What Is Feline Infectious Peritonitis(FIP)?

Feline infectious peritonitis (FIP) is a serious and often fatal viral disease that affects cats. It is caused by a type of coronavirus known as a feline coronavirus (FCoV) and can affect cats of any age, breed, or gender. FIP is more common in young cats and in multi-cat households where cats are in close contact with each other.

Symptoms of Feline Infectious Peritonitis(FIP)

Symptoms of Feline Infectious Peritonitis (FIP) It may take several weeks to months for cats to show symptoms of FIP. The initial signs of FIP can range from depression to changes in appetite to fever. 

Wet Feline Infectious Peritonitis (FIP) Wet FIP is characterized by fluid accumulation in the chest and abdomen, giving cats a pot-bellied appearance. This form of FIP progresses more quickly than the dry form, making it easier for veterinarians to diagnose. Other symptoms of wet FIP may include:
  • Fever
  • Weight loss
  • Loss of appetite
  • Breathing difficulties
  • Lack of energy

Dry Feline Infectious Peritonitis (FIP) Dry FIP involves the growth of inflammatory tissue in organs such as the liver, kidneys, eyes, and brain, as the body tries to remove the infection. Unlike wet FIP, it does not cause much fluid buildup, making it harder to diagnose and slower to progress. Other symptoms of dry FIP may include:

  • Fever
  • Weight loss
  • Bleeding or discharge from the eyes
  • Blindness or vision loss
  • Seizures
  • Poor muscle coordination

Some cats may develop a combination of both wet and dry FIP, or they may switch between forms as the disease progresses. The type of FIP a cat develops may depend on their immune system and factors such as stress or living in crowded conditions.

Is my cat at risk for developing FIP?

Any cat that carries FeCV is potentially at risk for developing FIP, but younger cats are at greater risk of developing FIP, with approximately 70% of cases diagnosed in cats less than 1 1/2 years of age and 50% of cases occurring in cats less than 7 months of age. The most common mode of transmission of FeCV is believed to occur when infected queens pass along the virus to their kittens, usually when the kittens are between five and eight weeks of age. Cats that are housed in high-density facilities (i.e. shelters, catteries) appear to be more susceptible to the development of FIP, as are pure bred cats, male cats, and geriatric cats, for reasons that remain unclear.

How Is FIP Diagnosed?

There is no single test that can reliably diagnose Feline Infectious Peritonitis (FIP). Some refer to the Feline Coronavirus (FCoV) titer test as an "FIP test," but this is incorrect as it only indicates exposure to the virus and does not confirm FIP.

A proper diagnosis of FIP requires a combination of diagnostic tests, including a physical exam, a complete blood count, RT-PCR of effusion (for wet FIP), and PCR (RT-qPCR) on fine-needle aspirates (for dry FIP), among others. Only with these tests and careful evaluation can a veterinarian make an accurate diagnosis of FIP.  

The ALB/GLOB ratio is often used as a laboratory marker for FIP. In cats with FIP, the ratio is typically below 0.7, which indicates a decreased concentration of albumin (ALB) relative to globulins (GLOB). However, it is important to note that the ALB/GLOB ratio alone is not a definitive diagnostic test for FIP and must be evaluated alongside other diagnostic tests and clinical findings to confirm a diagnosis.

Is FIP Contagious? 

No. Feline Coronavirus (FCoV), the virus that can mutate into FIP, is highly contagious among cats. It is shed through feces, and cats who share litter boxes or groom each other are at risk of exposure. However, most cats who are exposed to FCoV will pass it without issue, experiencing only mild symptoms such as diarrhea or cold-like symptoms.

Once FCoV mutates into FIP, the mutated virus is no longer contagious. FIP is not directly contagious between cats. However, it is believed that FIP has a genetic component, meaning that littermates or cats with a genetic predisposition may be more likely to develop FIP. A family history of FIP increases the risk of FIP in siblings.

How Is FIP Treated?

According to Dr. Pedersen's case study, a successful course of treatment with GS441524 for Feline Infectious Peritonitis (FIP) is 84 days, administered daily. Some cat owners have discontinued treatment once their cat's blood work and diagnostics returned to normal. However, the few cats who relapsed were among those who did not complete the full 84-day protocol. Cats who undergo the full 84-day treatment and remain symptom-free during an 84-day observation period following the conclusion of treatment are considered cured of FIP.

GS441524 is available in both injectable and pill form, with the dosage based on the cat's weight and symptoms. You can check our dosage calculator

Dr. Pedersen's attribution:

Can I protect my cat from getting FIP?

As mentioned in the above FAQ "Is FIP contagious?", other cats in the household cannot catch Feline Infectious Peritonitis (FIP) from an infected cat. However, it is important to support the immune system of all cats in the household to prevent the virus from mutating into FIP. Healthy cats with a strong immune system can pass and clear the coronavirus without developing FIP.

What do I do during the 84 days treatment?

During the 84-day treatment period for Feline Infectious Peritonitis (FIP) with GS441524 (injection or pills), it is important to administer the medication daily and consistently. You should also monitor your cat's weight on a weekly basis to adjust the dosage accordingly.

Additionally, it is recommended to take your cat for Complete Blood Count (CBC) blood work with a chemistry panel on day 30, day 60, and day 83 of the treatment period. These tests can help identify any potential complications, such as anemia, liver or kidney problems. Based on the results, we can recommend supplements and adjust the treatment plan as needed to ensure the best possible outcome for your cat.

Are any drugs contra-indicated during antiviral treatment for FIP?

At present, there are no known drug interactions with GS-441524, Remdesivir, GC376 or Molnupiravir.  For Remdesivir, it has been noted in humans that concurrent treatment with chloroquine, hydroxychloroquine is not recommended.

If additional medications are required concurrent with antiviral administration, especially at the beginning of treatment, it may be wise to prefer drugs that do not have known neurological side effects so as to not cloud the diagnostic picture.

Immune-suppressive drugs, such as corticosteroids should be avoided when possible so as to prevent impairment of the immune response.  While such drugs may be temporarily helpful to stabilize a patient, they should be discontinued as early as is possible without compromising patient stability.

I've heard that flea treatment is not recommended during treatment.  Is that so?

There is no scientific evidence that usage of flea treatment compromises the effectiveness of treatment with GS-441524 or other antivirals used to treat FIP.  There is also no scientific evidence that usage of flea treatment during treatment causes greater risk.

Flea treatments do have the possibility of neurological or other side effects which could cloud the diagnostic picture, so it is preferable to use a product that the cat has successfully used in the past without issue.  However for a stable patient there is no contraindication to using flea control medication.  As with any medication the benefits and risks should be weighed.

Should cats diagnosed with FIP be quarantined?

It is not considered necessary to quarantine a cat who has been diagnosed with FIP  as horizontal transmission of the mutated FIP virus is considered extremely uncommon, if it happens at all.  Studies have confirmed that even in cases where cats in close contact with each other developed FIP, the virus mutated independently from FECV within each cat rather than horizontal transmission of the mutated FIP virus.

That said, research has shown that FIPV is present in the feces of some cats with FIP, which does make horizontal transmission theoretically possible.  Additionally, research has also shown that even when the mutated virus is shed, it does not seem very contagious.

Recent research has supported a "circulating virulent–avirulent FCoV" theory (as opposed to horizontal transmission) as an explanation for clusters of cases sometimes seen in multi-cat environments, particularly shelters, catteries and rescues.

Is it safe to vaccinate a cat during treatment?  What about during the 3 month observation period?

Typically, routine vaccinations for cats during antiviral treatment for FIP is discouraged unless the cat is unvaccinated (or of questionable vaccine status) and is at risk of exposure to disease.  For example, it may be wise to give FVRCP vaccines unvaccinated kittens in a rescue setting, even during treatment for FIP.

Once treatment has ended there is no reason that a cat cannot be vaccinated, including during the 3 month "observation period" following treatment.  As a practical matter however, since relapses are more likely to reveal themselves in the first few weeks following cessation of treatment, it may be wise to avoid vaccines immediately following treatment simply to prevent confusion of any vaccine reaction or stress reaction with an FIP relapse.