Conjunctivitis – Feline Herpes Viral Conjunctivitis

What is feline herpes viral conjunctivitis?

Conjunctivitis is the medical term used to describe 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 or may be secondary to an underlying systemic or ocular (eye) disease (also see handout "Conjunctivitis in Cats").

Feline herpesvirus conjunctivitis 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. In most cases, herpesvirus conjunctivitis is self-limiting and will resolve within two weeks. Many cats that are 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 recurrent ocular disease such as conjunctivitis, approximately 80% of infected cats will become permanent carriers and can infect other cats throughout their life.

What are the clinical signs of feline herpes viral conjunctivitis?

"Signs often appear suddenly and are especially common after stressful situations."

The most common clinical signs of conjunctivitis are squinting or closing of the eye; red, swollen tissue surrounding the eye and eyelids; ocular discharge that may range from clear to yellow-greenish in color; and upper respiratory symptoms such as sneezing or nasal discharge. These signs often appear suddenly and are especially common after stressful situations such as travel, boarding, surgery, or illness. 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 (for further details on this disease, see the handout called "Chlamydial Conjunctivitis in Cats ").

Young kittens with herpes viral conjunctivitis may have such severe infection that their eyes become sealed shut with discharged matter. In this situation, the eyes must be opened or permanent damage, even blindness, may occur. These kittens also typically have runny noses, nasal discharge, sneezing, and coughing.

What diagnostic testing is indicated for feline herpes viral conjunctivitis?

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 surface of the eye. Identification of feline herpesvirus DNA by polymerase chain reaction amplification (PCR testing) is the most sensitive test available for diagnosing infection by FHV-1. Unfortunately, if the virus is in a latent state (the patient is not showing clinical signs), diagnostic testing is usually unrewarding. 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?

"If there are corneal ulcers, it is important to treat these appropriately."

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 important 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 medications

• L-lysine – nutritional supplement often used lifelong to aid in reducing viral replication

• Vaccination with herpes and calicivirus vaccine may be beneficial in stimulating local immunity

• Acyclovir, an oral antiviral medication may be used in severe or poorly responsive cases. Because of its potential toxicity in cats, only cats with a confirmed herpesvirus infection should receive this medication, and it should be started at a low dose. With this medication, it is necessary to monitor the patient’s blood through complete blood count (CBC) testing every two to three weeks.

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, supplementing the diet with L-lysine daily, reducing stressful situations, and proper vaccination against preventable causes are your cat's best defense.

It is important 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.