Yes even if I did not have chickens they are a big no no for horses. I have saw a horse who had EPM. Beautiful black Tennessee Walking Horse mare that at 7 years old was unsafe to ride and almost unsafe at that point to even lead. She had to be euthanized before she was 8 1/2. It was tragic really as she was a Jose Jose daughter who is a big name in the walker industry. They were not even able to use her as a broodmare.Possums are an introduced species here, in about 30 years they have become very numerous. Not happy they have been introduced here, not much I can do other than ensure they stay out of the barn, they are bad news for horses and chooks!