Feline Calicivirus Infection | Cat Flu

symptoms of cat flu

Feline Calicivirus Infection in Cats

Feline calicivirus is a highly contagious virus that is one of the major causes of common upper respiratory infections (URIs) or cat flu in cats.  The virus attacks the respiratory tract (nasal passages and lungs), the mouth (with ulceration of the tongue), the intestines and the musculoskeletal system. It is highly communicable in unvaccinated cats, and is commonly seen in multi-cat facilities, shelters, poorly ventilated households and breeding catteries.

Vaccination against the calicivirus is strongly advised. This infection can occur in cats of any age, but young kittens older than six weeks have been found to be most susceptible.

Symptoms and Types of Feline Calicivirus

The following symptoms typically present themselves suddenly:

  • Loss of appetite (anorexia)
  • Eye discharge
  • Nasal discharge
  • Development of ulcers on tongue, hard palate, tip of nose, lips or around claws
  • Pneumonia
  • Difficulty breathing after development of pneumonia
  • Arthritis (inflammation of joints)
  • Lameness
  • Painful walk
  • Fever
  • Bleeding from various sites


Cats typically acquire feline calicivirus (FCV) after coming into contact with other infected cats, such as in a cattery, boarding facility or shelter. But because FCV disinfectants are not very effective against FCV, the virus may persist in the environment, which means that cats may come into contact with it without known exposure to other cats.

Lack of vaccination or improper vaccination is thought to be an important risk factor, as well as lowered immune response due to pre-existing infections or diseases.


You will need to give your veterinarian a thorough history of your cat’s health, onset of symptoms, and possible incidents or conditions that might have led to their current illness. Your veterinarian will perform a thorough physical exam to evaluate all body systems along with the overall health of your cat.

Depending on the conclusions of the physical exam, your veterinarian may recommend further diagnostic tests. A complete blood profile will also be conducted, including a chemical blood profile, a complete blood count and a urinalysis. The results of these tests, however, are often non-specific and do not provide consistent findings for an initial diagnosis.

To obtain a specific diagnosis, a test involving identification of FCV antibodies is conducted. These antibody tests can be used to detect and measure the levels of feline calicivirus antigen and/or antibodies corresponding to the viral antigen (feline calicivirus). A more advanced test that may be used involves growing the isolated viruses under controlled conditions using a technique called cell culture.

Diagnostic imaging can be used to determine any damage to the lungs; chest X-rays may show changes in the lung tissue, including consolidation of lung tissue in cats with pneumonia.


Your cat will need to be hospitalized for intensive care and treatment if it has developed pneumonia, is experiencing severe life-threatening hemorrhages, or is not eating and drinking. Oxygen will be given if your cat is unable to breathe comfortably due to pneumonia.

While there is no specific medication that is given for viral infections of this type, broad spectrum prescription pet antibiotics are given to prevent or treat the secondary bacterial infections that are commonly seen with viral infections.

Ophthalmic antibiotics are prescribed for use in the affected eyes, and veterinary prescription pain medication can be prescribed for patients with painful walking. Some cats with calicivirus require the placement of feeding tubes until their ulcers have healed and they are willing to eat on their own.

Living and Management

Your cat requires good nursing care while recovering from the calicivirus infection. This may include cleaning the cat’s eyes and nose to prevent accumulation of secretions, applying medication and preparing special food.

Your veterinarian will recommend a cat food diet made up of highly nutritious and easily digestible foods, to be given at regular intervals so as to maintain a positive energy balance and to prevent malnutrition. If your cat is suffering from oral ulcers, it will need to be given soft foods.

Respiratory discomfort and breathing difficulties are also common, so advise your veterinarian if these develop.

Before bringing your cat home from the veterinary hospital, deep-clean all surfaces. While this may not eliminate the virus, it will reduce the amount of virus in the environment. This step is especially important if you have other cats or expect to add cats to your family.

Even though vaccinations have not eliminated this virus, an FCV vaccine is still the best preventative for your cat, and may reduce the symptoms should your cat acquire the virus. The vaccine is given as a series of boosters to kittens and then every one to three years to adults.

Despite vaccination, many cats are carriers for the virus—that is, they have the virus but do not show any symptoms.

Your cat’s overall prognosis depends on the severity of the symptoms. Cats with uncomplicated cases of pneumonia, for example, typically recover within three to four days. However, severe pneumonia may be life-threatening. Oral ulcers and arthritis symptoms, on the other hand, generally resolve without complications.


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