Feline Herpesvirus (FHV-1), also known as Feline Viral Rhinotracheitis (FVR), is an important cause of upper respiratory disease (URD) and eye inflammation in cats and other members of the cat family worldwide. FHV-1 is an alphaherpesvirus which contains double-stranded DNA.

It is likely that most cats will be exposed to the infection during their lifetime. There is only one serotype of the virus and all isolates are genetically similar.

Clinical signs are typically seen as mild to severe upper respiratory disease. Nasal and ocular discharges are common. Additional clinical signs include conjunctivitis(infection in the tissue surrounding the eye), sneezing, anterior uveitis (infection in the anterior chamber of the eye itself), stomatitis (mouth infection), and are sometimes accompanied by salivation and coughing. In severe cases, pneumonia will be a complication of infection. In rare cases, abortion is possible but is probably due to the systemic disease rather than by direct effect of the virus. Skin lesions called herpetic ulcerative dermatitis may occur and are exhibited by chronic, nonhealing skin ulcers of the facial and nasal areas that are not responsive to treatment. The disease usually is self-limiting ( runs a one to two week course) although some individuals will develop chronic infection. All ages of cats are susceptible to infection although kittens typically are more severely affected.

Virus is shed in the oral, conjunctival, and nasal secretions of infected cats. Transmission is mainly by direct cat-to-cat contact, but indirect transmission may occur due to environmental contamination or contaminated objects. FHV-1 may also be carried by a contaminated handler to a susceptible cat. Aerosol droplets may also transmit the virus up to two meters although is not considered to be a major source of viral transmission. The virus is typically infectious for only 24 hours in the environment. Infected cats shed virus for one to three weeks. Most, if not all, infected cats will become lifelong, latently infected carriers. The virus persists in latent form contained within the trigeminal ganglia (group of nerves), although other tissues may also be involved in harboring the virus. A proportion of these carriers will have a recurrence of clinical signs and viral shedding following periods of stress or corticosteroid treatment.

A presumptive diagnosis is based on the presence of typical clinical signs. Diagnosis is confirmed by virus isolation from conjunctival, nasal, or oral swabs.

Treatment is largely supportive. Antibiotics are given to prevent secondary bacterial infections from causing complicating bacterial pneumonias. Antihistamines are given to relieve congestion. Ophthalmics may be necessary for conjunctivitis. Dehydration must be corrected and in severe cases force feeding may be of necessity. There are antiherpesvirus drugs used in human medicine such as acyclovir but they have not been shown to be sufficiently active against FHV-1 or are too toxic for use in the cat. Orally administered L-lysine, Viralys® manufactured by Vet Solutions, may be useful in treating acutely and latently infected FHV-1 cats by decreasing the severity of the eye lesions and viral shedding associated with infection. Viralys® is manufactured as a palatable gel.

FHV-1 is easily inactivated in the environment through the use of a dilute hypochlorite solution (one part Clorox to 40 parts of water), as well as most disinfectants and detergent mixtures typically effective against viruses.

Modified-live and inactivated FHV-1 vaccines for injection are commercially available. In some countries, MLV vaccines for intranasal administration are also available. Intranasal vaccines provide protection to the virus faster, usually in two to six days. Following injectable vaccination there is likely to be up to three years of protection, according to the Feline Advisory Panel. The panel also adds that this protection is not always complete and may decline as the vaccination interval increases. FHV-l is considered to be a core vaccine by the panel. An initial series of vaccinations should be started as early as six weeks of age and continued every three weeks until the kitten is over 16 weeks of age. Cats should then be vaccinated again at one year later and again at one to three year intervals dependent on vaccine manufacturers’ recommendations and risk of exposure. Cats at high risk of exposure such as those that are boarded, go to cat shows, outside cats, or those that could be picked up by animal control and placed in a shelter should be vaccinated shortly before such a risk is encountered.


References:
“The 2006 American Association of Feline Practitioners Feline Vaccine Advisory Panel Report”. JAVMA, Vol 229, No. 9, November 1, 2006. pp1405-1441.
“Detection of Feline Herpesvirus 1 DNA in Skin Biopsy Specimens from Cats With or Without Dermatitis. JAVMA, Vol 229, No.9, November 1, 2006. Pp1442-1446.
Ettinger, Stephen DVM and Edward C. Feldman DVM. Textbook of Veterinary Internal Medicine. 6th Edition 2005, Elsevier, Inc. pp.667 – 669.