er events where he'll encounter horses from other barns needs protection against diseases that spread from horse to horse. Horses who stay home need this protection, too, if other horses could bring infection onto the farm. This can happen right under your nose because horses can be latent carriers of some pathogens (including EHV), harboring them and sometimes shedding them without showing signs.
- Vaccines trigger an immune response to specific pathogens—viruses, bacteria and other disease-causing organisms—without causing disease. If the real deal shows up later, your horse can mount a faster and more powerful defense because his immune system is primed for it.
- When most horses in a given population are vaccinated, disease has less opportunity to spread. All the horses in the group gain a measure of protection from this.
Is vaccination enough to prevent disease in all horses who receive it? For some diseases the answer is no, but that doesn't mean you should skip vaccinations. A vaccinated horse may get sick, but the course of his disease is likely to be less severe. And vaccination can still help control the spread of disease through a population.
EHV is especially challenging. "As far as I know, none of the EHV vaccines prevent the initial infection that can lead to latency," says Dr. Traub-Dargatz. But vaccination makes sense for high-risk groups like show horses and broodmares, she says. It may not prevent initial infection or end transmission risk, but viral shedding may be less within a population of vaccinated horses. "We don't have a vaccine with a label claim for preventing the neurological form of this disease, but we don't know that having a well-vaccinated population does not reduce the risk of this form. So we can't say vaccinate and don't worry, but at a population level we still have reason to recommend vaccination."
Vaccination isn't the only line of defense, she adds: "We believe reactivation and shedding may occur with stress, so we can reduce risk by reducing stress." Hauling horses with compatible trailer partners and stopping to rest before they're exhausted, controlling biting flies and other nuisances, and maintaining consistency in your horse's life are a few ways to do that.
Event organizers can also take steps to minimize disease spread, so before you go, ask about biosecurity—the procedures in place for reducing contagion before or during an outbreak. Are there requirements (such as health certificates) for horses who take part? Is there a plan for monitoring horse health at the event? How were stalls cleaned and sanitized after the last event at the facility? What's the plan for handling and isolating any contagious horses?
"Having a biosecurity plan reduces response time, which is key in limiting disease spread," Dr. Traub-Dargatz says. In California, state animal health officials have now developed a "biosecurity toolkit" for equine events, she adds, to help event organizers think through the details of their plan. It's online at www.cdfa.ca.gov/ahfss/Animal_Health/Equine_Biosecurity.html
When California state veterinarians visited the HITS Thermal facility to assess risks in January, they found no reason to close or place restrictions on the show. HITS organizers decided to take some extra precautions all the same. Daily ship-ins were barred, which kept some local horses off the grounds. Anyone bringing horses to the show had to disclose where the horses came from and where they had been. Trainers and handlers were asked to limit contact between horses, take each horse's temperature twice a day and report fevers of 102 or higher to the vet clinic on the grounds. The organizers also set up isolation stalls where any such horses could be kept for further evaluation.
Other events took special precautions during the California outbreak, too. The U.S. Equestrian Federation authorized alternative saddlery inspection procedures for dressage competitions: Stewards could check bits and other equipment visually, without touching horses, to reduce the risk of spreading infection.
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