Equine infectious disease surveillance in Northern Europe

By Fleur Whitlock

Equine infectious disease occurrences remain an ever-present threat, irrespective of the country where a horse resides. With climate change and increased international horse movements, monitoring and surveillance of infectious disease is more important than ever. But how is this conducted in our equine population?

In Northern Europe and the majority of countries worldwide, there are three infectious respiratory diseases commonly found to be circulating in horse populations (referred to as ‘endemic’). These include the viral diseases: equine influenza and equine herpes; and the bacterial disease: strangles. It is essential that horse keepers and their veterinary surgeons remain vigilant and knowledgeable around how these diseases present to ensure rapid implementation of control measures if they occur and more importantly what actions to take to prevent them in the first place. 

Why is surveillance vital?

Identifying and controlling infectious diseases when they occur is important to limit both the number of infected horses on a premises and the disruptive and costly effects that disease can have on commercial enterprises,  as well as avoiding the spread of infection to the wider horse population. To optimise control and prevention measures, diseases are monitored at a national and international level, through surveillance activities. 

How is surveillance conducted?

There are two main ways that equine surveillance is conducted:

1. Statutory reporting of notifiable diseases 

Diseases that are notifiable under veterinary or human health legislation in horses may include (but are not limited to and will have country-specific designation): African Horse Sickness (AHS), Contagious Equine Metritis (CEM), Dourine, Equine Viral Arteritis (EVA), Equine Infectious Anaemia (EIA), Glanders and West Nile fever. These diseases have been designated as notifiable, either due to their potential implications for human health, equine health or trade. Statutory reporting is required if a disease is suspected due to suspicious clinical signs or confirmed through diagnostic testing, such as those recommended by the HBLB International Codes of Practice before horses are bred each year. The specific approaches to their occurrences will be disease- and country-dependent but may include movement restrictions and testing of the in-contact population as a minimum. Information gathered from these outbreak investigations is evaluated and shared with the wider industry, through platforms such as the World Organisation for Animal Health - World Animal Health Information System (OIE-WAHIS) (https://wahis.oie.int). 

2. Voluntary disease investigation and reporting of positive laboratory test results for non-notifiable diseases

If a horse is examined and undergoes confirmatory diagnostic testing through a laboratory and either the veterinary surgeon or laboratory contributes to surveillance initiatives, the diagnosis may be reported (Figure 1). Alongside this, epidemiological data relating to horse-specific factors such as the horse’s age, breed, vaccination status and specific factors such as approximate geographical location, number of resident horses on the premises and history of recent horse movements may also be available. In addition to this, to increase our understanding about pathogens and how they are changing over time, further analysis of the pathogen isolated from the infected horse(s) may be conducted to determine factors such as the particular strain of the pathogen. Information such as this can then be utilised to inform factors such as vaccination requirements. However, given the necessary voluntary steps that are required for a confirmed disease diagnosis to reach the reporting stage through this surveillance method, reported cases may not reflect the true extent of disease in a particular region or country. Also, some bias in the type of outbreaks that get reported may exist as detection and reporting may favour more severe cases, particular groups that undergo required testing or be more likely to be sampled due to subsidised testing costs existing in a particular country. 

Figure 1: The pathway of surveillance.

Examples of surveillance initiatives 

Country-specific initiatives may be available to encourage diagnostic testing of suspect infectious cases through incentives such as subsidised laboratory fees. In the UK, equine vets can submit nasopharyngeal swab samples from horses with signs that could be indicative of equine influenza, for free PCR testing at a designated laboratory—with this scheme funded by the Horserace Betting Levy Board (HBLB) and overseen by Equine Infectious Disease Surveillance (EIDS), University of Cambridge, United Kingdom. In addition to this scheme, EIDS maintains a surveillance network of all commercial laboratories conducting equine influenza testing in the UK, encouraging the voluntary reporting of positive samples and the sharing of associated epidemiological and virological information. Both schemes enable monitoring of equine influenza in the UK, and this is essential given that equine influenza viruses naturally change and adapt, giving the potential for new strains to be more infectious or to emerge beyond the protection imparted by current vaccines. In addition to equine influenza, the UK closely monitors laboratory-confirmed occurrences of equine herpes virus-1 (EHV-1), given its ability to cause neurological signs and abortion in pregnant mares and death of newborn foals. Strangles is also under surveillance with epidemiological and bacteriological data collected and analysed to improve our understanding of this frustrating contagious disease and contribute to improving its control and prevention.

What disease reporting platforms are available?

Figure 3: Examples of the international and country-specific reporting platforms monitored by the International Collating Centre (ICC): an interim email report issued by ICC and a recent embedded disease alert.

Country-specific reporting platforms exist worldwide, and these predominantly notify stakeholders—usually through email alerts—about laboratory-confirmed disease occurrences in the reporting country. Examples in Europe include France’s Réseau D'épidémio-Surveillance En Pathologie Équine (RESPE, www.respe.net), the Netherlands Surveillance Equine Infectious Disease Netherlands (SEIN, www.seinalerts.nl), Belgium’s Equi Focus Point Belgium (EFPB, www.efpb.be) and Switzerland’s Equinella (www.equinella.ch). 

Figure 3: Examples of the international and country-specific reporting platforms monitored by the International Collating Centre (ICC): an interim email report issued by ICC and a recent embedded disease alert.

Complementary to this, the International Collating Centre (ICC) is overseen by EIDS and supported by the International Thoroughbred Breeders’ Federation (ITBF) and International Equestrian Federation (FEI) and has for over 30 years collated outbreak reports from available country-specific reporting contacts and platforms worldwide. In addition, EIDS receives reports directly from veterinary surgeons and diagnostic laboratories (Figure 2). Collated reports are sent to registered subscribers on an almost daily basis through an email that contains embedded links to specific ICC outbreak alerts. A quarterly summary report is also produced and emailed to subscribers four times a year and is available in the resources and archive section of the ICC website (https://equinesurveillance.org/iccview/). Reported outbreaks are predominately made up of at least one case that has had the diagnosis confirmed through laboratory testing. It is therefore expected that those outbreaks that reach the reporting stage by the ICC will not reflect true infectious disease frequency within the international equine population; and a country with no reported outbreaks of a disease does not necessarily mean that the disease is not present in that country. 

Figure 3: Examples of the international and country-specific reporting platforms monitored by the International Collating Centre (ICC): an interim email report issued by ICC and a recent embedded disease alert.

There is an interactive ICC website enabling analysis of all international infectious disease outbreaks reported through the ICC, which was launched in August 2019; and outbreak data for all of 2019 onwards is available through this platform. Through the ICC, infectious disease outbreak information is shared with stakeholders throughout the world, ensuring people remain up to date through this active communication network. 

In addition to the ICC, EIDS has an equine influenza-specific platform, EquiFluNet (www.equinesurveillance.org/equiflunet), which presents influenza outbreak reports for the UK and worldwide.

A summary of the recent findings of surveillance initiatives

Equine influenza 

Figure 2: European countries reporting equine influenza outbreaks in Europe through the ICC for 2019, 2020 and 2021.

During 2019, Europe experienced an epidemic of equine influenza with widespread welfare and economic effects, including the temporary ceasing of horseracing in the UK. During 2021, influenza occurrences in Europe reported by the ICC returned to a more expected level (Figure 3). However, the potential of viral strain changes alongside international horse movements makes monitoring and surveillance of this virus essential.

Equine herpesvirus-1 (EHV-1)

EHV-1 is endemic in Europe, and the ICC regularly reports on occurrences of EHV-1 disease. An example of an ICC report released during 2020 detailed an outbreak of EHV-1 neurological disease on a premises in Hampshire, United Kingdom, with multiple equine fatalities (Figure 4 – left panel). Another example of an ICC report included a widespread neurological EHV-1 outbreak that occurred in Spain at several international show jumping events during 2021 (Figure 4 – right panel).

Figure 4: The International Collating Centre(www.equinesurveillance.org/iccview) reports detailing outbreaks of equine herpesvirus-1 neurological disease in Hampshire, United Kingdom in January 2020 (left) and Valencia, Spain in February 2021 (right). 

West Nile fever (WNF)

Figure 5: European countries reporting equine WNV outbreaks in Europe reported through the ICC from 2019, 2020 and 2021.

WNF is caused by West Nile virus (WNV) by biting mosquitoes, with birds acting as sources of the virus. It is a zoonotic disease, meaning humans can become infected if bitten by an infected mosquito. The ICC has reported equine cases across Europe over recent years (Figure 5). Given that many countries in Europe remain ‘free’ from WNV, it is still possible  for horses to have neurological signs such as weakness and incoordination or even death following infection. Humans can also be affected if bitten by an infected mosquito, so monitoring and surveillance of equine WNF occurrences, alongside mosquito, bird and human surveillance are essential. By way of example, WNV was confirmed in birds and humans in the Netherlands for the first time in 2020, but as of March 2022, it has not yet been confirmed in horses.

Summary

Having an appreciation of how and why surveillance of equine infectious diseases are conducted helps to improve engagement with and encourage an increased contribution to surveillance initiatives. A well-informed view on equine infectious disease outbreaks worldwide ensures continued advancements in enhancing control and prevention measures. This in turn will help reduce the risk from disease outbreaks and ensure the industry can continue to operate to its full potential.

Sources for further information about equine infectious diseases and their control and prevention are available

More information about equine infectious diseases and prevention/control:

• Horserace Betting Levy Board’s International Codes of Practice 2021: https://codes.hblb.org.uk/

• Equine Infectious Disease Surveillance (EIDS) website, hosting the International Collating Centre (ICC) and Equiflunet: www.equinesurveillance.org

• Sign up to receive International Collating Centre reports by contacting EIDS: equinesurveillance@gmail.com

Gerald Leigh Memorial Lectures 2020 - minimising risk from equine infectious disease - how it will hopefully help support education on equine infectious disease

By Celia M Marr

IN ASSOCIATION WITH:

COVID-19 has affected all corners of the thoroughbred world and has changed lives, work patterns and the social activity that underpins racing. One of its minor impacts was that this year, the Gerald Leigh Memorial Lecture series, usually coordinated by Beaufort Cottage Educational Trust at the National Horseracing Museum, Palace House, Newmarket each summer, was cancelled.

This annual lecture series is supported by the Gerald Leigh Charitable Trust in honour of Mr Leigh’s passion for the thoroughbred horse and its health and welfare. Coincidentally, the topic which had been selected for 2020 was Minimising Risk from Equine Infectious Disease. Finding that a meeting was impossible, the trustees organised for presentations to be filmed remotely, and these are now available online.

THE LECTURES SERIES INTRODUCTION BY NICK WINGFIELD DIGBY, CHAIRMAN, BEAUFORT COTTAGE TRUST

Gastrointestinal disease is a common problem in foals and youngstock with potentially serious illnesses involved. Dr Nathan Slovis, director of the McGee Center, Lexington, Kentucky, USA, explained that by six months of age, 20% of foals will have had infectious diarrhoea. Dr Slovis presents a concise and very practical account of how we can minimise risk of infection in this age group. 

The specific causes of gastrointestinal disease vary with age. Foals frequently display mild diarrhoea at around the time of the foal heat, generally a problem that will clear up uneventfully. Major infections in foals include rotavirus, Salmonella, Clostridium perfringens, Clostridium difficile. Infectious disease can be life-threatening if infection leads to shock, so every gastrointestinal case should be assessed carefully; early intervention is critical. 

Vaccines are available to help minimise risk of rotavirus but prevention relies primarily on proper hygiene and appropriate choice of disinfectants, which vary depending on the particular microorganism concerned.

PRESENTATION BY DR NATHAN SLOVIS, DIRECTOR OF THE MCGEE CENTER, LEXINGTON, KENTUCKY

Diagnosis: PCR and ELISA technologies

The speed and availability of laboratory testing have been revolutionised in recent years with the introduction of ELISA and PCR technology. The enzyme-linked immunosorbent assay (ELISA) is an immunological assay commonly used to measure antibodies, antigens or proteins. An ELISA test relies on finding a molecule which is unique to a virus or bacteria and is used to find several equine pathogens, including rotavirus, Clostridium difficile and Clostridium perfringens.  

PCR technology rapidly makes millions to billions of copies of a specific DNA sample, allowing the lab to take a very small sample of DNA and amplify it to a large enough amount to study in detail. Rapid tests are now available, which have revolutionised the diagnostic approach across a huge range of equine infections; relevant to foal diarrhoea is that this technology is used for rapid testing of faecal samples for Salmonella.

In addition to being extremely quick, both PCR and ELISA tests are very sensitive. Dr Slovis emphasised how important this is in early identification of diseases with the potential to spread rapidly in young horses.

Auditing environmental contamination

All the speakers in the webinar series spoke of the importance of robust biosecurity and common themes emerged in all four webinars regardless of the animals’ age or whether respiratory, skin or gastrointestinal infection is involved.

Dr Slovis’ clinical practice includes offering services to identify areas of environmental contamination. This involves a detailed inspection of all areas on the farm together with laboratory testing for the common pathogens. Key benefits of a facility evaluation service are to help support staff education and to highlight areas of weakness in biosecurity practices; and farmers and vets can work together to devise practical solutions to farm-specific problems. In his webinar, Dr Slovis shows some great examples of what not to do, which are drawn from his extensive experience of advising on biosecurity practices in equine facilities.

THE PRESENTATION BY PETER RAMZAN, A MEMBER OF THE RACING TEAM AT ROSSDALES LLP, NEWMARKET, UK:

Infectious challenges in young horses on training yards

Peter Ramzan, member of the Racing Team at Rossdales LLP, Newmarket discussed how to reduce risks when horses move into training. Piet is a fellow of the Royal College of Veterinary Surgeons and has written extensively on a range of disorders affecting horses in training. He summarised three areas relevant to this age group: lower respiratory tract disease, ringworm and the rare but sporadic disease threats such as strangles and neurological herpes.

Lower respiratory tract disease

This problem is mainly responsible for coughing and affects around 80% of two-year-olds and 25% of three-year-olds. Research in Newmarket has shown that for every 100 horses, there are around 10 cases each month, but prevalence varies between yards and seasons with a peak in early spring. Bacteria are believed to be a more common cause than viral infection, but both can cause coughing and can occur simultaneously. 

Prevention is better than cure

Exposure to disease-causing microorganisms is inevitable and cannot be prevented, but risk of clinical disease can be reduced by optimising immunity. It is helpful if exposure occurs prior to or early in training. Ramzan concluded that homebreds that have bypassed public sales and the inevitable mixing with other horses there are at greater risk of interruptions to their training when they do enter yards as two-year-olds. He went on to emphasise that it is not necessarily helpful to aggressively treat respiratory infections in pre-training—better to let infection run through yearlings and young two-year-olds, providing that they remain mildly affected as this helps them build immunity to protect them during their racing careers.

As well as discussing the biosecurity measures which apply across all age groups and disease threats, particular points that Ramzan emphasised for reducing the impact of infectious disease in training yards included the importance of avoiding the introduction of yearlings to the main yards before the end of the season and adoption of a strategic vaccination programme. Vaccines should be given to horses in a year ahead of the influx of yearlings while maintaining immunity throughout the racing season; autumn and spring boosters are most likely to achieve this.

Antimicrobial stewardship

It is increasingly clear that overuse of antimicrobials is promoting resistance to these potentially lifesaving drugs. Vets and trainers should avoid their use, except where bacterial infection is highly likely,  or ideally confirmed with laboratory testing. Ideally the lowest class of antibiotics should be used first, reserving protected classes, such as enrofloxacin and ceftiofur. Ramzan shared data from his practice over the last two decades which showed an alarming increase in resistance to oxytetracycline, which is the commonly used antimicrobial. Conversely, in the same period, oral trimethoprim sulphonamide, which is not used as much as it could be, has had a rise in sensitivity, likely because it is not used as often as it could be.

Herpes virus Type 1: a uniquely challenging foe

Professor Lutz Goehring,  head of Equine Medicine and Reproduction at Ludwig-Maximilian University, in Munich, Germany, has had a distinguished research career focussed on equine herpes type 1 (EHV1). This virus has the potential to cause both abortion storms and outbreaks of neurological disease in all age groups, including horses in training. 

PRESENTATION BY PROF. LUTZ GOEHRING IS HEAD OF EQUINE MEDICINE AND REPRODUCTION AT LUDWIG-MAXIMILIAN UNIVERSITY, IN MUNICH, GERMANY.

Are you aware of the risks of EHV? ==================================

Equine Herpes Virus is a real threat to horse health and performance. Racing yards can be particularly vulnerable to outbreaks, but there are some easy steps you can take to reduce the risks.

Dr Wendy Talbot, vet at Zoetis explains: EHV is a contagious viral infection causing respiratory disease, abortions and neurological disease. Carrier horses show no clinical signs, but the virus can be reactivated at any time and spread to other horses and this is more likely to happen during times of stress. ^1,2,3

EHV can be transmitted by direct horse-to-horse contact and by nasal or ocular discharge, which can spray or travel through the air over short distances. It can also be spread by sharing infected equipment, and via people who have been in contact with infected horses. This is why it’s crucial to have good biosecurity measures in place at yards, races, training and sales events. ⁴

Signs of the virus can be visually obvious or very subtle: horses may have a nasal discharge, weepy eyes, swollen glands and a cough and fever or a less noticeable lethargy, lack of appetite and reduced performance. ^1,5

Vaccination against EHV is important because it helps tip the balance in favour of the horse’s immune system and reduces viral shedding.

Vaccination programmes should run concurrently with rigorous hygiene and isolation protocols to help minimise the risks of EHV spreading.

It’s also important not to mix unvaccinated horses with vaccinated ones to provide the best level of protection. ^6,7

If you think any of your horses may have any symptoms of respiratory disease,isolate them immediately and contact your vet to discuss the next course of action.

FOR FURTHER INFORMATION FOLLOW THIS LINK

1. Slater J (2014) Equine Herpesviruses. In: Equine Infectious Diseases. Eds., D.C. Sellon and M. Long, Saunders, St. Louis. P151-169

2. Allen GP (2002) Respiratory Infections by Equine Herpes Virus Types 1 and 4. International Veterinary Information Service.

3. Slater J. What is Equine Herpes Virus? Accessed August 2019 https://www.horsedialog.co.uk/Health/WhatisEHV.aspx

4. Allen, GP (2002) Epidemic disease caused by equine herpesvirus-1: recommendations for prevention and control. Equine Veterinary Education; 14(3):136-142.

5. Davis, E. (2018) Disorders of the respiratory system. In: Reed SM, Bayly WM, Sellon DC, eds. Equine Internal Medicine, 4th ed. St Louis, MO: Elsevier:313-386.

6. Lunn, DP., et al. (2009) Equine herpesvirus-1 consensus statement..J Vet Intern Med. 23(3). 450-461

7. Equine herpesviruses: a roundtable discussion Philip Ivens, David Rendle, Julia Kydd, James Crabtree, Sarah Moore, Huw Neal, Simon Knapp, Neil Bryant J Richard Newton Published Online:12 Jul 2019 https://doi.org/10.12968/ukve.2019.3.S2.1

EHV1, like its virus relatives that cause cold sores in humans, has the ability to become latent. This means that the virus can sit in an inactive form in certain nerves and lymph node tissues, only to be reactivated and start to spread amongst groups of horses. While latent, the virus is out of reach of the immune system. Latent infection with EHV1 is widespread in horse populations globally.

Reactivation of EHV1 is not a common event, but it is associated with “stressful” situations such as mixing with new horses, transport, above-normal exercise, and in mares with foaling. Understanding the mechanisms involved in reactivation, spread to other horses and subsequent uptake of the virus into tissues—such as the placenta and fetus to cause abortion and to the spinal cord to cause neurological signs and paralysis—has been the main focus of Prof Goehring’s research career.

EHV1 is easy to kill with soaps and disinfectants when it is outside the body, again highlighting the importance of good biosecurity practices in studs and training yards. The virus spreads from horse to horse when there is close contact and droplets breathed out by an infected horse are inhaled by another. Shortly after inhaling the virus, there is a short temperature spike and then a second more intense spike usually occurs 8-10 days later. Neurological signs or abortion will typically come days or weeks after this second temperature spike.

Outbreak mitigation 

Early detection and effective quarantine are the mainstays of EHV1 outbreak prevention. In the face of a potential outbreak, swift action to stop spread is critical. Movement on and off the property must cease. Horses with subtle clinical signs—slight nasal discharge, lymph node enlargement and fever—can now be tested very quickly for EHV1 using a nasal swab PCR. Horses should be tested to identify any that are shedding the virus; and any which are positive must be removed to isolation. Horses housed near these individuals should be quarantined in case they are incubating the disease. Horses in the early stages of infection may benefit from treatment to prevent neurological complications.

Distance is the key to stopping this droplet-aerosol infection; and although the distance does not need to be great, more is always better. Traditionally racehorses exercise in strings. An exercising horse which is shedding virus creates a tail of viral particles trailing behind it. In his webinar, Prof Goehring talked about the advantages of increasing distance between exercising horses and showed the benefits of exercising alongside rather than one behind the other. When there is infection around, consideration should also be given to the order horses go out to exercise, with those least likely to have infection exercising first.

Immunity, current and future vaccines

Following infection or vaccination, horses produce both antibodies and specialised cells with the ability to fight off EHV1 infection. Vaccination can be expected to reduce both the clinical signs and the shedding of virus if they are challenged. However, this immunity gradually wanes with time and with currently available herpes virus vaccines, repeat vaccination every six months is recommended

. 

It is also important to understand that there is a balance between immunity level and infectious dose such that horses which are challenged with a very high dose of virus are more likely to develop fever than those that are exposed to a low dose—this again highlights the importance of effective biosecurity practices on studs and training yards. 

Finally, although not yet available for equine herpes viruses, novel sub-unit vaccines introduced for similar herpes viruses in humans have been shown to cement latent virus into its hidden location and stop reactivation. Prof Goehring suggested this technology may be the light at the end of the tunnel for horses because this novel approach may reduce the likelihood of the outbreak initiation, which begins with reactivation of latent virus. 

PRESENTATION OF DR. RICHARD NEWTON, DIRECTOR OF EPIDEMIOLOGY AND DISEASE CONTROL AT THE ANIMAL HEALTH TRUST, KENTFORD, UK.

Lessons from the European flu epizootic 2019

Although current attention is on COVID-19, it is important to reflect on lessons from the equine influenza outbreak which affected many countries in Europe last year. Dr Richard Newton, epidemiologist and an authority on equine infectious disease, coordinated much of the UK’s surveillance and communication during this outbreak, working at that time at the Animal Health Trust, Newmarket, Suffolk.

Equine influenza is a contagious rapidly-spreading viral respiratory disease. Common signs of infection include fever and coughing; and coughing is an important factor in spread as infected particles are released and can spread over wide distances to affect others. Unlike EHV1, there is no carrier or latent state, and the flu virus needs chains of transmission to persist in a horse population; an infected horse has to pass the virus on to another in order for the infection to perpetuate in a group. Vaccination is used to break these chains of transmission by reducing susceptibility. However, flu virus evolves continuously, constantly producing new strains; and in order to be effective, vaccine strains must keep up with this evolution and be updated periodically. 

The R number: what does it mean?

The R number, or basic reproduction number, is the number of cases on average that one case generates over the course of its infectious period. If the R number is less than one, the chain of transmission will die out, and infection will cease. Vaccination plays a major role in reducing the R number by limiting the number of susceptible animals.

Lessons from 2019

Flu occurred in several countries in Europe last year. In the UK, we saw two waves of this infection whereas other countries, notably Ireland and Holland, had different patterns. The Clade 1 strain of virus involved in the 2019 outbreak had not been seen in Europe for over a decade.

Flu mainly affects non-vaccinated horses but can occur in vaccinated animals, particularly if a new strain challenges a population. Fortunately, prompt action by the British Horseracing Authority last year minimised flu occurrence within our racing population. In January, based on information coming out of other European countries,  the BHA veterinary committee advised six monthly booster vaccinations.  

A six-day stoppage in racing and horse movements after flu was identified in a racing yard in early February. The majority of flu outbreaks occurred in unvaccinated horses, and the second spike seen in the summer of 2019, was associated with horse gatherings at shows and fairs. Nevertheless 18% of flu cases involved appropriately vaccinated animals, some of which might have been vaccinated after contracting infection, while many of the others were nearing the time when a booster was due. 

The UK’s racing populations are highlight connected, and the racing stoppage was prompted by the occurrence of flu in vaccinated animals. This break provided the necessary pause during which the scale of infection could be assessed. A huge number of racehorses were tested, and Dr Newton explained that an important conclusion from this experience was that there is a need to scale up lab testing capacity to support such a response in future, particularly if we were to be challenged by a completely novel strain of flu.

What did we do well?

Racing heeded the earliest warnings with its six-month booster recommendation, applied a lockdown and implemented test and trace and finally, on releasing lockdown, racing applied biosecurity precautions, concepts now familiar to us all in relation to COVID-19. 

Dr Newton acknowledged that these lessons were missed or ignored outside of racing, leading to a second wave in  the non-thoroughbred during the summer; and horse owners and event organisers did not adequately embrace the simple messages regarding the importance of vaccination and isolation. Many of the outbreaks which occurred last summer were associated with the introduction of new animals on a premise. The UK horse population has a low national vaccine coverage, estimated at around 40%—a statistic which puts the UK in a poor light compared to other European countries where uptake in the general horse population is much higher. 

Do we need to improve vaccines and vaccine strategy?

Vaccine strains are continuously reviewed by The World Organisation for Animal Health (OIE)  panel—critical work which in the UK is supported by the Horserace Betting Levy Board. Currently there is insufficient scientific evidence to recommend an equine influenza vaccine strain update, although this might not be far away. On the other hand, reducing booster vaccine intervals is clearly beneficial. Flu vaccines work by stimulating the horse to produce antibodies which decline with time. There is variation in vaccine response between individual horses with some animals less well protected than others. Dr Newton reviewed information from multiple studies and outbreaks and concluded the weight of evidence overwhelmingly supports a six-monthly booster. Increasing vaccine uptake across the national herd will involve improved education in the non-thoroughbred world but is critical to supporting herd immunity. Improved awareness will benefit all horses including thoroughbreds.

Take-home messages

All four speakers highlighted practical biosecurity measures as critical in reducing the risks of infectious disease. Vaccines are essential for both flu and EHV1. They are not infallible, and ongoing research will lead to improved vaccine technology. Most important of all is that education of people working with thoroughbreds, and across the wider equestrian world, will help support early recognition and management of disease when it occurs. This year’s Gerald Leigh Memorial Lectures will hopefully help support this education by making information on equine infectious disease available online.

CLICK HERE FOR USEFUL RESOURCES ON VETERINARY ADVICE RELEVANT TO THE THOROUGHBRED

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