Introduction
Upper respiratory infections in cats are mainly caused by two viruses: the feline viral rhinotracheitis(or feline herpes virus) and the feline calicivirus. While these viruses are highly contagious, only cats in certain conditions seem to be more at risk for developing these types of infections.
Causes of URI in Cats
Environmental causes
One of the leading causes of upper respiratory infections in cats is living conditions which are overcrowded and/or unsanitary. Upper respiratory infections tend to spread rapidly through catteries, shelters, pet stores, and in households with multiple cats. The viruses which cause upper respiratory infections can quickly spread through contaminated airborne particles, but this is not the only reason why cats in overcrowded conditions seem to be particularly prone to developing these infections. Cats in overcrowded conditions tend to have high stress levels, and these high stress levels can lower their immune system’s ability to fight off a virus.
Outdoor, unvaccinated, cats may also develop upper respiratory infections. Outdoor cats may come into contact with other cats which carry upper respiratory infections. As the virus is carried through the air, any contact with another cat which involves hissing and spitting can be enough to spread the virus.
Immune related
Cats with compromised immune systems are also at a risk for developing upper respiratory infections. These cats may be elderly, or they may have underlying medical conditions such as diabetes, feline leukemia, or feline immunodeficiency virus. Young kittens with undeveloped immune systems are also highly susceptible to developing severe upper respiratory infections if they come into contact with the causative viruses.
In some cases, a pregnant cat may carry the feline viral rhinotracheitis virus without showing any symptoms. However once the cat has her kittens and begins nursing, her immune system can be lowered and she can again develop an active infection. If this occurs, then her kittens may become infected with the virus.