After three horses in Nevada tested positive for EHV-1 this week, the State Veterinarian recommended that horse events be postponed to help slow the spread of the contagious disease. The announcement has lead to a lot of fear within the horse community. It seems like everyone is talking about EHV-1, speculating about where it came from and where it might strike next. Unfortunately, there is also a lot of misinformation spreading. As with all communicable equine diseases, it’s important to know the facts so that you can keep your horses safe.  

What is it?

Equine Herpesvirus (EHV) is a family of viruses that is found in horses all over the world. There are several types of EHV. The recent cases in Nevada are type 1 – a respiratory infection which can progress to respiratory disease causing neurological problems or abortion in pregnant mares.  

EHV-1 is surprisingly common. Many domestic horses have been exposed to the virus but will never develop symptoms and the virus remains inactive. However, symptomatic EHV-1 is not a regular occurance in Nevada. According to the Nevada Department of Agriculture, these are the first reported cases of EHV-1 in the state in at least three years.  

Shared water sources can spread communicable diseases such as EHV-1.

How is it spread?

EHV-1 is typically spread through coughing, sneezing, or nasal secretions. Direct horse to horse contact, as well as contact with contaminated feed, equipment, clothing, or tack can also spread the disease. Once a horse is infected, the virus can become latent for the rest of the horse’s life. What that means is that during times of stress or transport, the virus can emerge and the horse can silently shed and put other horses at risk for infection.  

What are the risk factors?

  • Horses under 5 years old
  • Performance Horses
  • Older horses
  • Horses who are stabled
  • Transportation
  • Horses with a compromised immune system
  • Mules & donkeys can be silent shedders, so can pose an increased risk of transmission to horses.

What are the symptoms?

After exposure, incubation may be as short as 24 hours but is typically 4-6 days or longer. Check your horse’s temperature twice daily, in the morning and at night. Also check before administering any medications as some can lower body temperature. Contact your veterinarian if you detect any of the following symptoms:

  • Fever of 102 or higher. The fever may go undetected and may be the only clinical sign noted in an infected horse.
  • Discharge from the eyes or nose
  • Respiratory symptoms
  • Swelling of the limbs
  • Spontaneous abortions
  • Enlarged lymph nodes under the jaw or throat
  • Lethargy
  • Neurological signs such as unsteady gait, weakness, urine dripping, lack of tail tone, and recumbency
It’s important to listen to recommendations from the State Veterinarian regarding quarantines to slow the spread of communicable diseases.

How can you prevent infection?

There are vaccines available, but they control the disease – they do not prevent it. Many horses produce post-vaccine antibodies against EHV, but the presence of those antibodies is not indicative of protective immunity. Repeated vaccination appears to reduce both the frequency and severity of the disease and limits occurence of abortion.

The time between exposure and illness can vary from two to 14 days. If you self quarantine and practice good biosecurity on your property and during travel, you can do a lot to prevent further spread of the virus. Here are some tips on prevention:

  • Clean and disinfect your horse trailer if you haul horses other than your own.
  • Disinfect stalls or stable areas before moving your horse into them at show grounds or a new facility. A quarternary-ammonium or phenolic-based disinfectant is best. Many horse show travelers put it in a spray bottle and spray liberally before moving in.
  • Quarantine new horses for 30 days before introducing them to your herd.
  • Monitor temperatures prior to traveling and never ship a horse who has had a fever within 5 days of a haul.
  • Bring your own water and water buckets to events.
  • Avoid common areas.
  • Change your boots if you are going into another horses pen.
  • If your barn is exposed do not take your horse off the property until a veterinarian says it is okay.
  • People cannot be infected, but they can transport the disease. Wash your hands, clothing and equipment, and avoid using the same equipment on different horses.

The virus can be viable for several weeks in the environment once it has been shed. Shedding typically lasts from 7-10 days but can be much longer, therefore a period of 28 days after clinical signs have abated is recommended before restrictions on quarantine should be lifted.

After an outbreak of EHV-1 in 2011 many equestrian events were postponed or canceled, including the annual Pony Express Re-ride from Missouri to California. Each piece of mail that year was stamped to explain the delay in delivery.

Why doesn’t the NDA identify facilities?

EHV-1 is a reportable animal disease. That means when a veterinarian determines a positive case of a communicable disease, they must report it to the Nevada Department of Agriculture. The state uses this information to track infection rates and take action if needed. For example, the State Veterinarian might make recommendations or impose quarantines – as he has done in response to the recent EHV-1 cases. You might hear rumors of other cases, but the NDA is the best source of accurate information.

When the NDA announces infections or quarantines they do not identify the exact facilities involved, which can be frustrating for worried horse owners. Nevada Revised Statute 570, which pertains to diseased animals, has a confidentiality clause built into it. It says that information regarding infection of reportable diseases must be kept confidential unless there is a public health emergency risk.

The Bottom Line

Practice good biosecurity and you will greatly minimize the risk of exposure to EHV or any other communicable disease. Check for updates regularly on recent outbreaks, but make sure you get your information from a reputable source such as one that works with the Nevada Department of Agriculture. As with all things, be wary of what you read on social media and confirm information before passing it on. This will reduce the chance of rumors or panic in horse communities.