What is feline herpes viral conjunctivitis?
Conjunctivitis is the medical term for inflammation of the tissues surrounding the eye. These tissues include the lining of the eyelids and the third eyelid, as well as the tissues covering the front part of the eye or globe. Conjunctivitis may be a primary condition secondary to an underlying systemic or ocular (eye) disease (see the handout "Conjunctivitis in Cats" for more information).
Feline herpesvirus conjunctivitis is a form of primary conjunctivitis caused by the highly infectious feline herpesvirus (FHV-1). Herpesvirus infection is the most common cause of conjunctivitis in cats.
Usually, herpesvirus conjunctivitis is self-limiting and will resolve within two weeks. Many cats infected with FHV-1 do not show any signs of clinical illness (i.e., they have a latent infection). Although it is estimated that less than 45% of adult cats with latent herpesvirus infection will develop a recurrent ocular disease such as conjunctivitis, approximately 80% of infected cats will become permanent carriers and can infect other cats throughout their lifetime.
What are the clinical signs of feline herpes viral conjunctivitis?
The most common clinical signs of conjunctivitis include:
- Squinting or closing of the eye
- Red, swollen tissue surrounding the eye and eyelids
- Ocular discharge that may range from clear to yellow or green
- Upper respiratory symptoms, such as sneezing or nasal discharge
These signs often appear suddenly and are especially common after stressful situations (e.g., travel, boarding, surgery, illness, etc.).
Chemosis, a condition in which the membranes that line the eyelids and surface of the eye appear to have fluid in them, is more commonly associated with Chlamydophila felis infections (see the handout "Chlamydial Conjunctivitis in Cats" for more information).
Young kittens with herpes viral conjunctivitis may have such a severe infection that their eyes become sealed shut with the discharged matter. The eyes must be opened in these cases, or permanent damage, even blindness, may occur. These kittens also typically have runny noses, nasal discharge, sneezing, and coughing.
How is feline herpes viral conjunctivitis diagnosed?
Diagnosis is based primarily on medical history and physical examination. Corneal staining with fluorescein dye is often performed to look for any ulcers that may have developed on the eye’s surface. Identifying feline herpesvirus DNA by polymerase chain reaction amplification (PCR testing) is the most sensitive test for diagnosing an FHV-1 infection.
"Diagnosis is based primarily on medical history and physical examination."
Unfortunately, diagnostic testing is usually unrewarding if the virus is in a latent state (the patient is not showing clinical signs). Since decreased tear film production has been associated with FHV-1 conjunctivitis, specific tests to assess the tear production may be recommended in some cases.
What is the treatment for feline herpes viral conjunctivitis?
Treatment is determined by your cat's specific clinical signs and problems. It is important to remember that these infections are usually mild and self-limiting. However, if corneal ulcers develop, it is essential to treat these appropriately and thoroughly to prevent permanent eye damage (for further details, see our handout "Corneal Ulcers in Cats").
The following are common treatment regimens used in treating recurrent feline herpes viral conjunctivitis:
- Topical antibiotics, such as tobramycin (Tobrex®), fusidic acid (Isathal®), and oxytetracycline (Terramycin®)
- Topical anti-viral medications, such as idoxuridine ophthalmic solution and trifluridine ophthalmic solution (also called triflurothymidine)
- L-lysine supplementation. Although initially thought to reduce the duration of disease, evidence of lysine’s effectiveness at reducing herpes conjunctivitis is limited. If cats are stressed by its administration, lysine can worsen signs.
- Probiotics, such as Purina Fortiflora®, have decreased the severity of a herpes virus infection when added to the cat’s diet.
- Vaccination with intranasal herpes and calicivirus vaccine two to three times yearly may be beneficial in stimulating local immunity.
Famciclovir oral anti-viral medication, used as a herpes virus treatment in humans, has also been effective against the feline herpes virus. The doses and protocols for this drug are still being investigated, but it has been found that when given orally, famciclovir is secreted in tears. This means the active drug is given orally but acts as a topical treatment.
What is the prognosis for a cat diagnosed with herpes viral conjunctivitis?
There is no cure for herpesvirus infections. The therapeutic goal is to reduce the frequency and severity of recurrences. Most cats respond well to medical management and lead relatively normal lives. Minimizing the chance of infection, feeding a premium diet, reducing stressful situations, and proper vaccination against preventable causes are your cat's best defenses. Your veterinarian may also recommend lysine supplementation daily if your cat takes it easily.
It is essential to note that many cats fully recover from herpes viral conjunctivitis and become carriers of the virus for life. Other cats may contract FHV-1 infection from contact with an infected cat. It is common for entire households of cats to be infected with FHV-1 and experience periodic outbreaks.
