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Herpes Virus: Putting the “Crud” into Recrudescence

By Kim Everson, DVM

For the past week I’ve been battling a hideous cold sore on my upper lip which puts me in the frame of mind to discuss upper respiratory infections in cats. If that seems like an incongruous association it may help to understand that both conditions are caused by a herpes virus. Human cold sores result from infection with Herpes simplex virus type 1 (HSV1) while many cats with chronic or recurrent upper respiratory infections have feline herpesvirus-1 (FHV1).


Most cold sore sufferers contracted the virus in early childhood (often before the age of seven). Approximately 80% of Americans have been exposed to HSV1. Similarly, FHV1 infections are usually acquired during kittenhood with 80% of the cat population being affected.

HSV1 is spread from person to person through kissing or through sharing drink glasses, utensils, lip gloss, toothbrushes, and so on. Self-infection, or spread from a primary oral location to other parts of the body (eyes, fingers, etc.), can happen by touching the sore and not washing hands properly. Yikes! In cats, FHV1 spreads by direct contact with infected ocular or nasal secretions. The virus can be transferred on a caretaker’s clothing or inanimate objects (this is called “fomite” transmission) from sick cats to healthy ones which contributes to herpes virus epidemics in humane societies and shelters. Unlike Kennel Cough in dogs, feline herpes is unlikely to spread far through aerosolization of virus via sneezing or coughing.

Symptoms of feline herpesvirus include fever, sneezing, nasal discharge and conjunctivitis in the eyes. Some cats are left with permanent damage in the affected eye with reduced vision from scar tissue. Occasionally infection in the eye is so severe that surgical removal of the eyeball is required!  Bacterial infections secondary to the feline herpesvirus are common causing secretions to become thick and greenish. Pneumonia is uncommon but possible.

Cold sore symptoms begin as a tingling in the skin then progress to blistering and then a scabby wound. Cold sores usually occur around the mouth but can affect the nostrils, chin, cheeks and even eyes. Interestingly, I just learned that cold sores are not canker sores! Canker sores are non-contagious ulcerations affecting the lips and soft tissue inside the mouth caused by stress, injury, allergy or bacteria.

cat-silIf you’ve ever suffered from a cold sore you understand that it tends to reappear in the same spot each time and often emerges during times of stress or illness. This is because, unlike romance, herpes lasts forever. Seriously. Once infected, the body begins fighting a guerrilla war it can’t win. The virus goes into hiding or hibernation on a particular nerve pathway until it senses weakened immune defenses resulting from another illness, exhaustion or injury. Then it creeps to the skin surface to wreak havoc and reproduce.

Many adult cats brought into my veterinary clinic for evaluation and treatment of a “cold” actually are showing reappearance, or “recrudescence,” of their herpes virus. In cats, anything from the stress of a new family member to serious organ failure can lower the immune system awakening the latent herpes virus. I have found that treating the underlying problem in these cats hastens their recovery from the viral upper respiratory infection.

Fortunately for cats, vaccination against FHV1 (also called feline rhinotracheitis) is available to lessen  severity of symptoms as well as reduce the spread of the virus. Vaccination for FHV1 is usually given as part of a combination “distemper” vaccine, which includes protection against several other feline diseases. There is no vaccine available to prevent or lessens symptoms of cold sores from HSV1 in people.

Because herpes is a virus, antibiotic therapy is unnecessary and inappropriate unless a secondary bacterial infection has developed. Duration of a cold sore outbreak can last 8-12 days in people. Several special ointments have been developed to shorten the duration of the outbreak. Healthy living, sun protection and immune boosting supplements may help prevent recurrence.

I have seen symptoms of feline herpes virus drag on for weeks to months. A non-resolving upper respiratory infection in a cat may be a warning sign of an underlying illness or lowered immune system. Unfortunately, some severely affected cats are left with permanent damage in their eyes and nasal passages that predispose them to a lifetime of weepy eyes, gooey noses and frequent bacterial infections. Several of the anti-viral medications available for humans have been used to treat feline herpes virus infections: some can be effective while others cause serious side-effects. Never give your cat any human medication without first checking with your veterinarian! L-Lysine is regularly used in cats to inhibit replication of the virus and speed recovery. While L-Lysine is available over-the-counter, check with your veterinarian for dosing instructions.

People often suggest to me that their cat gave them a cold (or vice versa), but this is highly unlikely. While cats and humans may both be plagued by a herpes virus, subtle genetic differences between the different strains dictate which animal can be infected and how. So if you come down with a cold sore, please don’t blame your kitten–even if you have been planting lots of kisses!

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