Feline Herpes Virus (FHV-1)

FHV-1 is a viral disease that affects cats, primary infection tends to occur in kittens and young cats. The infection is typically spread via body fluids such as respiratory fluid (e.g., sneezing). Once infected,
approximately 80% of cats will become persistently infected with the virus, meaning it cannot be cleared from the body. The virus hides from the cat’s immune system and becomes ‘latent’. In this latent state, the virus is hidden and sleeping, meaning patients won’t show the symptoms of the disease.

The virus can re-awaken to re-infect cats later in life and symptoms are visible at this point. Stressful events and some medications can cause the virus to ‘re-awaken’ causing repeat and recurrent infections, and more rarely immune mediated disease directed at the viral material within the body.

What are the symptoms?

Symptoms can vary based on the age of the patient and where the virus is localised.

In kittens that become infected before their eyelids open, swelling of infectious material can occur behind the eyelids (ophthalmia neonatorum), and pus-like material can sometimes be seen leaking out. In severe cases this can lead to vision compromise and potential loss of the eye, if the infection causes ulcerations to the eye that deepen to the point of eye rupture. Kittens will also often display respiratory signs alongside the ocular signs.

n young cats with a primary infection, respiratory signs (e.g., sneezing and nasal discharge) along with conjunctivitis (inflamed conjunctiva) and keratitis (inflamed cornea) with or without corneal ulcerations (lesions within the cornea) are the main signs. Fever, lethargy, and anorexia can also occur. Rarely, if the conjunctivitis is intense, adhesions can form (symblepharon) between the conjunctiva and other regions of the eye, which can lead to serious complications for the eye.

In older cats with a repeat / recurrent infection, the symptoms are more varied. These include recurrent corneal ulcerations, keratitis, conjunctivitis.

There are also some conditions where we think FHV-1 plays a role in their development. These include corneal sequestrums, feline eosinophilic keratitis, uveitis (inflammation inside the eye) and dermatitis (irritation of the skin around the eyes). These are discussed in more detail in separate leaflets.

Diagnosis

Due to the nature of the virus, diagnosis can be challenging. Often a presumed diagnosis is made based on the cat’s history and the clinical examination. However corneal and conjunctival swabs can be used to aid with the diagnosis and rule other conditions out.

Management

Treatment is not possible in the sense we cannot fully rid the body of the virus. Therefore, we aim to treat the signs and symptoms, which vary based on the type of FHV-1 infection present.

For primary infections, antiviral drops or tablets are used to help reduce the viral load on the patient. Antibiotics may be needed, either tablets, drops, or both to help with possible secondary bacterial infections. Tear replacement drops are often beneficial as the virus can reduce normal tear production and tear quality. If the infection is severe sometimes patients need to be hospitalised for fluid therapy and supportive care.

Recurrent infections do not tend to affect the rest
of the body as severely but can still have significant local effects on the eye. These are often managed with antiviral eye drops (or antiviral tablets in some cases) alongside tear replacement drops (some patients may need these long term), as well as medications needed for any ulcerations or other secondary  complications present.

For both primary and secondary FHV infections, reducing stress and modulating the home environment plays a key role in the long-term success of the treatment. This includes; ensuring multiple places to hide, choices for water bowls and drinking (and water bowls in locations away from food) and use of calming plug-ins. Stress factors and triggers are often numerous, including new pets in the home or nearby, moving house or home changes, new people, and other sudden changes to the home environment.

There has been discussion into the use of interferon eye drops and oral L-lysine supplementation, but there is limited clinical research data to suggest they are very effective.

Please do not hesitate to contact Eye Vet should you have any concerns following treatment.