Thsi also happened to my chickens. Are they sneezing some? I called my vet and he got me some Tylan and I put it in all of their drinking water. Kept the sick ones away every time I noticed one sleeping too much and standing around with a crusty nose I put them in with the sick ones. Kept on with Tylan every other day in water and they all got well and the others never got sick. Vet said to depopulate but I didnt and have not had another sick one with this and its been 2 months. good luck, I also put TAO in their eyes and they opened up after a couple of days and nostrils became clear within a week. Good Luck.