Feline Herpesvirus (FHV-1): The Chronic, Recurring Cause Behind "Cat Flu" Flare-Ups

Most cats that had a snotty-nosed kittenhood never fully clear the virus that caused it. Feline herpesvirus doesn't work like a cold that comes and goes for good; it settles into the nervous system and stays for life, quietly waiting for a stressful week to bring it back.

Just how common this actually is

Feline herpesvirus type-1 (FHV-1), also called feline viral rhinotracheitis, is genuinely widespread. VCA Animal Hospitals notes that up to 97% of cats are exposed to it at some point in their lives, and up to 80% of exposed cats end up with a lifelong infection. Of those, close to half will periodically shed the virus again later, almost always tied to a stressful stretch.

Why it comes back instead of just going away

After the initial infection, FHV-1 doesn't get cleared by the immune system the way many viruses do. It retreats into nerve tissue, particularly the trigeminal ganglion, and sits there in a dormant state. Stress, another illness, a new home, a new pet, or even boarding can suppress immune function just enough to let the virus reactivate and start shedding again, sometimes with symptoms and sometimes without any visible signs at all.

The eye problems that make FHV-1 different from a typical cold

FHV-1 is the single most common cause of feline corneal ulcers, according to the Cornell Feline Health Center, and a specific branching pattern called a dendritic ulcer is considered a telltale sign of the virus. Repeated flare-ups over a cat's life can, in more severe or poorly managed cases, progress to deeper corneal damage and, rarely, permanent vision loss in the affected eye. This eye-specific risk is a big part of why a cat with recurring squinting, redness, or discharge in one eye is worth taking seriously rather than assuming it's just allergies.

The L-lysine supplement, and why it's fallen out of favor

For years, L-lysine was a go-to recommendation for managing FHV-1, based on the theory that it blocks the virus's use of another amino acid, arginine, that it needs to replicate. That theory hasn't held up. A 2015 systematic review published in BMC Veterinary Research examined the available clinical trials and mechanistic research and found no evidence that lysine supplementation helps prevent or treat FHV-1 infection, concluding that its continued use "because of the complete lack of any scientific evidence for its efficacy" should stop. The ABCD's clinical guideline reflects this shift too, no longer recommending lysine as part of standard management.

What actually helps manage flare-ups

Since FHV-1 can't be cured, management is about reducing how often and how severely it flares. MSPCA-Angell's therapeutic review points to reducing stress and environmental triggers as one of the most effective, evidence-supported strategies, alongside antiviral medications like famciclovir for active flare-ups, particularly ones involving the eyes. A stable routine, minimizing sudden changes, and giving a cat places to retreat and feel secure genuinely reduce reactivation frequency for a lot of cats.

Frequently asked questions

Is FHV-1 the same virus as human herpes?
No, they're different species-specific viruses. FHV-1 doesn't infect people, and human herpesviruses don't infect cats.

Can a cat with FHV-1 live a normal life?
Yes, most cats with FHV-1 live entirely normal lives with occasional, manageable flare-ups, especially with reduced stress and prompt attention to eye symptoms when they appear.

Is there a vaccine for FHV-1?
Yes, it's part of the standard core FVRCP vaccine. It doesn't prevent infection entirely but significantly reduces how severe illness is, which is one more reason the kitten vaccination schedule matters.

Sources

• VCA Animal Hospitals, "Herpesvirus Infection in Cats (Feline Viral Rhinotracheitis)"
• Cornell Feline Health Center, "Corneal Ulcers"
• Bol, S., Bunnik, E.M., "Lysine supplementation is not effective for the prevention or treatment of feline herpesvirus 1 infection in cats: a systematic review," BMC Veterinary Research, 11 (2015): 284
• ABCD (European Advisory Board on Cat Diseases), "Guideline for Feline Herpesvirus Infection"
• MSPCA-Angell, "Feline Herpesvirus: Therapeutic Review"

This article is for general information and isn't a substitute for advice from your own veterinarian, who can properly diagnose and manage FHV-1 flare-ups in your specific cat.