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“If we want to continue to show safely during springtime, which is known to be a period of high risk for Equine Herpes Virus (EHV), we have to be extra cautious and put in more effort,” Dr. Emmanuelle Van Erck Westergren – a European specialist in equine internal medicine at Equine Sports Medicine Practice in Waterloo, Belgium – tells World of Showjumping. “Every measure that you can take to mitigate the risks will help not only you and your horse, but it will be beneficial for the whole community as well.”

In 2021, a fatal EHV-1 outbreak – which started in Valencia, Spain – resulted in the reported deaths of 18 horses in mainland Europe, confirmed related cases in ten countries, as well as a six-week shutdown of all international events in mainland Europe. In February 2023, EHV-1 cases were reported at FEI events in Belgium and Spain, while in 2024, EHV-1 cases were reported in France. Prior to Helsinki International Horse Show in the Finnish capital this February, several EHV-1 related fatalities were reported, while currently, national shows in Sweden have had issues relating to EHV-1.

World of Showjumping spoke with Dr. Emmanuelle Van Erck Westergren about the importance of biosecurity and how to best avoid another major outbreak.

Outbreaks of the Equine Herpes Virus (EHV) – with its different strains – occur annually, usually in the spring, Emmanuelle explains. “Every year, 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 spring.”

“EHV-1 is a single virus capable of causing very different clinical outcomes — from no symptoms at all, to respiratory disease, to neurological damage — all depending on how the infection develops within the individual horse," Emmanuelle continues to explain. 

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.”

When it comes to biosecurity at FEI events, there are several important rules in the FEI Veterinary Regulations to be followed. In March 2022, the FEI published a report on the 2021 EHV-1 outbreak, which concluded that while it was not possible to pinpoint a single reason or a single responsible person for the deadly outbreak, it was caused by several risk factors being present within a limited space and time, a lack of compliance with the FEI Veterinary Regulations, a lack of preparedness, in combination with poor decision making and lack of cooperation with the FEI Headquarters once the outbreak had been confirmed. 

“In Valencia, all the horses were housed in a big tent where they were mixed together,” Emmanuelle explains about the 2021-outbreak. “It's important that the organizers create areas that are separated in units, so whenever anything happens in one of the units, circulation from one unit to the other can be restricted and the horses that are within one unit stay among each other. The same applies for the people who are around; individuals can also carry diseases around as the virus can stay on clothes and equipment.”

“Usually, the transmission is from nose to nose; there needs to be some closeness between the horses,” she continues. “The problem with sharing a warm-up area is for example that when the horses are out exercising together, they're breathing in and out at a higher intensity of ventilation and that promotes the circulation and inhalation of viruses. The horses will emit small particles of nasal secretions, or they will snort, and because they're breathing more heavily, it goes further in distance."

“Our biggest problem is that you have horses that are healthy carriers, and they can shed the virus, meaning they can excrete it in their nasal secretions and contaminate other horses without being overtly sick,” Emmanuelle points out. “Another horse that would have a weaker immunity or that is younger, would then be more prone to developing a disease.”

While there are several vaccines available to protect against EHV-1, the FEI has not made vaccination mandatory citing distribution challenges in different countries. “The problem with viruses is that they can mutate,” Emmanuelle explains. “It takes a lot of time and money to develop vaccines. If there is a shift in the profile of the viruses, meaning that they start to mutate, then some vaccines can become slightly less efficient. That could be one of the limiting factors of vaccination on the longer term. The other thing is that you have some owners that for varying reasons don't want to vaccinate their horses, but still declare that their horses have been vaccinated. Normally that is something that the FEI has addressed, with the mandatory use of the HorseApp to declare vaccinations, reducing the room for cheating. However, vaccines only bring protection at the level of the group; when at least 75% are vaccinated, is the risk of having an outbreak significantly lower.”

“Your horse should be vaccinated once a year against EHV-1,” Emmanuelle continues. “However, when there was the outbreak in Valencia, a scientific study actually showed that the vaccine did not prevent the horses from developing the neurological form, which is the most severe form, but it certainly protected the number of horses that were affected. When you're vaccinating, in part you are protecting your horse, but you're mainly doing a favour to the group. Your horse could have a bad form of the disease, but the fact that you vaccinated, a critical number of horses protects the herd. It's strongly recommended, but it's not mandatory, neither for EHV-1 or EHV-4, while influenza vaccine is compulsory.”

“I would vaccinate my horses at the exit of winter so that they have some protection during a period where horses are at higher risk,” Emmanuelle shares her point of view. “I know that the French Federation, for instance, required EHV vaccinations for racehorses and for the national jumping competitions after the major outbreaks.”

Supporting the horse’s immune system is the best prevention method for any disease. “An interesting scientific study showed that if horses are exposed to other infections – like fungal infection or bacterial infection – their immune system is disrupted, creating a higher risk of catching EHV-1. This study recommended  that your horse be kept in an environment that does not promote inhalation of bacteria or fungus. Unfortunately, with global warming, you find a lot of fungus in the hay and straw. Beyond focusing on environmental quality and reduction of dust and other contaminants in the horse's direct environment, the hygiene of the forage is a very good way of trying to reduce risks for the horse. The healthier and stronger the immune system is, the better,” Emmanuelle points out.

“We know that wood shavings are naturally less contaminated,” Emmanuelle says when asked what show organizers could do to help with this point. “Wood contains natural antiseptics that make it impossible for bacteria and fungus to grow. That's one thing for the bedding. Additionally, they can provide high quality hay or offer hay steamers so that the hay can be steamed. Disinfecting the boxes before the horses come in and when the horses leave and taking care of good sanitation are the necessary basics. The idea is not to have the horses in a sterile environment, but in a clean area.”

“For horses that are traveling all the time, we do some blood tests regularly just to see where the immunity is at, and some airway samples when necessary so that we're sure that we're maintaining them,” Emmanuelle explains about the management of high-level sport horses that travel a lot, which in turn puts an extra burden on their immune system. “Traveling reduces the cleaning of the airways; the horses produce mucus naturally, and when they travel, the mucus becomes thicker and the expectoration slows down. Just putting on an inhalation mask with saline will make the mucus more fluid. There are products that are not doping that you can give preventatively because they prevent bacteria and fungus from growing inside the horse. You can also support the immune system by making sure that the horses’ diet is appropriate, that they have supplementation if necessary, with vitamin C – which supports the immune system – or vitamin E, that is also good for promoting the health of the airways.”

“It's important to make sure the horse's immune system is competent,” Emmanuelle highlights. “A rational use of medication is important because some medication can affect the immune system and you want to give only something that helps the horse, not something that creates more problems. As an example, when injecting horses with cortisone for orthopaedic issues, you have to take into consideration that cortisone will depress the immune system as well.”

“What is really interesting is that new validated tests that within 30 minutes give you a reading on what the status is for the horse, are currently coming to the market,” Emmanuelle tells about the future. “You take a swab, and a machine can process your sample and test for EHV-1, EHV-4, influenza and strangles. Previous tests were not as sensitive or as specific, but these new systems are much more reliable. That could be a game-changer.”

“The measure of taking the temperature is one thing, but now that we have tests that are more reliable and not that expensive either, I think that it's less expensive to test than to handle an outbreak. That's clearly what the future will be like; to test these horses.”

“Taking the temperature is important as well, because it encourages the grooms and riders to monitor their horses and how they're doing in terms of their health,” Emmanuelle points out. [Editor’s note: As per article 1027.2 in the FEI Veterinary Regulations, “While Horses are present on the Event venue, their rectal temperature must be taken at least twice daily and recorded by the PR using FEI HorseApp. - - “

“Additionally, it is the responsibility of show organisers to provide boxes that have been disinfected, because some of the viruses can remain on site for prolonged periods of time. [Editor’s note: As per article 1008.5 in the FEI Veterinary Regulations, “The FEI Stables Area and all stables must be cleaned and disinfected, in accordance with Annex X and sealed before the arrival of Horses, ensuring they are free of contamination and disease vectors.”] You want to make sure that the horses come in an area that has not been occupied by an infected horse.”

“At some showgrounds, there are areas where a lot of progress could be made in terms of basic hygiene. The horses should be housed in stables that are clean, with non-dusty hay – that would be the basic effort. I don't know if the FEI and national federations need to make more rules; it really comes down to enforcing the rules that already exist, and making sure that if there's something that you see that is not acceptable, you speak up.”

2.4.2026 No reproduction of any of the content in this article will be accepted without a written permission, all rights reserved © World of Showjumping.com. If copyright violations occur, a penalty fee will apply.