Equine flu Q & A


flu-testingWhat is equine influenza and how does it spread?

It’s a respiratory disease which affects Equidae – horses, donkeys and mules. It’s not usually fatal, but horses may contract the likes of pneumonia and other serious complications as a result. It’s spread through nasal discharge, and the coughing and snorting that go with most chest infections. It is highly contagious. The reactions of horses vary widely. Some develop only a fever and a cough, while others get very sick. It may take a horse a few months to completely recover to full fitness.

Why such big concern about its spread?

In countries such as New Zealand and Australia, which haven’t had the disease, there will be no resistance in the local equine population. That means it will spread very quickly and many horses will catch it. The recovery time will create huge disruption to all equine-related sports. Interestingly, since the Australian outbreak in August 2007, New Zealand is the only country left with a major equine population that remains free of the disease in its general population. While most horses get over the disease, veterinarians report more post-infection problems with equine flu than with most other respiratory infections. Heart problems and pneumonia, for example, are not uncommon.

Does it have an incubation period?

EI is transmitted directly from acutely infected horses to susceptible horses. Horses with the disease remain infectious for up to seven to 10 days. The dry, harsh-sounding cough may linger for several weeks.

The disease has a very short incubation period (time from infection to symptoms) of two to six days and clinical signs usually resolve in one to three weeks.

How long is an infected horse contagious?

About 15 days.

What does the virus do?

It attacks the airway lining, which becomes inflamed and can ulcerate. The animals gets a sore throat and cough as a result. They have trouble clearing mucus from their airways, and areas of damage resulting from the infection are more prone to bacteria infections.

What are all the symptoms?

  • A high temperature of 39-41deg C (103-106deg F), lasting for one to five days.
  • A dry, harsh-sounding cough that may linger for several weeks. Some horses may cough only two or three times a day, but others more frequently. Coughing is generally worse when eating hay or hard feed.
  • Nearly all horses will develop a clear, watery nasal discharge that may turn green or yellow as secondary infections developed.
  • Swollen lymph nodes under the jaw, a clear eye discharge, depression, lethargy, loss of appetite.
  • There may be swelling in the lower limbs.
  • Animals are often depressed, off their food, are stiff and reluctant to move.
  • Other signs include runny nose and eyes.
  • Pneumonia may develop in the very young and very old. This may be fatal in a few cases.

How long does recovery take?

Horses suffering from equine influenza should be given complete rest. As a general rule horses should have a week of complete rest for every day they have a raised temperature. Generally horses require at least 30 days complete rest after infection, or longer if they suffer a fever for more than 4 days. Like people with influenza, individual horses recover at different rates. After about 30 days of complete rest, only light exercise is recommended for a further 30 days, then fitness should be built up by gradually increasing work.

Can people catch it?

No. But they can transfer it from one horse to another, on their hands or their clothing. Mostly, you would expect the disease to spread from just coughing. Once exposed to the virus, a horse is likely to come down with the flu in about three days.

How long does the virus live for?

On hard, non-porous surfaces like plastic: 24-48 hours
Cloth and paper: 8-12 hours
Canal water: up to 18 days

Thorough cleaning with soap or detergent and water and disinfectant easily kills the virus.

How do I decontaminate myself?

EI is a fragile virus and is easily killed. Simply soap and water or detergents will kill the virus. If in contact with a suspicious horse, it is recommended that you change clothes and boots, shower with soap, and shampoo hair. Avoid contact with horses for 48 hours.

How do I decontaminate my equipment and vehicles?

Thorough cleaning with soap or detergent and water and disinfectant can easily kill the virus. The virus is killed by exposure to sunlight for 30 minutes.

Is there a carrier status?

Horses who recover will not infect other horses.

Will my horse become infected again?

Infection with this strain of EI will result in immunity, although not for life. Therefore, if challenged again by the same virus in the near future your horse will not redevelop the disease.

What is the recovery period?

It is suggested that it takes 30 days for repair of this tissue. For equine athletes, a subsequent 30 days is also advised prior to the recommencement of work.

Is there a vaccination available?

Yes. In countries where the flu is present, many horses are vaccinated annually. Vaccinated horses can still show symptoms, which these will be much milder than unvaccinated horses.

Equine influenza can be prevented by vaccination with the appropriate equine influenza virus strain but vaccinations have to be repeated every few months, as the immunity from the vaccine is short-lived (about three to four months).

• See: Equine influenza treatment and care

Are there side effects with vaccination?

There can be. Side effects can include:
• A transient swelling (max. diameter 5cm) which regresses within 4 days may appear at the injection site.
• Pain and local hyperthermia can occur in rare cases.
• A slight increase in temperature (max 1.5C) may occur for one (1) day, exceptionally two (2) days.
• In exceptional circumstances, apathy and reduced appetite may be observed the day after vaccination.
• In exceptional circumstances a hypersensitivity reaction may occur, which may require appropriate symptomatic treatment.

What are the risks of an outbreak in New Zealand and Australia?

The ease with which horses can be moved around the world these days obviously increases the risk of infection. However, there are quarantine controls, and it helps that the symptoms of equine flu reveal themselves in only three days.

Very recent arrivals should be kept isolated and their status checked. Generally the clinical signs are sufficient to base a diagnosis on but these need to be confirmed with laboratory tests.

What happens if the disease is not successfully eradicated?

If infection becomes widespread, nationwide and is considered uncontrollable, Australia will adopt a system of twice-yearly vaccination and will live with periodic outbreaks.

If Equine Influenza gets to New Zealand, what is the likely scenario?

Should the disease arrive in New Zealand and depending how quickly it is diagnosed we will be faced with undertaking the same measures as Australia of stopping all horse movement for at least 30 days. The stables involved and other affected places would be placed under quarantine for at least four weeks. All horse movement would be prohibited and all horse events cancelled for the same period of time. Movement of people in contact with sick horses would also be limited. All equipment, transport vehicles, fences, stables and stalls would need to be cleaned and disinfected with an anti-viral disinfectant.


Originally published on Horsetalk.co.nz in September, 2007.


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One thought on “Equine flu Q & A

  • February 8, 2019 at 9:20 pm

    Hi, we have a foal on our yard,not mine, who’s temp 41.3 cough, nasal discharge, blood tests were taken, borderline strangles, tested again two later, vet diagnosed, originally foal was on antibiotics, taken off these immediately by vet, no abscess appeared on foal and although a little better still has a terrible cough. We are starting to think it is flu, is there any chance it could be this.

    Same precautions probably still apply and our yard is on lock down,

    Any extra advice would be useful


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