Calicivirus Threat

All cats should be vaccinated against this dangerous disease agent. Kittens are especially at risk.


If your typically healthy, playful cat suddenly becomes lethargic and suffers frequent bouts of sneezing and sniffling, there’s a good chance that she’s come down with what might be called “a bad cold.” If that’s the case, it’s quite possible that the cause of her discomfort is infection with the feline calicivirus (FCV), which is diagnosed in an estimated 40 to 50 percent of cats with upper respiratory illness.

Most other cases of such disorders in cats are caused by infection with a different virus — the herpesvirus — or with a bacterial agent or other microorganism. Feline herpesvirus produces the most severe symptoms and is more likely to result in eye ulcers.

What to look for
Although the adverse signs of FCV infection will typically diminish in severity within a few days, veterinary consultation should still be pursued. The first signs of infection tend to be mild and transitory, with signs primarily involving the respiratory system. But the persistent presence of FCV in a cat’s system can progress to cause a variety of other systemic problems, such as open sores within an animal’s oral cavity, inflammation of tissues in its eyes (conjunctivitis) and even lameness.

FCV, like all other viruses, is not a living organism. Rather, it may be described in general terms as a complex submicroscopic structure consisting of genetic material that is encased in a protein shell. Also like other viruses, FCV has an irrepressible inclination to reproduce itself rapidly and without limit in the body of an animal that it has infected.

And once the virus has entered the host’s body, its fundamental goal is to make as many copies of itself as rapidly as possible. It is the gradually overwhelming proliferation of the viral particles that produces the clinical signs signaling its presence.

How it is spread
In order to be infected with FCV, says Linda Ross, DVM, an associate professor of small animal medicine at Tufts, a cat has to somehow come into direct contact with the virus, which is present in an infected animal’s saliva, nasal and eye discharges, and possibly its feces and urine. FCV can be spread through the air by inhalation, she points out. If, for instance, an infected cat sneezes, viral particles can be sprayed several yards through the air and inhaled by an uninfected cat. Also, says Dr. Ross, “If an infected cat sneezes on your hand and then you pet another cat, that cat is likely to become infected when it grooms itself.”

And because the virus is frequently transmitted through licking and grooming, a kitten can become infected while being coddled by her FCV-infected mother. Moreover, FCV particles can survive for a week or more at room temperature in the external environment; they can therefore persist and pose an infectious threat on the surfaces of such objects as litter boxes, food dishes, and even an owner’s clothing. “The spread of this virus can be an especially big problem in crowded shelters,” Dr. Ross points out, “where infected and uninfected cats are housed in close contact.”

Most initial indications that a cat has been infected with the virus involve the upper respiratory system, she notes, with initial infection manifesting itself — typically in the form of persistent sneezing and occasional coughing — within a week or so of exposure to the virus.

In the best case, says Dr. Ross, the signs of infection will be mild, and an FCV-infected cat will not even run a slight fever. “It’s like the common cold in humans,’ she points out. “The infection will run its course and everything will clear up — maybe within only three or four days.

But in other cases, the cat will run a high fever and oral ulcerations will start to appear. Because of these sores, the animal’s mouth may hurt when it tries to eat or drink, so it can become dehydrated and lose weight. If this goes on for two weeks or so, the cat may require intravenous fluids and, in some cases, the veterinarian may have to install a feeding tube in the animal’s esophagus to provide nutrition.

Kittens are most vulnerable
In general, Dr. Ross says, kittens are especially vulnerable to infection with the most common strain of FCV, while adult cats are more likely to be affected by a different and more dangerous type of this virus, called virulent systemic feline calicivirus (VS-FCV).

Also at increased risk are cats whose immune systems have been weakened as the result of infection with another viral disease, such as that caused by infection with the feline immunodeficiency virus (FIV) or feline leukemia virus (FeLV).

Best protection
The best protection against severe FCV infection, she points out, is vaccination. “The vaccine that is currently used is excellent,” says Dr. Ross, “and if cats are appropriately vaccinated, they won’t get seriously infected.” The American Association of Feline Practitioners and other veterinary organizations currently recommend that kittens should be vaccinated when they are eight to 10 weeks of age, and again three or four weeks later. In addition, they should receive subsequent booster shots every one to three years thereafter.

A common concern among cat owners is whether their cats’ illness is contagious to them. The symptoms are indeed similar to the human flu, but FCV cannot transfer from cat to human (or vice versa).


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