Virulent Systemic Feline Calicivirus: FCV’s Bigger, Badder Brother

Jessica Yankus

Feline calicivirus (FCV) is a common virus of cats (domestic and wild) that produces a variety of clinical signs including fever, ocular and nasal discharge, conjunctivitis, limping, and most typically oral ulceration. FCV is a small, non-enveloped, single stranded RNA Vesivirus of the family Caliciviridae. It is a highly contagious virus which is transmissible through the secretions of infected cats. This particular virus is difficult to eradicate because of its highly stable, non-enveloped nature and the fact that recovered cats continue to harbor the virus (in their tonsils and oropharynx) and shed it persistently. Being an RNA virus, FCV is also prone to mutation due to the lack of a ‘proof-reading’ ability of its polymerase. This results in various strains of the virus. Adult cats infected with non-virulent strains are typically non-fatal but can have approximately 30% mortality in kittens that subsequently develop pneumonia or severe upper respiratory infection.

In recent years, there have been an increase in the number of cases associated with a particularly virulent strain of FCV which, unlike the typical FCV, causes severe systemic disease. First reported in 1998, virulent systemic feline calicivirus (VS-FCV) has been associated with typical FCV ulcerations on the tongue, mouth and nose, and high fever, facial and limb edema, ulceration, crusting and focal hair loss (face, muzzle, paws, and pinnae), multiple organ involvement and damage, and death. The clinical signs of this syndrome manifest from the virus’ tropism for endothelial and epithelial cells. Typically, VS-FCV presents with high mortality and is also highly contagious and seems to more frequently infect healthy, vaccinated adult cats.

Diagnosis of this particularly virulent strain of FCV can be challenging as it is still an emerging disease. Blood chemistries performed on afflicted patients are typically non-specific and diagnosis should be made by clinical signs and ultimately real time polymerase chain reaction (RT-PCR) for viral genome sequencing to differentiate the VS-FCV strain from other FCV strains. Specific clinical signs that differentiate VS-FCV from traditional FCV is the sustained high fever. Cats with traditional FCV are typically febrile for one day and this physical exam finding may no longer be present once the patient is evaluated. Cats infected with VS-FCV will present with a high fever of prolonged duration.


                                    

Feline patient with virulent systemic feline calicivirus (VS-FCV). Clinical signs include facial edema, ulcers present on nose, ocular and nasal discharge, and skin lesions on pinna. 

                                       

A) Peripheral edema and skin lesion of the forelimb B) Ulcers on tongue

C) Alopecia and crusting of the forelimb D) Crusting of paw pads 

Typical FCV vaccines only protect against two or three cross-reactive strains of the virus. These traditional vaccines do not prevent against virulent systemic feline calicivirus. CalciVax produced by Fort Dodge Animal Health is the only vaccine that has been proven effective against VS-FCV (DVM360 Magazine, 2007). The vaccine, which gained licensure in 2007, contains one strain of VS-FCV and traditional FCV strains as well. The vaccine has reportedly proven effective against severe challenges of the vaccine strain with no vaccinated cats showing signs of VS-FCV (DVM360 Magazine, 2007). However, since FCV is prone to frequent mutation, the strain included in the vaccine may or may not be effective against all strains of VS-FCV. Vaccination for traditional strains of FCV is considered a core vaccine for all domestic cats and VS-FCV targeted vaccination is indicated for cats considered at high risk of VS-FCV.

Awareness of this highly virulent strain of FCV and its clinical signs will aid in prompt diagnosis. Ultimately, knowledge of the specific characteristics of VS-FCV will lead to better prevention and control of outbreaks of this deadly newcomer.

Citation 

Hurley, Kate F., Patricia A. Pesavento, Niels C. Pedersen, Amy M. Poland, Erin Wilson, and Janet E. Foley. "An Outbreak of Virulent Systemic Feline Calicivirus Disease." Journal of the American Veterinary Medical Association 224.2 (2004): 241-49. AVMA. Web. 30 Apr. 2013. http://avmajournals.avma.org/doi/abs/ 10.2460/javma.2004.224.241?journalCode=javma.

Klopfleisch, R., A. Meyer, and O. Kershaw. "Feline Calicivirus-associated Virulent Systemic Disease: Not Necessarily a Local Epizootic Problem." The Veterinary Record 168.22 (2011): n. pag. Veterinary Record. Web. 30 Apr. 2013. http:// veterinaryrecord.bmj.com/content/by/year.

Reynolds, Brice S., Hervé Poulet, Jean-Luc Pingret, Dominique Jas, Sylvie Brunet, Celine Lemeter, Mélanie Etievant, and Corine Boucraut-Baralon. "A Nosocomial Outbreak of Feline Calicivirus Associated Virulent Systemic Disease in France." Journal of Feline Medicine & Surgery 11.8 (2009): 633-44. SciVerse. 7 Feb. 2009. Web. 30 Apr. 2013. http://www.sciencedirect.com/science/article/pii/ S1098612X08002787.

Subbiah, E. VM 8124 Veterinary Virology Course Notes, Feline Viruses. Spring 2013; Lecture 27.

"CaliciVax Updated to Cover Virulent System Feline Calicivirus." DVM 360. N.p., 1 Feb. 2007. Web. 01 May 2013. http://veterinarynews.dvm360.com/dvm/Feline Center/CaliciVax-updated-to-cover-virulent-system-feline-/ArticleStandard/ Article/detail/408460.