Feline herpesvirus is a common upper respiratory infection of cats. Most cats are exposed at some point during their life. Once exposed to the virus, most cats develop sufficient immunity to destroy the virus and antibodies to prevent reinfection. Some cats, like some people, develop latent infection. This means the virus isn’t destroyed, but goes into remission, and can be reactivated during times of stress or illness.

Signs of herpes infection in cats are highly variable and range from mild conjunctivitis (“pink eye”) to life-threatening illness. In severe cases, upper respiratory infection, fever, loss of appetite, marked pink-eye and ocular and nasal discharges occur.

Secondary bacterial infections are common. Signs are usually most severe in kittens and unvaccinated cats. Sometimes, herpesvirus infections can be chronic and cause sporadic conjunctivitis over the life of the cat. Diagnosis is now made with DNA tests from swabs of the mucosa of the eyes and throat of infected cats.

Treatment is directed at the secondary bacterial infections that occur with the primary viral infection. Herpes is a virus, so therapies against viruses are rarely curative. There are many drugs that are tried, such as idoxuridine and cidofovir. These drugs are expensive and require frequent dosing and can be irritating. Oral lysine is an inexpensive supplement that can be used long-term to try to keep the viruses in submission.

Additional supportive measures may also be helpful. Application of moist, warm compresses helps keep the eyes clean and free of discharge. Often, corneal ulcers develop that need intensive drugs to prevent the eye from rupturing and losing sight.

Early and adequate vaccination of cats helps prevent herpes infection. Severe infections do not often recur if the cat has a good immune system, but low-grade signs of herpes may recur sporadically throughout the cat’s life. Herpes is most likely to reactivate sporadically during times of stress.

Dr. Karsten Fostvedt is a veterinarian at St. Francis Pet Clinic in Ketchum.

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