Feline Herpesvirus: Symptoms, Treatment and Prevention

Medically reviewed by: Kinga Wojtczak, Doctor of Veterinary Medicine, specialist in canine and feline diseases

Cat flu (feline upper respiratory infection) is a very common disease, seen especially in young kittens, as well as in animals with concurrent chronic diseases or those treated with glucocorticoids. The disease is caused by several different pathogens that produce various clinical signs of varying severity. Not all of the pathogens that cause cat flu can be eliminated completely—after the cat has recovered and the main clinical signs have subsided, the disease becomes chronic or dormant (in other words, latent).

Herpesvirus is one of these pathogens. What are the classic signs of herpesvirus infection? Is it life-threatening for animals? And will every animal that has come into contact with herpesvirus show clinical signs? How should you care for a cat that has developed signs of the disease? In this article, I describe herpesvirus infection in cats.

Cause of the disease

Herpesvirus is a microorganism often isolated from cats. It can colonize various parts of the body: the nose, the conjunctiva, the respiratory epithelium, and also the reproductive tract. Infection occurs through contact with a sick animal, especially with its nasal, ocular and respiratory secretions. Kittens most often become infected from their mothers during everyday grooming. The pathogen can also be carried on blankets, bedding and the owner's hands. Infection can also occur when cats share bowls or a litter box.

Those most susceptible to infection are kittens about 3–8 weeks old, chronically ill animals (FIV and FeLV carriers) and cats living in large groups of animals (catteries, shelters). Cats are affected by feline herpesvirus type 1, or FHV-1. It is an enveloped DNA virus. The pathogen is fairly resistant to environmental conditions: at low temperatures and without exposure to light, it can remain infectious for months. Outside the cat's body, at room temperature, however, it is unstable and quickly loses its ability to infect. It is also not very resistant to disinfectants or to UV radiation.

Clinical signs of feline herpes

Herpesvirus seldom occurs as the only pathogen; most often the infection it causes is further complicated by Chlamydia, calicivirus and various bacteria, including the normal flora. Infection and the development of clinical signs occur 2–7 days after contact with the pathogen. The infection itself can last 10–14 days, but complications after the disease can last longer. In some animals clinical signs may not develop—such cats become asymptomatic shedders.

Clinical signs can be divided into two main groups—ocular signs and respiratory signs—and both groups can occur at the same time. Herpesvirus mainly causes upper respiratory tract infections. The virus attacks the epithelial cells of the nasal mucosa, causing increased mucus production, sneezing and severe irritation. Nasal discharge appears, serous at first and later (after a secondary bacterial infection) purulent or mucopurulent.

As the disease progresses, the infection spreads to the mouth and throat. The gums become painful and swollen, as does the back of the throat. Sometimes small vesicles filled with serous fluid may appear on the lining of the cheeks. The lesions do not involve the tongue (unlike calicivirus infection). Swallowing becomes quite difficult, and the whole mouth becomes painful. The large amount of discharge in the nasal passages and the difficulty breathing mean that the cat's sense of smell deteriorates considerably.

The loss of smell combined with a painful mouth means that the cat does not want to eat, is reluctant to drink water and shows no interest in food at all. In severe cases, the disease can lead to wasting and death of the animal.

Other signs of herpesvirus infection are infection of and damage to the eyeball, namely:

• conjunctivitis,
• keratitis (inflammation of the cornea),
• anterior uveitis (inflammation of the front part of the uvea),
• ulceration of the eye.

The first sign is conjunctival swelling and increased tear production—the eyes become moist and watery, with marked redness and puffiness of the conjunctiva. The third eyelid may protrude. The cat may be sensitive to light (photophobia), squint and avoid sunny spots.

Combined with severe swelling and a steadily increasing amount of discharge, the eyelids may stick together. Large amounts of discharge and bacterial complications can lead to corneal ulcers, and intense itching in this area—caused by the eyelids sticking together, large amounts of discharge on the eyelashes and the puffy conjunctiva—leads the animals to injure their own eyes by rubbing them with their paws.

Herpesvirus infection is particularly dangerous in pregnant breeding queens. It impairs placental function and reduces blood flow through the placenta; as a result, abortion and death of embryos inside the uterus may occur. Kittens that survive are born weak and small, with poor vitality. They very often die at an early age. They are also susceptible to all kinds of infections.

Sometimes the disease is self-limiting. About 10–14 days after the first clinical signs appear, they begin to resolve on their own. Such cats become carriers of the virus, and any drop in immunity can cause the signs to return. The signs then mainly affect the previously infected areas (that is, if the infection mainly involved the eyes, discharge from the conjunctival sac will appear; if it caused respiratory signs, the cat may start coughing).

Latent infection

As I mentioned above, after a cat has had cat flu, it is not always possible to completely eliminate herpesvirus from its body. Studies report that after recovery, the virus settles in the trigeminal ganglia of almost 97% of infected animals and stays there for the rest of the cat's life. Only about 3–8% of animals are able to eliminate the pathogen completely.

In very many cases, the disease enters a hidden phase, that is, latent infection. During latent infection, the animal may show mild clinical signs throughout its life, or periodically, when its immunity drops (for example, because of severe stress or a concurrent disease), show somewhat more severe signs. The most common sign of latent herpesvirus infection is mild gingivitis with no visible cause (no plaque, tartar or malocclusion irritating the gum mucosa).

The cat develops bad breath, is reluctant to eat dry food, may avoid chewing on the more painful side of the mouth, and also avoids drinking water. Its body weight drops, and the cat is also reluctant to groom—its coat is clumped and dull, and mats form. This condition may worsen as plaque and tartar build up on the teeth.

Herpesvirus may also contribute to loosening of the periodontal ligaments, and constant inflammation in the mouth promotes the development of resorptive lesions (tooth resorption) and periodontal disease. This is quite a dangerous situation, because many owners do not pay due attention to oral hygiene and only see a veterinarian when the signs are really pronounced. Early dental intervention, on the other hand, can slow the development of more serious conditions.

Another sign of latent infection may be a constant serous discharge from the conjunctival sac. After a cat has had cat flu, changes in the structure of the eye very often occur—conjunctival adhesions form, and the nasolacrimal duct may become narrowed or completely blocked. Excess tears do not drain properly from the conjunctival sac through the duct, so the area around the eyelids is constantly slightly moist.

Clumped, wet fur can cause moisture-related skin irritation, which in turn creates excellent conditions for the growth of microorganisms that can cause inflammation of the skin of the eyelids and the face.

Diagnosing feline herpes

The diagnosis is usually made on the basis of fairly characteristic clinical signs. Because asymptomatic infections are widespread, healthy cats carry the virus and shedding is limited in some phases of the infection, laboratory tests carry a high risk of false-positive and false-negative results. However, there are laboratory tests that can confirm the infection.

For testing, a conjunctival swab is usually taken when there are eye signs, a nasal swab when there is nasal discharge, or a swab from the reproductive tract (in cases of abortion or unsuccessful mating of breeding queens). Drawing blood to measure antibody titers is not a recommended test—a false-positive result can occur in cats that have been vaccinated regularly.

Treating feline herpes

An important part of treatment is a proper understanding of how the infection progresses. The drugs used in therapy are meant to limit the activity of the virus, not to eliminate it completely—that is simply not possible. Treatment is based on improving the patient's health and reducing the clinical signs; however, an infection caused by herpesvirus cannot be cured completely. Treatment should focus above all on suppressing the clinical signs.

If the signs are mainly ocular, the sick animal should be started on eye drops that reduce the risk of bacterial complications. The area around the eyes needs particularly careful hygiene—regular use of antiseptics and removal of any accumulated discharge are key to limiting bacterial complications. Lubricating eye products, preferably with hyaluronic acid or panthenol, are recommended (herpesvirus impairs the function of the goblet cells in the conjunctiva, which disturbs the quality of the tear film, so the eye is not properly lubricated).

Throughout treatment, the cat should wear a protective cone (e-collar) so that it does not cause mechanical damage to the eyeball with its sharp claws. An ordinary cone is often not enough, because cats look for protruding objects, edges and corners to rub the itchy eye against. In that case, a special ophthalmic e-collar with a frame at the front is needed.

After the excessive tearing has subsided, regular eye checkups are important to make sure the nasolacrimal ducts are not narrowed or blocked. A serious complication after the clinical signs have resolved is symblepharon, that is, adhesions of the conjunctiva to the cornea, eyelids and sclera. These adhesions prevent the eyelids from opening properly, block the nasolacrimal ducts, and may also cause corneal opacity and even perforation of the eyeball.

If adhesions develop, surgical intervention to separate the fused tissues may be considered, but this procedure carries a high risk of failure—the adhesions may form again after the surgery. If respiratory signs occur, it is important to start systemic antibiotics to limit bacterial complications of the infection.

The most commonly used drugs are amoxicillin with clavulanic acid or tetracyclines. It is important to use agents that thin the secretions accumulated in the airways (mucolytics), to make them easier to cough up, as well as nonsteroidal anti-inflammatory drugs (NSAIDs) to reduce fever. Saline nebulization can be very helpful. It is important to use antiviral and virustatic drugs, which reduce the activity of the virus in the infected tissues.

Immune-boosting products (beta-glucan-based supplements) may also have positive effects. Lysine supplements were also often recommended in the past; lysine was supposed to compete with arginine, which the virus needs to replicate. However, a 2015 review of the research did not confirm that it is effective either in preventing or in treating FHV-1 infection, and in cats excess lysine does not lower blood arginine levels. For this reason, lysine is not currently recommended as routine treatment.

Nutritional support for the sick animal is a very important aspect. As I mentioned above, a sick cat has a much poorer appetite because of the painful mouth and the impaired sense of smell. Food for a cat fighting an infection should be palatable, warmed (which makes it more aromatic) and finely minced, so that it does not require much chewing. The cat should not be force-fed (for example with a syringe)—this can cause a lasting aversion to food, as well as aspiration. If the cat still does not eat, the veterinarian may use an appetite stimulant, and if the cat has not eaten for about 3 days, place a feeding tube through which a high-energy food is given. The cat's hydration status should be monitored and, if necessary, appropriate fluid therapy should be given.

In treating an infection caused by herpesvirus, it is very important to provide calm surroundings and to minimize stress. The disease becomes active at times of stress and when immunity drops. For particularly sensitive cats, a pheromone collar or calming products are recommended for the duration of therapy.

Preventing the disease

To prevent infection, cats should be vaccinated regularly. Unfortunately, even having had the infection does not protect against reinfection—in herpesvirus infection, the cell-mediated immune response and the local immunity of the mucous membranes are very important, and some recovered cats do not even have antibodies in their serum.

As I mentioned above, the virus can also cause latent infections. Young kittens should be vaccinated at 9 weeks of age. The vaccination should be repeated after 3–4 weeks. If the kitten grew up in an environment where herpesvirus infections occurred, the vaccination should additionally be repeated at 6–7 months of age. Booster vaccinations should be given once a year. Vaccines contain live, attenuated (that is, rendered harmless) virus, so routine vaccination of pregnant queens is not recommended.

To limit the spread of infection in catteries, it is recommended that queens raise their kittens in rooms isolated from the rest of the colony. This reduces stress in the mother and the amount of pathogens in the young animals' immediate surroundings. This separation should continue until the young animals have been vaccinated. An important part of prevention is reducing stress in older cats or in cats with weakened immunity (for example, FeLV and FIV carriers). If a stressful moment is coming up in a cat's life, such as the owners going away and care by an unfamiliar person, it is a good idea to support the cat's immunity by giving beta-glucan products for 2–3 weeks.

As I mentioned, calming or pheromone products can be helpful. When introducing new animals into a group of cats, a 2-week quarantine should be observed.

FAQ