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Ask a Vet: How Contagious Is Feline Herpes?

It's less a matter of getting the virus -- most cats have it -- than knowing what causes flare-ups.

Dr. Eric Barchas  |  Sep 27th 2016


Catster writer Meghan Lodge wrote a post about her experiences having been exposed to a cat with feline herpes. Her piece is excellent and it contains a great deal of useful information. The good folks at Catster asked me whether I have anything to add to the feline herpes conversation.

First, let me very briefly recap Meghan’s story. Her mother-in-law adopted a cat who developed symptoms of a respiratory infection. Soon, the mother-in-law’s other cat developed similar symptoms. Both were diagnosed with feline herpes. In private conversation I learned that there was some initial and transient concern about whether the virus might spread to cats not living with the mother-in-law. In the end, it was concluded that the infection probably wasn’t a big deal.

What follows is my take on feline herpes.

Let’s get something straight right off the bat: Most forms of herpes are not sexually transmitted diseases. That herpes is unique to humans. It turns out that many species have their own herpes viruses, and some (such as humans), have more than one — in our case there is genital herpes and the far more common cold sore virus.

However, herpes’ reputation as a sexually transmitted disease can lead to some interesting veterinary exam room conversations. More than a decade ago a gentleman brought his cat to me. The cat had an eye infection. I mentioned herpes as a possible cause. The gentleman (perhaps I am being a bit charitable with the term) went straight to the TMI zone.

“I have herpes,” he said. “Could I have given it to my cat?”

I replied that although folks with cold sores often kiss their cats around the face, the human cold sore virus cannot spread to cats. He immediately cut me off.

“No,” he said, “I have genital herpes. Could I have given it to my cat?”

In the brief, awkward silence that followed I unfortunately couldn’t stop my mind from going there. Just what exactly was going on between the cat and the man at home?

I regained my composure and answered with one word.

“No.”

The feline herpes virus is species (or at least family, in the classification-of-animals sense) specific. It affects only cats (but not necessarily only domesticated cats). It is highly contagious among susceptible individuals. It is most readily spread by direct contact and exposure to bodily fluids. However, contact with contaminated items also may lead to infection.

Cats with symptoms of herpes infection usually develop so-called upper respiratory infections. The symptoms may include sneezing, coughing, nasal discharge, and a raspy meow. One or both eyes may water, or may produce yellow discharge. One or both eyes may squint, and the membranes around the eyes may swell. Some cats manifest only eye symptoms; in these cats the condition nonetheless is referred to as a respiratory infection.

There are many dozens of other known causative agents for upper respiratory infections. There are probably hundreds more that have yet to be discovered or that haven’t yet evolved. However, herpes is the most common and notorious of the bunch.

Since the dawn of time, older folks have been trying to keep younger folks from having sex. When I was one of the younger folks in the ’80s, there used to be public service campaigns about herpes. The campaigns always ended with the slogan: HERPES IS FOR LIFE!

It’s true for cats as for people. There is no cure for herpes, and infection lasts for life. In this matter, the feline herpes virus is especially similar to the human cold sore virus. Most people with the human cold sore virus (which is to say most people) experience one cold sore in their life. Their immune systems then suppress the virus and force it to lie dormant in a neurological structure called the trigeminal ganglion. Some unlucky folks will experience occasional dips in their immune system, usually due to stress (think of final exams), and the virus will seize its opportunity to break out of the ganglion and shed itself through a new cold sore.

The feline herpes virus also tends to break out and cause symptoms at times of stress. And what are the two most stressful things that can happen to a cat? Most experts believe they are rehousing and adding a new cat to a home.

Meghan’s mother-in-law was worried that she might have been responsible for the feline herpes situation in her home. Had she failed to do her due diligence before adopting the new cat? And had the new cat spread the virus to the one already in the house?

The answers are no, and probably not.

The feline herpes virus is similar to the human cold sore virus in another respect. It’s ubiquitous. Every cat has it. Most kittens catch it from their mothers in the first weeks of life. Herpes-free cats really only exist in specific, pathogen-free research environments.

I am reminded of a teenager who is being fired from a minimum wage job. The teenager might say to his boss, “You can’t fire me, because I quit!”

Well, a cat exposed to another one with a respiratory infection might as well say something similar: “You can’t give me herpes, because I already have it!”

If, indeed, both of Meghan’s mother-in-law’s cats were suffering from herpes (more on that in a moment), here’s what I believe happened. The new cat was stressed by time in the shelter and the move to a new house; the subsequent dip in immune function led to a flare-up of pre-existing herpes. The established cat was stressed by the addition of a new cat to the house; the subsequent dip in immune function led to a flare-up of pre-existing herpes.

Was it definitely herpes, though? It is possible to diagnose herpes through DNA testing; however, often the diagnosis is merely tentative. Like I said, there are dozens or hundreds of other causes of feline respiratory infections. So it is possible that the new cat transmitted something to the established cat. It’s just not likely to have transmitted herpes.

Let me close with a few words on treatment and prevention of herpes outbreaks. Meghan mentioned the use of L-lysine in her post. Veterinary formulations of this natural amino acid are available and are marketed to cats with frequent upper respiratory infections. Although L-lysine never did a darned thing to stop me from getting a cold sore during finals, it does seem to help many cats. More specific antiviral medications also are available for cats with severe infections. Antibiotics do not treat herpes, but they do often help with secondary, opportunistic bacterial infections that piggy-back on herpes symptoms.

Finally, the R in FVRCP is short for rhinotracheitis, also known as feline herpes. Thus, the FVRCP is touted to help bolster the immune system and reduce outbreaks of URIs. Like just about everything else regarding feline vaccination, this claim is the case of some contention in the veterinary community.

Herpesvirus infection is ubiquitous in cats, and it lasts for life. But Meghan was right: Usually it’s not a big deal.

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