Incubation & Latency

Clinical signs arise weeks, months, or in rare exceptions, years following initial infection. During this early latent/quiescent stage, cats are often fully asymptomatic or exhibit subtle, vague impairments.

Early Nonspecific Signs

Initial clinical presentations typically manifest as generalized systemic disruptions including:

• Stunted growth and physical retardation in kittens.
• Fluctuating, chronic fever unresponsive to traditional antibiotics.
• Anorexia, progressive weight loss, depression, and a rough/unkempt coat.

Respiratory Misconceptions

Upper respiratory infection (URI) signs observed during early stages are not directly caused by FIPV. FIPV itself does not cause URI; these signs stem from secondary opportunistic pathogens (e.g., Herpesvirus, Chlamydophila, Mycoplasma) exploiting the cat's early immunologic decline.

Drug Exclusion Rates

The blood-to-brain barrier in healthy felines excludes approximately 80% of systemic drugs, while the blood-to-eye barrier excludes roughly 70%. For instance, if a standard dose of GS-441524 yields an effective blood plasma baseline of 10 µM, the resulting levels in cerebrospinal fluid (CSF) drop to 2 µM, and aqueous humor levels drop to 3 µM.

Immune Shielding

These barriers create an evolutionary paradox. While protecting organs from external toxins, they also block the entry of systemic antibodies and immune lymphocytes. When FIPV crosses into the brain, spine, or uveal tract, it becomes shielded from the host's immune system, leading to standalone neurological/ocular disease forms.

Masked Blood Metrics

Inflammation isolated within privileged sites like the CNS is less likely to evoke a system-wide inflammatory response. Consequently, cats presenting with primary neurological FIP (or those experiencing a localized relapse) often show completely normal CBC and chemistry panels, with zero elevation in globulins or drops in albumin ratios.

Specific Ocular Manifestations

• Unilateral or bilateral anterior uveitis.
• Flocculant debris in the anterior chamber & cloudiness.
• Keratic precipitates forming on the posterior cornea.
• Anisocoria, chorioretinitis, retinal hemorrhages, and retinal detachment.

Specific Neurological Signs

• Vague dementia, aggressive behaviors, or compulsive licking of objects.
• Reluctance to jump, muscle twitching, or abnormal swallowing.
• Posterior ataxia, loss of conscious proprioception, and hyperesthesia.
• Spinal signs: Fecal/urinary incontinence, tail/hindleg paralysis, and lower-back pain.

Confirmatory Fluids & Imaging

• CSF / Aqueous Humor Analysis: Characterized by high protein and high nucleated cell counts (dominated by neutrophils and lymphocytes).
• RT-PCR Testing: Must target the FCoV 7b gene (the most abundant transcript) rather than the less sensitive S-gene mutations.
• MRI Patterns: Identifies meningeal/ependymal contrast enhancement, ventriculomegaly (hydrocephalus), and cerebellar herniation.

Nutrition & Hepatic Lipidosis

Cats that go without food for even a few days can rapidly develop fatal Hepatic Lipidosis (Fatty Liver) as body fat overwhelms the liver. To avoid this:

• Kittens require a minimum of 250 calories/day; adult cats require a minimum of 200 calories/day.
• If a cat is not eating, syringe feed a smooth slurry of high-calorie wet food (e.g., Hills a/d, Royal Canin Babycat) at 20-30 ml every 4-6 hours.
• Utilize anti-nausea medications (Cerenia, Ondansetron) and transdermal appetite stimulants (Mirataz gel on the inner ear pinna).
• Hydration Support: Mix extra water or unflavored Pedialyte into wet food, or use Purina HydraCare. Avoid syringe feeding pure water due to high aspiration risks.

Fluid Effusion Extraction Rules

• Abdominal Fluid Rule: Extraction should be strongly discouraged unless fluid volume is so massive it physically restricts the diaphragm and compromises breathing. Draining abdominal fluid strips vital proteins and complex fluids, which the body will rapidly try to replace at the expense of systemic hydration, potentially triggering hypovolemic shock. If drainage is mandatory, limit it to 1/3 of the total volume.
• Pleural (Chest) Fluid Rule: Fully drain thoracic fluid via ultrasound-guided thoracocentesis (chest tap) to relieve life-threatening dyspnea. Multiple taps may be required before antiviral therapy halts fluid production. Diuretics (like Lasix) do not clear FIP fluid effusions.

Clinical Symptom Management

• Oral GS Vomiting Window: If a cat vomits within 0 - 1 hours of receiving oral GS-441524, administer a FULL redose. If vomiting occurs within 1 - 3 hours, administer a HALF redose. After 3 hours, the medication is safely absorbed.
• Diarrhea: Manage with therapeutic probiotics (Fortiflora, Proviable, Pro-Pectalin) or pureed pumpkin (1-2 tsp twice daily; avoid pie fillings with onion/garlic toxins). Low-dose Metronidazole can be used safely if prescribed by a veterinarian.
• Hypothermia: If a cat's temperature is low, provide a hot water bottle or incubator. Never place a weak, non-ambulatory cat directly on an electric heating pad due to severe hotspot burn risks.