Upper respiratory infections (URIs) are among the most common welfare problems in cats, particularly in multi-cat households, rescues, and shelters. Though often considered mild, they cause significant discomfort and can become serious in kittens and immunocompromised cats.
Feline herpesvirus-1 (FHV-1): Accounts for approximately 40–50% of URIs. Causes acute signs then establishes lifelong latency in trigeminal ganglia. Reactivation occurs during stress, immunosuppression, or corticosteroid therapy, causing recurrent episodes throughout the cat's life.
Feline calicivirus (FCV): Accounts for 40–50% of URIs. More variable in its presentation than FHV-1 — some strains cause mainly oral ulceration, others more respiratory signs. Highly contagious. Unlike herpesvirus, FCV does not establish latency but shedding can persist for months to years after infection.
Bordetella bronchiseptica: A bacterial cause primarily in multi-cat environments and cats previously housed with dogs (from which it can transfer). Causes bronchopneumonia in kittens.
Chlamydia felis: Causes mainly conjunctivitis with mild respiratory signs. Common in multi-cat environments.
Acute URI causes sneezing, nasal discharge (initially serous, later mucopurulent), conjunctivitis, and oral ulceration (particularly FCV). Affected cats become anorexic — a major welfare concern in cats because hepatic lipidosis develops rapidly with food deprivation. Anosmia from nasal congestion removes the appetite stimulus. Kittens and elderly cats can deteriorate quickly.
Chronic FHV-1 causes recurrent conjunctivitis, keratitis (corneal ulceration), and nasal discharge. The eye disease can be painful and lead to blindness if untreated. Many cats with recurrent eye disease are experiencing chronic, incompletely controlled viral disease rather than allergic or structural problems as owners may believe.
Most URI diagnosis is clinical. PCR testing distinguishes causative agents when management decisions depend on the pathogen. FHV-1 positive cats can be managed with antiviral therapy (famciclovir) during active episodes; lysine supplementation is frequently recommended but evidence for efficacy is limited. Supportive care including nasal decongestants, appetite stimulants, nutritional support, and antibiotic treatment for secondary bacterial infection forms the basis of acute management.
Core feline vaccines include FHV-1 and FCV components. Vaccination does not prevent infection but significantly reduces severity of clinical signs. Vaccinated cats that develop URI typically recover faster with less severe welfare impact than unvaccinated cats. Annual boosters maintain protective immunity. In multi-cat environments with confirmed URI problems, reviewing vaccination protocols and using intranasal vaccines (providing mucosal immunity) may improve protection.
Stress is a major trigger for FHV-1 reactivation and reduced immune function across all pathogens. In multi-cat households, providing adequate resources (litter boxes, resting areas, feeding stations), maintaining predictable routines, and managing inter-cat conflict reduces URI risk. Air filtration, regular disinfection of shared surfaces, and isolation of new cats before introduction to existing residents all reduce transmission risk.
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