Clinical Symptoms of Feline Infectious Peritonitis (FIP)

Feline Infectious Peritonitis (FIP) is a systemic inflammatory disease caused by a mutated strain of feline coronavirus (FIPV). The clinical presentation of FIP is highly variable, depending on the system affected and the individual immune response. As reviewed by Pedersen et al. (2009) in the Journal of Feline Medicine and Surgery, the symptoms are often nonspecific and must be interpreted in combination with other diagnostic indicators【Pedersen NC, 2009】.

I. Common Systemic Symptoms (Non-Specific)

FIP often begins with vague and non-specific signs:

• Persistent Fever: Body temperature can exceed 40°C and typically does not respond to antibiotics.

• Lethargy and Anorexia: The cat may become sleepy, less interactive, and eat significantly less.

• Weight Loss: Despite a temporary appetite, weight continues to drop.

• Rough, Dull Coat: Often the earliest visual clue noticed by owners.

These signs are common across all FIP types and are usually the first symptoms observed.

II. Typical Clinical Syndromes

1. Effusive FIP (Wet Type)

• Abdominal Effusion: Causes bloated abdomen; fluid wave detectable on palpation.

• Pleural Effusion: Leads to labored breathing, shortness of breath, coughing, and exercise intolerance.

• Fluid Characteristics: Typically yellow, viscous, and protein-rich, with fibrin strands.

Studies report that 60–70% of FIP cases are of the wet form, which is easier to recognize due to visible effusion【Pedersen NC, 2009】.

2. Non-effusive FIP (Dry Type)

• Granulomas in Organs: Enlarged or nodular liver, kidney, spleen, lymph nodes.

• Chronic Low-Grade Fever and Progressive Weight Loss

• Absence of Effusion: Often misdiagnosed as neoplasia or chronic illness.

• Blood Test Abnormalities: Low A:G ratio (<0.4), high total protein, elevated α1-acid glycoprotein.

Diagnosis of dry FIP is more challenging and requires a combination of imaging, blood work, and immunologic markers【Addie et al., 2015】.

III. Organ-Specific Symptoms

1. Neurological FIP

• Behavioral Changes: Sudden aggression, confusion, or loss of direction.

• Ataxia: Uncoordinated gait, rolling, hind limb paralysis.

• Seizures, Nystagmus, Head Tilt

• Coma and Altered Consciousness in advanced stages.

Neurological involvement is among the most difficult clinical presentations, occurring in approximately 5–10% of FIP cases.

2. Ocular FIP

• Uveitis: Iris hyperemia and color changes.

• Aqueous Flare and Vitreous Opacity

• Retinal Hemorrhage or Vision Loss

• Abnormal or Asynchronous Pupillary Light Reflexes

Ocular FIP is often a localized manifestation of dry FIP and may require slit-lamp and fundoscopic exams for diagnosis.

IV. Laboratory Supportive Indicators

Lab parameters can aid clinical suspicion:

• A:G Ratio Decrease: < 0.4 (highly suggestive of FIP)

• Elevated Total Protein: > 80 g/L, especially increased globulins

• α1-Acid Glycoprotein (AGP): > 1.5 mg/mL

• Elevated FSAA (feline serum amyloid A)

• Positive Rivalta Test: For analyzing abdominal fluid

Definitive diagnosis requires integrating clinical signs, lab data, and imaging (ultrasound).

V. Conclusion

FIP symptoms can progress from mild GI discomfort to severe systemic inflammation. Early signs are often mistaken for common infections. Overlap exists between effusive and non-effusive types, and between organ-specific presentations. Therefore:

Multifactorial recognition + scientific evaluation + experienced veterinary judgment are key to identifying FIP.

Key References

• Pedersen NC. A review of feline infectious peritonitis virus infection: 1963–2008. J Feline Med Surg. 2009;11(4):225–258.

• Addie DD, et al. Feline infectious peritonitis: ABCD guidelines on prevention and management. J Feline Med Surg. 2015;17(7):570–582.

• Riemer F, et al. Clinical and laboratory features of cats with feline infectious peritonitis–a retrospective study of 231 confirmed cases. Vet Microbiol. 2016;183:183–190.