usualy occurs around green-up in the spring, when the midges that carry it hatch out, if its going to kill them it will in a couple days, if the deer are in good shape coming out of winter they will survive it, look for split hooves and open sores on the tongue. its not been known to affect humans, its safe to eat, just cook it done or at least to 160 degrees.
It happens about every year to some extent, bad years are very bad, have saw hundreds of carcasses rotting in the woods. we had it very bad about 15 years ago, but in 3 years the population was back where it was prior.
RR