Feline herpesvirus (FHV-1) is the virus that causes rhinotracheitis in cats. FHV-1 usually infects young cats, but can remain dormant for years, and reappear if the cat is stressed, is on high doses of corticosteroids, has a feline leukemia virus (FeLV) or feline immunodeficiency virus infection (FIV), or there is local irritation or bacterial infection of the eye. The most common eye conditions caused by FHV-1 are conjunctivitis and keratitis (inflammation of the cornea).
FHV-1 is one of the most common causes of conjunctivitis in cats. Young kittens are most commonly affected, with both eyes having considerable clear or cloudy discharge. In almost all cases, the kitten also has signs of a respiratory infection, such as nasal discharge. Oral ulcers are commonly present. In adult cats, often only one eye is affected, and there respiratory signs are often absent. For treatment, antibiotic ointments are often used to prevent secondary bacterial infections. If the infection is severe, especially in a kitten, antiviral drugs are used.
FHV-1 is the most common cause of corneal ulcers in cats. Any cat with a corneal ulcer should be considered to have an FHV-1 infection until proven otherwise, and antiviral medication should begin immediately. Ulcers resulting from FHV-1 are generally not deep unless they become secondarily infected with bacteria, so antibiotics are generally included in the treatment. Ulcers of the eye are very painful, so affected cats are often treated with oral or injectable pain relievers, and atropine ointment, which dilates the eye and reduces pain.
Idoxuridine is a common antiviral agent used in cats. L-lysine, which is an amino acid, has been found to interfere with the replication of FHV-1. L-lysine is administered orally and its use in combination with idoxuridine is recommended as the first choice of therapies. If this combination is not effective, other drugs, alone or in combination, may be used. Some of these are very expensive, but may be necessary to save the cat's sight.