That's a fowl misconception. It has a 100% mortality rate for turkeys. Chickens can survive with a much higher survival rate. Although anything would be higher with a 100% mortality rate. It's the reason why it is not recommended to keep turkeys and chickens together.
I'm in Texas near...
The lethargy, lack of appetite and sudden death are all in line with Blackhead.
Treatment is Acidified Copper Sulfate in their water for 3 days. Follow up immediately with probiotics. This is one of those instances where the treatment can kill already weakened birds. Probiotics are not an...