EIA is nasty. Horses are affected differently. Some horses decline so fast they are right on death's door and some seem to tolerate it longer before showing outward signs a couple of years later - it will still run them down in the end.
There is no cure - euthanasia is the only option if the owner won't or can't (financially) keep the animal under the strict quarantine guidelines for the rest of its life. DVM's and diagnostic labs (whichever run the test) are required by law to report their findings or risk losing their credentials. There's no hiding it if your horse comes up positive, but you are allowed to ask for a retest from another DVM and use a different lab but I've never seen a positive result turn out to be negative where I am....they've always still been positive on the retest.
Had someone call me once and ask what to do IF a horse came up positive with EIA and I told her what the law says - of course she was being mysterious - I could tell she was indeed talking about a real situation but she pretended it was hypothetical.
She didn't want the 'hypothetical' horse to be euthanized so she was brainstorming to me out loud that no one would ever know if 'said horse' was trailered across the state to a friend's house to live there but she wasn't going to tell the friend the horse tested positive - she planned to tell the vet or in her words 'whoever came knockin' that her husband shot and buried the horse. I don't know what happened in the end - as far as I know, that horse did get trailered to wherever her friend lived.
But it would have eventually succumbed. That was over 10 years ago - that horse is dead now.