If your cat has been diagnosed with feline herpesvirus (FHV), you may have a lot of questions. You are not alone—more than 50% of cats have FHV, but many show no signs. FHV is the No. 1 cause of viral respiratory problems in cats, and can also affect their eyes. Here are some facts about FHV and your cat.

What is feline herpesvirus?

FHV is in the same family as the human herpesvirus, but is species specific and affects only cats. As with human herpesvirus, the infection can be acute, and then the virus goes into a latent stage in the nervous system. Stressors such as a household changes, illness, boarding, travel, or corticosteroid use can reactivate the latent stage and cause renewed viral replication in the cat’s body. 

How is a cat infected with feline herpesvirus?

FHV infection is through direct contact with virus particles. This can be from the saliva, nose, or eye discharge of an infected cat, or from contaminated inanimate objects (i.e., clothing, toys, or food and water dishes).

How does feline herpesvirus affect eyes?

Ocular disease because of FHV is not always accompanied by respiratory signs. FHV infection can cause the following eye conditions:

  • Conjunctivitis — The tissue under the eyelids is called the “conjunctiva” and inflammation can result in swelling (i.e., chemosis), squinting (i.e., blepharospasm), and discharge. The conjunctiva can become so inflamed that kittens develop a partial or complete conjunctival adhesion (i.e., symblepharon), which may affect their vision for life.
  • Ulcerative keratitis — “Keratitis” means inflammation of the eye’s outer layer (i.e., corneal epithelium). Inflammation can cause erosions or ulcerations in the cornea, which may appear tree-like (i.e., dendritic), or as a single large ulcer in one geographic location. Corneal ulcers can cause scarring, and a deep corneal ulcer (i.e., descemetocele) can cause an eye rupture. 
  • Eosinophilic or stromal keratitis — This condition is an immunologic reaction to FHV that causes white plaques on the cornea, and can result in blindness.
  • Corneal sequestrum — A “sequestrum” is a brown or black spot that develops when a piece of the cornea dies off, and is rejected by surrounding healthy tissue. Although initially painless, the eye will become sore over time. Persian cats seem particularly predisposed. 
  • Keratoconjunctivitis sicca — Otherwise known as “dry eye” or “KCS,” tear production deficiencies can be caused by the virus infecting the tear-producing glands.

How is feline herpesvirus diagnosed?

A thorough history, examination, and testing by your veterinarian is the first step toward an FHV diagnosis. A PCR test can detect feline herpesvirus DNA in nasal, oral, or conjunctival swabs during the active stage, but since FHV is common in asymptomatic cats, a positive result is not definitive that the virus is causing the current illness. If your cat does not respond to standard treatment for respiratory or ocular conditions, that suggests they may have FHV. 

How is feline herpesvirus treated?

FHV treatment depends on disease severity. More advanced ocular lesions can require surgical procedures to address corneal damage and promote healing. Treating the virus involves a multi-modal approach that can include:

  • Antivirals — Antiviral medications inhibit, rather than destroy the virus. Topical antiviral eye drops, such as idoxuridine, trifluridine, or cidofovir, are often used, and require frequent administration. Oral antiviral medications, such as the human drug famciclovir, can be effective FHV treatment, and is also secreted in tears.
  • Antibiotics — Secondary bacterial infections can complicate treatment for an FHV infection. Topical antibiotic eye drops are often used to control the infection severity. 
  • L-Lysine — Oral supplementation with L-lysine can reduce the severity of FHV conjunctivitis, and prevent reactivation of latent infections. 
  • Probiotics — Certain brands of probiotics can decrease the severity of FHV.
  • Hyaluronate — Hyaluronate eye drops can support the conjunctiva cells and help maintain adequate moisture to keep a cat more comfortable.
  • Polyprenyl immunostimulant — This biological product stimulates cellular immunity against FHV and can reduce disease severity.
  • Interferon — Interferon may reduce the viral spread of FHV and decrease clinical signs associated with acute infection. 

What is the prognosis for feline herpesvirus?

The acute phase of FHV can be addressed with medications or surgery, but almost all cats will be lifelong carriers. Some cats will experience reactivation of the latent stage, with periodic flare-ups. Reactivation signs may be milder than the initial acute phase, but ocular manifestations are common.

How can feline herpesvirus be prevented?

The upper respiratory complex (i.e., FVRCP) vaccine can lessen the severity of FHV infection, but is not 100% effective for prevention. FHV is contagious, so avoiding group situations and practicing good hygiene is essential.

The Veterinary Vision Center team is here to support your cat’s eye health and help them live a good quality of life by your side. Don’t hesitate to contact us if you have questions or concerns about herpesvirus and your cat.