Types of FIP: Ocular vs Neurological FIP

Feline Infectious Peritonitis (FIP) was once considered a death sentence. Today, thanks to advances in antiviral treatment and diagnostics, this formerly untreatable disease is now survivable in many cases. FIP occurs when a benign feline coronavirus (FCoV), common in multi-cat environments, mutates into a deadly strain that invades the cat's immune system.

FIP exists in two broad forms: effusive (wet) and non-effusive (dry). While the wet form is more obvious due to fluid accumulation in the abdomen or chest, the dry form is often more insidious. Two particularly challenging subtypes of dry FIP are ocular FIP and neurological FIP—both of which can lead to delayed diagnosis and life-threatening complications if not recognised early.

In Australia and New Zealand, where veterinary awareness of FIP is growing, understanding the subtle and sometimes overlapping signs of these atypical forms is key to saving feline lives.

What is Ocular FIP?

Ocular FIP refers to the involvement of the eyes in the inflammatory process triggered by FIP. The virus causes immune-mediated vasculitis, affecting the blood vessels in the eye and leading to noticeable changes in appearance and vision.

Common Symptoms of Ocular FIP:

• Anterior uveitis: Inflammation of the front part of the eye; appears as a cloudy or bluish eye

• Iris color change: Affected eyes may appear darker, lighter, or uneven in color

• Aqueous flare: Protein leakage into the eye’s aqueous humour, causing a foggy appearance

• Retinal detachment or hemorrhage

• Vision loss: Often gradual and sometimes irreversible if not treated early

• Miosis (constricted pupils) or anisocoria (unequal pupils)

In many cases, the only clinical signs of ocular FIP are changes in the eyes. A cat may seem otherwise alert and healthy except for a sudden color change, eye cloudiness, or signs of discomfort like blinking, pawing at the eye, or avoiding light.

Veterinary ophthalmologists across Oceania are increasingly playing a role in identifying FIP early due to eye-related symptoms that precede systemic illness.

What is Neurological FIP?

Neurological FIP is the most severe and advanced form of FIP. It results when the mutated coronavirus infiltrates the central nervous system (CNS), causing inflammation of the brain and spinal cord. This form can be devastating and is often misdiagnosed as epilepsy, trauma, or idiopathic vestibular disease.

Common Symptoms of Neurological FIP:

• Seizures

• Ataxia (uncoordinated movement)

• Tremors or twitching

• Hind limb weakness or paralysis

• Nystagmus (involuntary eye movement)

• Head tilt or circling

• Behavior changes: confusion, disorientation, sudden aggression, or lethargy.

These symptoms often worsen progressively over days or weeks. In extreme cases, cats may become completely paralyzed or comatose. Neurological FIP is most commonly seen in older kittens or young adult cats, particularly those from shelters, rescues, or high-density breeding environments.

Due to the complexity of brain-related symptoms, this form often requires input from neurology specialists and advanced imaging tools such as MRI or CT scan—resources not always available in rural regions of Australia or New Zealand.

How Ocular and Neurological FIP Overlap

One of the challenges in diagnosing and treating FIP is that the ocular and neurological forms often overlap. A cat may initially present with uveitis (eye inflammation), only to develop hind limb weakness or seizures weeks later.

This progression occurs because the virus can spread from the eye to the central nervous system, or vice versa. In some cats, ocular and neurological signs may appear simultaneously, which can confuse both owners and veterinarians.

This overlap also complicates treatment, as these cases typically require higher doses and longer durations of antiviral medications such as GS-441524. Fortunately, Cure FIP Oceania provides treatment plans and support tailored to the more complex nature of these overlapping cases.

Diagnostic Challenges and Early Recognition

Diagnosing ocular or neurological FIP remains one of the biggest hurdles in feline medicine. Unlike wet FIP, which can be confirmed by analyzing fluid, these dry forms offer no easily accessible samples for laboratory confirmation.

Common Diagnostic Tools:

• Ophthalmic exams: May reveal retinal vessel changes, keratic precipitates, or hyphema

• Neurological exams: Assessing reflexes, gait, and cranial nerve function

• Bloodwork: Low albumin-to-globulin ratio (< 0.4), elevated total protein, lymphopenia

• MRI/CT scans: Identify brain or spinal cord inflammation

• CSF analysis: Can show elevated protein and WBCs, though risky to perform

• PCR or IHC (immunohistochemistry): May detect FCoV in biopsy or post-mortem samples

Because definitive diagnosis is often difficult, clinical suspicion and pattern recognition are critical, especially when other differentials (like toxoplasmosis or trauma) are ruled out.

In Oceania, more veterinarians are becoming aware of these subtle signs, especially in shelters and rescue settings where young cats are most vulnerable.

Prognosis and Treatment Approach

Ocular FIP Treatment:

Ocular FIP generally responds well to GS-441524 or similar antiviral agents, particularly if no CNS involvement is present. Vision often returns if inflammation is treated early, though permanent damage is possible in severe or late-stage cases.

• Typical duration: 84 days or more

• Administration: Oral or subcutaneous GS, with ophthalmic anti-inflammatories if needed

• Prognosis: Good to excellent if caught early
  

Neurological FIP Treatment:

This is the most difficult form to treat and requires higher doses of antiviral medication to cross the blood-brain barrier.

• Dosing: 8–10 mg/kg (or higher) of GS-441524 or equivalent

• Duration: Minimum 84 days; some cases require extended treatment

• Supportive care: Fluids, anti-seizure meds, corticosteroids in select cases

• Prognosis: Guarded but improving with early diagnosis and proper support

Many cats in Oceania have now survived neurological FIP thanks to early intervention, accurate dosing, and continued monitoring offered by Cure FIP Oceania and partnering vets.

Final Thoughts: Awareness Saves Lives

Ocular and neurological FIP represent the most subtle, complex, and challenging presentations of this disease. Yet, with growing awareness, improved access to antivirals, and support from organisations like Cure FIP Oceania, recovery is no longer a rare exception—it is increasingly becoming the norm.

If you live in Australia or New Zealand and suspect your cat is showing signs of FIP, especially unexplained eye or neurological symptoms, seek veterinary care immediately. Early diagnosis and treatment could be the difference between life and death.

Cure FIP Oceania is here to help—whether you're looking for treatment plans, veterinary guidance, or recovery monitoring tools.