I was thinking turkey pox.. Although all the pox cases I've seen the bird's head and neck and sometimes feet have "small" wartlike sores that scab over and fall off....I'm not a professional but I would medicate the water with oxytetracycline for all the turkeys...If it is pox there is nothing really you can do anyway...It will run its course and the birds will be fine in 2-3 weeks, that would be the dry pox....Conversely the wet pox can kill some of the birds but again I don't know of anything you can do except treat them for any other infections that may arise....Pox will affect all your turkeys eventually, unless you vacinated them at the first signs of trouble weeks ago....But it sometimes doesn't appear in all the birds at the same time...It can disapear then reappear later in other birds...Does it show any signs of resiratory distress? Did the first bird that died show any signs of respiratory stress before it died?