Equine Influenza (Horse Flu)

How to spot horse flu, what to do straight away, and why vaccination matters.

Quick Answer

Equine influenza is a highly contagious viral respiratory disease, and it spreads readily between horses.
If your horse has a fever, a harsh dry cough, nasal discharge, is off its food or seems dull, isolate it and call your vet straight away.
If your horse is struggling to breathe, or is a foal, an elderly horse or one with an existing breathing problem and shows any flu signs, call your vet immediately.
There is no direct treatment for the virus itself, so care is supportive, with rest and a low-dust environment.
Vaccination is the most important way to reduce the risk and impact of the disease, and your vet can advise on your horse's programme.

Equine influenza is one of the most important respiratory infections to know about, because one horse can quickly pass it to others. It is also present in the UK, and outbreaks occur from time to time.

This guide covers the signs, how the virus spreads, what to do if you suspect it, and how vaccination and biosecurity help. It is general information, not a diagnosis. Your vet must confirm what is wrong.

Two chestnut horses, one wearing a tartan stable rug, stand in an indoor stable, where equine influenza can spread quickly between horses

What is equine influenza?

Horse flu is a highly contagious viral disease of the respiratory tract. It affects horses, donkeys, mules and other equids. Equine flu viruses are distinct from the viruses that cause human and avian flu.

The HBLB Codes of Practice describe it as highly contagious but rarely fatal. The BHS adds that it can be fatal in serious cases, particularly when complications develop in foals, elderly horses and those with an existing respiratory disorder.

How horse flu spreads

In the air and by contact

The virus spreads in droplets when an infected horse coughs or sneezes, and by direct contact between horses. It can also travel indirectly on people, equipment, vehicles, feed buckets and stables that have not been cleaned between horses.

Your vet will advise on isolation and on how to protect other horses on your yard.

Before signs appear

Infected horses can shed virus before they show signs, so spread may happen before anyone notices the first case. The incubation period is short. Sources quote one to three days or one to five days.

A pale horse in a cream turnout rug faces the camera with green hills behind, a reminder that vaccination is the main protection against equine influenza

Where the risk is higher

Flu spreads quickly where horses mix, such as livery yards, events, sales and markets. New arrivals are a particular risk. The HBLB Codes note that many cases in earlier outbreaks followed new horses being introduced to stables.

Unvaccinated horses are at greatest risk. British Equestrian says the disease is often introduced to a premises by a non-vaccinated horse.

Current outbreaks

Equine Infectious Disease Surveillance (EIDS) runs the Equiflunet viewer, which shows where and when flu has occurred in the UK and worldwide. It only lists laboratory-confirmed outbreaks, so a region with no reports may still have disease. Check the EIDS website for the current picture.

Signs of equine influenza

The BHS lists a temperature above 38.5°C for one to five days, which can come before other signs. The Welsh Government guide lists fever, coughing, nasal discharge, loss of appetite and lethargy.

A raised temperature.
A frequent, dry, harsh cough.
Clear, watery nasal discharge that may turn thick and yellow-green a few days later.
Loss of appetite and lethargy.
Swollen, painful glands under and around the jaw.
Filling of the lower limbs, muscle soreness or conjunctivitis in some horses.

Not every horse looks equally unwell. Many fully vaccinated horses that meet the virus show mild signs or none. Even so, signs in a vaccinated horse should be taken seriously and investigated.

Our guides to Why Is My Horse Coughing? and Why Does My Horse Have Nasal Discharge? cover other causes.

Emergency: Contact a Vet Immediately If…

Your horse has laboured breathing or is struggling to breathe.
The horse is a young foal, an elderly horse, or a horse with an existing respiratory disorder, and it has any flu signs.
The temperature is above 38.5°C, as British Equestrian advises ringing your vet immediately in that case.

Call your vet or the nearest out-of-hours emergency vet straight away, and keep the horse isolated from others. Flu can lead to bronchitis or pneumonia, and young foals appear most susceptible to fatal lung complications.

When to Contact Your Vet

Your horse has a fever, harsh dry cough, nasal discharge, reduced appetite or lethargy.
Your horse seems unwell before a vaccination is due. It may be incubating a disease, and vaccinating then could cause a negative reaction.
A vaccinated horse shows signs of flu.
Your horse seems to be getting worse rather than better.
Your horse has been in contact with a suspected case.

Do not delay calling, and do not mix a suspect horse with others.

What to do if you suspect horse flu

Isolate the horse and call your vet.
Limit movement of horses on and off the premises.
Take your horse's temperature, and monitor in-contact horses closely.
Keep dust levels as low as possible so the respiratory system is not further affected.
Follow your vet's advice on isolation and on returning to work.

Do not wait for confirmation before you isolate. Take your horse's temperature regularly when it is well, so you know what is normal.

How vets diagnose and treat horse flu

Your vet will take a long nasal swab, and possibly a blood sample. A PCR test on the swab can confirm or rule out flu quickly. The HBLB-funded flu scheme offers free PCR testing of suspected cases through enrolled vet practices.

There is no direct treatment for the virus. The BHS says the best action is supportive care and plenty of rest, much as with human flu. Your vet can treat signs and complications where necessary.

Sources differ on recovery time. The HBLB Codes say most adult horses recover in a week to two weeks, but recovery can be prolonged if the horse is not rested. The BHS says full recovery may take several weeks.

Ask your vet before returning your horse to work, because going back too soon risks complications such as pneumonia.

Vaccination and prevention of equine influenza

The Welsh Government guide says vaccination is the most important way to reduce the risk and impact of equine influenza. Vaccines reduce the severity of illness, help horses recover more quickly and limit how much virus an infected horse spreads. No vaccine is 100% protective.

Keeping boosters up to date matters. The BHS warns that allowing a booster to lapse can mean restarting the initial programme, but booster timing rules differ between organisations, so talk to your vet. Our guide to Horse Vaccinations: What to Discuss With Your Vet covers the wider picture.

Governing bodies and many venues set their own flu vaccination requirements, and these change. The BHS says it is the owner's responsibility to check the relevant rules. Check the current rules with your governing body and your vet. Keep your horse's passport up to date, as vaccinations are recorded in it.

Isolate new arrivals before mixing them with other horses. Sources quote anywhere from 10 days to three weeks, so ask your vet how long suits your yard.
Do not share buckets, tack or grooming tools.
Clean and disinfect equipment, vehicles and stabling.
Wash your hands and change clothing after contact with other horses.
Monitor horses daily, and before travelling.
At events, avoid contact with other horses and make sure temporary stables are cleaned and disinfected.

Reporting and rules

The Welsh Government guide says equine flu is not a notifiable disease in Great Britain. The HBLB Codes say it is not notifiable to Defra, but racehorse trainers must report it to the British Horseracing Authority under the Rules of Racing. The BHA asks trainers to tell it immediately of any confirmed or potential case.

DAERA, in Northern Ireland, also describes equine flu as not a notifiable disease. Rules can change, so confirm the current position with your vet.

How Pet Med Direct Can Help

Suspected horse flu is a situation for your vet first. Please isolate your horse and call them before ordering anything.

Once your vet has advised, you can browse our equine range for everyday horse care. If your vet has prescribed a medicine, our guide to how pet prescriptions work explains the process.

Some pet medicines require a valid veterinary prescription. Pet Med Direct can only supply prescription medicines after the prescription has been checked. Always follow your vet's advice and the directions on the medicine label.

Frequently Asked Questions

Is horse flu notifiable?

The Welsh Government guide says it is not notifiable in Great Britain, and the HBLB Codes say it is not notifiable to Defra. However, racehorse trainers must report it to the BHA. Ask your vet if you are unsure.

How long does it take a horse to recover?

Sources differ. Some quote a week or two for most adult horses, while the BHS says full recovery may take several weeks. Horses that are not rested can take much longer.

Can vaccinated horses get flu?

Yes, but signs are generally milder. Properly vaccinated horses have good protection, and vaccination reduces the severity and helps horses recover more quickly. Signs in a vaccinated horse still need investigating.

Can I take an unvaccinated horse to a show?

Check with the organiser and your governing body. Vaccination rules differ between events, and horses that do not meet them may be refused entry. The BHS says carrying the passport is a legal requirement when transporting, and shows may check vaccination status.

Is equine influenza the same as human flu?

No. Equine flu viruses are distinct from the viruses that cause human and avian flu. It affects horses, donkeys, mules and other equids.

What should I do before vaccinating a horse that seems unwell?

Speak to your vet first. A lethargic horse that is not eating may be incubating a disease, and vaccinating at that point could cause a negative reaction.

Related Equine Health Guides

Sources and Further Reading

This article was researched from the sources listed above. It is general information for horse owners and is not a substitute for advice from your own vet.

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This article is for informational purposes only and does not constitute veterinary advice.
If you are concerned about your horse’s health, please consult a qualified veterinarian.