Feline herpesvirus (FHV-1) is a common cause of eye and upper respiratory infection in the cat. This virus is very common in the cat population, but it is not contagious to people and other species of animals such as dogs. Herpesvirus is easily passed from one cat to another through sneezing, coughing, grooming, and/or simply living in the same household with an infected cat. While it is quite contagious, most cats contract this infection from their mothers before they are even weaned. This virus is in the same family as the chicken pox virus. As you may know, some people will develop ‘shingles’ in their adult lives, which is a re-emergence of the chicken pox virus that has been lying dormant in the body since childhood. The same is true for cats with FHV-1. Clinical signs associated with infection can vary greatly between cats. Some cats will never have signs after the initial infection while other cats will have episodes throughout life.
Some cats affected with FHV-1 may only have mild conjunctivitis (redness and inﬂammation of the white part of the eye) of one or both eyes. Other cats have more severe disease and may show ocular and nasal discharge, conjunctivitis, coughing and sneezing. Cats may also develop ulcers of the cornea (the clear “window” in the front part of the eye). Corneal ulcers can be very painful and serious enough to cause noticeable scarring or even perforation of the normally clear cornea.
After initial recovery from the herpesvirus infection, an estimated 80% of the cats become a carrier of the disease. In other words, the disease goes into temporary remission but the cat may still be infectious. In these cats, stress and illness can reactivate the virus, causing repeated infections or recurrences of the clinical signs throughout life. Stressors may include moving to a new house, having new pets or houseguests in the household, construction/remodeling, a traveling owner, etc.) Repeated or chronic infections have been associated with diseases such as dry eye, symblepharon (adhesion of the conjunctiva to itself or to the cornea), corneal sequestrum (an abnormal brown plaque formation on the cornea), and possibly eosinophilic keratitis (an immune-mediated condition of the cornea).
The definitive diagnosis of feline herpesvirus infection is accomplished by laboratory testing. Many tests are available through a professional diagnostic laboratory. They include virus isolation, ﬂuorescent antibody (FA) testing, serology such as ELISA or serum neutralizing titers, and polymerase chain reaction (PCR) testing. It is important to realize that these tests may have false negative results. On the other hand, certain cats in the carrier state but without apparent clinical signs can also test positive for some of these diagnostic modalities. Since the disease is extremely common, it is not always necessary to perform diagnostic testing, but your veterinary ophthalmologist will discuss this with you at the examination.
Treatment for herpesvirus is aimed at controlling clinical signs and reducing secondary complications. It is important to note that there is no cure for herpesvirus, and once infected, your cat has the virus for life. Some animals will never have clinical disease after the initial infection while others may have frequent recurrences. Cats that have recurrent outbreaks often have a stressful trigger, which if identified can be avoided or minimized. This can reduce the number of outbreaks. Typically, therapy includes topical antiviral drops or ointment for the eye and occasionally an oral antiviral medication. Sometimes starting medications prophylactically (before a known stressor) the severity of the recurrent infection can be reduced. Some anecdotal reports state that L-lysine, an amino acid dietary supplement, can inhibit viral replication. This has been shown in a laboratory setting but not in cats with natural infection. There are no studies proving that Giving L-lysine as a supplement may benefit cats with herpesvirus as many owners feel it reduces outbreaks. In any event, there are no known side effects of L-lysine documented in the cat.
Vaccination against herpesvirus infection is included in the typical feline vaccination schedule provided by your primary care veterinarian. The vaccine minimizes the clinical signs of the herpesvirus infection but does not prevent future outbreaks. Additionally, the vaccination does not cure cats already infected with the herpesvirus.