Feline viral rhinotracheitis

  Feline viral rhinotracheitis (FVR) is an upper respiratory infection of cats caused by feline herpesvirus 1, of the family Herpesviridae. It is also known as feline influenza and feline coryza. Viral respiratory diseases in cats can be serious, especially in catteries and kennels. Causing one-half of the respiratory diseases in cats,^[1] FVR is the most important of these diseases and is found worldwide. The other important cause of feline respiratory disease is feline calicivirus.

FVR is very contagious and can cause severe disease, including death from pneumonia in young kittens. All members of the Felidae family are susceptible to FVR, in fact FHV-1 has caused a fatal encephalitis in lions in Germany.^[2]

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History

FHV-1 was first isolated from cats in 1958 in the United States.^[3]

Transmission

FVR is transmitted through the air and direct contact. It replicates in the nasal and nasopharyngeal tissues and the tonsils. Viremia (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 fomites. FVR has a two to five day incubation period.^[1] The virus is shed for one to three weeks postinfection.^[2] Latently infected cats (carriers) will shed FHV-1 intermittently for life, with the virus persisting within the trigeminal ganglion. Stress and use of corticosteroids precipitate shedding.

Symptoms

  Initial symptoms of FVR include coughing, sneezing, nasal discharge, conjunctivitis, and sometimes fever and loss of appetite. The symptoms usually resolve within four to seven days, but secondary bacterial infections can cause persistence of symptoms for weeks.^[2] Frontal sinusitis and empyema can also result.

FHV-1 also has a predilection for corneal epithelium, resulting in corneal ulcers, often pinpoint or dendritic in shape. Other ocular symptoms of FHV-1 infection include conjunctivitis, keratitis, keratoconjunctivitis sicca (decreased tear production), and corneal sequestra.^[4] Infection of the nasolacrimal duct can result in chronic epiphora (excess tearing). Ulcerative skin disease can also result from FHV-1 infection.^[5] FHV-1 can also cause abortion in pregnant queens, usually at the sixth week of gestation,^[1] 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 and bacteria, and predispose these cats to chronic bacterial infections.^[6]

Diagnosis

Diagnosis of FVR is usually by the symptoms, especially corneal ulceration. Definitive diagnosis can be done by direct immunofluorescence or virus isolation. However, many healthy cats carry feline herpes virus asymptomatically, so a positive test for FHV-1 does not necessarily indicate that symptoms of an upper respiratory tract infection are due to it. Early in the course of the disease, histological 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 of infected cells.^[7]

Treatment and prevention

Antibiotics are used to prevent secondary bacterial infections. There are no specific antiviral drugs in common use at this time for FVR, although one study has shown that ganciclovir, PMEDAP, and cidofovir hold promise for treatment.^[8] More severe cases may require supportive care such as intravenous fluid therapy, oxygen therapy, or even a feeding tube. Conjunctivitis and corneal ulcers are treated with topical antibiotics for secondary bacterial infection. L-lysine has been recommended anecdotally to suppress viral replication.^[9] A more recent study supports the use of L-lysine for treatment of ocular signs of FHV-1 infection.^[10]

There is a vaccine for FHV-1 available, but although it limits the severity of the disease and may reduce viral shedding, it does not prevent infection with FVR.^[11] Studies have shown a duration of immunity of this vaccine to be at least three years.^[12] The use of serology to demonstrate circulating antibodies to FHV-1 has been shown to have a positive predictive value for indicating protection from this disease.^[13] Most household disinfectants 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.^[11]

References