Dry FIP (Non-effusive Feline Infectious Peritonitis)

The non-effusive form of FIP without fluid accumulation; more complex symptoms and higher diagnostic challenges

Feline Infectious Peritonitis (FIP) is a fatal inflammatory disease caused by the mutation of feline coronavirus (FCoV) into a virulent strain known as FIPV. According to a comprehensive review by Prof. Pedersen (2009) in the Journal of Feline Medicine and Surgery, FIP is classified into two main clinical forms: wet (effusive) and dry (non-effusive). Dry FIP accounts for approximately 30–40% of cases, characterized by complex and variable clinical manifestations in the absence of fluid accumulation【Pedersen, 2009】.

1. Pathogenesis

Dry FIP shares a similar virological mechanism with wet FIP, but due to the host’s different immune responses, FIPV triggers chronic granulomatous inflammation without overt effusion. This form typically affects solid organs such as the liver, kidneys, lymph nodes, eyes, or central nervous system, resulting in multifocal inflammatory lesions.

2. Clinical Signs

Dry FIP develops progressively and presents with diverse clinical signs, often requiring a multi-dimensional diagnostic approach. Common features include:

1. General Non-specific Signs

• Persistent or intermittent fever (> 39.5°C)

• Lethargy, reduced appetite

• Progressive weight loss, poor coat condition

• Pale mucous membranes, anemia

2. Organ-specific Symptoms

• Enlarged organs or nodules: Palpable firm or irregular masses in liver, kidneys, spleen, or lymph nodes; visible on ultrasound.

• Ocular involvement (Ocular FIP): Uveitis, iris discoloration, vitreous opacity, retinal hemorrhage, or vision loss.

• Neurological symptoms (Neurological FIP): Ataxia, seizures, hindlimb paralysis, nystagmus, head tilt.

These symptoms may appear alone or in combination, forming a multi-systemic clinical picture.

3. Laboratory Features

As dry FIP lacks characteristic effusion, diagnosis depends on the following laboratory indicators:

• A:G ratio < 0.4 — highly suggestive

• Elevated total protein (> 80 g/L), particularly globulin

• Increased α1-acid glycoprotein (AGP)

• Elevated inflammatory markers (fsAA)

• Ultrasound: Organomegaly, echogenic changes, enlarged lymph nodes

• Tissue biopsy / IHC: Gold standard for confirmation, though not always feasible

According to Addie et al. (2015), the ABCD FIP guidelines recommend a combination of clinical, lab, and imaging data for presumed diagnosis【Addie et al., 2015】.

4. Treatment Options

The discovery of GS-441524 has made effective treatment for dry FIP possible:

• Recommended drug: NeoFipronis® (INN: Pronidesivir)

• Starting dosage:

  • Standard dry FIP: 15–20 mg/kg/day

  • Ocular/Neurological FIP: 20–30 mg/kg/day

  
  

• Suggested duration: 84 consecutive days with regular monitoring of weight, A:G ratio, AGP, etc.

Clinical studies indicate a treatment success rate of 80–85%, though recovery may take longer due to more severe organ involvement【Pedersen et al., 2019】.

5. Diagnostic Challenges & Recommendations

Dry FIP is often misdiagnosed as lymphoma, chronic renal disease, ocular inflammation, or epilepsy due to its atypical signs. Suggested strategies to improve diagnostic accuracy:

• Assess history (multi-cat households, recent stress, young age)

• Combine clinical signs with lab & imaging evidence

• Consider therapeutic trial with GS-441524 for response evaluation

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.

• Felten S, Hartmann K. Diagnosis of feline infectious peritonitis: a review of the current literature. Viruses. 2019;11(11):1068.