It was really bad in Illinois this year. At least where Im at. Basically,..Blue tongue is carried by a gnat that lays it eggs in stag net water. The larva hatch into the infested flys, fly up the deers nose and bite it. The deer becomes feverish and heads to water where some eventually die. Its hemorrhagic disease that cause the deers organs to more or less deteriorate. Those who survive it will be immune to it. Times of drought are when its worst. It has been around since the 70's but not this bad.