Herpes virus (FHV-1)

Feline Herpes virus (FHV-1) is very common in the worldwide cat population, with exposure rates greater than 90% reported. It causes cat ‘flu, and is also one of the most common causes of eye problems in cats.

More than 80% of cats exposed to FHV-1 become lifelong carriers, and around half of these cats will develop recurrent problems, which typically develop during periods of stress. This is called recrudescent disease.

©Ian Ramsey

The signs of infection tend to vary according to the age of the cat:

• Younger cats:
  • Adolescent or young adult cats usually develop primary disease. Signs of cat ‘flu are seen (sneezing, nasal discharge), along with conjunctivitis (sore, sticky eyes with increased discharge). Affected cats can also develop painful corneal ulcers.
• Recrudescent disease:
  • Recrudescent FHV-1 disease develops in older cats when dormant virus is reactivated from a latent stage. These cats do not usually show signs of cat ‘flu. Instead, the main signs are recurrent conjunctivitis, corneal inflammation, ulceration and discharge from the eyes. These signs 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 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.

In some cases, the appearance of a specific type of corneal ulcer, called a dendritic ulcer, is sufficient to allow a clinical diagnosis of FHV-1.

In other cases, diagnosis can be confirmed by swabbing (swabs can be taken from the surface of the eye and/or the throat).

It is not possible to eliminate FHV-1 from an infected cats 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. Examples of antiviral eye drops include ganciclovir and trifluorothymidine. These need to be applied 4x-6x daily until the ulcers heal.
• Antiviral tablets such as Famciclovir tablets may also be effective. These are often prescribed if it is difficult for the owner to apply frequent eye drops. A 2-3 week treatment is usually necessary.
• Other treatments – occasionally the use of interferon eye drops and L-Lysine tablets are advised but there is little evidence that these are effective, and they may even exacerbate the disease.
• Reduce stress. Finally, it is important to remember that the virus reactivates during periods of stress, so if stress levels can be reduced then the immune system should be able to overcome the disease and force the virus back into the dormant state. Identifying and reducing feline stress is not always easy. Try to reduce or eliminate any known stressors (see above) and perhaps consider setting aside some extra time in the evenings for a de-stressing cuddle or groom.