Feline upper respiratory infection refers to infections in the area of the nose, throat and sinus areas. It is caused by two major viruses: Feline Herpesvirus-1 (FHV) and Feline Calicivirus (FCV). Feline Chlamydia, a bacterial agent, also results in upper respiratory symptoms. Distinguishing among these three can be difficult, so it is not usually done.
Feline upper respiratory infection is very contagious. Cats at most risk include young kittens, unvaccinated cats, elderly cats and cats that are kept in close quarters with other cats such as shelters, catteries and even multi-cat households
The viruses and bacteria involved in upper respiratory infections do not live very long outside of the infected cat. The disease is transmitted by a variety of methods: Direct contact with an ill cat.
Contact with the virus through sneezing (sneezing can propel the virus or bacteria up to 4 feet away).
Contact with the virus on human clothing, food bowls or hands. Large amounts of the virus are present in the saliva, tears and nasal discharges.
Contact with a cat that is a carrier of the virus. Most common is a nursing carrier queen transmitting the infection to her kittens around the time of weaning.