Ocular infection with the feline herpesvirus is extremely common in cats. The virus is everywhere. Most cats are exposed as kittens. Kittens may be infected by the mother cat even at birth. Thus they may be infected even before their eyes have opened!
During the initial infection, the kitten typically shows all of the signs of an upper respiratory infection including sneezing, nasal discharge, and possibly a decreased appetite. Ocular signs are present as well and range from ocular discharge, swelling, and squinting. Most kittens are able to recover from this type of an infection within 1-2 weeks. They may never show any signs again, however the virus will persist in their system in a latent state. Cats may carry the virus for years without showing any signs. Asymptomatic carriers may shed the virus. Recurrences of ocular signs are possible at any point in the future, especially after stressful events. Fortunately, it is the minority of cats that have these relapses.
Most of the cats that come to this practice with signs of a herpes infection are actually having a flare-up of a previously latent infection. Your cat may have had the initial infection before you even got him or her. Thus the diagnosis may come as a total surprise to you. In many adult cats, only one eye is affected.
It is important for you to realize that the feline form of herpesvirus is species specific. In other words, it will not be transferred either to you, other family members, or dogs. Other cats are susceptible. Fortunately, it is rare for there to be an “outbreak” within a household of adult cats. Most cats have already been exposed and have apparently mounted an immune response to the infection. Very young and very old cats are the most sensitive. Certain medical conditions and certain medications (eg., prednisone) can increase the risk for herpetic eye problems.
Minimization of stress is important to the control of your cat’s eye problem. Many cats that show signs of a herpetic infection do so after a stressful event such as illness, surgery, boarding, or acquisition of a new pet in the household.
Unfortunately, the diagnostic tests that are currently available to definitively diagnose a herpes infection are unreliable. This is particularly true for chronic cases. The doctor may recommend testing in select cases. Most of the testing on our feline patients where we suspect a herpes infection is to rule-out secondary bacterial infections, alternative diagnoses, or other complicating factors (eg., eosinophilic disease).
The diagnosis of an ocular herpetic infection is best made by the doctor’s evaluation of the history of the eye problem, the signs in your particular cat’s eyes, as well as the response to therapy. Most of the cats that we see have already been treated medically and did not exhibit an appropriate response to therapy. This is in itself suggestive of a herpes infection.
The most important thing to remember is to try to remain patient. These types of infections can resolve quickly with antiviral treatments but some cases are extremely challenging to control. “Cure” is not a reasonable goal as there is not anything available to eliminate this virus from your cat’s system. The goals of treatment are to eliminate the signs of infection, to control ocular pain, and to prevent damage to the eyes that can lead to vision loss.
The antiviral medications available to treat this condition only inhibit, but do not destroy, the virus. This means that your cat’s immune system is extremely important to our goal of getting the active infection “into remission”. If your cat has a weak immune system due to age, immunosuppressive viral infections (eg., FIV or FeLV), or other medical conditions, it is likely to be particularly challenging getting the eye problem under control.
Medical therapy for your cat will most likely include an antiviral drop or ointment. Frequency of treatment with these medications is very important, because the drugs are only inhibiting the virus and not killing it. Treatment is likely to be required for at least 3 weeks (and for 1 week beyond remission of signs). Many cases require more chronic therapy. The most commonly used drugs in this category are idoxuridine and cidofovir. An oral treatment, famciclovir (Famvir) is used in some severe cases.
An antibiotic may be used if herpetic corneal ulcers are present and/or if there are signs of a secondary bacterial infection. A bacterial infection can quickly accelerate the rate of damage to the eye(s) by the virus. Atropine may be used to control pain in the eye. It will dilate the pupil in treated eyes and thus create some light sensitivity, but it can help to make your pet less painful during the healing period. Oral pain killers are sometimes necessary for extremely painful pets.
L-lysine is an amino acid (protein building block) that has shown some antiviral effects against both cat and human herpesviruses. It is a safe supplement that can be given to your cat to help inhibit the life cycle of the virus. It should be given with food, as it can cause vomiting if given on an empty stomach. It can be used long-term. It is available in many forms including tablet, capsule, fish-flavored powder (to mix with food), and oral paste. One of our doctors can give you the appropriate dosage. It is not usually effective as the sole treatment during an active infection. Its best use is either in combination with other antiviral treatments or for long-term use to reduce recurrences.
The herpes virus most commonly causes conjunctivitis (signs similar to “pink eye” of people) or corneal infection. Corneal infection may consist of cloudiness, redness, and/or corneal ulcers. The latter can be very painful.
The most common complications of a herpetic infection are scarring of the eye, non-healing corneal ulcers, corneal sequestration (brown degeneration of cornea, usually require surgery for healing), chronic tearing from the eye, eosinophilic keratitis or conjunctivitis, and inward rolling of the eyelids (“entropion”). Eosinophilic keratitis and conjunctivitis are conditions where there is infiltration of ocular tissues with the eosinophil, which is a type of inflammatory cell.
Due to persistence of the virus in your cat, recurrences are possible. An initial sign of flare-up can be upper respiratory signs. If your cat becomes sniffly or starts sneezing, please contact us about his/her eyes. In some patients, this is a good time to start antiviral treatments to try to prevent the eye problems.
Herpes infections cause some of the most common eye problems of cats. There is not a week that goes by where we don’t see a cat (usually many) with herpetic eye disease. We deal with this all of the time and are here to help you. Please call with questions or concerns.