Cat flu (feline upper respiratory infection)
Common infection of cats caused by feline herpesvirus and/or calicivirus. Most adult cats recover; kittens and immunocompromised cats can be seriously ill.
"Cat flu" refers to feline upper respiratory infections, most commonly caused by feline herpesvirus type 1 (FHV-1) and feline calicivirus (FCV). Many cats are infected as kittens — sometimes from their mother — and carry the virus for life, with flare-ups under stress.
Signs: sneezing, nasal and eye discharge (clear early, sometimes yellow-green if secondary bacterial), conjunctivitis, mouth ulcers (more typical of calicivirus), fever, lethargy, decreased appetite. Severity ranges from a mild week to severe illness requiring vet care.
Most healthy adult cats recover with supportive care: humidification, soft warm food, gentle wiping of nasal/eye discharge, fluid support. Antibiotics are reserved for cats with bacterial complications.
Kittens, senior cats, FIV/FeLV-positive cats, and brachycephalic cats can become seriously ill — corneal ulceration, pneumonia, severe dehydration. Same-day vet visit for these groups.
Vaccination against FHV and FCV is core and substantially reduces severity even when it doesn't prevent infection. Carrier cats need stress management to reduce flare-up frequency: stable routine, hiding spaces, food puzzles, gentle environmental enrichment.
L-lysine supplementation for herpes flare-ups has historically been recommended but recent evidence is weak. Stress reduction and prompt treatment of flare-ups have stronger support.