feline herpesvirus
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Feline viral rhinotracheitis (FVR) is an upper respiratory or pulmonary infection of
cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...
s caused by ''Felid alphaherpesvirus 1'' (FeHV-1), of the family ''
Herpesviridae ''Herpesviridae'' is a large family of DNA viruses that cause infections and certain diseases in animals, including humans. The members of this family are also known as herpesviruses. The family name is derived from the Greek word ''ἕρπει ...
''. It is also commonly referred to as feline influenza, feline coryza, and feline pneumonia but, as these terms describe other very distinct collections of respiratory symptoms, they are misnomers for the condition. Viral respiratory diseases in cats can be serious, especially in catteries and
kennel A kennel is a structure or shelter for dogs. Used in the plural, ''the kennels'', the term means any building, collection of buildings or a property in which dogs are housed, maintained, and (though not in all cases) bred. A kennel can be made ...
s. Causing one-half of the respiratory diseases in cats, FVR is the most important of these diseases and is found worldwide. The other important cause of feline respiratory disease is ''
feline calicivirus ''Feline calicivirus'' (FCV) is a virus of the family ''Caliciviridae'' that causes disease in cats. It is one of the two important viral causes of respiratory infection in cats, the other being '' Felid alphaherpesvirus 1''. FCV can be isolat ...
''. FVR is very contagious and can cause severe disease, including death from
pneumonia Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severi ...
in young kittens. It can cause flat-chested kitten syndrome, but most evidence for this is anecdotal. All members of the family Felidae are susceptible to FVR; in fact, FHV-1 has caused a fatal encephalitis in lions in
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
.


History

FHV-1 was first isolated from cats in 1958 in the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...
.


Transmission

FVR is transmitted through direct contact only. It replicates in the nasal and
nasopharyngeal The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struct ...
tissues and the
tonsil The tonsils are a set of lymphoid organs facing into the aerodigestive tract, which is known as Waldeyer's tonsillar ring and consists of the adenoid tonsil, two tubal tonsils, two palatine tonsils, and the lingual tonsils. These organs play ...
s.
Viremia Viremia is a medical condition where viruses enter the bloodstream and hence have access to the rest of the body. It is similar to ''bacteremia'', a condition where bacteria enter the bloodstream. The name comes from combining the word "virus" wit ...
(the presence of the virus in the blood) is rare. The virus is shed in saliva and eye and nasal secretions, and can also be spread by
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. FVR has a two- to five-day
incubation period Incubation period (also known as the latent period or latency period) is the time elapsed between exposure to a pathogenic organism, a chemical, or radiation, and when symptoms and signs are first apparent. In a typical infectious disease, the in ...
. The virus is shed for one to three weeks postinfection. Latently infected cats (carriers) will shed FHV-1 intermittently for life, with the virus persisting within the
trigeminal ganglion A trigeminal ganglion (or Gasserian ganglion, or semilunar ganglion, or Gasser's ganglion) is the sensory ganglion at the base of each of the two trigeminal nerves (CN V), occupying a cavity ( Meckel's cave) in the dura mater, covering the trige ...
. Stress and use of corticosteroids precipitate shedding. Most disinfectants, antiseptics and detergents are effective against the virus.


Clinical signs

Initial signs of FVR include
cough A cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles and microbes. As a protective reflex, coughing can be repetitive with the cough reflex following three ph ...
ing,
sneezing A sneeze (also known as sternutation) is a semi-autonomous, convulsive expulsion of air from the lungs through the nose and mouth, usually caused by foreign particles irritating the nasal mucosa. A sneeze expels air forcibly from the mouth and ...
, nasal discharge,
conjunctivitis Conjunctivitis, also known as pink eye, is inflammation of the outermost layer of the white part of the eye and the inner surface of the eyelid. It makes the eye appear pink or reddish. Pain, burning, scratchiness, or itchiness may occur. The ...
, and sometimes fever (up to 106) and loss of appetite. These usually resolve within four to seven days, but secondary bacterial infections can cause the persistence of clinical signs for weeks. Frontal
sinusitis Sinusitis, also known as rhinosinusitis, is inflammation of the mucous membranes that line the sinuses resulting in symptoms that may include thick nasal mucus, a plugged nose, and facial pain. Other signs and symptoms may include fever, head ...
and
empyema An empyema () is a collection or gathering of pus within a naturally existing anatomical cavity. For example, pleural empyema is empyema of the pleural cavity. It must be differentiated from an abscess, which is a collection of pus in a newly fo ...
can also result. FHV-1 also has a predilection for
cornea The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical ...
l epithelium, resulting in
corneal ulcer Corneal ulcer is an inflammatory or, more seriously, infective condition of the cornea involving disruption of its epithelial layer with involvement of the corneal stroma. It is a common condition in humans particularly in the tropics and the a ...
s, often pinpoint or dendritic in shape. Other ocular signs of FHV-1 infection include
conjunctivitis Conjunctivitis, also known as pink eye, is inflammation of the outermost layer of the white part of the eye and the inner surface of the eyelid. It makes the eye appear pink or reddish. Pain, burning, scratchiness, or itchiness may occur. The ...
,
keratitis Keratitis is a condition in which the eye's cornea, the clear dome on the front surface of the eye, becomes inflamed. The condition is often marked by moderate to intense pain and usually involves any of the following symptoms: pain, impaired e ...
,
keratoconjunctivitis sicca Dry eye syndrome (DES), also known as keratoconjunctivitis sicca (KCS), is the condition of having dry eyes. Other associated symptoms include irritation, redness, discharge, and easily fatigued eyes. Blurred vision may also occur. Symptoms range ...
(decreased tear production), and corneal sequestra. Infection of the
nasolacrimal duct The nasolacrimal duct (also called the tear duct) carries tears from the lacrimal sac of the eye into the nasal cavity. The duct begins in the eye socket between the maxillary and lacrimal bones, from where it passes downwards and backwards. T ...
can result in chronic epiphora (excess tearing). Ulcerative skin disease can also result from FHV-1 infection. FHV-1 can also cause abortion in pregnant queens, usually at the sixth week of gestation, although this may be due to systemic effects of the infection rather than the virus directly. In chronic nasal and sinus disease of cats, FHV-1 may play more of an initiating role than an ongoing cause. Infection at an early age may permanently damage nasal and sinus tissue, causing a disruption of ciliary clearance of
mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It ...
and bacteria, and predispose these cats to chronic bacterial infections.


Diagnosis

Diagnosis of FVR is usually by clinical signs, especially corneal ulceration. Definitive diagnosis can be done by direct immunofluorescence or virus isolation. However, many healthy cats are subclinical carriers of feline herpes virus, so a positive test for FHV-1 does not necessarily indicate that signs of an upper respiratory tract infection are due to FVR. Early in the course of the disease,
histological Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vis ...
analysis of cells from the tonsils, nasal tissue, or nictitating membrane (third eyelid) may show inclusion bodies (a collection of viral particles) within the
nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom * Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...
of infected cells.


Treatment and prevention

Polyprenyl immunostimulant is the only currently-approved treatment in the US for feline rhinotracheitis caused by herpesvirus. Effectiveness was demonstrated in a clinical study with cats experimentally infected with feline herpesvirus: 20 cats were treated with polyprenyl immunostimulant and 20 received a placebo. The study established that the severity of the disease was lower in the group treated with polyprenyl. Safety was demonstrated in 390 personally-owned cats from 2 days to 16 years of age, residing in 10 states (ibid). Antibiotics are commonly used to prevent secondary bacterial infection. There are no specific antiviral drugs in common use at this time for FVR, although one study has shown that
ganciclovir Ganciclovir, sold under the brand name Cytovene among others, is an antiviral medication used to treat cytomegalovirus (CMV) infections. Ganciclovir was patented in 1980 and approved for medical use in 1988. Medical use Ganciclovir is indicated ...
, PMEDAP, and
cidofovir Cidofovir, brand name Vistide, is a topical or injectable antiviral medication primarily used as a treatment for cytomegalovirus (CMV) retinitis (an infection of the retina of the eye) in people with AIDS. Cidofovir was approved for medical u ...
hold promise for treatment. More recent research has indicated that systemic
famciclovir Famciclovir is a guanosine analogue antiviral drug used for the treatment of various herpesvirus infections, most commonly for herpes zoster (shingles). It is a prodrug form of penciclovir with improved oral bioavailability. Famciclovir is mark ...
is effective at treating this infection in cats without the side effects reported with other anti-viral agents. More severe cases may require supportive care such as intravenous fluid therapy, oxygen therapy, or even a
feeding tube Eating (also known as consuming) is the ingestion of food, typically to provide a heterotrophic organism with energy and to allow for growth. Animals and other heterotrophs must eat in order to survive — carnivores eat other animals, herbi ...
. Conjunctivitis and corneal ulcers are treated with topical antibiotics for secondary bacterial infection. Lysine is commonly used as a treatment; however, in a 2015 systematic review, the authors investigated all clinical trials with cats as well as ''
in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called " test-tube experiments", these studies in biology ...
'' studies and concluded that lysine supplementation is likely not effective for the treatment or prevention of feline herpesvirus 1 infection.


Vaccine

There is a
vaccine A vaccine is a biological preparation that provides active acquired immunity to a particular infectious or malignant disease. The safety and effectiveness of vaccines has been widely studied and verified.
for FHV-1 available (
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 chemical ...
code: , plus various combination vaccines), but although it limits or weakens the severity of the disease and may reduce
viral shedding Viral shedding is the expulsion and release of virus progeny following successful reproduction during a host cell infection. Once replication has been completed and the host cell is exhausted of all resources in making viral progeny, the viruse ...
, it does not prevent infection with FVR. Studies have shown a duration of immunity of this vaccine to be at least three years. The use of
serology Serology is the scientific study of serum and other body fluids. In practice, the term usually refers to the diagnostic identification of antibodies in the serum. Such antibodies are typically formed in response to an infection (against a given mic ...
to demonstrate circulating antibodies to FHV-1 has been shown to have a positive predictive value for indicating protection from this disease.


Preventing spread of virus

Most household
disinfectants A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than st ...
will inactivate FHV-1. The virus can survive up to 18 hours in a damp environment, but less in a dry environment and only shortly as an aerosol.


See also

*
Feline vaccination Feline vaccination is animal vaccination applied to cats. Vaccination plays a vital role in protecting cats from infectious diseases, some of which are potentially fatal. They can be exposed to these diseases from their environment, other pets, or ...


References


External links


''Feline Upper Respiratory Disease'' from The Pet Health Library
{{DEFAULTSORT:Feline Viral Rhinotracheitis Cat diseases Animal viral diseases Herpesviridae