Possums are a huge carrier of this where I’m from
It's an American disease that's caused by spore contaminated water or food. It attacks the nerve system. It causes weakness and muscle wastage, sweating and slow reflexes if its in the spinal cord. It rarely reaches the brain, but when it does is can cause head tilting and facial paralysis, as well as seizures and behavioural issues. It can kill a horse if left untreated. Majority of horses improve with treatment but most do not completely recover and relapses are common.