Feline Upper Respiratory Infection

Feline upper respiratory infection (URI) is one of the most common illnesses seen in cats, especially those in shelters or multi-cat environments. It is caused primarily by two viruses: feline herpesvirus type 1 (FHV-1) and feline calicivirus (FCV). Together these account for around 90% of all feline URIs.

FHV-1 causes particularly persistent infections. Once infected, most cats remain lifelong carriers. The virus lies dormant in nerve tissue and can reactivate during periods of stress — a house move, a new pet, illness, or even seasonal temperature changes. This is why some cats seem to get "colds" repeatedly throughout their lives.

FCV infection tends to produce milder respiratory signs but is strongly associated with oral ulcers, which can make eating very painful. Some strains cause a more severe systemic disease called virulent systemic FCV (VS-FCV), though this is rare.

Treatment focuses on supportive care. Steam therapy (sitting with your cat in a steamy bathroom for 10–15 minutes twice daily) helps loosen nasal secretions. Keeping the eyes and nose clear of discharge prevents secondary infections. L-lysine supplementation is sometimes recommended to reduce FHV-1 replication, though evidence is mixed. Antibiotics are prescribed only when secondary bacterial infections develop — they have no effect on the viruses themselves.