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.
Regardless of the inciting cause, the symptoms of upper respiratory tract infections in cats are remarkably similar and can range from mild to very severe. The feline calicivirus tends to be associated with mild upper respiratory illness, while feline herpesviral infections are usually more servere.
Symptoms of Upper Respiratory Infection in Cats
There normally are two distinct phases in the course of feline upper respiratory tract illness: an acute phase, followed by a chronic phase. The symptoms, and their severity, can vary greatly, especially during the acute phase. Observable signs typically appear within two to three weeks after exposure to the infectious organism and reach peak severity about ten days later.
They typically include:
Sneezing (repeated bouts; severe)
Eye redness, irritation and inflammation (conjunctivitis)
Serous ocular discharge (watery secretions from the eyes)
Serous nasal discharge (watery secretions from the nostrils)
Loss of appetite (inappetence; anorexia)
By the fourth or fifth day of acute illness, cats typically develop some combination of the following symptoms:
Mucoid ocular discharge (slimy, goopy, thick secretion from the eyes)
Mucoid nasal discharge (slimy, goopy, thick secretion from the nostrils)
Purulent ocular discharge (secretion from the eyes containing pus)
Purulent nasal discharge (secretion from the nostrils containing pus)
Open-mouth breathing (from plugged nasal passages)
Difficulty breathing; respiratory difficulty; shortness of breath (dyspnea)
Audible wheezing; increased airway sounds
Severe eye redness/conjunctival swelling and irritation
Oral ulceration and erosion (stomatitis; especially of the gums, lips, soft palate and tongue; often starting as blisters [vesicles] that rise and then rupture)
Unwillingness to eat (due to pain; not from loss of appetite)
Unwillingness to drink (due to pain; not from loss of appetite)
Weight loss (sometimes to the point of emaciation)
Excess salivation/drooling (pytalism)
Facial and limb swelling/edema (uncommon)
The chronic phase of infectious upper respiratory disease in cats is called the "carrier state." Most but not all cats infected with feline herpesvirus and/or feline calicivirus become chronic carriers of the viral organisms after they recover from clinical signs of illness. When the cat's immune system is weakened – such as by excitement, illness, pregnancy, lactation, anesthesia, surgery, veterinary visits, car rides, introduction of new pets, changes in household personnel or routines or other causes of stress – the viral organisms can rapidly reproduce and be shed in oral and nasal secretions. The affected cat may or may not develop mild signs of respiratory illness, but they are ongoing sources of infection to other cats.
Cats at Increased Risk
Cats housed in crowded, unsanitary conditions have a heightened chance of developing upper respiratory tract infections. Free-roaming cats also have an increased risk of contracting an upper respiratory tract infection, as do very young kittens and unvaccinated adults.
Feline upper respiratory tract infections are most commonly diagnosed based upon the cat's history and observable symptoms. Bacterial and viral blood and tissue cultures may be used to identify the specific cause of an upper respiratory infection.
How to Diagnose Upper Respiratory Tract Infections in Cats
Cats with upper respiratory tract infections display classic clinical signs, regardless of the underlying cause of the disorder. Most veterinarians are well-acquainted with these symptoms, and they often are able to diagnose a respiratory tract infection based only upon the cat's history and a thorough physical examination. To rule out other possible causes of the cat's symptoms, many veterinarians recommend taking a blood sample and performing a complete blood count and serum biochemistry panel. A urine sample and urinalysis, and blood tests for feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV), are also part of the diagnostic process. Thoracic radiographs (chest X-rays), and possibly a computed tomography (CT) scan, are also available to help assess, identify or rule-out particular causes of feline upper respiratory disease.
The cat's history plays an extremely important role in the diagnosis of respiratory tract illness. Cats that live in overcrowded conditions (sometimes seen in animal shelters or commercial catteries) have a heightened risk of developing respiratory infections. Unvaccinated cats, especially those that live outdoors and are free-roaming, also have an increased risk of developing respiratory illness. Owners who adopt a cat or kitten from a shelter or pet store frequently notice signs of respiratory disease shortly after they bring their new pet home. They should consult a veterinarian as soon as possible if this happens.
Feline herpesvirus and calicivirus can only be positively identified through specialized blood and tissue tests. These are not always readily available in time to be of much use in making treatment decisions. Fortunately, specific identification of the causative agent is normally not necessary in cats with respiratory infections. The symptoms, and the treatment, usually are the same regardless of the underlying cause, and many veterinarians do not feel that identification of the causative organism is necessary for the cat's successful recovery and treatment. It may be worthwhile to identify the precise infective organism in breeding animals. Tissue and blood cultures can be helpful in those cases.
Upper respiratory tract infections are common in companion cats. When a cat starts sneezing, coughing and draining watery or goopy secretions from its eyes, nose and/or mouth, the owner should consult a veterinarian promptly. There is no one test available for diagnosing upper respiratory infections in cats. A diagnosis is most often based upon the cat's symptoms and history. In some cases, additional tests may be performed to ensure that the cat does not have an underlying medical condition that is contributing to the clinical symptoms.
Treatment of upper respiratory tract infections in cats typically involves well-managed supportive care and possibly administration of oral medications. The goals of therapy are to control secondary bacterial infections, maintain the cat's weight and hydration and keep the cat as comfortable – for as long - as possible.
Cats with upper respiratory tract infections should be isolated from other cats for at least three to four weeks, to prevent contagion. All bowls, bedding, crates, toys and other things that an infected cat has come into contact with should be thoroughly and regularly washed with a 1:32 dilute solution of bleach-to-water. People who touch an infected cat should be especially attentive to good hygiene, including washing their hands with soap and warm water and changing and laundering their clothes and shoes on a regular basis.
Most affected cats can be treated at home. This is preferable to in-hospital care, at least from the cat's perspective. At-home supportive care for cats with upper respiratory infections is very similar to how we care for people with "the flu." The cat should be in a calm, warm and quiet environment that promotes rest and relaxation. A home vaporizer will improve humidification and help to keep the cat's nasal passages moist. Some authorities recommend a cool steam vaporizer rather than a warm vaporizer. Placing the cat on a dry surface in a steamy bathroom for 10 to 15 minutes several times daily is also helpful. Many owners bring their cat into the bathroom with them while they shower or bathe.
Supportive treatments for upper respiratory infections in cats also include keeping the cat in a confined, stress free and comfortable in-home environment. The cat should be in a room that has a comfortable temperature. Free access to fresh water is important, and the cat's diet should be highly palatable. The cat's eyes and nose should be routinely cleaned if the cat is experiencing eye or nose discharge. Cats with respiratory illness usually have runny noses and goopy eyes. Owners should gently cleanse their cat's eyes and nose with warm water on a soft tissue or cotton ball as frequently as necessary to remove the infectious secretions. They should dispose of those tissues or cotton balls in a place that is reliably inaccessible to other animals.
Cats with upper respiratory tract infections often have difficulty eating, because they cannot smell their food. In addition, when they develop oral ulcers, affected cats frequently refuse to eat or drink due to pain. This can cause dramatic weight loss and profound weakness. Owners should feed highly palatable foods that have a strong, pungent smell, such as canned tuna, canned mackerel or strained meat baby food. Some cats will need to be force-fed either by hand or through a tube. High-calorie nutritional paste supplements are also available and can be recommended or provided by a veterinarian. If a cat becomes dehydrated during its illness, subcutaneous or intravenous fluids can be administered by the owner or by a veterinarian. Water can also be given using a needleless syringe or eye dropper.
Broad-spectrum oral antibiotics can be used to treat bacterial causes of upper respiratory tract infections in cats. Decongestant drops may be recommended to shrink swollen nasal membranes. Topical ointments and artificial tears are available for cats whose eyes are affected. Topical or systemic antiviral drugs may also be appropriate. Appetite stimulants can help cats that are anorexic, and pain medications (analgesics) can help cats with oral sores. The amino acid, L-lysine, can be helpful to reduce the severity of respiratory infections in cats that test positive for feline herpesvirus.
Most cats with upper respiratory tract infections have a good to very good prognosis, if they receive prompt and effective treatment. Young kittens, and cats with especially virulent viral infections, have a more guarded prognosis. Infected adults rarely die from upper respiratory tract infections. Unfortunately, the death rate in very young kittens can approach fifty percent.