FIP Veterinary Advisor

Comprehensive, evidence-based guidance for diagnosing and treating Feline Infectious Peritonitis based on ABCD (European Advisory Board on Cat Diseases) Guidelines and research from UC Davis Veterinary School.

When to Use This Skill

Use this skill for any FIP-related veterinary consultation, including:

• Evaluating cats with clinical signs suggestive of FIP
• Interpreting diagnostic test results (FCoV PCR, antibody tests, effusion analysis)
• Planning treatment protocols with GS-441524 or alternative antivirals
• Monitoring treatment response and making dosage adjustments
• Managing treatment complications or relapses
• Distinguishing FIP from similar diseases
• Advising clients on prognosis, treatment options, and costs

Core Principles

1. Evidence-Based Medicine

All guidance derives from peer-reviewed research and established veterinary guidelines:

• ABCD diagnostic criteria (November 2024)
• UC Davis treatment protocols (Dr. Niels C. Pedersen)
• Published field trials and clinical studies

2. Preponderance of Evidence Approach

FIP diagnosis requires multiple supporting findings - never one test alone:

• Weight signalment, history, clinical signs, and laboratory findings together
• Use diagnostic flowcharts systematically
• Consider overall clinical picture over isolated test abnormalities

3. Treatment is Now Possible

GS-441524 has transformed FIP from uniformly fatal to >85% curable:

• Provide realistic hope while maintaining honesty about challenges
• Support veterinarians working with clients using various drug sources
• Focus on patient welfare regardless of drug procurement method

Quick Reference Guide

Diagnosis Checklist

High Suspicion Indicators:

• Age <2 years with multi-cat household
• Persistent fever non-responsive to antibiotics
• Swollen abdomen (effusion) or dyspnoea
• Hyperglobulinaemia with low A:G ratio (<0.4)
• Effusion: High protein (>35 g/L), low cells (<5×10⁹/L), yellow, Rivalta positive
• Ocular changes (iris color change, uveitis, perivascular cuffing)
• Progressive neurological signs

Proceed to Diagnostic Flowcharts: See diagnostic-flowcharts.md for detailed decision trees.

Treatment Quick Start

Initial Dosing (GS-441524):

• Wet/dry FIP (no CNS/ocular): 4-6 mg/kg SC daily × 12 weeks
• Ocular FIP: 8 mg/kg SC daily × 12 weeks
• Neurological FIP: 10 mg/kg SC daily × 12 weeks

Essential Monitoring:

• Weekly: Weight, temperature, clinical signs
• Monthly: CBC and chemistry panel (focus on hematocrit, globulin, albumin, A:G ratio)

For detailed protocols: See treatment-protocols.md

Workflow: Diagnostic Approach

Step 1: Initial Assessment

Gather complete information:

Signalment & History:

• Age, breed, sex
• Multi-cat household?
• Recent stressors (rehoming, vaccination, neutering)?
• Siblings or contacts with FIP?
• Duration and progression of clinical signs

Physical Examination:

• Temperature, weight, body condition score
• Presence of effusion (abdominal, thoracic, pericardial)
• Ocular examination (uveitis, iris changes, retinal changes)
• Neurological assessment (ataxia, paresis, seizures)
• Abdominal palpation (organomegaly, masses, lymph nodes)

Laboratory Tests:

• CBC: Look for anemia, lymphopenia, microcytosis
• Chemistry: Total protein, albumin, globulin, A:G ratio, bilirubin
• Alpha-1-acid glycoprotein if available

Step 2: Categorize Clinical Presentation

Determine which diagnostic tree to follow:

Tree A - Effusion Present: Use when fluid detected by POCUS or physical exam → See diagnostic-flowcharts.md - Tree A

Tree B - No Effusion, Non-specific Signs: Use when no fluid but suspicious clinical picture → See diagnostic-flowcharts.md - Tree B

Tree C - Neurological Signs: Use when neurological abnormalities predominate → See diagnostic-flowcharts.md - Tree C

Tree D - Ocular Signs: Use when ocular abnormalities predominate → See diagnostic-flowcharts.md - Tree D

Step 3: Perform Confirmatory Testing

Based on diagnostic tree:

Effusion Analysis:

• Biochemistry: Protein, Rivalta test, A:G ratio
• Cytology: Cell count, cell types
• FCoV RT-PCR (quantitative preferred - high loads more specific)
• Immunostaining for FCoV antigen (high specificity)

Tissue Sampling (FNA or Biopsy):

• Target abnormal organs (lymph nodes, kidney, liver, spleen)
• Cytology assessment
• FCoV RT-PCR
• Immunostaining for FCoV antigen

Gold Standard:

• Histopathology consistent with FIP
• Positive immunohistochemistry for FCoV antigen in lesions

Step 4: Rule Out Differential Diagnoses

Consider and systematically exclude other conditions:

Key Differentials by Presentation:

For effusive disease:

• Lymphocytic cholangitis, pyothorax, septic peritonitis, congestive heart failure, lymphoma

For neurological disease:

• Toxoplasmosis, trauma, thiamine deficiency, middle ear disease

For ocular disease:

• Toxoplasmosis, lymphoma, bartonellosis

Full differential diagnosis guidance: See differential-diagnosis.md

Step 5: Establish Diagnosis Confidence Level

Confirmed FIP:

• Histopathology + positive immunohistochemistry

FIP Very Likely:

• Positive immunostaining on effusion/FNA/CSF with consistent clinical picture
• High FCoV RNA loads on RT-PCR with consistent cytology and clinical signs

FIP Possible:

• Clinical signs + laboratory findings suggestive, but confirmatory tests not yet performed or inconclusive

FIP Less Likely:

• Negative confirmatory tests
• Alternative diagnosis more consistent with findings

Workflow: Treatment Planning

Phase 1: Pre-treatment Assessment

Confirm Diagnosis:

• Establish diagnosis confidence level
• Collect samples for FCoV detection if not already done
• Document baseline parameters

Baseline Documentation:

• Complete CBC and chemistry panel
• Body weight
• Temperature
• Photographs of clinical signs (effusion, ocular lesions)
• Activity level and appetite assessment

Client Communication:

• Explain diagnosis and prognosis
• Discuss treatment options (including legal status, costs, duration)
• Set realistic expectations (>85% cure rate with proper protocol)
• Discuss monitoring requirements
• Obtain informed consent

Phase 2: Initial Treatment

Select Starting Dose:

Determine appropriate dosage based on disease form:

• Wet/dry FIP without CNS or ocular involvement: 4-6 mg/kg daily SC
• FIP with ocular involvement: 8 mg/kg daily SC
• FIP with neurological involvement: 10 mg/kg daily SC

Administration Guidance:

• Injectable GS-441524 preferred (oral acceptable if ≤10 mg/kg equivalent)
• Subcutaneous injection
• Rotate injection sites systematically
• Consider gabapentin pre-treatment (5-10 mg/kg PO) for injection pain

Supportive Care:

• Nutritional support (appetite stimulants if needed)
• Fluid therapy if dehydrated
• Thoracocentesis only if dyspnoeic
• Analgesics as needed
• Short-term prednisolone acceptable for severe inappetence (few days only)

For comprehensive treatment protocols: See treatment-protocols.md

Phase 3: Monitoring Protocol

Daily/Weekly Owner Monitoring:

• Daily temperature
• Weekly weight
• Activity level and appetite
• Clinical signs progression or resolution

Veterinary Monitoring:

• Blood work every 4 weeks (minimum)
• CBC: Hematocrit, lymphocyte count
• Chemistry: Total protein, albumin, globulin, A:G ratio, bilirubin

Expected Response Timeline:

• 24-72 hours: Temperature normalization, appetite improvement
• 2-4 weeks: Near-normal behavior, effusion resolution, weight gain starting
• 8-10 weeks: Blood values normalizing, activity surge
• 12 weeks: Treatment completion assessment

Response Assessment: Create graphs tracking weight, temperature, A:G ratio, globulin over time for objective monitoring.

Phase 4: Dosage Adjustments

Weekly Weight Adjustments:

• Adjust dose for weight gain weekly
• Do not decrease dose for initial weight loss
• Significant weight gain expected (some cats double body weight)

Increase Dosage If:

• Slow improvement in clinical signs
• Blood values not improving adequately (after 4-8 weeks)
• Poor activity levels despite treatment
• Original clinical signs not resolving
• Development of ocular signs during treatment (increase to 8 mg/kg)
• Development of neurological signs during treatment (increase to 10 mg/kg)

How to Increase:

• Add 2-5 mg/kg to daily dose
• Continue increased dose minimum 4 weeks
• Extend total treatment duration to accommodate
• Expect positive response within days to 2 weeks

No Response to Increase:

• Consider further increase if <15 mg/kg
• Evaluate drug quality
• Reassess diagnosis
• Consider drug resistance developing
• Evaluate for concurrent disease

Phase 5: Treatment Completion

Assess All Criteria Before Stopping:

Outward Health Signs (all required):

• Normal activity level
• Normal appetite
• Appropriate weight gain/growth
• Quality coat (excellent indicator)
• Clinical signs resolved

Blood Test Normalization (all required):

• Hematocrit normal
• Lymphocyte count normal
• Total protein normal
• Albumin normal
• Globulin normal or near-normal
• A:G ratio normalized

Additional Considerations:

• Minimum 12 weeks treatment completed
• No fever
• No effusion
• No neurological or ocular signs

Critical Principle: Focus on OVERALL clinical picture. Do not extend treatment based solely on single marginally abnormal value if cat is otherwise healthy and all other parameters normal.

Phase 6: Post-Treatment Monitoring

12-Week Observation Period:

• Continue monitoring weight, activity, appetite
• Blood work at 4 and 8 weeks post-treatment
• Watch for relapse signs

Relapse Indicators:

• Return of fever
• New neurological signs
• New ocular signs
• Weight loss
• Decreased activity
• Rising globulin or falling A:G ratio

Relapse Management: If relapse occurs:

• Restart treatment at higher dose (minimum previous dose + 5 mg/kg)
• Duration: Minimum 8 weeks
• Use injectable form only (especially if >10 mg/kg)
• See treatment-protocols.md - Relapse Management

Workflow: Prevention and Multi-Cat Management

When clients have multiple cats or are concerned about prevention after an FIP diagnosis:

Risk Assessment

Evaluate environment:

• Number of cats in household
• Group stability (additions/removals)
• Hygiene practices
• Stress levels
• Space availability

Provide guidance based on risk level:

• Low risk (1-3 stable cats): Basic hygiene, monitor for illness
• Moderate risk (4-6 cats): Enhanced hygiene, stress reduction
• High risk (>6 cats, cattery, shelter): Rigorous protocols, consider testing

Full prevention guidance: See prevention-management.md

After FIP Diagnosis in Multi-Cat Household

Immediate advice:

• Other cats likely already exposed to FCoV (not mutated form)
• No need to isolate FIP cat from stable household
• Focus on stress reduction for all cats
• Monitor others for clinical signs (siblings highest risk)

Long-term recommendations:

• No routine testing of other cats needed
• Excellent litter box hygiene
• Avoid adding new cats during treatment period
• Watch for FIP signs in young cats/siblings

Cattery or Breeding Questions

When FIP occurs:

• Pause breeding temporarily
• Consider testing breeding cats for FCoV shedding
• Siblings of FIP cat at higher risk
• Do NOT cull entire cattery
• Do NOT use antivirals prophylactically

Prevention strategies:

• Small stable groups
• Early weaning and kitten separation
• Minimize stress
• Maintain genetic diversity
• See full cattery guidance in prevention-management.md

Workflow: Managing Complex Cases

Drug Resistance

Recognition:

• Inadequate response despite dosage increases
• Disease progression on treatment
• Relapse shortly after treatment completion

Management:

• Escalate dosage up to 15 mg/kg
• Consider combination therapy (GC376 + GS-441524) if available
• May achieve disease control without cure
• Quality of life assessment if resistance progresses

Full guidance: See treatment-protocols.md - Drug Resistance

Neurological FIP

Special Considerations:

• Higher starting dose required (10 mg/kg minimum)
• Blood-brain barrier limits drug penetration
• Higher relapse risk
• Permanent CNS damage possible even with cure

Monitoring:

• Standard protocols plus neurological assessment
• Advanced imaging (MRI) may be needed
• CSF analysis for diagnosis and monitoring

Prognosis:

• Lower cure rate than wet/dry FIP
• Some permanent deficits may persist even after virus clearance
• Peripheral nerve damage may slowly recover
• Central nervous system damage typically permanent

Injection Site Reactions

Prevention:

• Systematic site rotation
• Proper injection technique (subcutaneous, not intramuscular)
• Avoid between-shoulder area

Management:

• Gabapentin pre-medication
• Clean 4+ times daily with dilute hydrogen peroxide (1:5)
• Usually heal within 2 weeks
• Rarely need additional treatment
• Severe reactions (vasculitis-type) may need short-term low-dose steroids

Financial Constraints

Supportive Conversation:

• Acknowledge financial reality
• Discuss treatment duration and total costs transparently
• Consider shorter proven protocols (42 days for effusive cases)
• Explain monitoring requirements and costs
• Discuss euthanasia as humane option if treatment not feasible

Ethical Framework:

• Patient welfare is paramount
• Quality of life assessment ongoing
• Euthanasia preferable to untreated suffering
• Support client decision-making without judgment

Client Communication Guidance

Explaining FIP Diagnosis

Key Points to Cover:

• FIP is caused by mutation of common feline coronavirus
• Mutation occurs within individual cat (not typically transmitted cat-to-cat in mutated form)
• Historically always fatal, now treatable with antivirals
• Diagnosis based on preponderance of evidence, not single test
• FCoV antibodies in many healthy cats (not diagnostic of FIP)

Avoid:

• Guaranteeing 100% diagnosis without histopathology
• Blaming owner for cat's FIP (stress factors are just associations, not causes)
• False hope or false doom
• Jargon without explanation

Discussing Treatment Options

Present Honestly:

• Treatment availability varies by region
• GS-441524 not licensed for veterinary use in many areas
• Clients may obtain from unregulated sources
• Variable drug quality possible
• Treatment is expensive (typically thousands of dollars)
• Duration is lengthy (12+ weeks minimum)

Emphasize:

• 85% cure rate with proper protocol

• Importance of veterinary monitoring
• Commitment required (daily injections, regular monitoring)
• You will support monitoring regardless of drug source

Prognostic Factors:

• Young cats: Better outcomes
• Wet FIP: Easier to treat than dry
• No neurological involvement: Better prognosis
• Early treatment: Better outcomes

Setting Expectations

Realistic Timeline:

• Rapid initial response (24-72 hours) expected
• Near-normal by 2-4 weeks in most cases
• Full treatment 12+ weeks
• 12-week observation period after treatment
• Total commitment: 6+ months

Financial Reality:

• Estimate total costs including drug, monitoring, supportive care
• Discuss payment plans if available
• Acknowledge this is major financial commitment

Possible Outcomes:

• Cure (>85%)
• Relapse requiring additional treatment
• Drug resistance (partial or complete)
• Treatment failure
• Financial limitation requiring euthanasia

Supporting Difficult Decisions

When Treatment Not Pursued:

• Validate client's decision
• Emphasize quality of life
• Discuss euthanasia as compassionate option
• Provide grief support resources

When Treatment Fails:

• Explain not a failure of client commitment
• Some cats develop resistance
• Euthanasia discussion when appropriate
• Support through grief

Special Scenarios

Multi-cat Households

Risk Assessment:

• Other cats likely already exposed to FCoV
• Mutation theory: Each FIP case requires new mutation
• Direct transmission of mutated form unlikely in natural settings

Management Recommendations:

• No need to isolate FIP cat from established household
• Reduce stress for all cats
• Monitor other cats for clinical signs
• Consider testing siblings if feasible
• Excellent litter box hygiene

Cattery Considerations:

• Pause breeding during FIP case
• Siblings at higher risk
• Avoid stress (overcrowding, excessive showing, frequent sales)
• Do NOT use antivirals as "preventive" (resistance risk)

Preventive Measures

Reduce FIP Risk:

• Small stable groups (≤3 cats ideal)
• Reduce stress in multi-cat households
• Excellent litter box hygiene
• Avoid overcrowding

FIP Vaccine:

• Available in some countries (Felocell FIP)
• Given intranasally at ≥16 weeks
• Efficacy controversial
• Not recommended by ABCD
• Most cats already exposed before vaccine age

Testing for FCoV:

• Fecal PCR can identify shedders
• Allows separation in catteries if feasible
• Requires multiple samples (intermittent shedding)
• Most practical in breeding operations

Key Principles Summary

1. Diagnosis requires preponderance of evidence - Multiple findings, not single test

2. Follow diagnostic trees systematically - Don't skip steps or premature closure

3. Rule out treatable alternatives - Many differentials are curable

4. Confirm diagnosis before treatment when possible - Collect samples early

5. Treatment requires commitment - 12+ weeks, daily injections, regular monitoring

6. Monitor objectively - Weight, temperature, blood values, not just subjective assessment

7. Adjust treatment based on response - Increase dose if inadequate response

8. Overall clinical picture matters most - Not single test value in isolation

9. Young cats with wet FIP have best prognosis - Neurological worst prognosis

10. Support clients through entire journey - Regardless of drug source or ultimate outcome

References and Resources

Detailed Information

For comprehensive details on specific topics:

• Diagnostic Flowcharts: diagnostic-flowcharts.md

  • Evidence weighting system
  • Four diagnostic trees (A, B, C, D)
  • Confirmatory testing interpretation
  • Treatment trial considerations

• Treatment Protocols: treatment-protocols.md

  • Detailed dosing by disease form
  • Monitoring protocols and parameters
  • Dosage adjustment guidelines
  • Relapse management
  • Drug resistance handling
  • Injection site management
  • Supportive care recommendations

• Differential Diagnoses: differential-diagnosis.md

  • Effusive diseases
  • Neurological diseases
  • Ocular diseases
  • Infectious diseases
  • Neoplastic conditions
  • Metabolic/toxic conditions
  • Diagnostic approach algorithms

• Prevention and Management: prevention-management.md

  • Environmental management strategies
  • Multi-cat household guidance
  • Cattery breeding considerations
  • Shelter management protocols
  • FCoV testing interpretation
  • Vaccination discussion
  • Risk reduction strategies

Evidence Base

This skill is based on:

• ABCD (European Advisory Board on Cat Diseases) Guidelines, November 2024
• UC Davis Veterinary School research (Dr. Niels C. Pedersen group)
• Published field trials of GS-441524
• Peer-reviewed veterinary literature

Limitations

What This Skill Cannot Do:

• Replace histopathology for definitive diagnosis
• Guarantee treatment success (resistance, misdiagnosis possible)
• Provide legal advice on drug procurement
• Replace clinical judgment in complex cases

When to Seek Additional Expertise:

• Complex neurological cases requiring advanced imaging
• Ophthalmological procedures (aqueous humour sampling)
• Surgical interventions needed
• Treatment-refractory cases
• Concurrent complex diseases

Quick Decision Trees

Is This FIP?

1. High suspicion signalment? (young, multi-cat, stressed) → Yes: Continue assessment → No: Consider alternative diagnoses more

2. Compatible clinical signs? (fever, effusion, neurological, ocular) → Yes: Continue workup → No: Reconsider diagnosis

3. Laboratory findings supportive? (high globulin, low A:G, appropriate effusion) → Yes: Proceed to confirmatory testing → No: Reconsider or investigate further

4. Confirmatory testing? (positive immunostaining or high PCR loads with appropriate sample) → Yes: FIP very likely, consider treatment → No: FIP less likely, consider alternatives or continue monitoring

5. Alternative diagnoses ruled out? (See differential-diagnosis.md) → Yes: Proceed with FIP management → No: Investigate alternatives

Should Treatment Be Started?

1. Is diagnosis FIP very likely or confirmed? → No: Complete diagnostic workup first → Yes: Continue assessment

2. Owner commitment available? (financial, time, emotional) → No: Discuss alternatives including euthanasia → Yes: Continue planning

3. Baseline tests obtained? → No: Obtain CBC, chemistry, weight, photos → Yes: Continue planning

4. Appropriate starting dose determined? (based on disease form) → No: Review treatment-protocols.md → Yes: Initiate treatment

5. Monitoring plan established? → No: Set up schedule for owner tracking and vet checks → Yes: Begin treatment

Is Treatment Working?

1. Early response (24-72 hours)? (temperature, appetite, activity) → No: Consider dosage increase or reconsider diagnosis → Yes: Continue treatment

2. Short-term response (2-4 weeks)? (clinical signs, weight) → No: Increase dosage → Yes: Continue current dose

3. Mid-term blood values (4-8 weeks)? (improving toward normal) → No: Increase dosage and investigate → Yes: Continue treatment

4. All parameters normal at 12 weeks? → No: Extend treatment or increase dose → Yes: Stop treatment, monitor for relapse

Troubleshooting Common Issues

"Clinical signs not improving despite treatment"

Assess:

• Verify drug quality and source
• Check dosage calculation (mg/kg correct?)
• Evaluate injection technique
• Review diagnosis (is it actually FIP?)
• Check for concurrent disease
• Consider partial drug resistance

Action:

• Increase dosage by 2-5 mg/kg
• Recheck blood work
• Consider imaging for complications
• Reassess diagnosis if no response to increase

"Blood values not normalizing"

Assess:

• Which specific values abnormal?
• Overall clinical picture (is cat healthy appearing?)
• Magnitude of abnormality (slightly off vs markedly abnormal)
• Trend over time (improving vs static vs worsening)

Action:

• If single marginally abnormal value + healthy cat → Consider stopping at 12 weeks
• If multiple abnormal values → Extend treatment
• If markedly abnormal → Increase dosage

"Owner reports injection site problems"

Assess:

• Site rotation adequate?
• Injection depth correct?
• Severity of reaction
• Pattern (every injection vs specific sites)

Action:

• Review injection technique with owner
• Recommend gabapentin pre-treatment
• Dilute hydrogen peroxide cleaning protocol
• Consider switching to oral if dosage allows (<10 mg/kg equivalent)

"Suspected relapse after treatment"

Assess:

• Clinical signs (fever, weight loss, decreased activity?)
• Blood work (rising globulin, falling A:G?)
• Form of relapse (CNS, ocular, systemic?)
• Time since stopping treatment

Action:

• Confirm relapse with blood work
• Restart treatment at higher dose (previous + 5 mg/kg minimum)
• Plan minimum 8-week retreatment
• Use injectable form
• Consider inadequate initial treatment or resistance developing

"Client wants to stop treatment early"

Assess:

• Reason for wanting to stop (financial, improved cat, injection difficulty?)
• Current duration of treatment
• Clinical response so far
• Risk of relapse

Discussion:

• Explain relapse risk if stopped prematurely
• Consider shorter proven protocols if appropriate (42 days for effusive)
• If financial: Discuss options, payment plans
• If cat looks healthy: Review objective measures
• Support decision while providing education

Action:

• If <8 weeks: Strongly discourage unless cat unhealthy
• If 8-12 weeks with complete response: May consider in selected cases
• If ≥12 weeks: Assess stopping criteria
• Document discussion and decision

Remember

• FIP is no longer an automatic death sentence
• Support and guide clients through difficult journey
• Use objective measures for decision-making
• Be honest about prognosis, costs, and commitment
• Each case is individual - guidelines inform, not dictate
• Preserve quality of life as paramount goal
• You are the cat's advocate and the client's support

When in doubt, consult the detailed reference documents or relevant literature.