Feline calicivirus (FCV) is a

virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...

of the family ''

Caliciviridae The ''Caliciviridae'' are a family of "small round structured" viruses, members of Class IV of the Baltimore scheme. Caliciviridae bear resemblance to enlarged picornavirus and was formerly a separate genus within the picornaviridae. They are ...

'' that causes disease in cats. It is one of the two important viral causes of respiratory infection in cats, the other being feline herpesvirus. FCV can be isolated from about 50% of cats with upper respiratory infections.

Cheetah The cheetah (''Acinonyx jubatus'') is a large Felidae, cat and the Fastest animals, fastest land animal. It has a tawny to creamy white or pale buff fur that is marked with evenly spaced, solid black spots. The head is small and rounded, wit ...

s are the other species of the family

Felidae Felidae ( ) is the Family (biology), family of mammals in the Order (biology), order Carnivora colloquially referred to as cats. A member of this family is also called a felid ( ). The 41 extant taxon, extant Felidae species exhibit the gre ...

known to become infected naturally.

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 An RNA virus is a virus characterized by a ribonucleic acid (RNA) based genome. The genome can be single-stranded RNA (ssRNA) or double-stranded (Double-stranded RNA, dsRNA). Notable human diseases caused by RNA viruses include influenza, SARS, ...

, FCV has a high elasticity of its

genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...

, 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 virulent strains. In persistently infected cats, the

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

for the major structural protein of the viral

capsid A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or m ...

(the outer protein coat of a mature virus) has been shown to evolve through immune-mediated positive selection, which allows the virus to escape detection by the

immune system The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...

. 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 Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...

and

endothelium The endothelium (: endothelia) is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the r ...

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. Most of the outbreaks of VS-FCV have been reported in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

. It was originally described in 1998 in Northern

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

. The

prevalence In epidemiology, prevalence is the proportion of a particular population found to be affected by a medical condition (typically a disease or a risk factor such as smoking or seatbelt use) at a specific time. It is derived by comparing the number o ...

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%. FCV replicates in the oral and respiratory tissues, and is secreted in

saliva Saliva (commonly referred as spit or drool) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which ...

feces Feces (also known as faeces American and British English spelling differences#ae and oe, or fæces; : faex) are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the ...

urine Urine is a liquid by-product of metabolism in humans and many other animals. In placental mammals, urine flows from the Kidney (vertebrates), kidneys through the ureters to the urinary bladder and exits the urethra through the penile meatus (mal ...

, and respiratory secretions. It can be transmitted through the air, orally, and on

fomite A fomite () or fomes () is any inanimate object that, when contaminated with or exposed to infectious agents (such as pathogenic bacteria, viruses or fungi), can transfer disease to a new host. Transfer of pathogens by fomites A fomite is any ...

s. Infected cats usually shed the virus for two weeks. Following this period, infected cats never shed the virus again or become latently infected and shed the virus continuously or intermittently.

Co-infection Coinfection is the simultaneous infection of a host by multiple pathogen species. In virology, coinfection includes simultaneous infection of a single cell by two or more virus particles. An example is the coinfection of liver cells with hepati ...

with either feline herpesvirus or feline immunodeficiency virus causes a more severe disease.

Clinical signs

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 Conjunctivitis, also known as pink eye or Madras eye, is inflammation of the conjunctiva, the thin, clear layer that covers the white surface of the eye and the inner eyelid. It makes the eye appear pink or reddish. Pain, burning, scratchiness ...

, nasal discharge, sneezing, and ulceration of the mouth ( stomatitis).

Pneumonia Pneumonia is an Inflammation, inflammatory condition of the lung primarily affecting the small air sacs known as Pulmonary alveolus, alveoli. Symptoms typically include some combination of Cough#Classification, productive or dry cough, ches ...

may develop with secondary

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

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 An epidemic (from Greek ἐπί ''epi'' "upon or above" and δῆμος ''demos'' "people") is the rapid spread of disease to a large number of hosts in a given population within a short period of time. For example, in meningococcal infection ...

, with a mortality rate of up to 67%. 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. Later signs include fever,

edema Edema (American English), also spelled oedema (British English), and also known as fluid retention, swelling, dropsy and hydropsy, is the build-up of fluid in the body's tissue (biology), tissue. Most commonly, the legs or arms are affected. S ...

of the limbs and face,

jaundice Jaundice, also known as icterus, is a yellowish or, less frequently, greenish pigmentation of the skin and sclera due to high bilirubin levels. Jaundice in adults is typically a sign indicating the presence of underlying diseases involving ...

, and

multiple organ dysfunction syndrome Multiple organ dysfunction syndrome (MODS) is altered organ function in an acutely ill patient requiring immediate medical intervention. There are different stages of organ dysfunction for certain different organs, both in acute and in chronic ...

. 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

culture Culture ( ) is a concept that encompasses the social behavior, institutions, and Social norm, norms found in human societies, as well as the knowledge, beliefs, arts, laws, Social norm, customs, capabilities, Attitude (psychology), attitudes ...

polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to make millions to billions of copies of a specific DNA sample rapidly, allowing scientists to amplify a very small sample of DNA (or a part of it) sufficiently to enable detailed st ...

, and immunohistochemical staining.

Treatment and prevention

There is no specific treatment for FCV.

Antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy ...

s are used for secondary bacterial infections, and immune modulators, such as lymphocyte T-cell immune modulator, have been used for immune support. Nursing care and rehydration are used for dehydrated and anorexic cats.

Corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are invo ...

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 antibodies lasts in the kitten from three to nine weeks. 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. FCV

vaccination Vaccination is the administration of a vaccine to help the immune system develop immunity from a disease. Vaccines contain a microorganism or virus in a weakened, live or killed state, or proteins or toxins from the organism. In stimulating ...

will not always prevent disease, but can reduce the severity. FCV vaccines come in two types, inactivated (

ATCvet The Anatomical Therapeutic Chemical (ATC) Classification System is a drug classification system that classifies the active ingredients of drugs according to the organ or system on which they act and their therapeutic, pharmacological and chemica ...

code: ) and attenuated (live, but not virulent; in various combination vaccines). They have been shown to be effective for at least three years. 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. The only vaccine licensed for prevention of VS-FCV is CaliciVax, manufactured by Fort Dodge Animal Health, a division of

Wyeth Wyeth Pharmaceuticals Inc. was a pharmaceutical company until it was purchased by Pfizer in 2009. The company was founded in Philadelphia, Pennsylvania, in 1860 as John Wyeth and Brother. Its headquarters moved to Collegeville, Pennsylvania, a ...

. It also contains a strain of the traditional FCV virus. 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.

Quarantine A quarantine is a restriction on the movement of people, animals, and goods which is intended to prevent the spread of disease or pests. It is often used in connection to disease and illness, preventing the movement of those who may have bee ...

is best for control of FCV in 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 Missouri (''see #Etymology and pronunciation, pronunciation'') is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it border ...

in 2007 led to the

euthanasia Euthanasia (from : + ) is the practice of intentionally ending life to eliminate pain and suffering. Different countries have different Legality of euthanasia, euthanasia laws. The British House of Lords Select committee (United Kingdom), se ...

of the entire cat population (almost 200 cats) to contain it. FCV may survive several days to weeks in a dry environment and longer in a cooler, wet environment.

Quaternary ammonium compound In organic chemistry, quaternary ammonium cations, also known as quats, are positively-charged polyatomic ions of the structure , where R is an alkyl group, an aryl group or organyl group. Unlike the ammonium, ammonium ion () and the primary, sec ...

s are not thought to be completely effective, but a 1:32 dilution of household

bleach Bleach is the generic name for any chemical product that is used industrially or domestically to remove color from (i.e. to whiten) fabric or fiber (in a process called bleaching) or to disinfect after cleaning. It often refers specifically t ...

used with a detergent and sufficient contact time does seem to kill the virus. 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 showed that

Theaflavin Theaflavin (TF) and its derivatives, known collectively as ''theaflavins'', are antioxidant polyphenols in tea, polyphenols that are formed from the condensation of flavan-3-ols in tea leaves during the enzymatic oxidation (sometimes erroneously re ...

and its derivatives but not

Kaempferol Kaempferol (3,4′,5,7-tetrahydroxyflavone) is a natural flavonol, a type of flavonoid, found in a variety of plants and plant-derived foods including kale, beans, tea, spinach, and broccoli. It is also found in propolis extracts. Kaempferol i ...

significantly inhibited entry of FCV into cells. On the contrary, authors of the second article 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 Norovirus, also known as Norwalk virus and sometimes referred to as the winter vomiting disease, is the most common cause of gastroenteritis. Infection is characterized by non-bloody diarrhea, vomiting, and stomach pain. Fever or headaches may ...

, a common cause of

gastroenteritis Gastroenteritis, also known as infectious diarrhea, is an inflammation of the Human gastrointestinal tract, gastrointestinal tract including the stomach and intestine. Symptoms may include diarrhea, vomiting, and abdominal pain. Fever, lack of ...

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, the effectiveness of handwashing on FCV removal, and the use of

ozone Ozone () (or trioxygen) is an Inorganic compound, inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , break ...

gas to inactivate FCV found in hotel rooms, cruise ship cabins, and healthcare facilities. 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 ''In vitro'' (meaning ''in glass'', or ''in the glass'') Research, studies are performed with Cell (biology), cells or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in ...

''.

References

External links