I didn't know about tick paralysis until I read that article; makes our ticks here look pretty harmless, and I've always hated them!
Seems odd that two of the last 4 surviving horses went down even after being treated for ticks & after being given the anti-venom or whatever they called it, and odd too that the paralysis didn't quite fit the typical symptoms of tick paralysis.
I do notice that no one lives on the property, and the horses obviously weren't being checked daily since the first deaths were reported by people passing by. Any early symptoms those first horses had would have been missed but perhaps earlier detection & treatment wouldn't have helped anyway.
Just unthinkable to lose such a high percentage of horses.