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Dr. Emmanuelle Van Erck Westergren on the EHV-1 outbreak: “We have to improve the protection of our horses by vaccinating and providing better biosecurity measures”

Sunday, 28 March 2021
EHV-1 (neurological form)

Dr. Emmanuelle Van Erck Westergren
Dr. Emmanuelle Van Erck Westergren. Photo © Wilhelm Westergren.


Text © World of Showjumping


International equestrian sports in Europe have been brought to an abrupt halt after an aggressive EHV-1 outbreak of the neurological form. While the situation in Valencia, Spain – where the outbreak originated – now is under control, the official numbers from the FEI show that seventeen horses so far have lost their lives. World of Showjumping spoke with Dr. Emmanuelle Van Erck Westergren – a European specialist in equine internal medicine at Equine Sports Medicine Practice in Waterloo, Belgium – to learn more about EHV.  

"We have to increase the number of vaccinated horses"

Outbreaks of the Equine Herpes Virus (EHV) – with its different strains – occur annually, usually in the spring, Emmanuelle explains. “Every year, between the months of March and April, we have a period with a higher number of airborne particles – fungi and pollen – that affect the horses’ airways and trigger inflammation,” Emmanuelle says. “The virus takes that opportunity to penetrate the body. This is why we normally see more cases during this period of the year. Then, in a place like at the Valencia Spring Tour, you have a very high concentration of horses in a small area, and the higher the concentration, the higher the risk of contamination. The fact that there are horses that have not been together for some time, due to Covid-19 having stopped the sport, can also play a role – suddenly putting together a lot of horses in a single spot, helps the germs spread. In my opinion, the reason this outbreak took such proportions must be that it arrived in a population of horses where not all were appropriately vaccinated. The vaccine reduces symptoms and viral shedding, lowering the amount of virus circulating within a population."

"There is only a single form of EHV-1 virus that infects the horse through the airways," Emmanuelle continues to explain. "It can induce either no signs, respiratory symptoms or in some more rare cases distressing neurological signs. However, it is the same virus that has the potential to do all this. A vaccination targets this single virus and is therefore protective against all forms of EHV-1. It protects by reducing the risk of infection, and because it helps the horses’ immune systems to defend themselves against the virus, it reduces the risk of all forms of EHV-1. Vaccinated horses can still shed the virus, but the amount of virus shed is significantly reduced, thus reducing the risk for all other surrounding horses. Hence, a vaccination makes a difference for individuals as well as the community.”

While there is a EHV vaccine, it is not mandatory. “I think it should be mandatory though,” Emmanuelle says. “In France, the EHV vaccine was made mandatory for trotters. As a result, the amount of the virus circulating and the severity of it has gone down in that population. We can see that with the vaccine, we don’t only protect one single horse but a whole herd. I think there is a lesson to be learned – in particular from this outbreak: We have to increase the number of vaccinated horses."

Compared to the other strains of the Equine Herpes Virus, EHV-1 is more aggressive. “Once the virus has entered the respiratory system, it can either remain silent or produce respiratory symptoms,” Emmanuelle says. “In some instances, it can also migrate to the uterus of pregnant mares, causing abortion, or to the spinal cord – the neurological system of the horse – causing neurological symptoms. It is not that the strain itself causes more neurological symptoms; a bit like in people, some individuals react worse to a virus than others. Some horses get more severe symptoms, and we are not sure why the response from one horse is different to the other.”

Combined testing gives more complete information

During the current outbreak, the test results have seemed inconsistent and Emmanuelle explains the reasons why. “The recommended test is a PCR test from a nasal swab,” Emmanuelle explains about the testing options. “It has to be done on the first day the horse comes back from a contaminated zone, or if the horse presents symptoms, and it must be repeated 14 days later. The reason for this is that horses can be carriers and not have symptoms. After a short incubation, the horse can start shedding and become contagious, whether he has symptoms or not. The shedding can last for ten days. So if the horse is negative on day one, it does not necessarily mean the horse does not have the virus. Testing before and after the incubation period – which is between two to ten days – we have the highest chance to check if the horse is positive or not.“

In some cases, horses have either first tested positive and been negative on re-test, or vice versa. “The virus gets in, it circulates in the body and after a while, the horse stops shedding it,” Emmanuelle explains. “When the virus is in the blood but no longer shed by the airways, a PCR test will be negative, but a blood test will be positive. That is why ideally, you would want to have both: A blood test and a PCR from a nasal swab. This way, you can combine the information: Is the horse still contagious for others – positive PCR test of a nasal swab – or is the virus inside the blood, which means it has entered the second phase of the disease and even though the virus is still circulating in the horse, the horse is no longer contagious?”

Enforcing the biosecurity regulations

“I think we need to improve biosecurity at the shows,” Emmanuelle points out. “We already have the FEI biosecurity requirements for event organisers as well as the FEI Veterinary Regulations, but rules also need to be enforced. We don’t want to have our shows stopped; we want to keep our horses competing. In order to do that, we have to make sure we have learned the lessons from this outbreak. We have to improve the protection of our horses by vaccinating, providing better biosecurity measures and making sure there is enforcement.”

In the case of biosecurity, the responsibility is shared between everyone present at a showground. The organising committee’s (OC) role is stated in article 1017 of the FEI Veterinary Regulations (VRs), which reads: “OCs are responsible for ensuring that all biosecurity requirements, as set forth in these VRs, are strictly followed at all times”. Article 1029.2 highlights the responsibilities of the person responsible (PR), which is the rider: “While Horses are present on the Event venue, their temperature should be taken at least once daily and recorded by the PR. Any change in the health status of the Horse should be immediately reported to the VD.”

Containing the virus

To get control over the outbreak, one of the first measures the FEI took in use was to block all horses that had competed in Valencia since February 1. However, the event had been running for a week prior to this date and the block was first enforced on February 22. By then, several horses that had competed in Valencia had moved on – either to their home stables or to other venues, such as the Sunshine Tour in Vejer de la Frontera. “The reason why horses were blocked was to stop the spread of the disease throughout Europe,” Emmanuelle explains. “When you have a population that is known to have been exposed – horses that are all together on a showground – that is a high risk population. It was the same with Covid-19, when there were people on a cruise ship with positive tests, no one was allowed out – they wanted to prevent contamination to the continent. The situation for the horses in Valencia was a similar case. Risk horses should be kept contained in a single area, because if they get out, and you are not sure if they are positive or not, they can potentially contaminate many others. The damage has been done once healthy and infected horses – or even in-contacts – are on the same showground. What you want to do then is to damage control and not spread it out.”

To best protect the horses, Emmanuelle highlights that it is important to expose them as little as possible. “That is why the shows have been stopped: To avoid horses coming in contact with each other. At home, if you are in a stable where horses recently came back from a show, those horses need to be in quarantine,” Emmanuelle says. “They should be in their own set of stables, with no communication between them and the other horses. No communication means no direct communication – where the horses can touch each other – but no indirect contact either. Horses can get contaminated indirectly through people taking care of them. If you for example go and feed the horses that are in quarantine with the same food trolley and buckets you use for the other horses in the yard, you are going to possibly bring the virus with you. It is very important to keep things separate. You should have a single person dedicated to the quarantine horses and not someone who circulates between areas. Also, testing is important. If you are worried, testing your horse is a good thing to do. You can also monitor the temperature – just make sure to disinfect yourself and the thermometer in between horses!”

While the FEI is working on their Return To Competition-protocols, Emmanuelle is of the opinion that it is difficult to answer when competitions will be able to resume. “If people respect the situation and don’t circulate with their horses, the virus can be contained fairly easily. If people don’t follow the rules and go from one stable to the other without properly disinfecting their hands and shoes, changing clothes, they can be carrying the virus around. The situation is evolving positively, people have acted responsibly and I am confident we are close to putting this nightmare behind us,"  Emmanuelle closes off. 



Emmanuelle Van Erck Westergren is the president of the Belgian Equine Practitioner Society (BEPS).  She graduated from the Ecole Nationale Vétérinaire de Maison Alfort (France) and did a PhD on respiratory functional tests in horses at the University of Liege (Belgium). She is a diplomate of the European College of Equine Internal Medicine (ECEIM). Emmanuelle founded her specialized referral practice, the Equine Sports Medicine Practice based in Belgium and consults internationally.

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