Respiratory disease can result in poor performance or even an inability for the horse to reach an event.  Transmission of the viruses occurs by direct or indirect contact with the infective discharges of affected animals.  An estimated 75% of horses in the UK are ‘carriers’ of the herpes virus, those that show few symptoms but are capable of shedding virus into their surrounds.  The disease caused by a herpes viral infection will present when triggered by stress factors such as training, transport and horse shows/racing events.  A practical ‘whole herd’ approach to vaccination is often recommended by your veterinary surgeon.