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, . 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

12th February 2019

Dr Richard Newton et al paper on

Optimising vaccination strategies in equine influenza.”


and the layman’s explanation on the BHA website



NTF comment on the resumption of racing on Wednesday

It is great that racing – both flat and jump – resumes today.

From the outset, the NTF supported the BHA’s strict containment strategy once cases of equine influenza were reported. Our policy was shaped by the unanimous opinion of trainers on the NTF Council that to safeguard the race programme in the longer term, it was vital in the short term to stop the circulation of horses around the country to race meetings until the extent of the outbreak and consequent disease risk could be assessed.

Trainers are competitive creatures – they want to be racing. We encouraged the BHA to plan ahead for the moment when the BHA’s Veterinary Committee (which includes the NTF’s Veterinary Adviser Clive Hamblin) was satisfied the risk to the horse population was acceptable so racing could begin again.

Well done to the BHA, the Veterinary Committee and vets up and down the country for achieving so much in such a short space of time. Trainers – hats off to you. From day to day, you deal with multiple responsibilities and challenges but somehow maintain resilience. Coping with the racing shutdown and testing requirements has added enormous stress to an already pressurised training operation. Some of you have questioned the industry disease containment policy – we accept that will always happen when events present the sport with difficult decisions.

Less welcome are the control measures agreed by the Veterinary Committee. These have produced different outcomes for different trainers and owners; some will be able to race, some won’t for at least a few more days. The NTF was not in favour of a requirement for runners to have had a flu vacc within the last six months. Some horses react poorly to the vaccine so unplanned vaccinating mid-season is undesirable, especially for Cheltenham bound horses so close to the big event. The control measure will also deprive some yard and not others from participating in the rescheduled trial races and other essential prep or qualifying runs. We tried yesterday morning to persuade the BHA to use some flexibility and though they wouldn’t budge, they acted quickly to refund entry fees and put on alternative races.

We are assured the scientific case for a recent flu vaccination is strong so we have had to accept that decision as a condition of the most desirable outcome for all – the resumption of racing today.


Racing to resume on Wednesday 13 February

11/02/2019 @ 23:15:00

The British Horseracing Authority (BHA) tonight announced a risk-managed return to racing will take place from Wednesday this week.

After consultation with its veterinary committee, and based on the latest tests conducted by the Animal Health Trust, the BHA’s Chief Regulatory Officer, Brant Dunshea, tonight confirmed that racing could resume, but only with strict biosecurity controls in place.

This decision to return racing in a controlled, risk-managed manner was unanimously supported by the industry veterinary committee.

Brant Dunshea said:

“Our approach since hearing about the first positive results last Wednesday has been based on accumulating as much information as we could as quickly as possible so we could properly understand the risks of this virulent strain of flu spreading to more horses. That would be harmful to them and damaging to any trainers’ yards that became infected.

“It has also been our intention to ensure that we avoid an issue that could result in a long-term disruption to racing with the risk of many of our major events being unduly impacted.

“After analysis of thousands of samples, and no further positive tests on Monday, we still only have two confirmed sites of infection. We have put robust containment measures in place around both.

“From the testing and analysis conducted the disease appears to be contained at present. The BHA veterinary committee believe that the swift controls on movement that were put in place have clearly helped to restrict the spread of this virus.

“There have been significant logistical issues associated with testing and processing so many tests in such a short space of time. Fortunately, owing to the tireless efforts of the Animal Health Trust, trainers and their local vets, and BHA staff, the vast majority of yards which had been placed on hold will be in a position to resume racing.

“Clearly, there is some risk associated with returning to racing. This risk has been assessed and, based on the evidence – and ensuring biosecurity measures are in place – the level of risk is viewed as acceptable.”

As such the BHA has confirmed that two scheduled Jump fixtures will go ahead at Musselburgh and Plumpton on Wednesday 13 February, alongside the All Weather fixtures at Southwell and Kempton.

Return to racing

As part of the controlled return, the BHA has developed a risk framework which allows us to categorise individual trainers by the level of risk they have been exposed to. The ability of runners to return to racing from those yards will depend on the risk categories the yards are placed in.

We are finalising overnight which category individual trainers will currently be placed in. The BHA will contact trainers tomorrow morning to inform them of their category and eligibility to run.


Trainers who hold entries for Wednesday are advised to declare at 10am on Tuesday. Confirmed declarations will not be issued to the media, betting organisations and data customers until 1:30pm. In this period the BHA will review all declarations to ensure none have been declared which do not meet the risk criteria.

Please note declarations for Thursday’s Flat All Weather meetings will now be at the 24 hour stage.

Biosecurity measures

In addition to the risk factors outlined above, and as an interim measure, the BHA has ordered that no entries or declarations will be accepted from horses that have not been vaccinated [for equine influenza] in the previous six months. Trainers are advised to check current vaccination records before declaring tomorrow morning. In addition, all trainers will be required to provide a health declaration upon arrival at a racecourse.

The BHA’s Director of Equine Health and Welfare, David Sykes said:

“The BHA and the veterinary committee agree that, on balance, the level of risk is acceptable for a return to racing.

“We have developed a risk model, which the veterinary committee support, in order to assist the return to racing.

“We will observe closely those horses who are taken to the racecourse and will intervene as a precaution to prevent a horse running or accessing a racecourse if we believe it might put other horses at risk of infection.

“The veterinary committee are of the view that an unprecedented amount of this disease has been identified in Europe. This is not a typical endemic period and it was essential that precautions be taken to protect the horse population.”

Rescheduling of races

In preparation for a return to Racing the BHA’s Racing department has identified a number of key Jump races which should be rescheduled. The identified races are based on their place in the Pattern and races which provided essential opportunities.

The following races have been rescheduled:
Races rescheduled
Full race conditions will be circulated tomorrow and a further review will take place of any gaps that have been caused at all levels of the race programme with a view to adding in additional race or fixtures as required.

A similar exercise will also commence for Flat races in the coming days.

About the Veterinary Committee       

The British Horseracing Authority (BHA)’s Veterinary Committee advises on all veterinary matters affecting racing and the health and welfare of racehorses. It contains representatives of the BHA, Association of Racecourse Veterinary Surgeons (ARVS), British Equine Veterinary Association (BEVA), National Trainers Federation (NTF), Racehorse Owners Association (ROA), Animal Health Trust (AHT), Thoroughbred Breeders Association (TBA), Racecourse Association (RCA) and Independent expertise.

BHA update regarding equine influenza case

10/02/2019 @16:35:00

Testing at licensed yards across the country is ongoing, with a view to quickly assessing and containing the potential spread of the highly contagious equine influenza virus which is affecting vaccinated horses.

The BHA is continuing to build a picture of the potential spread of the disease by testing as many horses as possible from potentially exposed yards. The data collected will help to build an evidence base which will allow a decision to be made on Monday as to whether racing can return on Wednesday 13 February.

Surveillance update

The Animal Health Trust (AHT) has now received several thousands of samples and is working through the process of testing those samples. The latest update that has been provided to the BHA confirms that no further positive cases have been identified from the testing carried out yesterday. Owing to the volume of testing being carried out the AHT have not been able to provide a precise figure as to the number of tests carried out, but they are of the view that the numbers processed will be roughly equivalent to the 720 which were processed the previous day.

Amongst the samples that have been tested are those of the remaining 27 horses from the yard of Rebecca Menzies. All horses in this yard have now tested negative, though the yard will remain under close surveillance and further testing will be carried out.

Analysis remains ongoing with more swabs being returned all the time, and yesterday 5,000 extra swabs were distributed to trainers to assist with the logistical challenges of testing this many horses.

The AHT have also publicly confirmed that a non-thoroughbred, unvaccinated horse has sadly had to be humanely euthanized after having contracted the virus. This shows the threat posed by the disease in unvaccinated horses and the importance of biosecurity procedures and movement restrictions to contain the possible spread of the disease.

Equine influenza should not be confused with or compared to the common ‘bug’ that might impact some yards from time to time. It is the most potentially damaging of the respiratory viruses that occur in UK equines, and it can be particularly serious for younger horses, which is of particular concern with the breeding season about to start. Trainers are required under the rules to notify the BHA should a case of equine influenza be identified or suspected in their yard.

Return to racing

A pragmatic and evidence-led approach is being adopted in order to enable the BHA to make decisions on Monday as to whether racing can return on Wednesday 13 February. A prioritisation plan for testing is being adopted, which is based on the proximity of horses to a positive test, or to a yard returning a positive test. Swabs will continue to be collected and tested from other horses, but some are being fast tracked. Separately, a specific plan is being formed as to what the clearance process will be for individual yards to return to racing.

This process will remain ongoing through today and tomorrow with a view to sufficient evidence being gathered to make a decision on Monday evening as to whether racing can return on Wednesday. We appreciate everyone’s patience and understanding that as much evidence as possible must be gathered prior to making a decision as to when racing can safely return.

Should racing be given the go ahead to return on Wednesday then declarations for all races would take place on Tuesday.

David Sykes, Director of Equine Health and Welfare for the BHA, said:

“The data is encouraging and provides a further indication that the precautionary safety measures have helped to contain the spread of disease. However, the picture is still developing and it remains the case that we will make an evidence-based decision about the situation on Monday.

“It remains paramount that, for the sake of our horse population, we do not take any unnecessary risks. This is not a common cold, it is a highly contagious and potentially serious disease.

“The prioritisation exercise with regards to testing will help deliver a detailed picture of the spread of infection. Targeted testing, alongside the wide survey of data we have already gathered, will help provide a clear picture as to the scale of the spread of the disease. Any decision will include guidance and input from veterinary experts, including the industry’s veterinary committee.

“We are also working through the process that will be followed in order to give specific yards the all clear to resume racing. This will balance the clear need for yards to resume business as soon as possible with ensuring that we do not put horses at the risk of unnecessary harm. We are liaising with the NTF and trainers on this process.”

Testing costs

As confirmed last night, the BHA and Horserace Betting Levy Board (HBLB) have agreed to pay a contribution to owners or trainers for the costs incurred where the BHA has required samples to be taken, including the cost of the swabs and the veterinary fees involved. We are working on the exact details with the NTF and HBLB and will confirm the reimbursement policy and process as soon as possible, but it will be based on a fixed fee per horse sampled.

The BHA is extremely grateful to HBLB for their important support and contribution.

BHA update regarding equine influenza case

08/02/2019 @ 14:25:00

The BHA has committed to providing meaningful daily updates regarding the ongoing situation in relation to the equine influenza case.

The analytical work is continuing, which involves testing of horses from a number of trainers yards across the country and seeking to isolate any issues we find in a bid to ensure that the situation is under control as much as possible, to protect the health of animals and to put racing back on the road as soon as is safely possible.

We will provide material updates with regards to any new cases and give as much information as is relevant and appropriate each day, while also respecting confidentiality and privacy of potentially affected people.

The BHA team is working closely with trainers, the NTF and other parts of racing, from who we have had excellent levels of cooperation. The Animal Health Trust is processing tests in their hundreds as quickly as possible and, alongside the project team at the BHA, is working throughout the weekend to help build an overall picture of the issue.

This process will continue over the coming days in order that an informed and evidence-based decision can be made on Monday as to whether racing can return on Wednesday. In the meantime we ask that everyone involved in the sport continues to be vigilant, restrict where possible all movements of horses and people and maintains the highest standards of biosecurity.

Of the samples that have been returned so far, three further positive results for equine influenza have been reported, all from the original affected yard. This means that in total six positive tests have been returned from the horses tested so far from this yard. Of the four horses from this yard who competed at fixtures this week, one has returned a positive sample so far – Raise A Spark, who competed at Ayr on 6 February. The test on this runner relates to a sample taken the following day, and the horse showed no clinical symptoms on raceday.

It was in anticipation of this risk that the decision was taken by the BHA to restrict movement of horses on a precautionary basis at the yards of 120 other trainers who competed at these fixtures, and to suspend racing until Wednesday at the earliest. This action was taken to mitigate the impact of any of the runners which competed at these fixtures being found to be infected by the virus.

We request that media respect that the priority of the yard in question now is to follow the necessary procedures to minimise the impact of this incident, and therefore not to contact the yard. Any queries on this matter should be directed to the BHA. The BHA would like to reiterate its thanks to the trainer for his cooperation and the responsible manner in which he has deal with this issue.

Testing of horses at the 120 yards which have been put on hold is continuing on an ongoing basis. No further positive samples have been reported as yet.

However, a separate suspicious case – which has not yet been confirmed as a positive sample – has been identified at another yard. No links have been identified between this yard and the original yard. This yard had runners at the fixtures at Newcastle on 5 February and Wolverhampton on 6 February, and as such the BHA has taken the further precautionary steps of placing all 54 yards of trainers who also had runners at these fixtures on hold and initiating testing of horses from these yards.

The BHA is working closely with the Animal Health Trust in order to manage the logistical challenge of providing sufficient swabs and handling the volume of tests being sent through the facility, considering that testing of a total of 174 yards is now taking place. It will not be possible to test every horse from every yard before the end of the weekend, but we will work with trainers to identify any priority or risk horses and ensure that they are tested. This will all form part of the picture that is built in order to assist the decisions that will be made on Monday.

Equine flu – Statement from Donald McCain


7 February 2019 -For immediate release


The National Trainers Federation is issuing the following statement from trainer Donald McCain to provide some background information about the cases of Equine Influenza at his Bankhouse premises in Cheshire.

“I have been aware of the recent news about Equine Influenza outbreaks in France and Ireland, and over the last couple of days, I have been concerned about the health status of a small number of horses in the yard. Their welfare is at the front of our minds, so at my request, our veterinary surgeon has examined them regularly and we have followed his advice on testing and treatment. It was by following this protocol that the positive results for equine flu came to light yesterday evening. The BHA were contacted immediately and we are liaising closely with them about biosecurity and management of all the horses at Bankhouse.

“Bankhouse follows all the available advice on disease control and all our horses are fully inoculated. We are scrupulous about observing the health status of horses in our care and taking the necessary steps to treat any condition that may affect them. It follows we would never race any horses that we could have known were infected. Over the last 2 months, all potential runners have been scoped and their blood checked within 36 hours of their races to ensure that only healthy horses compete for the yard.

“When new horses arrive at our yard we, as much as possible, try to keep them separate but at this stage cannot know if the infection came from recent arrivals or from horses returning from racing. We have 3 confirmed cases and this morning have taken blood and swabs from all the others for testing.”

Comment from David Sykes, BHA Director of Equine Health and Welfare, “We would like to thank Donald McCain for his cooperation in this matter, and for the responsible manner in which he has dealt with this issue, under the guidance of his veterinary surgeon. He has acted professionally with the interests of the racing industry and the health of his horses as his priority.”

Mr. McCain will provide updates in due course.


The National Trainers Federation represents the interests of British licensed racehorse trainers.

For more information, please contact Rupert Arnold, NTF Chief Executive, on 01488 71794 or 07899 797010. E-mail:

For more information on the National Trainers Federation, please go to

Getting to grips with Strangles: working together to break the strangles-hold

A workshop was held at the Animal Health Trust visitors centre and seminar room, Lanwades Park, Suffolk on the 5th October 2017 to share the latest research news and discuss progress towards the prevention and eradication of this disease.

strangles Figure 1

A brief introduction to strangles and Streptococcus equi

Dr. Andrew Waller (AW), Head of Bacteriology

Strangles, caused by Streptococcus equi, is one of the most frequently identified infectious diseases of horses world-wide. Approximately 600 outbreaks are identified in the UK each year, but AW reported that many more outbreaks are likely to occur where samples are not submitted to diagnostic laboratories for analysis or a veterinarian is not called upon to examine affected horses. AW described the classic clinical signs of disease and presented details of complications that can lead to mortality rates of up to 10% in some outbreaks.

The ability of S. equi to persist in the guttural pouches of horses that have recovered from strangles is critical to its onward transmission and the occurrence of new outbreaks. The horse is a global traveller and AW explained how the AHT has collaborated with researchers across 22 countries to determine if the occurrence of strangles outbreaks is linked to the international movement of horses. DNA was sequenced from 703 isolates of S. equi from around the World. AW showed examples of the same strain-type being shared between Europe and the USA; the USA, Europe, Japan and Israel; Europe and Australia; Australia, New Zealand and the United Arab Emirates (UAE) and Argentina, Europe and the United Arab Emirates. In particular, the UAE shared 14 different strain types with countries from around the World. AW described how the UAE had taken a proactive response to this information, requiring the mandatory screening of horses pre-export. Such screening had identified four new carriers of S. equi in 2016/2017 prior to export, which likely prevented the occurrence of several new outbreaks. Some discussion took place on whether such measures could be introduced more widely in the UK as a pre-purchase/movement check. It was noted by some that they have seen outbreaks of strangles linked to the import of animals to the UK, most notably from Ireland. AW commented that a collaborative project with Vivienne Duggan (University College Dublin) found that 133 of 319 (42%) healthy horses at unregulated events in Ireland were seropositive using the AHT’s strangles blood test, whilst 16 of 162 (10%) of Irish Thoroughbreds also tested seropositive1.

Dealing with strangles

Dr Richard Newton (RN), Director of Epidemiology and Surveillance

Although strangles is often regarded as an inevitable rite of passage for horses, it is now possible to eradicate strangles and prevent future cases. RN’s presentation described routes of transmission utilised by S. equi to spread through horse populations and the value of good biosecurity towards mitigating this risk. He highlighted the importance of identifying and treating outwardly healthy carrier horses, which are frequently overlooked, but can continue to trigger outbreaks for months or years after they themselves have recovered from strangles.

Recommendations for minimising the impact of an outbreak and the eradication of S. equi were described and discussed. The ‘traffic-light’ system of separating infected animals with clinical signs (Red group) from animals they have had contact with, but that do not have clinical signs (Amber group) from horses (Green group) that have no clinical signs and that have had no contact with horses in the Red or Amber groups, remains the gold standard approach to reducing the number of animals affected and the severity of clinical signs. Again the importance of biosecurity and decontamination of equipment and clothing was emphasised. The use of Virkon and Safe4 disinfectants is known to kill S. equi. Post-outbreak clearance methods using serology to identify healthy horses that were exposed to S. equi and then following up with guttural pouch endoscopy and lavage to identify persistently infected carriers were discussed. Redwings Horse Sanctuary highlighted their success on flushing guttural pouches immediately post-acute disease in order to minimise the development of persistently infected carriers and the subsequent need to use antibiotics.

RN then described protocols for preventing strangles through the quarantine and screening of new arrivals. He presented new results highlighting how vaccination in the face of an outbreak of strangles had confounded post-outbreak serology on a European farm. Approximately half (37 of 75) of vaccinated horses seroconverted compared with none of 18 non-vaccinated horses in a separated barn. As a result of vaccine-induced seroconversion, many more horses had to be examined to see if they had become persistently infected during the outbreak than would otherwise have been needed. RN said that vaccines that do not interfere with diagnostic tests are urgently required. He also commended the ‘Speak out on Strangles’ campaign being run by Redwings, which raises awareness of strangles and encourages openness and best practice so that future outbreaks can be prevented.

How does Streptococcus equi cause strangles?

Dr Romain Paillot (RP), Head of Immunology

RP gave a presentation describing S. equi’s journey through the horse, highlighting the many interactions the organism has with the equine immune response (Figure 1). He described how superantigens, which are produced by several disease-causing bacteria, potentially misdirect and interfere with the immune response helping the bugs to cause disease. He explained that superantigens are produced by some human pathogens and how they play a pivotal role in devastating diseases including toxic shock and necrotising fasciitis.

RP explained that in strangles, the production of superantigens is restricted to the site of infection within abscessed lymph nodes, which may explain why strangles rarely triggers toxic shock-like clinical signs in horses. RP went on to show how the production of superantigens by S. equi is important to its ability to cause strangles in horses by potentially assisting S. equi to colonise and invade the lymph nodes of horses and/or generating a strong but unregulated inflammatory response, which may help S. equi to cause lymph node abscesses. In this manner the production of superantigens may be used by S. equi to cause more consistent disease in horses. In agreement with this theory, RP presented new results showing that the infection of ponies with strains of S. equi lacking superantigens led to an unusual disease progression, with some ponies developing an early onset of clinical signs while others developed no clinical signs. Overall there was a significant reduction in the number of lymph node abscesses that were formed by the superantigen-deficient strain. In the light of these results, RP suggested a complex and important role for superantigens in assisting S. equi to cause strangles.

Vaccine design and the launch of our new BBSRC-funded project.

Dr Coral Dominguez-Medina (CD), Post-doctoral scientist

CD described the current array of vaccines that are produced around the World that seek to protect horses from strangles. Cell-free vaccines such as Equivac S (Zoetis), Strepguard (MSD Animal Health) and Strepvax II (Boehringer Ingelheim) are available in Australia and the USA. These vaccines are based on surface extracts of S. equi cells, but little data on the protection they confer is available and so these vaccines are not licensed for use in Europe.

The Pinnacle IN live vaccine (Zoetis) is available in the USA, Canada and New Zealand. The vaccine is given intranasally and provided protection against strangles. However, CD explained how the vaccine strain can cause adverse reactions and even strangles in some horses. As a result this vaccine is not available for use in Europe.

The only currently available strangles vaccine in Europe is Equilis StrepE (MSD Animal Health). CD explained how this vaccine is based on a live strain of S. equi that is administered into the upper lip of horses. The vaccine protects horses from strangles, but has a short-lasting effect and can occasionally cause adverse reactions. Vaccination with Equilis StrepE interferes with the currently available diagnostic tests (see above).

CD presented data from the recent Dorothy Havemeyer meeting on strangles concerning a new protein-based vaccine, Strangvac (Intervacc AB), which is in development. She showed how the vaccine protected 95% of ponies from developing strangles when tested two weeks after the intramuscular administration of the third vaccine dose. The vaccine did not interfere with the diagnostic tests and was safe when given by intramuscular injection. However, protection decreased over a 2-month period and so CD said that, if the vaccine becomes available, it may be necessary to give horses a booster vaccination in the face of an outbreak or before they travel to high-risk events.

CD then went on to describe new work at the AHT, which is funded by the BBSRC, towards improving the level of protection that strangles vaccines provide. The project harnesses the immune-stimulating activity of a modified superantigen (see above), which normally misdirects the immune response, so that it instead strengthens the immune response following vaccination. CD explained how the modified superantigen will be fused to vaccine proteins, which can either be used directly, or be employed as a sticky coat on the surface of live vaccines. This project has the potential to solve a significant problem in the development of safe and effective vaccines that protect against strangles. Furthermore, CD explained that the coupling of the modified superantigen to other vaccines could also be used to help protect other animals including pigs, cattle, sheep and humans.

Discussions then took place about the short duration of protection provided by strangles vaccines and the long-lasting natural protection generated following recovery from strangles. Historically, it has been hard to demonstrate that natural immunity is not enhanced by the presence of persistently infected carriers within populations of recovered horses. However, Redwings spoke about a group of Irish horses that had recovered from strangles and been cleared of carriers before being transported to their premises in Norfolk. This group of horses had been exposed to large levels of S. equi during the outbreak of strangles at Redwings in 2015. However, none of the Irish horses developed clinical signs of strangles, providing evidence that the natural immunity provided post-recovery is indeed long-lasting and effective. It was felt that modification of vaccine preparations, such as in the new BBSRC-funded project has the potential to provide immune responses in vaccinated animals that may be more akin to those produced following natural infection. It might also be possible to study immune cells from recovered horses to better understand how they provide a higher level of protection than is achieved using the currently available vaccines.

The authors would like to thank Nick Angus-Smith (Newmarket Stud Farmers Association), Jill Crook (National Trainers Federation), Samantha Chubbock (World Horse Welfare), Nicolas de Brauwere and Roxane Kirton (Redwings), Philip Ivens (Buckingham Equine Vets), Fleur Varley (Bell Equine Vets) and Penny McCann (Zoetis) for taking part in and contributing to this workshop.


 Figure 1: Illustration of the lifecycle of S. equi.

The bacterium is taken up from the environment by a horse via the nose or mouth from which it transitions to the submandibular and retropharyngeal lymph nodes. Here it uses a variety of mechanisms, several of which remain unknown, to establish a site of infection leading to the formation of abscesses. Abscesses burst externally or into the guttural pouch where incomplete drainage of pus can lead to the establishment of persistent infection in some horses. Shedding of S. equi from abscess material from acutely affected horses or from the guttural pouches of persistently infected animals into the environment completes the lifecycle of S. equi.