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.
Cats, and especially kittens, are prone to developing respiratory disease. Respiratory diseases often present with the same clinical signs, despite their many different causes. While there are many different types of respiratory diseases in cats, most of them are grouped under the heading of "feline upper respiratory disease complex." Due the similarity of clinical signs and the difficulty in diagnosing the precise cause of the condition, feline upper respiratory disease complex is a name which is used to identify classic feline respiratory disease symptoms.
Types of Respiratory Disease in Cats
The most common respiratory diseases in cats are viral. The feline herpesvirus (FHV) and feline calicivirus are the most common causes of feline upper respiratory tract infection. Other viruses can be primarily or secondarily involved.
Bacterial infections are also among the most common causes of feline upper respiratory tract disease. Bordetella bronchiseptica and Chlamydophila felis are the most common bacterial culprits.
Respiratory disease in cats can also be caused by fungal infections, particularly by inhalation of the soil-borne fungus, Coccidiodes immitis. This is uncommon in domestic cats.
In some cases, allergies can cause or contribute to feline asthma and respiratory disease. Cats can be allergic to a number of environmental and other allergens, including chemicals, ingredients in food, plants, pollen or a number of other things.
Feline respiratory infections are diagnosed most commonly based upon the cat's history and clinical signs. Bacterial and tissue cultures may also be used to diagnose the specific cause of the respiratory infection.
Diagnosing Respiratory Infections in Cats
Cats with respiratory infections display classic clinical signs, regardless of the underlying cause of the disorder. Most veterinarians are well-acquainted with these symptoms, and they are often able to diagnose a respiratory tract infection in cats, or kittens, based only upon a history and physical examination. To rule out other possible causes of the symptoms, many veterinarians recommend a complete blood count and serum chemistry panel, a urinalysis, and a FeLV and FIV test. Thoracic radiographs (x-rays) and possibly a CT scan are also available to help assess, identify or rule-out particular causes of feline respiratory disease.
The cat's history plays an extremely important role in respiratory infection diagnosis. Cats that live in overcrowded conditions (such as in shelters or catteries) are at an especially high risk for developing respiratory tract infections. Unvaccinated cats, especially those that live outdoors, are also at risk for infection. Frequently, owners that adopt a cat, or kitten, from a shelter or pet store may notice that their pet shows signs of respiratory disease shortly after it come home.
Specific identification of the causative agent is normally not necessary in cats with respiratory infections. The signs, and treatment, usually are the same regardless of the underlying cause. It may be worthwhile to identify the precise causative organism in breeding animals. Tissue and bacterial cultures can be used to identify which viruses and/or bacteria are causing the infection. However, many veterinarians do not feel that this information is necessary for the cat's successful recovery and treatment.
Treatment of upper respiratory tract infections in cats typically involves supportive care, with the goal being control of secondary bacterial infections and keeping the cat comfortable and well-fed.
Treating Respiratory Infections in Cats
Most affected cats will be treated at home, which is preferable to in-hospital care, at least from the cat's perspective. At-home supportive care for cats with respiratory disease is very similar to how we care for people with "the flu." The cat should be in a calm, warm and quiet environment, and a vaporizer in the room is recommended to keep the cat's nasal passages moist. Placing the cat in a steamy bathroom for 10 to 15 minutes several times daily is also helpful. Cats often have runny noses and "gooey" eyes with respiratory illness. Owners should gently cleanse the cat's eyes and nose with warm water on a tissue or cotton ball.
Cats with respiratory infections often have difficulty eating because they are unable to smell their food. Some pet owners may need to force-feed their cats, or give their cats a very high-calorie nutritional paste. If a cat becomes dehydrated during its illness, subcutaneous or intravenous fluids may need to be administered by the owner or by a veterinarian.
Antibiotics are available to treat bacterial causes of upper respiratory tract infections in cats. Topical ointments and artificial tears are also available for cats whose eyes are affected. Topical and systemic antiviral drugs may also be recommended. Appetite stimulants may be necessary for cats that are anorexic. Cats should be fed a very pungent and highly palatable diet to overcome their decreased sense of smell. Nasal decongestant drops are also available.
The amino acid, L-lysine, can be helpful to decrease the severity of respiratory outbreaks in cats that are positive for feline herpesvirus.