FHV-1, feline herpes, is common in the UK cat population, and is one of the causes of cat ‘flu’.
It is also a common cause of eye disease in cats. In fact, more than 80% of cats exposed to FHV-1 become lifelong carriers of the virus, and around half of these will develop recurrent problems. The signs of infection tend to vary according to the age of the cat. It may require specialist veterinary ophthalmology.
Kittens that are affected with feline herpes before they open their eyes (before 10-14 days) can suffer a severe conjunctivitis behind the closed eyelids. The eyes become sore, swollen and pus may leak onto the skin. The kitten may also show signs of respiratory disease such as sneezing and coughing. If not acted upon quickly the disease can progress to corneal ulceration and even perforation causing the loss of the eye or eyes. Long-term complications of feline herpes include dry eye and adhesions of the conjunctiva to the surface of the eye.
Older Kittens and Young Adults
There is usually sudden onset conjunctivitis of both eyes accompanied by discomfort. They may develop inflammation of the cornea (the clear surface of the eye) and corneal ulceration which can be particularly painful. This is called keratitis. Again, respiratory infection often occurs simultaneously.
Herpes-related disease in older cats usually occurs when the virus is reactivated from a latent stage in an individual infected earlier in life. These cats do not usually show respiratory signs although they may have a history of cat ‘flu. The main signs are recurrent conjunctivitis, corneal inflammation, ulceration and discharge from the eyes. These signs of feline herpes may get worse during ‘flare ups’, which often develop after a period of stress. It can be difficult to identify stress in some cats, but common stressors include recent boarding at a cattery, moving house, or the introduction of a new pet (or baby!) in the household.
Some older cats develop a low grade but progressive inflammation of the cornea due to persistent feline herpes (FHV-1) infection. This is often not painful but can cause a gradual deterioration in vision as the cornea becomes more cloudy and scarred. This condition, called stromal keratitis, is particularly difficult to treat.
It is not possible to eliminate feline herpes (FHV-1) from an infected cat but we can treat the clinical signs associated with infection.
- Antibiotic eye drops do not treat the viral infection itself but can be used to prevent secondary bacterial infections.
- Antiviral eye drops/ointments are most commonly used when there is corneal ulceration or acute conjunctivitis. The most effective treatment available in the UK is an eye drop called TFT (trifluorothymidine). Although this is the best treatment available, it is relatively expensive and requires frequent application (5x to 6x daily for 2-3 weeks). It can also cause eye irritation in some cats, although this is not common. If we recommend the use of TFT then we need to order it on a ‘patient-by’patient’ basis. Other antiviral eye treatments, such as acyclovir (ZoviraxTM), tend to be much less effective.
- Occasionally the use of interferon eye drops and L-Lysine tablets are advised but there is little evidence that these are effective.
- Reduce stress! Finally, it is worth remembering that the feline herpes virus reactivates during periods of stress, so it is worth trying to reduce stress levels in your cat. This is not always easy, but try to minimize the effects of any stressors in your cats life, and perhaps consider setting aside some extra time in the evenings for a de-stressing cuddle or groom!
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