Cat flu encompasses upper respiratory infections (URI) caused primarily by feline herpesvirus 1 (FHV-1) and feline calicivirus (FCV). These viruses infect the respiratory tract, eyes, and mouth, causing a spectrum of disease from mild sneezing to severe, potentially fatal illness. Welfare management requires understanding the pathogens, their persistence, and appropriate treatment.
Causative Agents
Feline herpesvirus 1 (FHV-1): Causes rhinotracheitis — severe nasal and upper respiratory inflammation. After primary infection, FHV-1 establishes latency in sensory ganglia. Stress, corticosteroid use, or intercurrent illness can trigger reactivation and recurrent clinical signs throughout the cat's life. Ocular involvement (conjunctivitis, corneal ulcers) is characteristic of FHV-1.
Feline calicivirus (FCV): Causes milder URI typically, but also oral ulceration (characteristic tongue and palate ulcers) and limping syndrome in kittens. Virulent systemic FCV (VS-FCV) strains cause severe, often fatal systemic disease — fortunately uncommon. FCV is not latent but persistent infection may occur.
Secondary bacterial infections (Pasteurella, Bordetella, Chlamydia) exacerbate primary viral disease.
Clinical Signs
- Sneezing — often severe, paroxysmal
- Ocular and nasal discharge — initially serous, progressing to mucopurulent
- Conjunctivitis and chemosis
- Corneal ulceration — FHV-1; may cause corneal scarring and chronic eye problems
- Oral ulcers — FCV
- Inappetence from nasal congestion and oral pain
- Fever and lethargy in moderate-severe disease
Treatment
No specific antivirals are highly effective against FHV-1 at practical dosing:
- Supportive nursing care — cleaning nasal and ocular discharge, steam inhalation to ease congestion, warming food to increase palatability
- Lysine supplementation — anti-FHV-1 effect by competing with arginine; evidence mixed but widely used
- Famciclovir (converted to penciclovir) — the most evidence-supported antiviral for FHV-1; used in severe cases
- Antibiotics — for secondary bacterial infection (doxycycline for Chlamydia; amoxicillin-clavulanate for other bacteria)
- Eye drops — antiviral (idoxuridine) or antibiotic for ocular involvement
- Appetite stimulants and assisted feeding in inappetent cats
Prevention
Core vaccination against FHV-1 and FCV is recommended for all cats. Vaccines do not prevent infection but significantly reduce clinical severity. FHV-1 latency means even vaccinated cats can experience recurrent disease — particularly during stress. Isolation of newly acquired cats, particularly in multi-cat households and catteries, prevents introduction and spread.