Title: Feline calicivirus

{{Short description|Species of virus}}
{{Virusbox
| name = Feline calicivirus
| image = Feline calicivirus.jpg
| image_alt = Electron micrograph of Feline calicivirus virions
| image_caption = [[Electron micrograph]] of Feline calicivirus virions
| parent = Vesivirus
| species = Vesivirus felis
| synonyms = 
* ''Feline picornavirus''
| synonyms_ref = &lt;ref name=ICTV&gt;{{cite web |title=ICTV Taxonomy history: ''Feline calicivirus'' |url=https://ictv.global/taxonomy/taxondetails?taxnode_id=20182810 |website=International Committee on Taxonomy of Viruses (ICTV) |access-date=9 January 2019 |language=en }}&lt;/ref&gt;
}}
'''Feline calicivirus''' ('''FCV''') is a [[virus]] of the family ''[[Caliciviridae]]'' that causes disease in [[cat]]s.  It is one of the two important viral causes of respiratory infection in cats, the other being [[feline viral rhinotracheitis|feline herpesvirus]].  FCV can be isolated from about 50% of cats with upper respiratory infections.&lt;ref name=Fenner_1993&gt;{{cite book|author1=Fenner, Frank J. |author2=Gibbs, E. Paul J. |author3=Murphy, Frederick A. |author4=Rott, Rudolph |author5=Studdert, Michael J. |author6=White, David O. |title=Veterinary Virology |edition=2nd|publisher=Academic Press, Inc.|year=1993|isbn=978-0-12-253056-2}}&lt;/ref&gt;  [[Cheetah]]s are the other species of the family [[Felidae]] known to become infected naturally.&lt;ref name=Fenner_1993/&gt;

==Viral structure and pathogenesis==
Different strains of FCV can vary in [[virulence]] (the degree of pathogenicity within a group or species of microorganisms or viruses as indicated by case fatality rates and/or the ability of the organism to invade the tissues of the host).  Being an [[RNA virus]], FCV has a high elasticity of its [[genome]], which makes it more adaptable to environmental pressures.  This not only makes the development of vaccines more difficult, but also allows for the development of more [[virulence|virulent]] strains.&lt;ref name=Radford&gt;{{cite journal |vauthors=Radford A, Coyne K, Dawson S, Porter C, Gaskell R |title=Feline calicivirus |journal=Vet Res |volume=38 |issue=2 |pages=319–35 |year=2007 |pmid=17296159 |doi=10.1051/vetres:2006056|url=https://hal.archives-ouvertes.fr/hal-00902847/file/hal-00902847.pdf |doi-access=free }}&lt;/ref&gt;  In persistently infected cats,  the [[gene]] for the major structural protein of the viral [[capsid]] (the outer protein coat of a mature virus) has been shown to evolve through immune-mediated [[directional selection|positive selection]], which allows the virus to escape detection by the [[immune system]].&lt;ref&gt;{{cite journal |vauthors=Coyne K, Reed F, Porter C, Dawson S, Gaskell R, Radford A |title=Recombination of Feline calicivirus within an endemically infected cat colony |journal=J Gen Virol |volume=87 |issue=Pt 4 |pages=921–6 |year=2006 |pmid=16528041 |doi=10.1099/vir.0.81537-0|doi-access=free }}&lt;/ref&gt;

A form of FCV has been found to cause a particularly severe systemic disease in cats, similar to [[rabbit hemorrhagic disease]] (which is also caused by a calicivirus).  This virus has been called '''virulent systemic feline calicivirus''' (VS-FCV) or FCV-associated virulent systemic disease (VSD).  The disease is caused by direct viral invasion of [[epithelium]] and [[endothelium]] and secondary host immune response. Strains of VS-FCV have seemingly risen independently of one another since first being described, meaning that not all cases of VS-FCV have spread from a single case.&lt;ref&gt;{{cite journal |vauthors=Ossiboff R, Sheh A, Shotton J, Pesavento P, Parker J |title=Feline caliciviruses (FCVs) isolated from cats with virulent systemic disease possess in vitro phenotypes distinct from those of other FCV isolates |journal=J Gen Virol |volume=88 |issue=Pt 2 |pages=506–17 |year=2007 |pmid=17251569 |doi=10.1099/vir.0.82488-0|doi-access=free }}&lt;/ref&gt;  Most of the outbreaks of VS-FCV have been reported in the [[United States]].&lt;ref name=Radford/&gt;  It was originally described in 1998 in Northern [[California]].&lt;ref name=DVM&gt;{{cite journal | title = CaliciVax updated to cover virulent systemic feline calicivirus | journal = DVM | pages = 61 |date=February 2007 }}&lt;/ref&gt;

The [[prevalence]] of FCV varies depending on the environment.  In private households, FCV is present in about 10% of cats (either in active or carrier state), while the prevalence in shelters or catteries is 25 to 40%.&lt;ref name=Radford/&gt;

FCV replicates in the oral and respiratory tissues, and is secreted in [[saliva]], [[feces]], [[urine]], and respiratory secretions. It can be transmitted through the air, orally, and on [[fomite]]s.  Infected cats usually shed the virus for two weeks.&lt;ref name=Foley_2005&gt;{{cite book|editor=August, John R.|chapter=Calicivirus: Spectrum of Disease|author=Foley, Janet E.|title=Consultations in Feline Internal Medicine Vol. 5|publisher=Elsevier Saunders|year=2005|isbn=978-0-7216-0423-7}}&lt;/ref&gt;  Following this period, infected cats never shed the virus again or become latently infected and shed the virus continuously or intermittently.&lt;ref&gt;{{cite journal |vauthors=Coyne K, Dawson S, Radford A, Cripps P, Porter C, McCracken C, Gaskell R |title=Long-term analysis of feline calicivirus prevalence and viral shedding patterns in naturally infected colonies of domestic cats |journal=Vet Microbiol |volume=118 |issue=1–2 |pages=12–25 |year=2006 |pmid=16911860 |doi=10.1016/j.vetmic.2006.06.026 |pmc=7117452 }}&lt;/ref&gt;  [[Co-infection]] with either [[feline viral rhinotracheitis|feline herpesvirus]] or [[feline immunodeficiency virus]] causes a more severe disease.

==Clinical signs==
[[Image:Katzenschnupfen Calici.jpg|thumb|Feline calicivirus infection in a cat, showing [[Mouth ulcer|ulceration]] over the rostral end of [[tongue]] and secondary [[gingivitis]], [[faucitis]] and [[ptyalism]]. Note that [[rhinitis]] is also present.]]
Clinical signs in cats infected with FCV may develop acutely, chronically, or not at all.  Latent or subclinical infections often become clinical when the cat is stressed, such as at the time of adoption.  Acute signs of FCV include fever, [[conjunctivitis]], nasal discharge, sneezing, and ulceration of the mouth ([[stomatitis]]).  [[Pneumonia]] may develop with secondary [[bacteria]]l infections.  In addition to stomatitis, some cats may develop a [[polyarthritis]], both probably immune-mediated through [[immune complex]] deposition.  Stomatitis and polyarthritis can develop without any upper respiratory infection signs, but fever and loss of appetite may occur.  Less commonly, [[glomerulonephritis]] can develop in chronic cases secondary to immune complex deposition.  The great variability of clinical signs in individual cases of FCV is related to the relative virulence of different strains of the virus.

VS-FCV can cause a rapid [[epidemic]], with a mortality rate of up to 67%.&lt;ref name=Foley_2005/&gt;  Initial clinical signs include discharge from the eyes and nose, ulceration in the mouth, anorexia, and lethargy, and occur in the first one to five days.&lt;ref name=forum&gt;{{cite journal | last = Rosenthal | first = Marie | title = VS-FCV may be more prevalent than previously thought | journal = Veterinary Forum | volume = 24 | issue = 2 | pages = 23 |date=February 2007 }}&lt;/ref&gt;  Later signs include fever, [[edema]] of the limbs and face, [[jaundice]], and [[multiple organ dysfunction syndrome]].

Diagnosis of FCV is difficult without specific tests, because the signs are similar to other feline respiratory diseases, especially [[feline viral rhinotracheitis]].  The presence of stomatitis may indicate FCV.  Specific tests include virus [[microbiological culture|culture]], [[polymerase chain reaction]], and [[immunohistochemistry|immunohistochemical stain]]ing.

==Treatment and prevention==
There is no specific treatment for FCV.  [[Antibiotic]]s are used for secondary bacterial infections, and immune modulators, such as [[Lymphocyte T-Cell Immune Modulator|lymphocyte T-cell immune modulator]], have been used for immune support. [[Nursing care]] and rehydration are used for dehydrated and [[anorexia (symptom)|anorexic]] cats.  [[Corticosteroid]]s or [[azathioprine]] may be used for polyarthritis. [[Stomatitis]] is very difficult to treat.  Antibiotics, corticosteroids, and tooth extractions all have been used with varying success.  Cats on corticosteroids must be monitored carefully for worsening of any upper respiratory infection.

Natural immunity from [[Maternal Passive Immunity|maternal antibodies]] lasts in the kitten from three to nine weeks.&lt;ref name=Foley_2005/&gt;  After that, kittens are susceptible to FCV.  Previous infection does not guarantee lifelong immunity, since an antigenically dissimilar FCV (such as VS-FCV) can cause infection.  However, usually after the age of three years, FCV infections are mild or asymptomatic.&lt;ref name=Foley_2005/&gt;  FCV [[feline vaccination|vaccination]] will not always prevent disease, but can reduce the severity.  FCV vaccines come in two types, inactivated ([[ATCvet]] code: {{ATCvet|I06|AA07}}) and attenuated (live, but not virulent; in various combination vaccines).  They have been shown to be effective for at least three years.&lt;ref&gt;{{cite journal |vauthors=Gore T, Lakshmanan N, Williams J, Jirjis F, Chester S, Duncan K, Coyne M, Lum M, Sterner F |title=Three-year duration of immunity in cats following vaccination against feline rhinotracheitis virus, feline calicivirus, and feline panleukopenia virus |journal=Vet Ther |volume=7 |issue=3 |pages=213–22 |year=2006 |pmid=17039444}}&lt;/ref&gt;  Attenuated FCV vaccine has been shown to possibly cause mild upper respiratory infection. Inactivated vaccine does not, but it causes more local inflammation and possibly predisposes the cat to [[vaccine-associated sarcoma]].&lt;ref name=Foley_2005/&gt;  The only vaccine licensed for prevention of VS-FCV is CaliciVax, manufactured by Fort Dodge Animal Health, a division of [[Wyeth]].  It also contains a strain of the traditional FCV virus.&lt;ref name=DVM/&gt;  Since VS-FCV has arisen from variant strains of FCV, it is not certain that a vaccine for one virulent strain will protect against all virulent strains.&lt;ref&gt;{{cite journal | last = Hurley | first = Kate Frances | title = Facts about Feline Calicivirus | journal = Clinician's Brief | volume = 5 | issue = 6 | pages = 30 |date=June 2007 }}&lt;/ref&gt;

[[Quarantine]] is best for control of FCV in [[cattery|catteries]] and kennels.  However, FCV is very contagious, and latently infected cats will continue to shed viruses, so complete control is difficult.  An outbreak of VS-FCV at a [[humane society]] in [[Missouri]] in 2007 led to the [[animal euthanasia|euthanasia]] of the entire cat population (almost 200 cats) to contain it.&lt;ref&gt;{{cite journal | title = Humane Society has to put down facility's 200 felines after mass virus outbreak | journal = DVM | pages = 20S |date=July 2007|url=https://www.dvm360.com/view/humane-society-has-put-down-facilitys-200-felines-after-mass-virus-outbreak}}&lt;/ref&gt;  FCV may survive several days to weeks in a dry environment and longer in a cooler, wet environment.  [[Quaternary ammonium cation|Quaternary ammonium compound]]s are not thought to be completely effective, but a 1:32 dilution of household [[bleach]] used with a detergent and sufficient contact time does seem to kill the virus.&lt;ref name=Radford/&gt;

Herbal extracts as a source of compounds with an antiviral activity has attracted significant attention recently. Two researches independently published in 2016 screened a library of natural chemicals against FCV. The first one&lt;ref&gt;{{Cite journal|last=Ohba|first=Mai|last2=Oka|first2=Tomoichiro|last3=Ando|first3=Takayuki|last4=Arahata|first4=Saori|last5=Ikegaya|first5=Asaka|last6=Takagi|first6=Hirotaka|last7=Ogo|first7=Naohisa|last8=Zhu|first8=Chelsea|last9=Owada|first9=Kazuhiro|date=April 2017|title=Antiviral effect of theaflavins against caliciviruses|journal=The Journal of Antibiotics|language=en|volume=70|issue=4|pages=443–447|doi=10.1038/ja.2016.128|pmid=27756911|issn=0021-8820|doi-access=free}}&lt;/ref&gt; showed that [[Theaflavin]] and its derivatives but not [[Kaempferol]] significantly inhibited entry of FCV into cells. On the contrary, authors of the second article&lt;ref&gt;{{Cite journal|last=Seo|first=Dong Joo|last2=Jeon|first2=Su Been|last3=Oh|first3=Hyejin|last4=Lee|first4=Bog-Hieu|last5=Lee|first5=Sook-Young|last6=Oh|first6=Seung Hyun|last7=Jung|first7=Ji Youn|last8=Choi|first8=Changsun|title=Comparison of the antiviral activity of flavonoids against murine norovirus and feline calicivirus|journal=Food Control|volume=60|pages=25–30|doi=10.1016/j.foodcont.2015.07.023|year=2016}}&lt;/ref&gt; claimed that kaempherol showed anti-FCV activity, but theaflavin treatment was insufficient. This striking difference may be (at least partially) explained by differences in testing conditions. Indeed, further studies of activity, as well as molecular mechanisms of action, needed.

==Use in research==
Because of the similarity of FCV to [[norovirus]], a common cause of [[gastroenteritis]] in humans, FCV has been used as a surrogate for it in research.  For instance, studies have been done on the survival of FCV in foodstuffs,&lt;ref&gt;{{cite journal |vauthors=Mattison K, Karthikeyan K, Abebe M, Malik N, Sattar S, Farber J, Bidawid S |title=Survival of calicivirus in foods and on surfaces: experiments with feline calicivirus as a surrogate for norovirus |journal=J Food Prot |volume=70 |issue=2 |pages=500–3 |year=2007 |pmid=17340890|doi=10.4315/0362-028X-70.2.500 |doi-access=free }}&lt;/ref&gt; the effectiveness of handwashing on FCV removal,&lt;ref&gt;{{cite journal |vauthors=Mori K, Hayashi Y, Noguchi Y, Kai A, Ohe K, Sakai S, Hara M, Morozumi S |title=[Effects of handwashing on Feline Calicivirus removal as Norovirus surrogate] |journal=Kansenshogaku Zasshi |volume=80 |issue=5 |pages=496–500 |year=2006 |pmid=17073262|doi=10.11150/kansenshogakuzasshi1970.80.496 |doi-access=free }}&lt;/ref&gt; and the use of [[ozone]] gas to inactivate FCV found in hotel rooms, cruise ship cabins, and healthcare facilities.&lt;ref&gt;{{cite journal |vauthors=Hudson J, Sharma M, Petric M |title=Inactivation of Norovirus by ozone gas in conditions relevant to healthcare |journal=J Hosp Infect |volume= 66|issue= 1|pages= 40–5|year=2007 |pmid=17350729 |doi=10.1016/j.jhin.2006.12.021}}&lt;/ref&gt;  It is also used in general Caliciviridae research due to its being one of the few of that group of viruses that grows well ''[[in vitro]]''.&lt;ref&gt;{{cite journal |vauthors=Stuart A, Brown T |title=Entry of feline calicivirus is dependent on clathrin-mediated endocytosis and acidification in endosomes |journal=J Virol |volume=80 |issue=15 |pages=7500–9 |year=2006 |pmid=16840330 |doi=10.1128/JVI.02452-05 |pmc=1563722}}&lt;/ref&gt;

==See also==
*[[Feline vaccination]]
*[[Calicivirus]]
*[[Limping calici]]

==References==
{{Reflist}}

==External links==
*[http://www.veterinarypartner.com/Content.plx?P=A&amp;S=0&amp;C=0&amp;A=613 ''Feline Upper Respiratory Disease'' from The Pet Health Library]
*[https://www.vetres.org/articles/vetres/pdf/2007/02/v06220.pdf?access=ok PDF file of an excellent journal article on FCV]
*[https://web.archive.org/web/20090223234201/http://wyethah.ca/feline.asp?pageid=f1 ''Wyeth Animal Health Podcast'' featuring Dr. Gary Norsworthy on VS-FCV July 2007]
*[https://www.youtube.com/watch?v=LJZQnjk6uao ''poor cat was living his last moments on the roadside but no one came to help him!'' Example of disease partial healing]

{{Domestic cat}}
{{Taxonbar|from=Q13499373}}

{{DEFAULTSORT:Feline Calicivirus}}
[[Category:Vesiviruses]]
[[Category:Cat diseases]]
[[Category:Animal viral diseases]]
[[Category:Vaccine-preventable diseases]]