Feline Herpesvirus (FHV-1) in cats: eye signs, flare-ups, and how to care for your cat
Feline Herpesvirus type 1 (FHV-1) is one of the most common viral infections in cats, and the main agent behind what owners call cat flu. Most cats live full, comfortable lives with it, but the virus stays in the body for life and can flare up during stress or illness. This guide covers the signs, what treatment can and cannot do, home care, and what recovery realistically looks like.
What this guide covers
Jump to any part of the care journey.
1What is FHV in cats?
Feline Herpesvirus type 1 (FHV-1) is a highly contagious DNA virus and the primary cause of feline viral rhinotracheitis, part of the feline upper respiratory disease complex. It is found in cat populations everywhere. Feline herpes, cat herpes virus, FHV-1 and feline viral rhinotracheitis all describe the same infection.
Acute respiratory flare
The first and most familiar phase. Bouts of sneezing, clear nasal discharge, mild lethargy and a reduced appetite.
Ocular FHV-1
The hallmark of the disease. Conjunctivitis, tearing, squinting and corneal ulcers, including the branching dendritic ulcer that is characteristic of this virus.
Recurrent or chronic disease
Repeated respiratory flares, facial or nasal skin sores known as herpetic dermatitis, and long term snuffles in cats with permanent nasal damage.
Latent carrier state
After the first infection the virus retreats into the nerves and stays there permanently. It cannot be cleared, but in most cats it stays quiet and only reactivates under stress.
Because of latency, treatment focuses on controlling flare-ups and protecting the eyes, not on eliminating the virus.
Recognising the signs of FHV
The clinical picture varies with the cat's age, stress level, and whether other infections are present. Sneezing together with sore, weeping eyes is the most telling combination.
Why the eyes matter most
For many cats, Feline Herpesvirus (FHV-1) shows up first and worst in the eyes. The virus attacks the surface of the eye and can cause painful corneal ulcers. Left untreated, severe ocular disease can threaten the eye itself.
If your cat is squinting, keeping an eye closed, or has a cloudy spot on the eye surface, treat it as urgent and contact your veterinarian. Eye flares are where prompt antiviral and supportive care make the biggest difference.
What treatment can do
No treatment removes Feline Herpesvirus (FHV-1) from the body, so the goal is to shorten flares, ease symptoms, and protect the eyes. Famciclovir is the oral antiviral most established for this virus in cats and is considered systemically safe when dosed appropriately. HerpX delivers famciclovir in a fixed strength 180 mg feline tablet, designed for consistent weight based dosing rather than fractioning human cold sore tablets.
- Oral antiviral therapy with famciclovir, a prodrug of penciclovir, to bring active flares under control.
- Supported by published feline pharmacokinetic and clinical work, including a 59 case clinical series covering ocular, respiratory and dermatologic disease.
- Topical eye antivirals for active corneal disease, with lubricating drops, fluids and nutritional support.
- Antibiotics only when a secondary bacterial infection is present, since antibiotics do not act on the virus itself.
HerpX indicative dosing
Famciclovir is dosed by body weight at approximately 90 mg/kg every 12 hours, the approach supported by published feline studies. Exact dosing depends on your cat's weight and your veterinarian's assessment, so confirm the number of tablets per dose with your veterinarian. Continue past resolution of signs as directed, and do not taper or reduce antiviral dosing without veterinary direction.
Safety: never give human cold sore creams or human antiviral tablets on your own. Acyclovir and valacyclovir are associated with toxicity in cats. Famciclovir is not suitable for every cat, including those with acute kidney failure, severe liver disease, or a known sensitivity to famciclovir or penciclovir. Use only medication your veterinarian has prescribed.
Home care during a flare
Home care does not replace veterinary treatment, but it makes a real difference to comfort and recovery. Focus on these four areas.
Reduce stress
Stress is the single biggest trigger for flare-ups. Keep routines steady, minimise upheaval, and give a multi cat home enough space, litter trays and hiding spots.
Keep the face clean
Gently wipe away eye and nasal discharge with a clean, damp cloth, using a fresh area for each eye.
Open up the airways
Sitting with your cat in a steamy bathroom for a few minutes, or using a humidifier, helps loosen nasal congestion.
Protect appetite
A blocked nose dulls smell, so cats stop eating. Warm the food, offer strong smelling wet food, and watch intake closely. A cat that stops eating needs to be seen quickly.
Keep other cats separate during active flares to limit spread. Feline Herpesvirus (FHV-1) passes easily between cats, but it does not infect people or dogs.
Recovery expectations
Recovery here means a comfortable cat with controlled signs and protected eyes, not a virus free cat.
Flares improve
Most flares improve within days to a couple of weeks with prompt, appropriate care.
The virus stays
Even after a full recovery your cat carries the virus for life and may have occasional flare-ups, usually around stressful events.
Carriers look healthy
Some cats look completely well but can shed virus and infect other cats during a flare.
A minority need a plan
Some cats develop chronic signs such as long term snuffles or recurrent eye problems, and need an ongoing management plan with their veterinarian.
Common questions about FHV
Is FHV contagious to other cats? +
Yes. It spreads easily between cats through direct contact, sneezing, and shared bowls or bedding, especially in multi cat homes and shelters.
Can my cat infect me or my dog? +
No. Feline Herpesvirus (FHV-1) infects cats. It is not the same virus as human cold sore herpes and it does not spread to people or dogs.
Is there a cure for FHV? +
No treatment eliminates the virus, because it stays latent in the nerves for life. Flares can be controlled well, and most cats live normal lives with good management.
Will FHV come back after treatment? +
Possibly. Famciclovir treats the active infection but cannot eliminate the latent virus that remains dormant in nerve tissue. Reactivation typically happens during stress, illness or immunosuppression. This is normal herpesvirus behaviour, not treatment failure.
Does famciclovir prevent relapse? +
No, but it reduces the severity and duration of flares when they occur. Repeat courses are often effective for managing recurrent episodes. Stress reduction and good nutrition help lower how often they happen.
When should I retreat? +
If signs return, such as sneezing, eye discharge or lethargy, contact your veterinarian. Early treatment shortens recovery time.
Can vaccinated cats still get FHV? +
Yes. Vaccination reduces the severity of disease but does not fully prevent infection or carrier status.
Does L-lysine help? +
L-lysine is widely sold for Feline Herpesvirus (FHV-1), but the published evidence is mixed and several studies found no clear benefit. Discuss it with your veterinarian rather than relying on it as a main treatment.
Why does my cat keep getting eye infections? +
Recurrent eye infections are a classic pattern, driven by reactivation of the latent virus during stress. A plan focused on stress reduction and prompt antiviral care during flares helps.
What is the difference between FHV and FCV? +
Both cause cat flu and share symptoms. Feline Herpesvirus (FHV-1) tends to affect the eyes and nose, with conjunctivitis and corneal ulcers. Feline Calicivirus (FCV) tends to cause mouth and tongue ulcers with drooling. A swab test tells them apart.
Managing a flare right now?
Early antiviral care shortens flares and protects your cat's eyes. Review HerpX with your veterinarian, or read the guide to understand what to expect.
This page is for general educational purposes and does not replace veterinary advice. Feline Herpesvirus (FHV-1) treatment decisions, including antiviral choice, dosing and duration, remain the responsibility of a licensed veterinarian who has examined your cat.
