Feline upper respiratory tract infections 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. Upper respiratory tract infections affect the upper airways (trachea and bronchi), which also include the throat, mouth, nose, sinuses, and in some case the eyes.
Causes of Respiratory Infections in Cats
The vast majority of feline upper respiratory tract 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). There are several strains of these viruses, and vaccinations are available which target the most prevalent viral strains. Rarely, other microorganisms are involved, including Bordetella bronchiseptica, Chlamydophila felis, feline reovirus or various mycoplasmas.
The feline herpesvirus and calicivirus do not live long in the environment. They 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 virus 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 causative viral organisms and shed them continuously, even though they no longer show overt signs of illness. Fortunately, vaccines are available to prevent, or at least to minimize, the symptoms of feline upper respiratory tract infections.
Prevention of Feline Upper Respiratory Tract Infections
It can be difficult and time-consuming to identify and isolate cats that are asymptomatic carriers of an infectious upper respiratory virus. Introduction of any new cat into a multi-cat household or commercial cattery presents a potential source of infection. New cats should be isolated from existing cats for at least two weeks. If signs of respiratory disease are observed, the cats should be taken to a 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 upper respiratory infections caused by herpesvirus or calicivirus is to prevent 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 with an unknown vaccination history 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. Moreover, vaccination will not eliminate the chronic carrier state in a cat, once it is established.
A dilute bleach solution (1:32 ratio of bleach to water) can be used to successfully disinfect the physical environment of cats infected with viral and/or bacterial upper respiratory tract infections. Good hygiene is a very important part of preventing feline respiratory infections. To prevent the spread of feline upper respiratory infection in multi-cat households, pet owners should also be sure to wash their hands with a regular disinfectant after they come into contact with their infected cat. Pet owners should also be aware that clothes and shoes can carry upper respiratory infection viruses for a short time.
Once a cat develops an upper respiratory tract infection, it can take days to weeks for clinical signs to appear. Most cats recover without treatment. In some cases, however, they will need supportive and medical care, especially if their symptoms are severe or if they develop secondary bacterial infections. Even after a cat recovers from an upper respiratory tract infection, it 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, and they may develop signs of respiratory disease during times of stress or suppression of their immune system.
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 cats. Fortunately, the viruses that cause feline upper respiratory tract infections do not infect people, and those that infect people do not infect cats.