I read your other post and my vet said that it can, besides being transmitted by flies, it can be soil borne, so after she lanced it and while it is draining that my horse should be in the stall, so as not to contaminate the pasture. When the abscess is draining is when it is contagious.
After she lanced the abscess, I also hosed and bleached the floor. I also need to change clothes after flushing out the wound before handling the other horses.
The best time to plant a tree was 20 years ago, the second best time is today.