Feline Herpesvirus

For PCR testing, samples of blood are taken or swabs of nasal, oropharyngeal or conjunctivae mucosae are taken by cotton swabs (are provided by laboratory). Laboratory provides two swabs for one animal – each swab can be used for sampling of different mucosae. Swabs will be analysed together like a mixed sample. If you like test the swabs separately, we will charge you two analysis – it is necesary to ask for separately testing!

Aetiology

Transmission

Diagnostics by means of polymerase chain reaction (PCR)

Clinical symptoms

Treatment

Aetiology
Herpes viruses belong according to their structure to dsDNA (double stranded DNA) viruses, which are characteristic by long-time persistence in the infected organism. These viruses belong to the most common viruses in animals and are the cause of a wide spectrum of diseases in humans and animals. The herpesviruses are represented by Feline Herpesvirus 1 (FHV-1) that belongs to the family Varicellovirus. This virus was first isolated in 1958 by Crandell and Maurer in the USA. Like other herpesviruses, alphaherpesviruses establish latent infections after acute phase of the disease with periodical virus reactivation. Reactivation from latency is sometimes connected with recurrent disease symptoms and can occur spontaneously or more likely upon stress situations. The stress factors may be, for example, participation in a dog show, crossing, change of environment, new member in the household, etc. The virus may not be shedding immediately after the stress situation, but occurs in principle with a delay of 4 to 11 days. During the latent phase, FHV-1 as well as CHV (Canine Herpes virus) resides in ganglions of the trigeminal. In hosts with suppressed immune system, the viruses become activated and cause repeated disease. FHV-1causes damage to mucous membrane cells and is the cause of feline viral rhinotracheitis (Rhinotracheitis contagiosa felium) and eye disease.

Transmission
In acute phase, the virus is present prevalently in nasal, eye and oral secretions. The virus is transferred mainly by direct contact with an infected cat or by nursing the kittens by infected mother cat. The development of the infection in kittens depends on the level of maternal antibodies. FHV-1 transmission in utero (transmission from mother to kittens during the intrauterine development) has not been known so far and there is no other host than a cat.
Animals with acute infection are clearly one of the most significant sources of the virus. In cats with latent infection (carriers), the virus can be shed spontaneously and infect cats with weakened immune system (according to Smith K. C. at col. 1997). It is probable that all cats which had acute form of FHV-1 are carriers of this disease. However, less than half of them is serious from the epidemiological point of view (i.e. are shedding virus under natural conditions).
In large breeding stations with bad hygiene habits, the cat resting places, food or coat care tools are the risk factors as regards the contamination transmission. In external environment, FeHV-1 survives only for a short time. It can be eliminated by regular cleaning using common disinfectants and by washing the cat beds.
The probability of secondary viremia (condition, when the virus circulates in bloodstream to various organs) is low. However, it may occur in newborn kittens or individuals with a seriously weakened immune system. If the course of the disease is more serious, it may lead to the necrosis of epithelium of respiratory tract and osteolytic changes in turbinate bones. FHV-1 appears in peripheral body parts with lower temperature.

Diagnostics by means of polymerase chain reaction (PCR)
PCR test identifies FHV-1 by amplifying specific sequences of viral DNA. A great advantage of this procedure is its specificity and extremely high sensitivity of the reaction. For PCR testing, samples of blood or swabs of nasal, oropharyngeal or conjunctivae mucosae are taken by a cotton swab   (is provided by laboratory).
Recent studies, focused on the detection of the presence of DNA of the feline herpesvirus by PCR and method of determination of FHV-1 antibodies, have proven higher sensitivity of the PCR test method. At time, when the antibodies against the herpsevirus in cat decrease, a more prolonged presence of viral DNA has been found in the secretion of infected cats.

Clinical symptoms
The first signs are usually depression, sneezing, loss of appetite and fever, followed by increased production of ocular and nasal discharges. These initial clinical signs may be accompanied by excessive salivation. In severe cases, breathlessness (dyspnoea) and coughing may also develop. Relatively frequent is the occurrence of oral ulceration. In young and weakened animals, a primary viral pneumonia may occur.

FHV-1 is connected with a large number of eye and stroma diseases in cats:

• Acute conjunctivitis in newborn cats (ophthalmia neonatorum) - in the period before opening the eyelids, it causes purulent discharges under the eyelids and corneal damage and in severe cases even cornea cracking.
• conjunctivitis - herpesvirus is the main cause of acute and chronic conjunctivitis; the inflammation is usually bilateral, accompanied by congestion and increased ocular discharge; it occurs mostly bilaterally after an incubation period of 2 to 6 days, in most cases, the clinical signs usually abate within 10-20 days
• Inflammatory disease of cornea (keratitis) - the FHV-1 virus causes dendritic ulcers on the cornea.
• Chronic stromal keratitis - may develop after repeated inflammations of cornea due to FHV-1, associated with chronic inflammatory changes, such as neovascularisation, inflammatory cell infiltrates, pigmentation, scars and fibrosis.
• Adhesion of the eyelid to the eyeball (symblepharon) - it results from serious conjunctival inflammations and in severe cases restricts the eye movement and causes damage to lacrimal gland
• Feline Corneal Sequestration - it refers to the development of an opaque, dark brown to black plaque on the cornea, which is a dead piece of corneal tissue. Sequestration develops in cats of various breeds and age. The predisposed breeds with the highest frequency of occurrence are Persian Cats, Siamese, Burmese and Himalayan Cats.
• Calcific band keratopathy - deposition of calcium in the corneal ulcers
• Anterior uveitis is an inflammation that affects the front or the anterior part of the eye; this includes iris, choroid and ciliary body - in humans, a link between the presence of HSV-1 (human herpesvirus) and the presence of the anterior uveitis has been proven. The research indicates that FHV-1 may be the cause of the anterior uveitis in cats.

Treatment
The prognosis for the most cats is good. However, older cats and kittens with weakened immune system do not usually respond well to the treatment. The treatment of the disease caused by herpesvirus is always symptomatic, based on combination of antibiotics and antivirotics and a specific treatment focused on administration of anti-inflammatory preparations. Supportive treatment consists in rehydration (organism hydration), improvement of nutritional status and administration of L-lysin, application of α-interferon and vitamin preparations. It is recommended to rinse the eyes and moisten them with available eye drops and an ointment. The available vaccines do not prevent from outbreak of the infection; they only help to suppress the clinical signs by activating the immune system of the cat. The kittens are protected up to the age of 8 weeks by the antibodies received through the mother´s milk. It is also recommended to keep the affected animal warm, as the replication of herpesvirus is reduced at temperatures above 37 ˚C. In affected breeds, it is suitable to introduce appropriate hygienic measures. FHV-1 is very sensitive to common disinfectant agents.

References:
Rosalind G., Susan D., Alan R., Etienne T.: Feline herpesvirus, Vet. Res. 38 (2007) 337–354

David Gould: FELINE HERPESVIRUS-1 Ocular manifestations,diagnosis and treatment options
, Journal of Feline Medicine and Surgery (2011) 13, 333–346

SE Andrew, College of Veterinary Medicine, University of Florida: Ocular manifestations of feline herpesvirus, Journal of Feline Medicine and Surgery (2001) 3, 9–16


Smith K. C. Herpesviral abortion in domestic animals. Vet J 1997;153(3):239-44.