Feline Herpes Virus

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.