Feline herpes virus [FHV] is the most frequent cause of conjunctivitis and corneal damage in domestic cats. It is thought that about 70% of cats show antibodies to the virus, indicating that they have been exposed to it.

The virus is transmitted from infected cats by direct contact as well as by aerosols. Nasal, oral and conjunctival routes of infection have been demonstrated and the virus is primarily shed in the secretions from these body systems for 1-3 weeks following infection.

Important characteristics of FHV:

•  Rapid rate of replication in surface cells of the mouth, nose and eye 
•  Severe cellular destruction ability 
•  Ability to produce a carrier state in cats following infection where the virus remains dormant in the cat 
•  Ability to recrudesce [or re-activate] from the dormant stage under conditions of stress

Following acute infection or subclinical infection, 20% of cats recover completely and 80% enter the latent or dormant phase and are asymptomatic. Of this latter group, 45% will recrudesce. Some will become an asymptomatic shedder whilst others [about 5%] show chronic or recurrent eye disease.

The typical stress events in a cat’s life that can re-activate the virus include:

•  introduction of a new affected kitten or cat 
•  moving house  
•  hospitalisation or cattery accommodation 
•  transporting to cat shows, on holiday etc 
•  stress during the mating season or been sent away for mating 
•  a new baby in the house 
•  constant harassment by dogs

Ophthalmic conditions associated with FHV

The common eye problems associated with FHV include:

•  Conjunctivitis 

  Inflammation of the conjunctiva causing excessive tearing and swollen conjunctiva. This may last from weeks to months and is frequently recurrent.

•  Keratitis

  FHV is the only known virus to cause inflammation of the cornea. Subsequent ulceration and even perforation is possible.

•  Corneal sequestrum 

  This is characterised by a dark brown mark of dead tissue in the central cornea. The dead tissue can eventually perforate the globe. This condition is most commonly seen in Persian and Chinchilla cats.

•  Symblepharon 

  This is most common in very young kittens and results from severe conjunctival damage where the affected tissues grow together causing adhesions. These frequently are conjunctiva to conjunctiva or conjunctiva to cornea. The free movement of the third eyelid may also be affected.

•  Eosinophilic keratitis 

  This is a far less common problem that results in a dense blood vessel and white crystalline invasion of the cornea.

•  Keratoconjunctivitis sicca [dry eye] 

  It is not been confirmed if the dry eye is due to viral destruction of the glandular tissue supplying the tears, or is from damage to the ductules carrying the tears to the eye surface.

•  Uveitis 

  This refers to inflammation inside the front chamber of the eye. Recent evidence suggests that FHV can be found in the fluids of the eye.

Not all affected cats show all these symptoms and thus treatment may vary according to the problems encountered. The veterinary ophthalmologist will examine your pet's eyes carefully and advise on the most appropriate treatment.