common symptom associated with feline herpesvirus-1 (FHV-1) is ocular
disease. In fact, it is the most frequent cause of conjunctivitis
and keratitis in domestic cats. Living with a cat with ocular
disease can be difficult, frustrating, and expensive to diagnose and
treat. Sometimes the only sign a cat will show is eye problems or
they can show a multitude of signs related to viral
rhinotracheitis. There are several forms of ocular disease caused
by FHV-1 which will be explained shortly. First, it is important
to understand the anatomy and physiology of the eye.
The cornea is the transparent front part of the eye. It is
composed of 5 layers which are made up of epithelium, collagen, and
endothelium with the epithelium being the outermost layer. When
the epithelium and some of of the collagen are missing, a corneal ulcer
will form. This can lead to pain due to unwanted nerve
stimulation. Eyes that have intact corneas are far less sensitive
than those with ulcerated corneas. Because FHV-1 attacks
epithelial cells, corneal epithelium is at risk of getting damaged as
the virus invades and replicates in those cells.
A current FVH-1 infection and viral replication along with a secondary
bacterial infection will lead to conjunctivitis. Conjunctivitis
is commonly seen in both eyes in this type of infection and redness
around the eye along with clear discharge is seen. Most cats will
recover from their first infection in 10-20 days, but if the infection
is severe or the cat's immune system is suppressed, this may lead to
recurrent or chronic conjunctivitis.
Keratitis, inflammation of the cornea, is only caused virally by
FHV-1. When this occurs, it is likely to be in an adult cat
stemming from the reactivation of a latent infection. When the
layers of epithelium and collagen, in the stroma, are damaged, this
leads to a corneal ulcer in which its outward signs depend on the depth
of corneal infection and chronicity. Keratitis can occur in one
eye or both, often without any respiratory signs.
Stromal keratitis, infection and inflammation of the deeper corneal
layer, is a less common disease of FHV-1 infection. It does have
importance however, due to the fact that it can potentially lead to
vision-threatening clouding over and scarring of the corneal
tissue. This condition is not a manifestation of a primary FHV-1
infection, but is rather, an accumulation of ocular disease periods
seen with chronic recurrent infections.