Overview

Feline calicivirus (also known as FCV), a common viral disease that affects cats, is characterized by upper respiratory symptoms, pneumonia, oral ulceration (sores in the mouth), and occasionally arthritis. It is a fairly mild flu-like condition and rarely causes serious complications.

Calicivirus is part of the feline upper respiratory infection (URI) complex, a group of viral and bacterial infections (e.g., FHV-1, chlamydiosis) that cause discharge from the eyes and nose. Calicivirus and feline rhinotracheitis virus account for 85% to 90% of all URIs in cats.

Incidence and Prevalence
Calicivirus occurs worldwide and affects all breeds of cats. Vaccination has reduced the incidence of clinical disease, but it hasn't decreased the prevalence of the virus. The virus is spreading, even though fewer cats show symptoms.

FCV Causes

There are numerous strains of feline calicivirus, and different strains cause different symptoms (e.g., one particular strain can cause ulcers on the paws as well as in the mouth).

Calicivirus usually affects the throat, and sometimes the lungs; the virus can also infect the intestines and has been isolated from feces. Calicivirus often occurs with another upper respiratory infection, such as feline herpes virus (FHV), rhinotracheitis virus, or chlamydiosis.

FCV Transmission
Calicivirus is spread through direct contact with the saliva, eye and nose discharges, and sometimes the feces, of an infected cat.FCV is resistant to many disinfectants and can survive outside the cat's body for as long as 8 to 10 days, so it may be present in dishes, litter trays, and clothing, even after a thorough cleaning. Many cats remain contagious for years, even though they may not show signs of disease. Healthy (i.e., asymptomatic), contagious cats are known as latent carriers.Calicivirus is very common in kittens, multicat households, and pet adoption shelters. Outbreaks can occur in overcrowded, poorly ventilated, or unsanitary conditions; and where the cats are poorly fed, or stressed, either physically (e.g., extreme temperatures) or psychologically (e.g., introduction of a new cat).

Calicivirus Signs and Symptoms

Calicivirus affects the upper respiratory system, the eyes, the musculoskeletal system, and the gastrointestinal tract. Common symptoms include the following:

Calicivirus infection usually develops suddenly. Most infected cats appear healthy and alert; they may have ulcers and no other symptoms (i.e., no fever or pain). Some cats may have mild secondary bacterial infections that are similar to those associated with FHV.

FCV Diagnosis

Calicivirus is usually diagnosed on the basis of clinical symptoms and the cat's medical history (i.e., the cat's vaccination status and past exposure). Blood tests usually are not informative. Other laboratory tests may be conducted to isolate the virus and confirm the diagnosis. These diagnostic tests include the following:

• Immunofluorescent assays of lung tissue—special proteins labeled with a fluorescent chemical to detect the presence of FCV antigens, proteins the immune system manufactures to fight the virus
• Oropharyngeal (throat) cultures
• Serum testing—to identify paired serum samples, a rise in titer over the course of 2 weeks is considered a positive diagnosis
• X-ray—to detect pneumonia

Differential Diagnosis
Clinical symptoms of FCV are similar to those of other feline upper respiratory infections, but cats with calicivirus are more likely to have ulcers in their mouth or on their paws.

Cats with rhinotracheitis virus sneeze more, have more eye discharge and inflammation, and are more likely to have pneumonia. Cats with feline chlamydiosis have chronic conjunctivitis (discharge, pain, and swelling of the eye caused by inflammation of the membrane lining the eyelid).

Calicivirus Treatment

Except in cases of severe pneumonia, treatment for feline calicivirus (FCV) is supportive and provided on an outpatient basis.

Make sure the cat eats and drinks enough. Offer foods that smell and taste good to them. If the cat has ulcers in the mouth, give soft foods. Keep the cat's eyes and nose clean and clear of discharge. Make sure the room your cat is staying in is warm, well ventilated, and well lighted.

Pneumonia should be closely monitored for the sudden development of labored, difficult breathing (dyspnea), which may require oxygen therapy. Oxygen therapy is the administration of oxygen through a facemask.

It may be helpful to use a humidifier, or put the cat in a bathroom while the hot shower is running. This helps break up the mucus in the upper airway.

Medications
Antiviral medications haven't proven beneficial for cats with calicivirus. To treat secondary infections and arthritic pain, the following medications may be prescribed:

• Antibiotic eye ointments to treat secondary bacterial infections in the eye that can cause conjunctivitis
• Oral antibiotics to prevent or treat secondary bacterial infections
• Pain medication for arthritis
• Vaccination to prevent the progression of the disease

FCV Prognosis

Clinical symptoms of calicivirus usually appear 3 to 4 days after infection. Once the cat's immune system starts producing antibodies to the virus, usually about a week after infection, recovery is quick. Unless the cat develops severe pneumonia, the prognosis is excellent. Even after the cat recovers and the symptoms disappear, FCV infection tends to persist, and the cat may be contagious for years.

FCV Prevention

Veterinarians recommend that all cats be vaccinated against calicivirus when they are vaccinated against FHV-1. Routine vaccination doesn't necessarily prevent infection, but it can prevent the development of severe disease. Kittens should be vaccinated at 8 to 10 weeks of age, then 3 to 4 weeks later. Cats should receive boosters every 1 to 3 years. Keep the cat indoors and away from other cats to prevent spreading the virus. Use a 1:32 dilution of household bleach to clean contaminated areas to prevent re-infecting the sick cat or infecting other cats with the virus.