Sorry I was missed that the problem had been solved. Being new I am just learning how to navigate through threads. I use Gail's books all the time. But I have an older copy of the health handbook and it didn't have teflon toxicity. After I saw the solution I mentioned it on another thread...
What about Marek's disease. The best book on chicken diseases IMO is The Chicken Health Handbook by Gail Damerow. Marek's is listed under the diseases that can cause sudden death and is listed as common. She says it can hit 30 to 50% of unvaccinated flocks and mortality can be nearly 100...
Possible. Chickens are not far removed from wild fowl and handle cold fine. Wild guess but could the heat actually encourage parasites in the coop, lice, mites?