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  • Equine Flu

Recent Flu Outbreaks Focus On Vaccination

Whilst many people in the horse industry have never seen a case of equine flu, vaccination remains key to keeping this contagious disease at bay.

Indeed the importance of continued vaccination has been demonstrated recently by series of outbreaks across the UK. All of these outbreaks have so far been in unvaccinated or horses with lapsed vaccination.

There have been 28 outbreaks across the UK from January to November 2014.


Equine flu is a serious issue for anyone owning or working with horses. It is an acute or ‘hit and run’ virus infection, is very contagious and can be spread by droplets in the air, or on inanimate objects such as horseboxes/stabling, tack and clothing.

A major outbreak in Australia in 2007 affecting 76,000 horses on 10,000 premises was eventually halted by restricting the movement of horses and by using a vaccine containing up-to-date strains, the same vaccine used here at milbournequine. The continent had been equine flu-free (therefore with no vaccination policy) but it’s understood that a stallion imported from Japan brought in the virus.

The imported quarantined horse had been vaccinated but it is believed the vaccine didn’t contain antigens active against the latest circulating strains. Also there was a break-down in procedures which subsequently allowed the virus to escape from the quarantine stables.

Australia was declared flu-free again 9 months after the outbreak began. At its peak the outbreak cost $1 million Australian dollars a day, with huge disruption to racing and other equestrian events.

Evolving Viruses!

Equine flu viruses, as with other flu viruses, undergo a phenomenon known as ‘antigenic drift’ due to the gradual accumulation of mutations in the genes. These mutations eventually lead to significant changes in the virus that can in turn lead to breakdown of immunity against vaccines which are not updated.

Currently the Florida sub-lineage (see diagram) is predominant and has itself diverged into two distinct viruses (known as Clades). These are referred to as Clade 1 and Clade 2, both of which now appear to account for all current isolates globally.

Surveillance data on flu viruses show that Clade 1 continues to predominate on the American continent whilst Clade 2 viruses continue to predominate in Europe. Although Clade 1 viruses have also spread to Europe - they were identified in the UK in 2007 and again in 2009, so far they are not predominateover Clade 2 viruses.

Staying Ahead With Updated Vaccination

This vaccine is an updated version of the one used to help contain the Australian outbreak. It was chosen at the time for its unique ‘canarypox’ technology which mimics natural infection to induce a strong immune response.

This is an important step for the prevention of equine flu, however we all need to do more to help increase the population of vaccinated horses within the UK herd!

It is also important to note that vaccinated horses may carry and shed the virus without showing any signs of the disease. This means that all unvaccinated in contact horses are at risk.

Approximately 45% of horses in the UK are vaccinated and the remainder are not vaccinated at all¹. Shortly, the first and only updated vaccine to contain the Clade 2 virus antigen will be launched by our vaccine supplier, Merial Animal Health.

The good news for horse owners is that vaccination is compulsory for membership of most official equestrian organisations. Therefore most of the higher risk travelling and competition horses are vaccinated, however it only takes a local event or gathering of horses with a carrier and an unvaccinated animal for the virus to take hold.

Signs of Equine Flu

So what happens if my horse does get flu or a new horse brings it on to the yard? Symptoms vary in severity but include high fever, nasal discharge, dry cough and a poor appetite. If you suspect your horse may have contracted flu, then a vet should always be called.

It is likely that your horse will be isolated whilst undergoing treatment. Mildly affected horses can recover in 2-3 weeks, however in serious cases secondary complications can occur and those that recover can end up with chronic respiratory problems.

If you think your horse(s) may be unvaccinated or their vaccination has lapsed, please contact the surgery to arrange a visit.