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Calici Virus

Signs of calicivirus in cats include:

•Nasal discharge
•Runny eyes
•Oral or nasal ulcers
•Hoarse voice

Despite the highly contagious nature of all the feline upper respiratory microorganisms, it is important to realize that most cats are at low risk for exposure. In order to get this kind of infection, a cat mustreside in the same home as an infected cat or share the same owner, toys, food bowls or litter boxes. Typically, infected cats come from the shelter, are outdoor cats, or are housed in close contact with lots of other cats, such as catteries or homes with large numbers of cats. Persian and Himalayan cats are predisposed to upper respiratory infection due to their inherent facial flattening. The average house cat who is not exposed to any rescued kittens, lives with only one or two other cats at most, and never goes outside is unlikely to become infected. Kittens are predisposed to infections due to their immature immune systems and are usually hit the hardest.

The primary infectious agents that cause feline upper respiratory infections are: herpesvirus and calicivirus, together accounting for about 90% of infections. Other agents include Chlamydophila, Mycoplasma, Bordetella, and others. It is always possible that cats or kittens may be infected with more than one infection agents.

Viruses are spread by the oronasal route, often from the saliva or mucus of an infected cat. The herpesvirus is rather fragile, surviving only 18 hours outside its host; calicivirus is considerably more hardy, lasting up to 10 days. Bleach will readily inactivate either virus but calicivirus is able to withstand unbleached laundry detergents.

To some extent, the combinations of signs and course of infection is determined by which of the numerous infectious agents may responsible for a particular respiratory presentation. As previously stated, ninety percent of feline upper reinfections are caused by either feline herpes (also called the rhinotracheitis virus) or feline calicivirus. Neither of these infections is transmissible to humans or to other animals.

Most feline upper respiratory infections run a course of 7 to21 days regardless of treatment, but it is important to realize that these infections are permanent and that herpesvirus infections can be recurring (a property of all types of herpes infections in many species). In kittens, herpes infections are known to sometimes drag on. Stresses such as surgery (such as neutering/spaying), boarding, or introduction of a new feline companion commonly induce a fresh herpes upper respiratory episode about a week following the stressful event and the active virus sheds for another few weeks. These episodes may recur for the life of the cat, although as the cat matures, signs become less and less severe and in many cases become subclinical and unnoticed by the owner. Cats infected with calicivirus may shed virus continuously, not just in times of stress, and may do so for life, although about 50% of infected cats seem to stop shedding virus at some point.

A cat with herpes or is contagious to other cats for a couple of weeks following a stressful event. Cats infected with calicivirus are contagious for several months after infection but do not seem to have at least clinically evident recurrences the same way cats with herpes do.

Signs for concern that veterinary care may be indicated include:

•Loss of appetite
•Open mouth breathing (this is never normal for a cat!)
•Extreme depression (which usually means high fever)

An upper resopiratory infection for a cat is usually just a nuisance like a cold usually is for a person. Sometimes, however, an upper respiratory infection can be serious. If a cat is sick enough to stop eating or drinking, hospitalization may even be needed to support him or her through the severe phase of the infection. A cat can actually become dehydrated from the fluid lost in nasal discharge, especially if compounded by refusal to drink water. Painful ulcers can form on the eyes, nose or in the mouth. In young kittens, pneumonia may result from what started as an upper respiratory infection.

If you think your cat or kitten is significantly uncomfortable with a cold, you should seek veterinary care ASAP.

Since 90% of cases are viral in origin and we have no antibiotics against viruses, it would seem odd that most feline upper respiratory infections are treated with anti-bacterial medications. The reason for this is that it is common for these viral infections to become complicated by secondary bacterial invaders. The antibiotics act on these.

What’s more, the next most common infectious agents after herpes and calicivirus are Chlamydophila felis (formerly known as Chlamydia psittaci) and Bordetella bronchiseptica, both organisms that are sensitive to third generation cephalosporins. For this reason, when antibiotics are selected, third generation cephalosporins and their relatives are frequently chosen. Oral medications and/or eye ointments are commonly prescribed.

For congestion, some human nose drop products can be used for relief. Consult your veterinarian before attempting any sort of home treatment. Other therapies frequently employed include low doses of interferon-alpha to stimulate the immune system and oral lysine supplementation, which interferes with herpesvirus reproduction.

For younger infected kittens, often the most significant factor in their ability to avert infection is maturation and gaining a more effective immune system with growth.

Occasionally infections can lead to more chronic symptoms, such as gingivitis (gum inflammation), conjunctivitis, or nasal congestion.

A commercial vaccine against feline calicivirus is available, and included in most kitten and adult cat core vaccine protocols.


Roger L. Welton, DVM
Founder and Chief Editor,
President, Maybeck Animal Hospital


Article updated 9/12/2012



13 thoughts on “Calici Virus

  1. Lesha says:

    I recently rescued moms w kittens and am having an outbreak of this calicivirus!!! I have no idea how to contain it since I have limited options for separation. Besides from what I’m reading it’s Airborne so can be transferred through vents

    New strains apparently can begin but I’ve heard u must bring a new cat in in order for this to occur and then I’ve heard that is incorrect! It can happen w same kittens – no new introductions required

    It has contaminated my own personal cat now and potentially another foster kitten who have never been in any sort of contact w any of these

    I have no idea what to do

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