Several different viruses can cause an upper respiratory infection (URI). Two in particular, the feline rhinotracheitis virus (also called feline herpesvirus) and the feline calicivirus, cause serious illness resulting in anorexia, high fever, and ulcers on the tongue and cornea. Other viruses cause mild sneezing for a few days, but rarely indicate a serious condition.

As a rule, the uncomplicated forms of these viral infections are no more severe than a mild cold in a human. However, even mild infections can become life-threatening if secondary bacterial infections develop in the nose, oral cavity (mouth), or eyes. When this occurs, loss of appetite represents the single most serious complication. With time, the anorectic cat may become malnourished and dehydrated. In some cases, death can occur.

Contributing Factors

In most cases, viral infections run their course and the cat makes a full recovery. However, when secondary bacterial infections develop, the prognosis is less certain. Concurrent infections with the immuno-suppressive viruses feline leukemia and feline immunodeficiency can also cause complications.

Prevalence

The rhinotracheitis (herpes) virus is by far the most prevalent upper respiratory virus. Some prevalence studies have found that 80-90% of all cats have been infected with this virus at some time.

Clinical Signs

Sneezing and ocular (eye) discharge are the most common signs of an URI. Initially, the nasal and ocular draining will be watery and clear. If secondary infection with bacteria develops, the fluid becomes thick and green or yellow in color. Depending upon which virus is involved, the conjunctiva (membranes lining the eyelid) and/or cornea (clear surface layer of the eyeball) may become inflamed or ulcerated. Also, ulcers within the oral cavity and on the surface of the nose may occur in some cases. Generally, the uncomplicated case will resolve in 4-21 days.

If the viral infection invades the sinuses, the delicate lacy bones called "turbinates" may be permanently damaged. Even after the viral infection has resolved, the damage may be irreversible. Frequently, secondary bacterial infections develop in the sinuses and become difficult or impossible to eradicate. This is called chronic sinusitis.

Causes/Transmission

Respiratory viruses are spread between cats by sneezing. When an infected cat sneezes, small droplets of nasal secretions are aerosolized. They infect other cats when they come in contact with oral, nasal, and ocular membranes.

Prevention

If a cat has not become infected with the rhinotracheitis virus or calicivirus, vaccination is usually successful in preventing infection. For cats that are already carriers of these viruses, it is still important to vaccinate. If a carrier cat should reactivate the virus and begin shedding, periodic vaccination provides the immune system with a "reminder" that triggers the production of antibodies to fight the infection. Thus, the cat may still develop an URI, but the the recovery will be faster and consequences less severe. Even indoor-only cats should be vaccinated, since most cats are already carriers of the viruses and need a periodic boost in immunity.

Prognosis

The prognosis is generally excellent if the cat continues to eat, secondary bacterial infections are managed aggressively, and no concurrent medical conditions exist. Infection with the immuno-suppressive viruses renders the cat less likely to recover, although it is not impossible. Long term problems can develop when the eyes or sinuses are involved.

Transmission to Humans

These viral respiratory infections pose no health risk to humans. Although URIs have been likened to the common cold, these viruses are not transmittable to other species.