Once again, the UK has been hit by an outbreak of infectious disease – but this time it’s horses that are affected. As a result, the headlines are full of “Horse Flu!!!” stories, racecourses are closed, and some people are recommending horse owners have their horses vaccinations “topped up” to minimise the risk. So what’s going on? How severe is the risk? And what can we do to minimise it?


What is Equine Flu?

Equine Influenza is, as its name would suggest, a close relative of the human influenza virus. And just like that one, it affects the respiratory tracts of susceptible animals – in this case, horses. Fortunately, however, unlike bird flu or swine flu, the equine version does not cause disease in humans (although there is some evidence that humans can carry it without becoming infected). The virus is rarely fatal in horses or donkeys, but affected animals require prolonged convalescence, and complications such as pneumonia aren’t uncommon. Although the disease is not notifiable in the UK, it is so contagious that outbreaks should ALWAYS be reported to your vet, who will notify the Animal Health Trust’s EquiFluNet (who are monitoring this outbreak).

The strain that appears to be present in the current outbreak is H3N8 – all flu viruses are characterised by their haemagglutinin and neuraminidase receptors, in this case H number 3 and N number 8. This is a Clade 1 virus that is a direct descendent of the Florida strain that first emerged in 1999. It is also a strain that has, from time to time, been reported to infect dogs, although fortunately this is rare – the Equine Flu strains don’t jump the species barrier easily.


What horses have been affected by this outbreak?

So far, there are 12 reported clusters of cases, in Essex, Cheshire, Derbyshire, Lincolnshire, Leicestershire, Yorkshire, Somerset and Middlesex. However, several of these have been in racehorses, and at least one affected yard reportedly sent runners to racing meetings (in all good faith) within the incubation period of the disease (but before it was diagnosed), meaning that it is likely that horses from distant areas are at least potentially at risk. The trouble with Equine Influenza is that it usually has a 3 day incubation period, in which the horse is infectious, but shows few or no signs of illness.

Of these, 7 of the 12 clusters involved unvaccinated horses, and vaccinated horses appear to be less at risk.


Why didn’t the vaccines work?

Unfortunately, flu viruses are very unstable things. Because they’re part of a group known as RNA viruses, they don’t copy themselves very efficiently when they replicate, and so they mutate and change very fast. It seems likely that this particular strain has mutated slightly (a process known as antigenic drift) to the point where the virus is capable of triggering an active infection.

It isn’t just one brand of vaccine either – 2 brands have been challenged in this outbreak, and the third challenged on the continent. All three have shown some breakdowns in protection, in the face of a very heavy virus challenge.


So is vaccination worth it?

Yes – because one of the interesting things about equine flu is that vaccination seems to offer some protection by reducing the severity of illness even if horses do develop symptoms. Vaccinated horses who develop symptoms usually recover within 48 hours (although they need to be rested for longer), whereas unvaccinated horses tend to be ill for 2-10 days. Unvaccinated horses are also usually more ill, and more likely to develop complications.


Where did it come from?

There have been cases of Equine Influenza reported sporadically in mainland Europe, however, none of these appear to be the same strain of the virus as in the current UK outbreak. At the moment, we don’t know exactly where this came from.


How can the risk of infection be minimised?

Fundamentally, by minimising horse-horse contact. This is why racing has been suspended until AT LEAST 13th February, to try and break the chain of transmission.

On a yard, suspected cases should be isolated as far as possible, but as the disease is so contagious, it’s important that all “In contact” horses are also placed in quarantine for at least 3 days (the usual incubation period).

Vaccination is always wise – even if vaccines don’t offer full protection against this strain, it is likely that they will reduce the severity of infection.


Should I be topping up my horse’s vaccines?

In recent outbreaks, it was noticed that horses who had been vaccinated within the last 6 months were less likely to develop disease than those vaccinated within a year, but more than six months ago. The immune memory for flu seems to fade quite rapidly, and some people are advising “top-up” vaccines. This is something to talk to your vet about, however, because the vaccines available in the UK are only licensed for annual use once the primary course is complete; as such, a “top-up” would strictly speaking be off-license use.


How would I know if my horses were affected?

The typical symptoms of Equine Flu are:

  • A dry cough, often described as being harsh-sounding
  • Fever
  • Laboured breathing
  • Tiredness and lethargy
  • Reduction in appetite
  • Swollen glands under the jaw
  • Runny nose (may be watery or thick)

Of course, there are many other illnesses with similar symptoms, but any horse showing these should be seen by a vet as soon as possible.


How can it be treated?

Essentially, just like human flu – rest and plenty of fluids! The vast majority of horses will recover well as long as they get enough rest – the old rule of thumb was a week off work for every day of fever. Antibiotics are not effective against viruses, and are not required in uncomplicated Equine Influenza, and are only indicated if pneumonia or other secondary infections develop.

Soft, wet food, a warm stable, lots of fluids, and plenty of TLC will see most horses make a full recovery.


If you think your horse might be infected, contact your vet immediately for advice and confirmatory tests – the more information we have about this outbreak, the better!