Calicivirus is a common virus infecting cats. It is one of many organisms that cause upper respiratory infections (URI), although some forms can cause more severe disease.

Signs include discharge from the eyes and nose, sores or ulcers in the mouth, fever, loss of appetite, and lethargy. Sometimes limping from arthritis or pneumonia may be seen. A rare form of calicivirus causes disease in other body systems as well and cause fluid build-up (edema), sores in the skin, vomiting, diarrhea, and pneumonia. This severe form is very contagious and is often fatal.

Calicivirus is not contagious to people but is very easily spread from cat to cat by contact with an infected animal or with surfaces that have been in contact with cats, such as bedding, food and water dishes, cages, hands, and clothing. The virus is very resistant to disinfection, and even with the best hygiene practices, it is very difficult to control its spread. Up to 25% of healthy-appearing cats may be carrying and shedding this virus. Kittens are most at risk, as well as unvaccinated cats or those with weak immune systems. All cats and kittens admitted to CHS receive vaccinations to help prevent URI’s (unless contraindicated by certain conditions), but no vaccine can prevent all cases of disease.

Diagnosis of the specific cause of a URI in a cat is difficult and costly, and the results may not reflect all the possible organisms involved. One of the classic signs of calicivirus is oral ulcers in cats which may also show other signs of an upper respiratory infection. The feline herpes virus can cause the same signs as calicivirus.

Infected cats are isolated immediately to limit the spread of disease. Antibiotics are usually given to prevent and/or treat bacterial infections that may occur at the same time, and eye ointments are used to treat conjunctivitis. Pain medication and treatments for oral ulcers may be used, and fluids are given under the skin or intravenously if needed to treat dehydration and fever. Many cats recover within 7-10 days, although ulcers may take longer to fully heal. Kittens may develop the more severe form later even if they have recovered from the initial infection.

Cats or kittens suspected to have had a calicivirus infection may be contagious for several months after recovery; so, it is recommended that these animals go to a home where there are no other cats. Resident cats that have been thoroughly vaccinated against calicivirus may be protected, but there is still a risk of them becoming infected.

If limping, loss of appetite, fever, or signs of a cold occur, consult your veterinarian immediately.