2 Dec 2016
The global nature of the equine industry makes it vital to consider the constant risk of notifiable exotic diseases. Josh Slater lists those relevant to the UK and emphasises the importance of awareness and risk-based biosecurity.
Josh Slater
Job Title
The UK, being an island, has definite biosecurity advantages. It is easier to maintain border controls on the importation of animals than those European countries with land borders and multiple points of entry.
However, this mindset also creates the risk of exotic diseases being seen as problems elsewhere in the world, rather than relevant to the UK.
This is not the case, however, and the challenge for the equine industry is getting the owner of a single horse in a local livery stable, who only travels to local shows, to think about the relevance of “exotic” diseases to him or her.
This challenge also extends to the veterinary profession and it is essential it shows leadership by influencing all tiers of the equine industry – from the elite professional competitors to the leisure rider – to think about the constant risk of exotic disease incursion.
Everyone in the industry needs to recalibrate their thinking about equine disease to include those considered exotic, after:
Two reasons exist why exotic disease incursion is a constant, growing threat – the nature of the industry and climate change.
The equine industry is a uniquely interconnected global industry – other than humans, no other animal travels as much as the horse.
Horses and equine biological products – including plasma, ova and semen – constantly move intercontinentally, internationally, nationally and regionally for both competition and trade. It could be flying horses to compete at the Olympics or taking them for northern or southern hemisphere breeding and racing, or moving horses regionally by road to compete in shows – horses are interconnected by contacts with other horses and humans like no other animal species.
The basic principles of biosecurity in farming are difficult to fully apply in the equine industry, especially in the amateur sectors. This creates an intrinsic level of disease risk requiring everyone in the equine industry to engage with disease awareness and biosecurity planning. The interconnectedness of the equine industry means only a small number of degrees of separation between horses of all types and uses.
The sectors of the industry moving regularly for competition, breeding or trade are used to thinking about exotic diseases as those not normally seen in the UK. Therefore, the real challenge for the industry is getting the owner of a single horse to think about the relevance of “exotic” diseases.
The outbreaks of EIA in 2010 and 2012 are potent examples of the concept of limited degrees of separation between horses. The Defra/APHA investigations found both outbreaks – despite initially appearing to be both geographically and, in some cases, epidemiologically distinct – were linked to the importation of a single shipment of horses from continental Europe.
So, while the owner of a single leisure horse in a livery stable in Devon or Northumberland may not have considered his or her horse to be part of an international network, the reality was different.
Although the reasons for climate change continue to be vigorously debated, the climate is changing; land surface and sea temperatures are rising.
The extent of change may be difficult to predict, but it is clear, in the northern hemisphere – in particular the more northern regions of Europe, including the UK – the effect of climate change has been, and will continue to be, wetter, warmer winters.
This has had a profound effect on the ecology of insect disease vectors, including midges, mosquitoes and ticks, with their range extending northwards over the past 20 years.
Milder winters have also resulted in year-round breeding and feeding activity, creating the opportunity for disease incursion into new geographical areas and for establishment of endemic infection cycles.
Diseases are made notifiable because they are judged to be economically important through impact on trade – equine viral arteritis (EVA) or contagious equine metritis (CEM) are examples – or because they have significant welfare and health impact, resulting in significant economic impact because of suspension of trade. EIA and African horse sickness (AHS) are examples of the latter.
Other diseases are notifiable because they have zoonotic potential. Both glanders and WNV fall into this category, despite the latter not being zoonotic from horses; it is zoonotic from birds, with the horse acting as a sentinel species for infection.
The UK equine industry’s legal framework is a combination of EU regulations and UK national legislation. So, while the referendum result may lead to changes to the framework over time, the situation is unlikely to change for the foreseeable future.
The major piece of European legislation governing equine diseases – Council Directive 90/426/EEC – covers the protection of trade and requires countries to only permit the movement of healthy horses. More specifically, movement of horses between countries is only allowed if those horses have come from premises free from specified diseases.
At European level, six equine notifiable diseases must be notified to the European Commission under Council Directive 82/894/EEC – AHS, dourine, EIA, all types of equine encephalomyelitis, glanders and vesicular stomatitis. Of these, only AHS has its own legislation (92/35/EEC), reflecting the predicted devastating welfare and economic effect of incurring this disease into Europe.
The European framework is translated into UK law through several pieces of national legislation in England, Scotland and Wales. Principally, the Infectious Diseases of Horses Order 1987 specifies the notifiable equine diseases. This is supplemented by both the Specified Diseases (Notification and Slaughter) Act 2006 and the Infectious Anaemia (Compensation) Order 2006, the latter of which covers compensation for slaughter of EIA-positive horses.
The laws in England, Scotland and Wales make all the equine diseases notifiable in Europe notifiable in the UK and, additionally, specify epizootic lymphangitis (Figures 1 and 2), EVA and CEM (Panel 1).
A 2013 consultation into the possible delisting of EVA and CEM as notifiable diseases, as part of the Government’s red tape challenge, concluded they should remain notifiable because of the significant economic impact they would have on the UK horse industry.
Defra/the APHA, working in partnership with the equine industry, are responsible for monitoring, surveillance and testing for notifiable diseases.
The Thoroughbred breeding and racing industry has a main role, having developed and funded several voluntary codes of practice for disease control produced by the Horserace Betting Levy Board.
These include codes for important endemic infectious and contagious diseases, as well as codes for CEM and EVA.
The codes represent best practice and have been important in controlling CEM and EVA through industry-funded surveillance and disease investigation.
Equine infectious and contagious disease is monitored internationally and reported through the World Organisation for Animal Health (OIE), allowing Defra/the APHA to take action at national level when required.
Each notifiable disease is relevant to the UK and relevance maintains them so. However, four diseases are of immediate relevance as a result of international movement of horses and climate change
EIA is a constant threat to the UK industry. It is present in Europe and has a persistent, but diminishing, endemic reservoir in Romania.
Significant progress has been made in controlling this disease, however, with a decrease from 1,513 outbreaks (2,973 cases) in 2010 to 573 outbreaks (634 cases) in 2014. This has been achieved through mandatory testing – about half a million tests are carried out each year.
Despite this, the movement of horses from Romania for onward use for equestrianism and slaughter for human consumption still presents a continuing risk to the European industry. This is reflected in the provision of enhanced testing of horses of Romanian origin.
EIA is spread by the transfer of contaminated blood from infected horses – especially during the unapparent (carrier or silent) phase of infection – by large biting flies such as horseflies and deer flies, or by veterinary instruments and needles.
In veterinary hospitals, acute cases present a particular risk through artificial infection cycles, haemorrhagic discharges or, again, veterinary intervention. The control of EIA in the UK is by mandatory slaughter.
Glanders is caused by Burkholderia mallei and a potential zoonosis. The disease is endemic in the Middle East and other parts of the world – including parts of Africa and South America – and is transmitted mainly orally, via feed and water.
It occurs in respiratory and cutaneous (known as farcy) forms, and the main differential diagnosis for this disease in the UK is strangles.
A disease alert in the UK in 2011 was subsequently negative, but positive horses were identified in Germany in 2015 and the Czech Republic in 2016. Control is by slaughter.
WNV is a vector-borne encephalitis virus of birds transmitted by Culex mosquitoes; humans and horses become infected as dead-end hosts through the bite of infected mosquitoes.
It has changed its ecology in the past decade, with stable endemic infection establishing in central Europe (Romania, Hungary, Austria and eastern Italy).
The virus responsible had been confined to its original territory in Africa until 2004. Previously, only WNV lineage 1 viruses had spread from Africa; it was responsible for the introduction of WNV to the US in 1999 and the establishment of endemic infection around the Mediterranean basin during the 1970s.
The later spread of WNV lineage 2 viruses to Europe was probably the result of the effects of climate change on Culex ecology and wild bird migration patterns, allowing the virus to become established endemically in local bird populations. Its spread northwards, combined with the establishment of the bridge vector Culex modestus in south-east England, means the UK needs to be vigilant for the first cases of WNV.
Control is by vaccination; a commercial vaccine is available in the UK.
AHS is the most feared of the equine notifiable diseases – and for good reason. Modelling predicts more than 90% of infected horses would die on first exposure if there was incursion into the UK.
The unexpected appearance of bluetongue virus in Europe in 2007 put all European countries on alert that the related orbivirus AHS virus could make a similar geographical jump. It shares the same midge vectors (Culicoides species) and, as happened with bluetongue, the virus would transmit via the UK Culicoides population.
AHS presents in two major clinical forms – a rapidly fatal respiratory form (Figure 3) and a less rapidly fatal cardiac form (Figure 4).
The risk of AHS entering the UK is very low because awareness and surveillance in the international industry is high. This does not mean, however, there is any room for complacency. Control is by compulsory slaughter.
The equine industry relies on international movement and trade, which creates an intrinsic level of disease everyone in the industry needs to be aware of and take action against.
A unique feature of the industry is the small number of degrees of separation between horses, irrespective of their use and value.
The key message for the industry is to be ready for the unexpected and think about exotic diseases in everyday equine practice.
The EIA outbreaks in the UK in 2010 and 2012, all of which originated from a single shipment of horses from Europe, remind of the need to think internationally.
Improving disease awareness and recognition, and excellent risk-based practical biosecurity are immediate priorities for all sectors of the industry.
