Upper respiratory tract infections in cats typically are caused by a combination of highly contagious viral and bacterial pathogens. Also called feline viral respiratory disease complex, feline influenza or simply “cat flu,” these infections are among the most common medical disorders faced by owners of domestic cats. They can become quite serious, even to the point of fatality.
Causes of Respiratory Infections in Cats
The vast majority of feline upper respiratory infections are caused with roughly equal frequency by two groups of viruses: the feline herpesvirus (which causes feline viral rhinotracheitis) and the feline calicivirus (which causes feline caliciviral disease). Rarely, other microorganisms are involved, including Bordetella bronchiseptica, Chlamydophila felis, feline reovirus or various mycoplasmas. The feline herpesvirus and calicivirus are shed from the eyes, nose and mouth of infected animals and are highly contagious between cats by direct contact with infected ocular, nasal or oral secretions. Sneezing is one of the most common routes of infection.
Cats also can become infected by touching contaminated food bowls, water bowls, litter boxes, shoes or clothing. People can transfer the viruses between cats on their hands. These microorganisms can survive in the secretions of infected cats for up to one month, depending upon the surrounding environmental conditions. Kittens, outdoor cats and cats living in crowded or unsanitary conditions are at an increased risk of contracting respiratory infections. Once the symptoms of acute infection have resolved, most cats become chronic carriers of the viral organisms and shed them continuously, even though they no longer show overt clinical signs of illness. Fortunately, vaccines are available to prevent, or at least minimize, the symptoms of respiratory infections.
Prevention of Feline Respiratory Tract Infections
It can be quite difficult and time-consuming to identify and isolate virus-positive cats from other cats in the household or in a breeding cattery. Introduction of any new cat presents a potential source of infection. New cats should be isolated from existing household cats for at least two weeks. If signs of respiratory disease are observed, they should be taken to the veterinarian and should not be allowed to come into contact with virus-free animals. Good hygiene, ventilation and living space are important as well.
The best way to prevent feline herpesvirus and calicivirus infection is to avoid exposure to the infectious organisms. Owners should be discouraged from allowing their cats to roam freely outdoors. The next best preventative route is to vaccinate cats against these organisms on a regular basis. Vaccines against herpesvirus and calicivirus typically are combined with a vaccine against feline panleukopenia and are given at least twice as part of a normal kitten vaccine protocol, with the last vaccination at or after 16 weeks of age. Adults can also be given a series of two vaccinations, three to four weeks apart. All cats should have a booster approximately one year after their last initial vaccination, and then another three years later. These vaccines are available in injectable-killed, injectable-modified live and modified live intranasal forms. They offer moderate to good protection against symptomatic disease. Unfortunately, no vaccine is effective 100% of the time. Vaccination will not eliminate the chronic carrier state once it is established.
A dilute bleach solution (1:32 ratio of bleach to water) can successfully disinfect the physical environment of cats infected with viral and/or bacterial upper respiratory tract infections.
Once a cat develops a viral upper respiratory tract infection, it can take days to weeks for clinical signs to appear. Most cats recover on their own. In some cases, however, they will need supportive care and medical treatment, especially if their symptoms are severe or if they develop secondary bacterial infections. Even after they recover from a respiratory tract infection, cats can still carry and shed the virus for months to years. This is referred to as a chronic carrier state. Cats that become infected and then clear the virus are not immune to reinfection.
The highly contagious nature of viral and bacterial respiratory infections in cats cannot be over-emphasized. Many owners have unknowingly brought this infection home to their cats on clothing, shoes or hands, after coming into contact with an infected cat. People who work with or otherwise have contact with potentially infected cats should always wash their hands and change their clothes before they interact with their own cat. Fortunately, the viruses that cause feline upper respiratory tract infections do not infect humans, and those that infect people do not infect cats.