Types of FIP: Ocular vs. Neurological FIP

Feline Infectious Peritonitis (FIP) is caused by a mutation of the feline coronavirus (FCoV) and is one of the most feared diseases among cat owners. While most pet owners recognize the wet (effusive) and dry (non-effusive) forms of FIP, there are also two advanced manifestations that require urgent veterinary attention:

• Ocular FIP

• Neurological FIP
  

These forms are typically associated with the dry form of FIP, but they can also occur in conjunction with the wet form or develop in cats during or after treatment.

Recognizing the symptoms early is critical for effective treatment and survival, especially in the Philippines, where veterinary access and diagnostics can vary.

What is Ocular FIP?

Ocular FIP occurs when the mutated coronavirus invades the eyes, causing inflammation in various parts of the ocular system. This form is particularly common in dry FIP cases and can be one of the first signs of internal viral activity.

Key Symptoms of Ocular FIP:

• Anterior uveitis (inflammation of the front of the eye)

• Hyphema (blood in the eye)

• Corneal clouding or discoloration

• Dilated or uneven pupils

• Sudden vision loss or blindness

• Ocular discharge

The inflammation may affect one or both eyes, and vision loss can progress rapidly if untreated. Cats may squint, avoid light, or appear disoriented due to partial or complete blindness.

What is Neurological FIP?

Neurological FIP is the most severe and difficult-to-treat manifestation of FIP. In this form, the virus crosses the blood-brain barrier and causes inflammation in the brain and spinal cord.

Common Signs of Neurological FIP:

• Wobbliness or uncoordinated walking (ataxia)

• Head tremors or shaking

• Seizures

• Circling or a strange gait

• Behavioral changes (aggression, depression)

• Neck pain or stiff posture

• Loss of bladder or bowel control

Symptoms may be subtle at first, such as a head tilt or slight imbalance, and then worsen over time. Neurological FIP often mimics other conditions such as epilepsy or toxoplasmosis, making diagnosis challenging.

How These Forms Differ from Classic FIP

Feature	Wet FIP	Dry FIP	Ocular FIP	Neurological FIP
Fluid Accumulation	Yes	No	Rare	No
Target Area	Abdomen or chest	Organs	Eyes (retina, uvea, optic nerve)	Brain and spinal cord
Progression Speed	Rapid	Slower	Variable	Can be fast once symptoms appear
Diagnostic Clarity	Easier (fluid-based)	Moderate	Harder	Most difficult to confirm
Treatment Response	High success rate	High	Moderate to high (if treated early)	More complex, longer treatment

Diagnosis Challenges in Ocular and Neurological FIP

These forms of FIP are notoriously difficult to diagnose, especially in regions like the Philippines, where advanced imaging and specialist veterinary care may be limited.

Diagnostic Tools Often Needed:

• Ophthalmic examination by a vet or veterinary ophthalmologist

• MRI or CT scan (for brain/spinal cord imaging)

• CSF tap (cerebrospinal fluid analysis) – confirms neurological inflammation

• Blood tests: elevated globulin, low A:G ratio, elevated WBC

• FCoV PCR testing (on CSF or aqueous humor from the eye)

Due to their invasive nature and high cost, many Filipino pet owners rely on symptom-based clinical diagnosis by an experienced vet.

Treatment Challenges and What to Expect

1. Higher Dosage Required

For both ocular and neurological FIP, treatment requires higher doses of GS-441524, an antiviral compound that targets the FIP virus. The standard dosage for these forms ranges from 8–10 mg/kg or higher daily, compared to 5–6 mg/kg for non-neuro cases.

2. Longer Treatment Duration

Cats with neurological or ocular involvement often require 84 days or more of continuous treatment. Regular monitoring is needed to assess neurological recovery and adjust doses.

3. Relapse Risk

These advanced forms carry a higher risk of relapse, especially if the antiviral treatment is stopped prematurely or dosed incorrectly.

4. Monitoring Tools

Recovery is measured by:

• Improvement in coordination, behavior, or vision

• Repeat blood tests

• Re-evaluation by your vet every 2–4 weeks
  

Final Thoughts: Hope for Ocular and Neurological FIP

Despite their severity, ocular and neurological FIP are treatable, especially with early detection and proper antiviral therapy. Thousands of cat parents worldwide—including many in the Philippines—have reported full recovery from even the most advanced cases.

By staying informed and recognizing the signs early, you can give your cat the best chance at survival.