Equine Herpes Scare

Local Case Causes Cancellaton & Concern

Lauren Davis Baker

Barb Crabbe, DVM of Pacific Crest Sporthorse was relaxing on a beach on the shore of Lake Tahoe when her cell phone began to ring. An outbreak of Equine-Herpes virus in the Northwest—owners were alarmed.

“After about 15 calls, I phoned home and had my own horses vaccinated,” Barb said. An initial report of a single horse showing signs of the neurological variety of Equine Herpes escalated into a rumor of several horses dead, fueling fears. Oregon Dressage Society made the decision to cancel their annual Breeders’ Show and several area barns went into quarantine.

Days later, Oregon State Veterinarian Don Hansen confirmed that the original case was not confirmed with the neuropathic (aka: scary) form of Equine Herpes Virus 1. Although EHV-1 was identified, it was the more common, prevalent form of the virus (as opposed to the more virulent form seen in outbreaks across the country). One Oregon horse and five Washington horses who had been directly exposed exhibited clinical signs consistent with the respiratory variety of EHV-1. Quarantines outside the affected barns were lifted and show managers breathed a sigh of relief.

Did people over-react? Not necessarily. “One thing that is confusing,” Dr. Crabbe elaborates, “is that both the ‘common’ form of EHV-1 and the ‘scary’ form can lead to neurologic symptoms. However, the neuropathic form is believed to be five to six times more likely to go in that direction.” Since a number of the cases in this recent outbreak exhibited neurologic symptoms, it’s easy to understand the public reaction—and confusion. “It’s also very difficult to differentiate between the two diagnostically.”

What can we learn from this experience? “Hunker down and don’t panic,” Dr. Crabbe recommends. “Question your sources of information.” While talking to your own vet can be useful, it’s also worth looking at university websites for reliable information.” (See sidebar for more tips & useful information.)

There are several important things horse owners should know about EHV and the horse management practices we can adopt to reduce risk. There are four forms of the Equine Herpes Virus, also called EHV or rhinopneumonitis (rhino). These forms can cause mild respiratory disease, abortion in pregnant mares, venereal disease, and neurological disease. EHV-1 is a subtype of the virus which can cause the neurological disease in addition to the respiratory disease or abortion response.

EHV-1 is not a new disease. In fact, it’s so prevalent worldwide that almost all horses have been exposed prior to two years of age and many are likely to be carriers.

The respiratory form of the disease is most common in horses under one year of age. Horses typically exhibit symptoms within one to 10 days of exposure and may be contagious for up to 28-days after infection.

The less common, but more dangerous, neurological form of the disease has a similar incubation time. Both diseases begin with fever but the neurologic form leads to ataxia (loss of coordination), and can cause tail weakness and loss of bladder function. Temperature monitoring twice a day can be useful as a diagnostic tool.

There’s a lot of controversy and confusion regarding vaccinating for EHV. Dr. Crabbe emphasizes that “There are vaccinations available to protect your horse from the respiratory disease and abortion from this virus. While there is not a vaccine available to protect against the deadly neurological form of EHV-1, vaccinating with Rhinommune several weeks prior to anticipated (or possible) exposure is a rational decision.”

Why? “This vaccine should boost your horse’s antibody levels and reduce nasal shedding (which can infect other horses) if he is exposed. In addition, it will stimulate cell-mediated immunity—which can help protect your horse.”

“Another option is to vaccinate with Pneumabort K, Prodigy, or Calvenza. These vaccines are demonstrated to produce the highest number of antibodies against the EHV-1 virus following administration. This may reduce nasal shedding if your horse contracts the disease, protecting other horses by reducing the spread of the virus.”

Be aware that vaccines can have negative side effect and you should allow your horse a few days off after vaccination. To be effective, horses need to be vaccinated every three months. Dr. Crabbe vaccinates her own horses prior to travel, preferably no less than 10 days in advance of the trip.

You should not vaccinate your horse if he has been exposed to the virus, as vaccination can possibly increase the severity of the illness. If you suspect your horse has been exposed, monitor for fevers for two to three weeks before vaccinating.

If you’re still afraid of Equine Herpes, keep this in mind: “Your horse is more likely to die from colic than EHV-1,” Dr. Crabbe advises. “The neurologic variety of EHV-1 is still a relatively rare disease in the U.S. horse population.” So, while there’s no cause for panic, it is important to minimize risk to your own horse and others. Read on for some simple, effective practices you can adopt into your own horse-keeping program.

Dr. Barbara Crabbe owns and operates Pacific Crest Sporthorse in Oregon City, Oregon. She specializes in veterinary care for the performance horse. She is an active dressage competitor and has written numerous articles for Dressage Today, Horse and Rider, and other national publications. Her new book “The Comprehensive Guide to Equine Veterinary Medicine” will be available this Fall, from Sterling Publishing.