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Feline Herpes Virus

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Feline Herpes Virus (FHV) is a common pathogen (infectious agent) that causes an upper respiratory disease and ophthalmic (eye) disease in cats. Exposure to this virus is common and known to be greater in breeding colonies, catteries, shelters, and multi-cat households. It is believed that many kittens are exposed to this virus following birth as the virus can be found in the birth canal of the mother.

Feline Herpes Virus (FHV) is a common pathogen (infectious agent) that causes an upper respiratory disease and ophthalmic (eye) disease in cats. Exposure to this virus is common and known to be greater in breeding colonies, catteries, shelters, and multi-cat households. It is believed that many kittens are exposed to this virus following birth as the virus can be found in the birth canal of the mother.

The virus can also be spread in an aerosol form, meaning a cat gets infected after exposure to the sneeze of an infected cat. Drying and sunlight can kill the virus, but it can live for many hours in a moist, cool environment.

The feline herpesvirus most commonly infects kittens and causes sneezing, ocular and nasal discharge, and a reluctance to eat and play. With good nursing care, the vast majority of kittens return to normal within several weeks. Vaccinated kittens may still develop the disease, but the illness tends to be less severe. Approximately 80% of FHV infected cats become latent carriers with a 45% chance of viral re-activation.

One of the more common ophthalmic problems seen in cats are infections caused by FHV. Adult cats with an eye infection due to FHV are more likely to be suffering from viral re-activation than from a primary (newly acquired) viral infection. This virus causes conjunctivitis (inflammation of the pink tissue surrounding the eye) and keratitis (corneal inflammation / scarring / ulcers). There can be other secondary ocular problems associated with FHV which will be mentioned later in this article. Occasionally, sneezing and concurrent mouth (oral) ulcers occur in some patients.

Whenever your pet is showing signs of a health issue your first step is to contact your primary care veterinarian. If it is indicated that your pet may suffer from Feline Herpes Virus or another serious condition, a veterinary specialist is available at an ExpertVet certified hospital.

Clinical Signs and Diagnosis

Feline herpes virus is most commonly an upper respiratory and ocular disease causing virus and is prevalent in environments with multiple cats or when new cats are introduced. The virus replicates in the upper respiratory tract and conjunctival tissue of the eye during primary infection. Symptoms accompanying the disease include sneezing, nasal discharge and discharge from the eyes. Some primary cases resolve with no eye involvement. However, when the eyes are affected, there are numerous ways the disease can manifest that vary due to the pet’s age, immune system, and viral load. Kittens can have scarring of the eyes from infection prior to and shortly after birth. FHV may remain dormant or “inactive” in the cranial nerves (often the trigeminal nerve ganglion) which serve the eyes. Adult cats may experience chronic or recurrent conjunctivitis and corneal infections / ulcers when the virus is “re-activated” from the nerves. There is evidence that many ocular diseases are associated with herpes virus and recurrence can be frequent.

A diagnosis is often made on clinical signs / symptoms and the history presented at the initial ophthalmic exam. There are many other diagnostic tests reserved for specific cases when necessary. A complete ocular exam is performed to address the various manifestations of this disease.

A FHV infection may be suspected anytime a cat has an eye infection that does not respond to antibiotics, which have no effect on viruses. One of the more common diagnostic tests to confirm a FHV infection involves applying topical anesthestic and taking cell (cytology) scrapings from the eye. The slide is submitted to a laboratory for a specific test procedure known as a Polymerase Chain Reaction (PCR) test. This test can be quite specific when compared to other tests. A different diagnostic test, known as the Indirect Fluorescent Antibody Test (IFA), can also be performed. While the IFA test is not as precise as the PCR test, performing both tests simultaneously indicates the presence of herpes better than using either test alone. Another test that can be used is virus isolation (VI), which actually grows the virus in tissue cultures. This test takes up to a month and is quite costly.


Treatment for ocular FHV infections can initially be nonspecific and directed at controlling secondary disease that caused by the infection. Topical and systemic antibiotics are often prescribed to treat the concurrent (or secondary) bacterial infection for both the respiratory and ocular components of this disease. Topical and systemic antiviral medication(s) can be used in conjunction with the antibiotics, but may be administered for poorly responsive / slowly resolving / chronic cases.

A common initial therapy is to start an oral form of the amino acid lysine. Lysine competes with another amino acid the virus needs to reproduce. Oral or topical antiviral drugs may also be used in conjunction with lysine. Sometimes surgery is required to repair the damage from the FHV infection to the eye.

Because it is not exactly known how long it takes for the anti-viral medciations to kill (or inactivate) the virus particles, treatment must be continued for four to six weeks or longer. Occasionally herpes virus can become resistant to these medications. Though it doesn’t happen often, this fact should be kept in mind, especially your cat initially improves and then relapses. If resistance to one medication occurs, a change to another medication can be made.

Surgical intervention is sometimes indicated when there is excessive scarring or deep (vision threatening) corneal ulcers / perforations. There is no cure for herpes virus in any species, but by eliminating or reducing outside risk factors, in most cases management of the disease is possible. Reducing stress by maintaining routine is also helpful. It is common to see recurrences requiring periodic medical treatment.

Management of FHV

We do not always know why our feline patients become “re-activated” or have a “flare-up” of the FHV infection, but we do know that in many cases stressful episodes can be the trigger. The feline herpes virus can hide quietly in your cat’s nerve roots (ie. in “inactive” status). During periods of stress, the virus travels down the nerves and injures the ocular tissues in one or both eyes. In some cases, one eye may be more involved than the other. Affected cats begin squinting, tearing, and may paw at the eye(s). Some cats may also sneeze, stop eating, and become lethargic.

As many people know, human herpesvirus may cause the lip and skin conditions known as “cold sores” and “shingles.” Just as with the human form of herpes virus, any stressful episode may cause a recurrence of the infection (or “flare up”).

In cats, a relapse may be triggered by the owner leaving town and a stranger coming in to feed the cats, being boarded, or strangers or new animals coming for a visit. Knowing this helps us understand the recurrence of FHV infections following stressful episodes. This can indicate a possible return of the herpes viral infection and requires retreatment with the medication.

The three most common stressful events that cause FHV re-activation in your pet are:

  1. A new cat or dog is brought into the household.
  2. Your cat is moved to a new household.
  3. You go away on vacation.

Basically, anything that alters the normal daily routine of your cat may permit viral re-activation.

More Information

Some cats contract FHV infections from their mothers. Other cats become infected when they are exposed to another cat that is a FHV carrier or has active clinical signs (ie. respiratory or eye infections). Stray cats, multi-cat households and homes where a new cat has been introduced are most likely to suffer this infection.

There are other herpes viruses specific to other species, including dogs, people, cattle, chickens and horses. In fact, most animals have their own type (species specific form) of herpes virus. These viruses will not infect other species, i.e., when a cat has herpesvirus, the owner is not at risk of contracting the disease.

There are other herpes related (directly or indirectly) conditions may develop during or after a primary ocular FHV infection or “flare up.” These may include the following:

  1. Tear film abnormalities / dry eye / low tear levels.
  2. Symblepharon (abnormal adhesions / scarring involving the corneal and conjunctival tissues).
  3. Corneal Sequestrum (focal areas of “dead” corneal tissue appearing as a black or brown plaque or scab on the surface of the eye).
  4. Narrowing or scarring of the nasolacrimal (tear drainage) system which causes tear spillage (epiphora) onto the face.
  5. Eosinophilic Keratitis – accumulation of white / yellow “cheese-like” plaques on the surface of the eye. These plaques are composed of eosinophils (a type of white blood cell).
  6. Recurrent / Slow Healing Corneal Ulcerations (superficial to deep). If the corneal ulceration becomes vision threatening (severe or progresses to a perforation), then surgery (ie. corneal graft, third eyelid flap, tarsorraphy, enucleation, other surgery) may be indicated.
  7. Corneal Lipid-Calcium Deposits (Corneal Mineralization) – this is a common post-inflammatory / post-traumatic finding to severe or chronic corneal disease. These deposits are non-specific to FHV corneal infections, as they can occur after any corneal trauma / inflammation / infection and in other species.

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