We've had the same problem with our chickens and turkeys this year. Duramycin in the water. BUt we still have lost many birds. We also find that one of the earliest symptoms is that their eyes crust shut. it helps a lot to gently peel the eyes open so the fluid can drain. Many of our chickens immune systems kicked in and they got better. We figure the weak ones didn't make it. Everyone got Duramycin, and we are hoping to powerwash the brooder, barn, and all our coops before winter to maybe prevent it from coming again. It hasn't killed all birds with symptoms, but if both eyes get crusted shut, they will starve to death, or dehydrate to death. So we watch for that.