Feline Herpesvirus (FHV-1): Signs, Treatment and Prevention

Feline herpesvirus type 1 (FHV-1) causes cat flu. It's very common, it spreads easily between cats, and most infected cats carry it for life.

Together with calicivirus, FHV-1 is behind about 90 percent of upper respiratory infections in cats. It affects the nose and throat and, often, the eyes.

How cats catch it

• Direct contact: nose-to-nose greetings, shared bowls, mutual grooming, and contact with nose or eye discharge
• Droplets: sneezing sends virus into the air over short distances
• Objects and hands: bowls, bedding, toys, carriers, clothing and hands. The virus is fragile and survives less than 18 hours outside the cat
• Queen to kittens: newborns are often infected by the mother in the first weeks

Risk is highest in shelters, breeding catteries, boarding facilities, multi-cat homes and for newly adopted cats. Kittens and unvaccinated cats get the sickest.

What the infection looks like

First infection

Signs start 2 to 10 days after exposure and usually last 7 to 14 days, sometimes up to 21:

• Sneezing, then nasal discharge that turns thick
• Red, sore eyes with discharge, often squinting
• Fever, tiredness and a low mood
• Loss of appetite, because blocked noses can't smell food
• Coughing and, sometimes, mouth ulcers

Most healthy adult cats recover with care at home. Kittens, older cats and cats with other illnesses can get pneumonia or become dehydrated.

Lifelong carriers

About 80 percent of infected cats become carriers. The virus sleeps in the nerves and the cat looks well. Stress can wake it up, and the cat sneezes again and sheds virus that can infect other cats. Common triggers:

• A move, new pets, boarding or other upsets
• Illness or other causes of a weak immune system
• Corticosteroid treatment
• Pregnancy and nursing
• Crowding

Flare-ups are usually milder than the first infection.

Eye and long-term problems

FHV-1 can damage the eye. Your vet may find:

• Corneal ulcers, often with a typical branching pattern
• Corneal inflammation and scarring
• Dry eye
• A patch of dead corneal tissue (sequestrum)
• Scar tissue joining the eyelid to the eye
• Rarely, loss of sight

Repeated infection can also leave a cat with a chronic snuffly nose.

When to see a vet

Book a visit if your cat sneezes for more than a few days, has thick discharge, squints or has a cloudy eye, stops eating, or seems low. Eye problems should be checked quickly, since ulcers can get worse fast. A cat that breathes with an open mouth, or hasn't eaten for a day or two, needs urgent help.

Our clinic is open Monday, Thursday and Friday 10:00 to 16:00, and Tuesday and Wednesday 09:00 to 17:00. Outside those hours, contact an emergency vet clinic. You can read about our veterinary services.

Diagnosis

Vets usually diagnose FHV-1 from the signs and the cat's history. Swabs for PCR testing can detect the virus, but a positive result doesn't prove FHV-1 is causing the illness, because the virus is found in healthy cats and PCR can pick up vaccine virus. Your vet weighs the result against the signs. Calicivirus, Chlamydia felis, Bordetella and Mycoplasma cause similar signs, as can allergies and foreign bodies.

Treatment

There's no cure, but treatment shortens and eases flare-ups:

• Antiviral medicine. Your vet may prescribe famciclovir tablets, the oral antiviral most often used, or antiviral eye drops for corneal disease. Never give a medicine meant for people or other animals
• Eye care. Eye drops or ointment, plus pain relief for ulcers
• Nursing at home. Wipe discharge from nose and eyes with warm water. Steam from a bathroom shower can ease congestion. Offer strongly scented, warm wet food
• Fluids and feeding help for cats that are dehydrated or not eating, sometimes in the clinic
• Antibiotics, only when a vet suspects a secondary bacterial infection, because they don't work against the virus

L-lysine supplements are widely sold. Studies haven't shown that they prevent cat flu, and the evidence is weak, so ask your vet before you spend money on them.

Vaccination

The vaccine against FHV-1 is a core vaccine for cats. It doesn't stop infection, but it makes illness milder and shorter.

• Kittens: a first dose at 8 to 9 weeks, a second 3 to 4 weeks later, and a third at 16 weeks or older
• Adults: a booster after the kitten course, then every 3 years for low-risk cats. Cats in multi-cat homes, that go outdoors or that stay in boarding catteries may need a yearly booster

Your vet sets the plan for your cat. If you plan boarding, check vaccination dates in good time. See our pet care page if you'd rather have a sitter visit your cat at home.

Prevention and home care

Multi-cat homes

• Separate a sick cat straight away, with its own bowls, tray and bedding
• Wash your hands between cats
• Wash bedding and toys, and disinfect surfaces. Dilute bleach kills the virus. Ask your vet how strong to make it, and keep cats away until the surface is dry
• Keep a new cat apart from the others for about two weeks, and have it examined and vaccinated first

Reduce stress

• Keep a steady routine
• Give each cat its own litter tray, bowl and rest spot, plus high places and hiding places
• Introduce new pets slowly
• Make changes gradually
• Keep regular vet checks and a good diet

Living with a carrier cat

Most carriers live normal lives. Expect occasional flare-ups, usually during stress, and start care early: reduce stress, offer food and fluids, and call the vet if signs last or the eyes are involved. Tell boarding staff, a sitter or a new owner that your cat carries FHV-1, and keep all cats' vaccinations up to date.

Outlook

Uncomplicated cases clear in 7 to 21 days. Eye damage can be permanent, and a few cats have long-term nasal trouble, but most carriers have good quality of life. Kittens and very ill cats have a more guarded outlook.