Calicivirus in Cats

Calicivirus in Cats

Feline calicivirus is one of many upper respiratory infections your cat or kitten may likely experience. Upper respiratory infections are the most common infectious diseases in cats and are easily spread in multi-cat environments. While they rarely cause death in adult cats, they often cause serious illness and death in young kittens. This disease cannot be transmitted from cats to humans.

Signs & Symptoms of Feline Calicivirus


  • Discharge from eyes, nose, or mouth
  • Labored breathing
  • Fever
  • Ulcers in the mouth
  • Limping
  • Lethargy
  • Anorexia

Causes of Feline Calicivirus

The majority of feline upper respiratory infections are caused by one of two viruses, herpesvirus or calicivirus. Cats may be infected with one or both of these viruses, as well as other bacterial and secondary infections, causing a "feline respiratory disease complex."

Calicivirus is typically transmitted by direct contact with infected eye, mouth, or nose discharge. Infected dishes, carriers, bedding, litter boxes, and human hands in multi-cat environments such as kennels and shelters may also be a route of infection.

This disease typically lasts one to two weeks, but cats generally become lifetime chronic carriers that shed the virus and display mild symptoms under stress.

A new form of the feline calicivirus known as virulent systemic feline calicivirus (VS-FCV) has been recognized to cause particularly severe systemic symptoms. This virus can be spread in more ways and more readily than the chronic or acute form of calicivirus. It causes significant organ damage, high fever, swelling of the face and limbs, and ulceration and hair loss on the ears, face, and feet, along with other respiratory signs. The severity of this virulent systemic form is thought to be caused by a secondary immune response. Fatality from VS-FCV is higher in adults than in kittens.


Diagnosis of Feline Calicivirus

Diagnosis always begins with a complete history and a physical exam. Your veterinarian will be most likely to recommend some variation of the following:

  • Physical Exam/History - Your veterinarian may diagnose this disease based on the signs and symptoms your cat is displaying. It may be more economical to perform in-house tests for diseases with similar symptoms to rule them out instead of sending samples to a lab.
  • Immunofluorescence - This is a technique used to illuminate either viruses or their antibodies in a tissue or culture using a fluorescent dye. Proteins labeled with a chemical specific to this disease will be used to detect the antibodies. They will appear under a microscope as a bright green spot on the slide.
  • Qualitative PCR Test - This "polymerase chain reaction" test is a very specific and sensitive DNA test that can be used to look for an agent in a cat’s DNA. Your veterinarian will obtain a swab of your cat’s throat and send it to a lab to test for the virus. This test may also be used to see if your cat has the chronic form of calicivirus and is shedding the virus after the symptoms have gone away.
  • Radiographs - This may show inflammation or infection in the lungs of your cat.

Treatment for Feline Calicivirus

If your veterinarian suspects upper respiratory infection caused by a calicivirus, they will likely do the following:

  • Isolate your cat in a cage with appropriate humidity and oxygen to ease breathing.
  • Encourage food and water intake to prevent dehydration and promote a strong cat with a healthy immune system.
  • Treat signs of dehydration with subcutaneous or intravenous fluids.
  • Antibiotics may be used in moderate to severe upper respiratory infections to treat or prevent primary or secondary bacterial infections.
  • Nasal passages may be cleared with nose drops put into alternating nostrils once a day for no more than five days.
  • Treat ulcers and lesions in the mouth with appropriate medication.
  • Limping from arthritis may be treated with corticosteroids or azathioprine.

Prevention of Feline Calicivirus

Calicivirus may be prevented by:

  • Keeping your cats up-to-date on all of their vaccines - a combination live vaccine for panleukopenia, rhinotracheitis, calicivirus, and other viruses is available, though like all vaccines may not be 100% effective. For it to be effective, it is recommended that cat owners adhere to a strict vaccine schedule.
  • Admit only vaccinated cats into your multi-cat household and use caution when introducing new cats.
  • Separate infected cats and unvaccinated kittens and prevent contamination of others by disinfecting hands, bowls, bedding, carriers, etc. with a bleach solution. Household disinfectants are not effective against the calicivirus
  • Use caution and vaccinate females intended for breeding.
  • Maintain a stress-free environment to prevent shedding of virus in chronically infected cats.