Equine Herpes Virus (also known as Rhinopneumonitis) is the latest infectious disease agent causing concern to local horse people. The outbreak in Florida this past winter highlighted the danger of the neurological form of this disease. While we are fortunate that there have been no local outbreaks this spring and into the summer, the reality is that the potential for new cases of EHVto occur still exists.

Herpes virus infections are very common in horses, mostly being acquired as youngsters under age 2. In as many as 80% of horses, the virus persists in the body long-term in a latent (inactive) state. When the horse is stressed (as by shipping, foaling, or another illness), its immune system can be weakened, allowing the virus to reactivate and multiply. Latency is also a charac teristic of human Herpes viruses: Herpes zoster infects children, causing Chicken Pox, and then remains dormant in the body until the immune system weakens with age, when the virus reactivates and multiplies in nerve tissue, causing Shingles. When the virus reactivates in the horse, he will shed virus, primarily through nasal secretions, and he may or may not develop clinical signs.

There are many strains of equine Herpes viruses, but the strains called EHV-1 and EHV-4 are of most concern. EHV-4 causes influenza-like respiratory disease and can be a severe problem in horses up to 3 or 4 years of age. EHV-1 causes abortion in pregnant mares and less commonly causes neurological signs and respiratory disease. It is a mutated form of EHV-1 that has been identified in outbreaks of neurological disease that have resulted in the quarantine of many racetrack barns, large show and school barns, and equine clinics over the past several years. While the ability of laboratories to definitively identify this virus is new, the mutated virus appears not to be: retesting of samples saved from out breaks 30 to 40 years ago have been found to have the same mutation. Experts are not sure why more cases seem to be occurring now is the virus becoming more prevalent? Is it just that veterinarians and laboratories have become better at identifying it? Does it have to do with increased mix ing of horse populations and/or increased stress in our modern horses' life styles?

The best way to protect your horse from this disease (and other contagious diseases as well) is to avoid exposure to sick horses or horses that are shed ding virus and, at the same time, try to minimize stress in his life. At the stable, quarantine of new or sick horses for 21 days should be practiced, ideally in a separate barn but if that is not possible in an end stall with (hopefully) empty stalls around it. EHV is shed in nasal secretions and susceptible horses are exposed by contact with clothing, tack, buckets, and barn and trailer and paddock surfaces contaminated by the shedding horse. Transmission through aerosols created by horses coughing or snorting was originally believed to occur but is now not thought to be common. The virus does not live for extended periods in the environment and is destroyed by normal washing and disinfecting of surfaces, so common sense hygiene is protective. On the trail, simply keep your distance from other horses.

Vaccination is an aid in the control of EHV but cannot be relied upon to prevent it in the individual horse. Several types of "Rhino" vaccines are available, and while in theory the modified live vaccine (Rhinomune) may stimulate a broader immune response, no vaccine has been shown to prevent neurological signs. The main benefit of vaccination is to increase herd immunity, thereby decreasing shedding and spreading of virus during out breaks and hopefully reducing the severity of clinical signs. Avaccina tion program for your barn should be discussed with your veterinarian.

Events at which horses gather for competition or showing are obviously potential venues for the spread of EHV. This past winter in response to the Florida outbreak and several local threats of outbreaks, the veterinary community developed recommendations for new rules to try to reduce risk. At present, many of these have not been implemented but if any new outbreaks occur they probably would be. If you take your horse to shows, events, or hunter paces, some of the rules and requirements you could encounter include:

(1) Proof of vaccination, generally not more than 90 days or less than 7 days prior to the competition or show. These time limits are intended to make sure your horse's immunity is at its peak.

(2) Temperature logs (twice a day recording of your horse's body temperature for 2 or more days prior to show/competition). The rationale here is that the earliest sign of EHV infection is a fever spike (often 104 -105 degrees) in a horse who otherwise looks completely normal. That horse can be shedding virus but may never become symptomatic or if he does, symptoms do not appear until the time of a second fever spike about a week later.

(3) Restrictions on where you may ride, walk, or stable your horse when a show or competition is hosted by another farm.

(4) Requests by show/competition organizers that you follow a few common sense rules such as avoiding direct contact between horses and not sharing water buckets, tack, etc. While EHVis certainly a cause for concern, keep in mind that this disease has been around for a long time and, while it can be serious, the absolute risk to any one horse is quite small. It is sensible that we take a few precautions but we should not let panic keep us from enjoying our horses.

Source: 2007 BRLA Newsletter