What is Feline Herpes Virus?
Feline herpesvirus-1 (FHV-1) infection is a viral disease that is omnipresent in the world’s cat population, with over 90% of all cats infected. The disease spreads by respiratory secretions, and does so largely from a queen to her kittens. This disease causes a marked inflammatory response in the corneas, and can hide from the immune system very effectively. The virus remains in hiding until times of stress, where the virus rapidly replicates in the corneal and conjunctival surface cells and causes ulceration. This is not a herpes virus that humans can catch from cats, and likewise cats could not have caught this herpes virus from humans.
Clinical signs within the eye include squinting and profuse ocular discharge.
Thankfully the presentation of FHV-1 infection is usually very typical, and a thorough examination combined with a detailed history can allow us to deduce the cause. Additionally, in-house stains applied to the eye can give us more information about the active state of the disease.
The treatment for FHV-1 is designed around managing the severity of herpes flare-ups, but it is impossible at this stage to rid cats of the viral disease. With appropriate treatment, the occurrences of eye problems can become . very infrequent (to almost never happening), and the severity of these episodes can be lessened to become very mild. Treatment involves around suppressing the rapidity of the virus replicating within the eye (and this can be done ideally with oral medications, or eyedrops if patient demeanour demands it), treating the diseased surface of the eye with topical antibiotics to prevent infection ongoing, and offering appropriate pain relief. Additionally, managing stressful or “trigger” events can make recurrences less likely. If treated appropriately, this disease can be managed so that it does not affect the cat’s quality of life.
What is Corneal Sequestra?
Corneal sequestra are unfortunately a common finding in cats, especially exotic breeds. This may occur as a response to local irritation,corneal ulceration, incomplete eyelid closure, or may occur spontaneously. There is some loose association with this condition and the presence of ulcerscaused by FHV-1. A sequestrum is hallmarked by a region of corneal degeneration with a brown-black discolouration. This is a region of mummified cornea imbedded within living tissue, and the body mounts an immune response on the eye to reject this tissue. This can cause great discomfort to the affected cats., and can eventually progress to become full thickness and rupture the cornea.
This condition can be identified rapdily, as it has a very unique appearance. However, we have the means to estimate the depth of corneal invasion with our OCT unit. This machine allows us to determine how deep the lesion is, and allows us to better plan for surgical excision of the sequestrum. We are the only veterinary clinic in Australasia with this diagnostic ability.
The treatment for sequestra involves the surgical removal of the mummified corneal tissue. We then often incorporate a graft over the corneal defect, which drastically reduces the rate of recurrence. If sequestras are left untreated, they can eventually (over a course of months and months) exfoliate on their own. However, they can also progress deep in the cornea and cause a globe rupture, which may necessitate eye removal. This whole process is also painful for the cat for the entire period, and so early surgical excision is always our recommendation.