From what I've been reading, and I have had some of this happen to me, Marek's is somewhat rare. Key word - SOMEWHAT. Not saying it isn't, but since I lost a few birds from this chicken paraylsis, I have also saved a few in the past few weeks, and the vitamin regimen was the thing that saved mine. Baby vitamins, two droppers full twice a day, for 5 days, then vitamins and electrolytes in the water, not both at the same time.