Calicivirus

 
A 3-dimensional representation of the Feline Calicivirus
http://locus.jouy.inra.fr/virim/iL004e.gif

Feline Calicivirus is found globally and can infect any felid, but has not been demonstrated to infect any other animal species.  This disease is rare in cats older than 1 year of age, but those infected and recovered may shed the virus for months to years.

Cats may be infected with FCV via the nose, mouth or the eye via aerosol transmission or fomites.  Oral ulcerations are the most common lesion.  They usually arise as vesicles on the margin of the tongue and rupture causing tissue death and subsequent ulcers.  Lesions in the lung are less common and typically originate as mild inflammation in the lung, which may eventually develop into an interstitial pneumonia.  In rare cases the virus may spread to the joints causing lameness and swelling.

In very cases, FCV can develop into Virulent Systemic Disease which is manifested by lesions forming in many areas of the body, edema, pneumonia and multiple organ damage.  It is believed that this severe FCV Virulent Systemic Disease is caused by mutations to the virus occurring within the individual infected cat, making the virus much more aggressive.

 
The vesicles and ulcers on the tongue of a cat infected with Feline Calicivirus.
http://www.cvm.okstate.edu/instruction/mm_curr/InfectiousDiseases/RNAviruses/Caliciviridae/FCV_Mouth_Clinical_1.jpg

The major clinical signs associated with this virus are conjunctivitis, upper respiratory signs including coughing, difficulty breathing and nasal discharge.  In addition vesiculation and ulceration of the oral epithelium are very common.  Animals infected with FCV may also display generalized signs of infection including fever, lethargy and anorexia.  Lameness may be observed in cats in which the virus has infected the joints.

Feline Calicivirus causes disease in many cats, however it rarely causes death in adult cats.  In young kittens, the mortality rate may be as high as 30%.  Animals that recover form calicivirus have a prolonged carrier state in which the recovered cat will shed virus for months to years from their mouth and upper respiratory tract.