Is It Really FIP? Common Misdiagnoses Every Cat Owner Should Know

Feline Infectious Peritonitis (FIP) is a disease caused by a mutation of the Feline Coronavirus (FCoV). Usually, when pawrents hear that their cat has been diagnosed with FIP, feelings of sadness, fear, and worry immediately set in.

And who could blame them? FIP spreads fast and aggressively. Without an accurate diagnosis and prompt treatment, your beloved feline’s life could be at serious risk.

The problem is, diagnosing FIP in cats is no easy task. That’s because several other diseases present with similar symptoms to FIP. This makes the possibility of a misdiagnosis quite high.

So, what can you do to avoid misdiagnosis? Let’s find out together! The CureFIP Oceania team has put together everything you need to know in this article.

Why Is FIP Diagnosis Often Confusing?

Diagnosing FIP can be tricky and confusing because the early symptoms can resemble those of many other illnesses. Common signs include fever, vomiting, loss of appetite, and weight loss.

On top of that, as we all know, FIP comes in four types: wet FIP, dry FIP, ocular FIP, and neurological FIP. Each type has different symptoms, which complicates the diagnostic process.

Things get even more challenging if the cat already has comorbidities. These underlying conditions may confuse vets further when determining the root cause.

That’s because vets have to distinguish whether the symptoms are due to the FCoV mutation or are the result of an existing illness.

The Importance of Accurate Diagnosis for Proper Treatment

Just like humans, cats need a correct diagnosis to stand a chance of making a full recovery. If a misdiagnosis happens, the disease may linger longer—or even cost a life.

For cats with FIP, an accurate diagnosis and swift treatment are key to recovery. The sooner and more accurately FIP is diagnosed, the better the cat’s chances of survival.

Currently, the most effective treatment for FIP is GS-441524. At CureFIP Oceania, this antiviral must be dosed based on the diagnosed FIP type, the cat’s weight, and lab test results.

That’s why it's essential to get the diagnosis right—so GS-441524 can work effectively inside the cat’s body.

Symptoms That Often Lead to Misdiagnosis

Here are some of the general FIP symptoms that also appear in other illnesses, leading to common misdiagnoses.

• High fever

• Persistent vomiting

• Digestive issues, from diarrhoea to constipation

• Loss of appetite

• Significant weight loss

• Fatigue and lethargy

• Swollen lymph nodes

Diseases Often Mistaken for FIP

Here’s a list of conditions that are frequently confused with FIP.

1. Toxoplasmosis

Toxoplasmosis is caused by a parasite called Toxoplasma gondii. Infected cats show symptoms such as fever, loss of appetite, lethargy, and seizures.

Now, lethargy and seizures are also common in cats with neurological FIP. This overlap makes things confusing and highlights the need for further testing to confirm the diagnosis.

2. FeLV (Feline Leukaemia Virus)

Much like FIP, this virus is spread through saliva, urine, and faeces. FeLV can even trigger the onset of FIP, and infected cats might seem healthy for a long time before severe symptoms show up.

3. FIV (Feline Immunodeficiency Virus)

This disease weakens a cat’s immune system, making them more vulnerable to other infections. Since it also affects multiple organs, FIV is often mistaken for FIP—even though the treatment approach is different. 

4. FPV (Feline Panleukopenia Virus)

Cats with FPV often show signs like fever, vomiting, diarrhoea, and appetite loss. These are very similar to FIP, which is why additional testing is crucial.

5. Inflammatory Bowel Disease (IBD)

IBD causes vomiting, diarrhoea, and weight loss due to inflammation in the gut. These signs are often mistaken for FIP—especially when the digestive tract is affected.

6. Lymphoma

As the name suggests, lymphoma affects a cat’s lymph nodes. Like FIP, it causes inflammation in internal organs, making it difficult for vets to reach a definitive diagnosis.

7. Cancer

Yes—cats can get cancer too. Like FIP, it’s dangerous and needs immediate attention.

The problem is, symptoms like fever, weight loss, fatigue, and lack of appetite are also seen in FIP cases. That’s why cancer and FIP are frequently confused.

Tests to Distinguish FIP from Other Illnesses

To confirm whether a cat truly has FIP, vets need to carry out several tests. So, what are they? Let’s take a quick look!

1. Blood Tests

A complete blood count (CBC) and blood chemistry panel are usually the first steps. These give vets a general overview of the cat’s health.

Typically, the vet will check levels of albumin, globulin, red and white blood cells, and the A/G ratio before recommending further testing.

2. Rivalta Test

This test is only used to confirm a diagnosis of wet FIP. That means it’s only applicable to cats with swollen bellies due to fluid build-up.

3. X-Ray and USG

X-rays and ultrasounds help vets assess internal organs. These tests are mainly used to spot fluid accumulation, organ enlargement, or signs of inflammation in the chest or abdomen.

4. MRI

MRI scans use magnets and radio waves to produce detailed images. This test shows the condition of soft tissues such as the brain, spinal cord, and blood vessels.

5. Biopsy

Biopsies involve taking a tissue sample from an organ or lymph node and sending it to a lab for examination.

However, due to high costs and slower results, vets tend to rely more on other types of tests.

When Should You Suspect It’s Not FIP?

If all tests are inconclusive and results remain unclear, you can try treatment with GS-441524 first.

To find the right dosage, have a quick chat with CureFIP Oceania via WhatsApp!

If your cat shows no improvement after two weeks or seems to reject the treatment, contact your vet immediately for further evaluation.

The Vet’s Role and the Importance of Ongoing Consultations

Seeing your usually playful cat suddenly quiet and weak is heartbreaking. That’s why you need the support and guidance of a skilled and experienced vet.

With the right diagnosis, you’ll be able to support your cat through their treatment journey. Recovery can be tough and draining.

But don’t worry—you’re not in it alone. CureFIP Oceania is here to help and answer any questions, even if you just need to vent about your concerns.

Once you've received the diagnosis and given the right medication as advised by CureFIP Oceania, don’t forget to carry out follow-up tests on days 30, 60, and 84.

This is important to check whether your cat is truly recovering—or if there might be signs pointing to another illness.

Case Study of Misdiagnose

A 16-week-old kitten was believed to have FIP due to symptoms like fever, weakness, and weight loss. 

But after she was humanely euthanized, testing revealed no signs of feline coronavirus. Instead, the true cause was a parasite called Toxoplasma gondii—which had infected her brain.

This kitten had a rough start: underweight, full of fleas, but seemed to recover after foster care. A month later, her health suddenly declined. 

Blood tests suggested dry FIP—common in young cats with fever and high globulin levels. But post-mortem exams told a different story.

Toxoplasma is a parasite cats can get from eating infected prey, like mice. It can even be passed from mother to kitten before birth. In this case, the brain inflammation caused by the parasite led to severe neurological symptoms.

This case is a powerful reminder: FIP isn’t the only disease with these signs. Proper testing is crucial—without it, cats may be misdiagnosed and lose their chance at the right treatment.

Conclusion

FIP is a disease that shares many symptoms with other conditions, making comprehensive testing essential before reaching a diagnosis. Trust your vet and the CureFIP Oceania Team to provide the best care for your cat.