Respiratory infections are among the most common of feline diseases.  Cats with upper respiratory infections typically show "flu-like" signs with sneezing, discharge from the eyes and nose, coughing, fever and loss of appetite.  Young kittens, and cats that have never been vaccinated, are the most susceptible.  While several viruses and bacteria may be involved, current research indicates that up to 90% of felines upper respiratory disease is caused by either feline calicivirus or feline herpesvirus-1, also known as the rhinotracheitis virus. 

In general, infections with rhinotracheitis virus or calicivirus produce similar disease with clinical signs such as discharge from the eyes or nose, ulcers on the tongue and gums, fever, and general loss of appetite and activity.  Illness usually lasts for 5-7 days and most cats make an uneventful recovery.  Some cats may, however, develop chronic (long-lasting) disease which resembles a severe, untreatable "cold."  Young kittens may be so severely affected that they die from the infection.  In most cases, it is not important to determine which virus is causing the desease because treatment is not directed at the particular virus but rather at supporting the cat until it recovers.

Up to 80% of cats that recover from feline rhinotracheitis virus or calicivirus infections, although no longer sick, continue to carry the viruses.  Shedding of the rhinotracheitis virus may be intermittent and is often associated with stress or use of steriods, whereas cats tend to shed calicivirus continuously for months to years.