Feline herpes is a highly common viral infection that targets a cat’s upper respiratory system and eyes. The virus, formally called feline herpesvirus type 1 (FHV-1), is one of the leading causes of upper respiratory infections in cats, and an estimated 80% of cats that catch it become lifelong carriers. It’s not transmissible to humans, but it can cause recurring bouts of sneezing, eye inflammation, and nasal congestion throughout an infected cat’s life.
How Cats Catch It
FHV-1 spreads through direct contact with an infected cat’s secretions. Sneezing near another cat, sharing water bowls, and mutual grooming are the most common routes. Kittens typically pick it up from their mother or littermates, and shelter environments are especially high-risk due to close quarters and stress. Studies of shelter cat populations have found FHV-1 in anywhere from 0% to 63% of clinically normal cats, depending on the facility. Among client-owned cats in the general population, the rate is much lower, roughly 6% to 12%.
The virus doesn’t survive long on surfaces compared to some other pathogens, but it can linger on shared food dishes, bedding, and hands long enough to spread between cats in the same household. A cat that appears perfectly healthy can still shed the virus intermittently, making it difficult to fully prevent transmission in multi-cat homes.
What the First Infection Looks Like
Symptoms typically appear two to six days after exposure. The initial infection hits hardest in kittens and young cats and usually looks like a severe cold: sneezing, nasal congestion, fever, and loss of appetite. The eyes are almost always involved, with redness, swelling, and a watery discharge that can turn thick and yellowish if a secondary bacterial infection sets in. Both eyes are usually affected.
In very young kittens whose eyes haven’t yet opened, the infection can cause pus to build up behind the sealed eyelids, a condition that requires prompt veterinary attention to prevent permanent damage. Older kittens and adults may develop small ulcers on the surface of the eye, sometimes in a distinctive branching pattern that vets recognize as a hallmark of the virus. Crusty sores can also appear on the skin around the eyes and nose.
Most cats recover from the acute phase within two to three weeks, but the virus doesn’t leave the body.
Why It Keeps Coming Back
After the initial infection clears, FHV-1 travels along nerve fibers and settles into a cluster of nerve cells near the base of the skull called the trigeminal ganglion. There, it enters a dormant state. The viral DNA sits quietly inside the nerve cells without producing new virus particles, which means the immune system can’t detect or eliminate it.
Periodically, the virus reactivates. Stress is the most commonly cited trigger: a move to a new home, boarding, the introduction of a new pet, illness, or surgery. But research on related herpesviruses shows that the majority of reactivation episodes can’t be tied to any specific event. They appear to happen spontaneously as part of the normal stresses of daily life. An estimated 45% of latently infected cats will experience spontaneous reactivation at some point.
During a flare-up, the cat may show milder versions of the original symptoms, or the virus may reactivate without any visible signs at all while the cat still sheds virus particles that can infect other cats.
Eye Problems Are the Biggest Concern
While the sneezing and congestion are uncomfortable, the most serious long-term consequences of feline herpes involve the eyes. Repeated bouts of inflammation can cause cumulative damage to the cornea and surrounding tissues.
- Corneal ulcers: The virus can invade the surface layer of the eye, creating small branching ulcers that are virtually impossible to see without a special fluorescent dye. These can expand into larger irregular ulcers if untreated.
- Corneal scarring: Chronic inflammation triggers blood vessel growth into the normally clear cornea, along with progressive scarring and pigmentation that can impair vision.
- Symblepharon: Severe inflammation can cause the inner eyelid lining to fuse to itself or to the surface of the eye. This can narrow the eye opening, block tear drainage, and permanently affect vision.
- Dry eye: Repeated infections can damage the tear-producing glands or block their ducts, leaving the eye chronically dry and vulnerable to further injury.
- Corneal sequestrum: A dark brown or black plaque of dead corneal tissue that sometimes forms after chronic ulceration. This often requires surgical removal.
Not every cat with feline herpes develops these complications, but cats with frequent flare-ups are at higher risk. Any sign of squinting, cloudiness, or discharge from your cat’s eyes warrants a veterinary exam.
How Vets Diagnose It
Most of the time, a vet diagnoses feline herpes based on the combination of symptoms: upper respiratory signs plus eye inflammation, especially in a young cat or one with a history of recurrent flare-ups. The distinctive branching pattern of corneal ulcers, when present, is considered virtually diagnostic on its own.
Lab testing with PCR (a technique that detects viral DNA) is technically the most sensitive method, but it has a frustrating limitation. Clinically normal cats can carry viral DNA in their eye tissues without being sick, so a positive result doesn’t necessarily mean the virus is causing the current problem. It could be an unrelated bystander, a secondary reactivation triggered by something else, or the actual cause. Meanwhile, a negative result doesn’t rule the virus out either, since shedding is intermittent. Many veterinary eye specialists have moved away from relying on PCR and instead base their diagnosis on the clinical picture.
Treatment and Management
There’s no cure for feline herpes. Treatment focuses on managing symptoms during flare-ups and reducing the frequency of recurrences. For mild episodes, supportive care like keeping the nose clear of discharge, encouraging eating (warming food helps when congestion dulls a cat’s sense of smell), and ensuring adequate hydration may be enough.
When flare-ups are more severe, particularly those involving the eyes, vets may prescribe an oral antiviral medication. This is the primary antiviral used in cats for FHV-1, and studies of cats treated with it have shown improved clinical signs with few side effects. Topical antiviral eye drops or ointments may also be used for corneal ulcers. If a secondary bacterial infection develops on top of the viral infection, antibiotics are added.
For cats with chronic eye complications like deep corneal ulcers, scarring, or corneal sequestra, more involved treatments including surgery may be needed.
L-Lysine Does Not Work
For years, the amino acid L-lysine was widely recommended as a supplement to reduce feline herpes flare-ups. The theory was that it would lower levels of another amino acid the virus needs to replicate. A systematic review of all available evidence found this doesn’t hold up. Lysine does not antagonize that amino acid in cats the way it was assumed to, and it has no antiviral properties. Multiple clinical studies found that lysine supplementation did not reduce infection rates, did not decrease symptom severity over the full course of illness, and did not lower viral shedding. Some studies actually found that cats receiving lysine had more frequent and more severe respiratory and eye disease than cats receiving a placebo. Despite its continued popularity, the scientific consensus is clear: lysine supplementation should be stopped.
Vaccination
The feline herpes vaccine is included in the standard FVRCP combination vaccine, which is considered a core vaccine for all cats. Kittens receive their first dose no earlier than six weeks of age, followed by boosters every three to four weeks until they’re 16 to 20 weeks old. After the kitten series, a booster is recommended around six months of age, then every three years for most formulations.
The vaccine doesn’t prevent infection entirely. A vaccinated cat can still catch feline herpes and become a carrier. What vaccination does is significantly reduce the severity of symptoms if infection occurs. For a virus this widespread and this difficult to avoid, that reduction in disease severity is the realistic and meaningful benefit.