Outbreaks will happen because the virus is like the Flu virus in people - it changes all the time. Here is a good article about EHV-1 -
Article. Read the whole article but I think this part is important enough to quote here so no one misses it -
"EHV-1 is a virus that has been around for a long, long time in the US and Canada in most populations of horses. Horses normally get exposed to EHV-1 viruses early in life, get a bit of a respiratory infection, get over the disease and have no further problems.
Some horses become what is known as persistently infected with the rhinovirus. They become intermittent shedders of EHV-1. They harbor the virus in their respiratory tracts for years. Then during times of immune system stress, they will shed EHV-1 virus through nasal secretions, and then infect others. This is what keeps the EHV-1 virus going year after year, and causing repeated outbreak problems all over the continent."
In today's world there really is no excuse for not knowing where diseases are emerging, where quarantines are in effect, etc. TheHorse.com has awesome email newsletters that go out weekly with the latest information on what is going on all over the US and even the world.
Albahurst - virology has not yet determined if this is a different strain than past neurological outbreaks. The bulk of outbreaks in the past several years have been the same strain that caused the outbreak at Findlay in 2003.