Clive Hamblin Bvet med MRVCS, NTF Veterinary Adviser, explains Equine Influenza

To help communicate the seriousness of the recent cases of Equine Influenza, our Veterinary Adviser, Clive Hamblin, has written an explanation of the disease and its transmission. He concludes with advice on biosecurity and vaccination. Below his account, we have inserted a link to a scientific paper by Dr Richard Newton (of the Animal Health Trust) and colleagues, demonstrating the increased immunity provided by vaccinating against equine flu at six monthly intervals.

Clive Hamblin writes:

On the eve of our return to racing, I would like to stress that we are not out of the woods yet, although we can perhaps see the odd patch of green between the trunks. It has been a fraught time for all concerned with airtime and column inches normally given to our sport of British horseracing, having to be filled with opinions from many people, some more informed than others.

The simple fact is we have seen an escalating problem with a mutation of a variant of equine influenza, initially seen on the continent and also in Ireland and now Great Britain. It has been reported in a number of individual outbreaks, across the land, most of which have been in unvaccinated horses, then more alarmingly in vaccinated horses and then with entry into the racing population, as you well know.

There is a wide range of pathogens affecting the respiratory tract of the racehorse, seen at intervals, across the spectrum of yards, many of which are viral and many bacterial, but make no mistake, these are not Equine Influenza. This latest outbreak is!! No, it is not Ebola, but it has the potential to bring racing to a coughing and spluttering halt and not just for 6 days.

I would like to commend the BHA and its officers, the Animal Health Trust and my fellow members of its Veterinary Committee for their prompt and sensible action. This break has enabled us to take stock and properly assess the situation prior to making an evidence-based programme for the recommencement of the sport, maintaining the best health of the national racehorse herd and with the least risk of further spread of this potentially debilitating disease.

It is perhaps of value to know how the disease progresses. Virus particles from an infected horse are discharged in a spray of water droplets when breathing, coughing or snorting and are inhaled by our horse. The virus gains access to the cells of the airway and rapidly multiplies, this is the period we call “incubation”, 48 hrs to 4 days in duration. This is then followed by the period when clinical signs are apparent although they may be subdued in vaccinated horses, particularly if that has been recently carried out. This is the period when the horse may be “shedding” virus (can be up to 10 days) and is the optimum time for swabbing (inserting a long swab through the nose and collecting mucous from the throat region ready for transporting to the laboratory). The laboratory will carry out PCR on this sample where any viral RNA (this virus’s equivalent of DNA) is multiplied many, many times and can then be identified. The immune system of our horse now is in full flight combating the virus invasion, the horse stops shedding and is now no longer infective to the rest of the population. Damage done to the respiratory tract will gradually repair allowing a return to training in due course.

The equine influenza virus cannot live for long outside its infected host but can live for short periods in secretions in a stable, lorry or on a groom’s clothing, providing another source of infection. The main source though is a newly infected horse and more often than not, a horse newly introduced into the herd. That could be from overseas, the Sales or perhaps a breaking or livery yard or a new intake horse from shared transport.

In the light of this new influenza outbreak we have two major weapons in our armoury, namely vaccination and biosecurity. There are quite a number of scientific papers supporting the evidence that vaccinating at 6 month intervals gives superior protection against equine influenza virus and hence the BHAs approach to resuming racing if the participants have been so protected. This was never going to please every owner and trainer, but the advice of world experts would be ignored at our peril.

With regard to biosecurity, the watchword is all new inmates should have a period in a quarantine unit, preferably some distance from the training yard. For those looking for a cracking good read, I refer you to the NTF Code of Practice for Infectious Diseases of Racehorses in Training booklet (or via the NTF website, https://www.racehorsetrainers.org/publications/pdfs/cop.pdf . Please, please pay particular attention to the sections on biosecurity……pages 3-11 and try and orchestrate the best arrangements you can.

Clive Hamblin Bvet med MRVCS

12^th February 2019

Dr Richard Newton et al paper on

“Optimising vaccination strategies in equine influenza.”