Glossary
Feline calicivirus
A common virus behind cat flu that causes sneezing, eye discharge and painful mouth ulcers, and sometimes severe illness.
Also called: FCV, calicivirus, cat calici
Feline calicivirus, or FCV, is one of the two viruses that cause most cases of cat flu, alongside feline herpesvirus. It spreads through sneezing, saliva and shared bowls, and it is common in shelters, breeding catteries and multi-cat homes.
The classic sign is ulcers on the tongue, gums or roof of the mouth, which make eating painful and cause drooling. Sneezing, runny eyes and a snotty nose often come with them. Some strains cause lameness and fever in young kittens, and rare, virulent strains cause swelling of the face and limbs, jaundice and a high death rate. Some cats clear the virus. Others become carriers that shed it for months or years, and long-term mouth inflammation such as stomatitis has been linked to it.
Vaccination is part of the FVRCP combination and is among the core vaccines. It lowers the severity of illness, though it does not always prevent infection because the virus has many strains. A cat that stops eating, has mouth sores, or struggles to breathe needs a vet. Ask your vet about supportive care and how to keep other cats at home safe.
Last reviewed November 7, 2026