top of page
Search

FIP in Cats: The Complete Scientific Guide to Symptoms, Diagnosis, and Antiviral Treatment

  • Writer: CURE FIP™ USA
    CURE FIP™ USA
  • Jul 23, 2023
  • 6 min read

Updated: Jul 30

Summary

  • FIP (Feline Infectious Peritonitis) is a deadly disease in cats caused by a mutation of the feline coronavirus (FCoV).

  • While FCoV is usually harmless, it can mutate into FIPV, triggering severe inflammation in the cat's organs.

  • There are two main forms of FIP: the wet (effusive) form, which involves fluid buildup, and the dry (non-effusive) form, which affects internal organs, the brain, or the eyes.

  • Common symptoms include persistent fever, weight loss, neurological signs, and ocular issues such as cloudy eyes.

  • FIP was once considered incurable, but antiviral treatment with GS-441524 has proven highly effective and life-saving.

  • Accurate diagnosis requires clinical observation, bloodwork, fluid analysis, and markers such as the A/G ratio.

  • Early detection and proper treatment dramatically increase the chances of full recovery.

FIP in Cats
FIP in Cats

What Is FIP and Why Is It So Dangerous?


Feline Infectious Peritonitis (FIP) is a viral, immune-mediated disease that almost always leads to death if untreated. It is caused by a mutation of feline coronavirus (FCoV)—a virus that is extremely common in cats, particularly those in shelters, catteries, or multi-cat households.


While FCoV usually lives harmlessly in the gut and causes only mild or no symptoms, a mutation within an individual cat can transform this benign virus into a deadly one—FIP virus (FIPV).


🔬 Scientific Basis: FIP results from internal mutation of the virus, not from exposure to another cat with FIP. Source: Pedersen NC (2014), The Veterinary Journal. (https://doi.org/10.1016/j.tvjl.2014.04.017)

The immune system's hyperinflammatory response to FIPV is what causes tissue damage and leads to clinical symptoms. This immune dysregulation is central to FIP pathology—more than the virus itself.


Which Cats Are Most at Risk?


FIP can affect any cat, but certain factors increase the risk:


Risk Factor

Explanation

Age

70% of FIP cases occur in cats under 2 years old

Stress

Recent adoption, transport, surgery, or overcrowding can trigger a viral mutation

Breed

Purebred cats like Bengals, Abyssinians, and Ragdolls are at higher risk

Weak Immunity

FIV-positive, FeLV-positive, or malnourished cats are more vulnerable

🧪 Study: Addie et al. (2021) observed that FCoV shedding rates can reach 90–100% in shelters and that mutation into FIPV happens more often under stress and immunosuppression (https://doi.org/10.3390/v13030517).

Forms of FIP: How the Disease Manifests


There are three major forms of FIP, based on how the immune system reacts:


1. Effusive (Wet) FIP


  • Most common form (~60–70%)

  • Fluid accumulates in the abdominal cavity (ascites) or pleural space (around the lungs)

  • Cats often present with a swollen belly, difficulty breathing, or sudden lethargy


2. Non-effusive (Dry) FIP


  • Occurs in ~30–40% of cases

  • Granulomatous lesions form in organs like the kidney, liver, lymph nodes, or eyes

  • Symptoms are vague: persistent fever, jaundice, neurological signs


3. Ocular and Neurological FIP


  • These may be standalone forms or occur alongside dry FIP

  • Ocular signs: anterior uveitis, hyphema, chorioretinitis, vision loss

  • Neurological signs: ataxia, tremors, head tilt, nystagmus, seizures


🔬 Scientific Confirmation:Tasker S (2018) emphasized that CNS and ocular involvement are hallmarks of dry FIP and require higher antiviral doses (https://doi.org/10.1177/1098612X18758592).

Early and Late Clinical Symptoms


FIP symptoms are non-specific early on, making it easy to misdiagnose. The disease often mimics lymphoma, toxoplasmosis, pancreatitis, or other infections.


Symptom Category

Early Symptoms

Advanced Symptoms

Systemic

Mild fever, poor appetite, low energy

Persistent fever, severe weight loss

Wet FIP

No visible signs initially

Swollen abdomen, fluid in lungs

Dry FIP

Intermittent fever

Organ failure, jaundice

Ocular FIP

None

Iris color change, blindness

Neuro FIP

Slight uncoordination

Paralysis, seizures, altered consciousness


Laboratory Indicators of FIP


FIP is suspected based on a combination of clinical signs, lab abnormalities, and response to GS-441524.


Key lab markers:


  1. Elevated Total Protein (>7.8 g/dL)

  2. Hyperglobulinemia and hypoalbuminemia (A:G ratio <0.5)

  3. Non-regenerative anemia

  4. Lymphopenia, neutrophilia, and mild leukocytosis


📊 A:G ratio is considered one of the most helpful screening tools.Source: Hartmann K. (2005). Veterinary Clinics of North America: Small Animal Practice (https://doi.org/10.1016/j.cvsm.2004.10.003).

Imaging and Cytology


  • Ultrasound: Detects abdominal effusion and organ enlargement

  • Thoracic radiographs: Show pleural fluid or masses

  • Cytology of effusion: High-protein yellow fluid, low cellularity

  • Rivalta test: Simple and sensitive for wet FIP (Positive = likely FIP)


🧪 Rivalta Test Accuracy: Sensitivity ~91%, specificity ~66% (Fischer et al., 2012)

Virology and Molecular Diagnostics


  • RT-PCR (Real-Time PCR):

    • Detects viral RNA in blood, tissues, or effusion

    • Positive result supports diagnosis, but a negative result does not rule it out


  • S gene mutation analysis:

    • Some labs offer this to detect mutations associated with FIP

    • Still limited in sensitivity


🔬 Review: Felten & Hartmann (2019) concluded that no current test alone confirms FIP, but combination testing increases diagnostic confidence (https://doi.org/10.3390/vetsci6040113).

GS-441524: The Antiviral That Revolutionized FIP Treatment


Before 2018, Feline Infectious Peritonitis (FIP) was considered a uniformly fatal disease. However, a groundbreaking study by Dr. Niels Pedersen (UC Davis) changed everything. He demonstrated that GS-441524, a nucleoside analog compound, could halt FIP virus replication and successfully treat the majority of affected cats.


CURE FIP™ USA GS-441524【20mg/ml, 8ml】
CURE FIP™ USA GS-441524【20mg/ml, 8ml】

🔬 Landmark Study (Pedersen et al., 2019):


  • 31 cats with both wet and dry forms of FIP

  • Treated with GS-441524 daily for 84 days

  • 81% (25/31) achieved full recovery and remained healthy for at least 8 months


📖 Journal of Feline Medicine and Surgery: https://doi.org/10.1177/1098612X19825701


How GS-441524 Works


GS-441524 is an adenosine analog that inhibits RNA-dependent RNA polymerase (RdRp)—a critical enzyme required for coronavirus replication.


Effects:


  • Stops replication of FIPV inside cells

  • Reduces inflammation caused by the abnormal immune response

  • Allows the body to repair tissue damage


🧬 Relation to Remdesivir: GS-441524 is the precursor to Remdesivir (used for COVID-19), but it offers better bioavailability and safety in cats for long-term use.


GS-441524 Dosing by FIP Type


Treatment generally lasts 84 consecutive days, with possible extensions in cases involving neurological symptoms or relapse. Dosage is calculated based on the cat’s actual body weight and FIP type.


FIP Type

Dose

Route

Wet FIP

5–6 mg/kg/day

Oral or subcutaneous

Dry FIP

6–8 mg/kg/day

Oral or subcutaneous

Neurological/Ocular FIP

8–10 mg/kg/day

Oral or subcutaneous

Relapse Cases

+1–2 mg/kg from prior dose

Oral preferred


📌 Notes:


  • Oral GS is preferred for long-term or neurological FIP patients

  • Subcutaneous injection is commonly used during the first 30 days, especially in acute cases


📖 Source: CureFIP™ Treatment Guidelines (based on Pedersen, 2019 + real-world data 2020–2024)


Clinical Improvement Timeline


Most cats show rapid clinical response to GS-441524—often within the first 3–7 days:


Day

Common Observations

3–5

Fever drops, appetite returns

7–14

Energy improves, weight stabilizes

30

Abdominal swelling reduces (wet FIP)

60–84

The cat returns to normal condition

90+

Bloodwork stabilizes, treatment ends


📈 Field data from CureFIP™ USA shows that over 85% of cats show significant symptom improvement within 14 days.


Safety and Side Effects


GS-441524 has an excellent safety profile. Side effects are rare and usually mild:


Side Effect

Frequency

Management

Injection site irritation

Common (injections)

Warm compress, switch to oral

Mild vomiting (oral use)

Rare

Administer post-meal

Mild WBC decrease

Very rare

Monitor with regular bloodwork


🔬 2023 Study (Dickinson et al.) confirmed GS-441524 is safe for up to 120 days of use in most cats.Feline Med Rev (https://doi:10.1016/j.jfms.2023.01.015).

CURE FIP™ USA Oral Treatment
CURE FIP™ USA Oral Treatment

Success Rates and Real-World Outcomes


Data from international FIP support communities indicate:


  • 80–90% of cats can achieve complete recovery

  • 5–10% may experience mild relapse, usually treatable with adjusted protocols

  • <5% do not respond, often due to delayed treatment or severe complications


Key success factors:


  • Early diagnosis and treatment

  • Strict adherence to the dosing schedule

  • Nutritional and immune system support during therapy


Aftercare: What Happens After 84 Days?


Once the 84-day treatment is completed:


  • Cats enter a 30-day observation phase

  • No medications are given, but appetite, weight, and energy should be monitored

  • A final blood test is done on day 30 to confirm stability


If all values are normal, → cat is declared clinically cured


📌 Relapse may occur within 1–2 weeks after ending treatment. Early signs include reduced appetite, fever recurrence, or neurological symptoms.

Frequently Asked Questions


Q: Is GS-441524 legal in the U.S.?

A: It is not yet FDA-approved, but is available through trusted suppliers like CureFIP™ under compassionate use.


Q: Can FIP spread to other cats?

A: No. Only FCoV is contagious. FIP occurs due to a mutation inside an individual cat’s body.


Q: Can a cat with FIP make a full recovery?

A: Yes. With GS-441524, thousands of cats have fully recovered and lived long, healthy lives.


Q: Is PCR testing required before treatment?

A: Not always. Clinical diagnosis and response to GS-441524 are often more practical in real-world cases.


Final Thoughts: A New Era for FIP Cats


FIP was once a death sentence. Today, thanks to breakthroughs in antiviral therapy such as GS-441524, the outlook for cats with FIP has drastically improved. With community support, medical guidance, and proper treatment, thousands of feline lives have been saved.


If you need help starting treatment or want to speak with a FIP treatment advisor, chat with us on WhatsApp — we're here to support you and your cat every step of the way.


CureFIP™ USA is committed to helping cat owners:


  • Provide high-quality GS-441524 (oral & injectable)

  • Offer dosing guides, monitoring support, and daily assistance

  • Ship rapidly across the country



Scientific References


 
 
 

תגובות

bottom of page