Grass sickness

[Dumpylump]

My friends lovely cob possibly has grass sickness. They initially thought it might be choke, but vet managed to tube him no problem. He doesn't have all the symptoms though, so it's still not certain, vet coming back this morning.

Poor boy pts this evening.

I am so sorry to hear this.

So very sorry. What a devastating thing to happen. Grass sickness is terrible.

Horrible illness, so sorry.

Yesterday was not a good day at all. We mucked out his stable and then totally disinfected it - and all brushes and stuff - just in case it was something different (goodness knows what though).
Then the vet came back in the evening.
I feel so sorry for my friend, and her daughter - who's v upset but getting ready for a show tomorrow with her pony - but also, selfishly, a bit worried about our own horse who's liveried at the same stable. I know it's not infectious as such, but the stuff I've read does indicate that horses nearby are more likely to get ill too, possibly because of grazing?
No one seems to really know what causes it, which makes it almost impossible to do anything to stop it.