an experienced vet will be able to feel significantly enlarged nodes during palpation.

Enlarged lymph nodes in the context of fever, weight loss, and other FIP symptoms are a strong indicator that further diagnostic tests are warranted.

Symptom 12 — Pale or anaemic appearance

Many cats with FIP develop anaemia a reduced red blood cell count as a result of the viral disease process. Anaemia in FIP can cause:

  • Pale or white-coloured gums (instead of the normal salmon-pink)

  • Weakness and reduced exercise tolerance

  • Rapid breathing even at rest

  • Cold extremities

You can check for anaemia at home by gently lifting your cat's upper lip and looking at the colour of the gums. Healthy gums should be a warm salmon-pink colour. Gums that are white, pale pink, or grey are a sign that your cat is not getting enough oxygen to the tissues — and this requires urgent veterinary attention.

 

 

How Symptoms Differ Between Wet and Dry FIP

Understanding the difference between wet and dry FIP symptoms helps you communicate clearly with your vet and ensures the right diagnostic pathway is followed from the start.

Symptom

Wet FIP

Dry FIP

Persistent fever

✅ Common

✅ Common

Rapid weight loss

✅ Common

✅ Common

Loss of appetite

✅ Common

✅ Common

Lethargy

✅ Common

✅ Common

Swollen abdomen

✅ Hallmark sign

❌ Not present

Breathing difficulty

✅ If chest fluid

❌ Rare

Jaundice

✅ Sometimes

✅ Sometimes

Neurological signs

❌ Rare

✅ Common in neuro FIP

Eye changes

❌ Rare

✅ Common in ocular FIP

Enlarged lymph nodes

❌ Less common

✅ Common

Rough coat

✅ Common

✅ Common

Pale gums / anaemia

✅ Common

✅ Common

 

 

When Do FIP Symptoms Appear?

Many cat owners wonder how long after coronavirus exposure FIP symptoms begin to show. The answer is not straightforward the incubation period varies considerably between individual cats.

In general, after a cat is exposed to feline coronavirus, the mutation to FIPV can occur weeks, months, or even years later. Furthermore, because the early symptoms of FIP — fever, lethargy, and weight loss — are non-specific and resemble many other conditions, many cats are not diagnosed until the disease has progressed significantly.

This is precisely why recognising the full picture of symptoms matters. A single symptom in isolation may not raise alarm. However, a combination of persistent fever, unexplained weight loss, and lethargy that does not improve with antibiotics should always prompt investigation for FIP.

cat with medication

 

 

What to Do If Your Cat Shows These Symptoms

If your cat is showing three or more of the symptoms on this list particularly fever, weight loss, lethargy, and either a swollen abdomen or neurological signs do not wait to see if things improve on their own.

Here is what to do immediately:

Step 1 — Contact your vet the same day. Describe all the symptoms you have observed, when they started, and whether any previous treatment has been tried. Ask specifically about the possibility of FIP.

Step 2 — Ask for blood work. Key diagnostic markers include the albumin-to-globulin (A:G) ratio, total protein levels, and a complete blood count. According to research from the University of California, Davis, an A:G ratio below 0.4 is strongly associated with FIP and should prompt further investigation.

Step 3 — If wet FIP is suspected, ask about fluid analysis. The Rivalta test and fluid protein analysis are simple, low-cost tests that can be performed on abdominal or chest fluid and provide strong diagnostic support.

Step 4 — Do not delay treatment if FIP is suspected. Wet FIP in particular can progress from manageable to critical within days. Many experienced FIP specialists recommend beginning GS-441524 treatment based on strong clinical suspicion rather than waiting for complete laboratory confirmation.

Step 5 — Calculate the correct dosage immediately. Use the FIP Cure Plus dosage calculator to calculate the right dose for your cat based on their weight and FIP type as soon as treatment is decided upon.

 

 

FIP Symptoms in Kittens vs Adult Cats

FIP is most commonly diagnosed in young cats between three months and three years of age, though it can affect cats of any age. In kittens, the disease often progresses even faster than in adult cats, making early recognition especially critical.

In kittens, the most commonly reported early symptoms are stunted growth, persistent fever, poor coat condition, and failure to thrive despite adequate nutrition. Wet FIP with abdominal swelling is particularly common in young kittens.

In older cats, dry FIP with neurological or ocular involvement is somewhat more common, though wet FIP can also occur at any age. Older cats may show symptoms more gradually, which can make the diagnosis easier to miss in the early stages.

For a detailed breakdown of FIP in young cats specifically, read our guide on FIP in kittens.

 

 

Is There Treatment for FIP?

Yes and this is the most important message in this entire guide.

FIP is no longer the death sentence it once was. GS-441524 antiviral treatment, pioneered by Dr. Niels Pedersen at UC Davis and supported by a growing body of peer-reviewed research including a landmark study published on PubMed Central, has transformed outcomes for cats with FIP across all forms — wet, dry, neurological, and ocular.

With correct dosing over the full 84-day treatment protocol, approximately 84 to 92 percent of cats treated with GS-441524 achieve sustained remission.

In other words, if you recognise these symptoms early and act quickly, there is a very strong chance your cat can make a full recovery.

FIP Cure Plus provides high-purity GS-441524 in both injectable and oral tablet form, shipping to 19 countries with 95% of orders dispatched within 24 hours.

 

 

Frequently Asked Questions About FIP Symptoms

What are the first signs of FIP in cats?

The earliest signs of FIP are often non-specific — persistent fever, lethargy, and gradual weight loss. In wet FIP, a swollen abdomen may develop within days. In dry FIP, the earliest signs may be subtle changes in energy, appetite, and behaviour that gradually worsen over weeks.

Can a cat have FIP without a swollen belly?

Yes. A swollen abdomen is the hallmark of wet FIP but is not present in dry FIP. Many cats with dry FIP show only fever, weight loss, and lethargy in the early stages. Neurological signs and eye changes may appear later as the disease progresses.

How quickly do FIP symptoms progress?

Wet FIP typically progresses very rapidly — from early symptoms to a critical condition within days to weeks. Dry FIP progresses more slowly, sometimes over several months. Both forms are ultimately fatal without treatment.

Can FIP symptoms look like other diseases?

Yes, FIP symptoms overlap significantly with other conditions including lymphoma, toxoplasmosis, and pancreatitis. This is why a combination of blood tests, fluid analysis, and clinical presentation is needed to reach a diagnosis rather than any single test alone.

My cat has a fever and is losing weight so does that mean they have FIP?

Not necessarily. Fever and weight loss can have many causes. However, if these symptoms are persistent, not responding to antibiotics, and are accompanied by other signs on this list especially a swollen abdomen or neurological changes — FIP should be investigated as a priority.

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

Contact your vet the same day. Ask for blood work including the A:G ratio. If wet FIP is suspected, ask about fluid analysis. If your vet suspects FIP, contact FIP Cure Plus immediately for guidance on starting GS-441524 treatment — time matters enormously with this disease.

How is FIP treated once symptoms are identified?

FIP is treated with GS-441524 antiviral medication over a standard 84-day protocol. The dose depends on your cat's weight and FIP type. Use the FIP Cure Plus dosage calculator for a personalised calculation, and read our complete FIP cure guide for the full treatment overview.

 

 

Published by FIP Cure Plus providing high-quality GS-441524 treatment and expert support to cat owners across 19 countries. If your cat is showing any symptoms of FIP, contact our team today. Every day counts.

 

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