FELINE HERPES VIRUS INFECTION AND CORNEAL EYE ULCERS
Herpes virus, or Feline Viral Rhinotracheitis, is the most prevalent viral disease of cats. It causes a mild disease in cats and kittens much like the common cold in people. 80% of cats have been exposed. Just as 90% of humans have Herpes simplex virus harbored in their nerve tissue from previous exposure to the Herpes simplex virus, 80% of cats, indoors or out, have Feline Herpes virus in their system.
Unless a cat's immune system is compromised by feline leukemia, cancer or other problems, the initial Herpes infection that most kittens get will run it's course in a week or two. Veterinarians often treat the infection with Terramycin eye ointment and with antibiotics, to lessen the risk of secondary bacterial infections like sinusitis and pneumonia. Major disease or death from infection with Herpes is rare. Ever afterwards, however, the cat that has been infected, even mildly, harbors the virus in its system.
When cats are stressed by other diseases, use of steroid medications for allergies, a new household, traveling, a new pet or baby in the house, or any other cause, they can shed Herpes virus from their systems again. Usually they will show no obvious signs of illness but virus can be found in their tears, nasal discharge or saliva. During this re-shedding time cats are contagious to other cats and kittens. This is why kittens often catch these viruses even though the adult cat in the house, or the cats around it at a humane society or pet store, have no symptoms of disease.
Some cats do show symptoms when their Herpes flares up. Just as some people get repeated Herpes cold sores from Herpes simplex virus in their system, some cats will repeatedly get corneal (eye) ulcers from Herpes virus. The immune system is keeping the infection at bay for the most part, but it can't get rid of it completely and it keeps flaring up to cause disease. Some cats will flare up with ulcers consistently whenever they get stressed or ill. Some patients get an ulcer every year when they come in to have their teeth cleaned. It’s not advisable to stop doing dental procedures on these cats, since dental care is so important to health, but you need to minimize problems as well.
Persian and Himalayan cats are especially likely to have problems because the shape of their face makes them prone to dry eyes and they can also have poor immune systems. Dental disease and sinus infections, which spread to the eyes via the tear ducts, also are more prevalent in these breeds.
Cats with recurrent corneal ulcers should be tested to determine if Herpes virus is the cause. A swab is taken of the conjunctiva (the inner lining of the eyelid) and sent to a lab in Colorado for a Herpes PCR test. If the test is positive, you have your diagnosis.
Unfortunately, as many as 20% of cats will test negative with this special test, even though they have the disease. This is because the virus can be lurking too deep in the ulcer or nerve tissue to be obtainable on the swab. If you and your vet have ruled out other causes of ulceration your veterinarian may still assume the cause is the herpes virus and treat for it.
Antiviral eye drops are usually effective at treating Herpes eye ulcers but they are expensive and have to be given very frequently when the ulcers flare up. An amino acid called Lysine, available at health food and nutrition stores, can be added to the food and seems to help cats fight the ulcers better. There are several eye medications that can be used and some cats respond better to one than another. Your veterinarian will need to work carefully with you to find the best treatment for your cat.
Some cats require lifetime therapy and others only need treatment for stresses like dental cleanings, moving and new additions to the household. Medication is usually tried first, but occasionally referral to a veterinary ophthalmologist is necessary for surgery on a persistent ulcer.
Although vaccinations for Herpes virus (the first three letters are Feline Viral Rhinotracheitis in an FVRCP distemper combination vaccine) in cats have been used for years they seem to have made no difference in the prevalence of respiratory disease in cats. Cats who have been vaccinated have milder symptoms and get better faster, but they still get the virus, and they still shed it later on. The new nasal vaccines seem to be more effective and work faster to protect kittens, but Herpes infection will not be eradicated in the near future.
