The Equine Expert

Ask the Expert – 4 important questions about the Equine Herpes Virus (EHV) answered!

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Tanja Schnuderl is a member of The Equine Expert LLC. She provides consulting and expert witness services specializing in barn management, horse behavior and appraising. With the ongoing spread of the Equine Herpes Virus, she answered five questions about what you need to know about the spreading Equine Herpes Virus (EHV) and how to protect your horses.

Why is the Equine Herpes Virus making headlines these days?
The Equine Herpes Virus (EHV) is not a new contagious horse disease but has been around for a long time. There are nine different strains of the virus, EHV-1 and EHV-4 are the most common ones and they normally cause mild respiratory diseases. (EHV-4 can in rare cases lead to abortion in unvaccinated, pregnant mares). For both, EHV-1 and EHV-4 are vaccines available and infected horses under treatment recover within a few weeks.
What has caused the current awareness is this: In some cases, EHV-1 causes Equine Herpesvirus Myeloencephalopathy (EHM), a neurological disease. This neurological version is far more dangerous than the above-mentioned respiratory disease. The severity of EHM is life-threatening with a fatality as high as 30%. Horses that test positive for EHV-1 and develop neurological signs are considered positive for EHM. If they respond to treatment and recover, horses may retain neurological deficits. Since the beginning of this year, we are seeing a worrisome increase in these cases. Up until now it is unclear why in some cases EHV-1 causes EHM and at this time there is no licensed vaccine for the neurological form available. Therefore, it is absolutely critical to keep the infection rates and the spread of EHV as low as possible.  

What symptoms or signs should we look out for in our horses?
As barn manager, I monitor the horses in my care closely every day for any signs and symptoms of sickness or injury. Part of my daily routine during AM and PM feed is to check for nasal discharge (snotty noses) and lethargic or depressed horses (e.g., the horse not being as chipper as it normally would be, disinterested in their food, standing in the back of their stall). If I would notice any of these, immediately take the temperature of the horse and check for a fever. For both, EHV-1 and EHV-4 the most common clinical signs are
-Nasal discharge
-Lethargy / Depression

Clinical signs of EHM would include additional neurological symptoms like
-Leaning against a wall/fence to maintain balance
-Not being able to rise (recumbency)

How can we avoid the spread of the virus?
In short: Isolation and Biosecurity.

If your horse develops fever, nasal discharge, neurological symptoms, or potentially has been exposed to an infected horse, isolate the horse immediately (in a paddock/stall without any contact to other horses) and notify your veterinarian.
EHV can be transferred through the air from horse to horse up to distances of 5 meters/16 feet.  An infected horse can transmit the virus to other horses through nose-to-nose contact and coughing. The virus can also be transmitted through shared equipment (tack, feed and water buckets) or through humans via undisinfected hands or clothes of people who have handled the infected horse.
Having a proper biosecurity plan and limited access to infected horses are key to avoid other horses getting infected.

How long should horses be quarantined?
The American Association of Equine Practitioners Foundation (AAEP) and the United States Animal Health Association (USAHA) recommend a 21-day quarantine, if the isolation is voluntary as precaution, e.g., for a new horse arriving at the farm, horses coming back from a busy show weekend being exposed to multiple other horses, etc.
For confirmed EHM cases, the quarantine issuing authority (typically the state animal health officials or horse racing authority) issues the quarantine and subsequently the quarantine release.

As with any health issues concerning your horse, please contact your veterinarian for diagnosis, treatment and advice.

Tanja Schnuderl is a team member with The Equine Expert LLC, a multi-discipline equine expert witness and consulting firm with expert equestrians offering legal expert witness and consulting services in court cases and legal matters. Tanja is an expert on Barn Management and Horse Behavior.  She is the Barn Manager for Moon Rising Farm just outside Washington DC and Principal of Sigma Equine LLC, an equine appraisal business. Tanja grew up in Germany and was a paralegal for many years.  For more information on Tanja Schnuderl email,


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