IBis the mildest of the respiratory diseases, and has much lower mortality--something like 0-25%. Chicks though will die, and it may affect egg laying or cause kidney damage in all. It's symptoms are lethargy, coughing/sneezing, nasal discharge--not the facial swelling and eye drainage and bubbling of some of the worse ones such as mycoplasma and coryza.. There really is no treatment since it is a virus, unless you get complications like pneumonia.I have done research on the different respritory diseases, and it's the only one that matches. They are gasping, and their faces are swollen around their eyes, and nose, they are also skinny, and small. My birds did have something, but it was just sneezing, and runny nose, and cleared up quickly. I'll be treating anyway, just to protect my own flock.