It's kind of scary when you think you might have something like Mareks in your flock. Many people just sit back and raise their chickens, and treat them however they can. Not all get it, and those that get it may not be that ill. From your reading you will find that there are several types of Mareks. Some will have the neurological symptoms, and others will later develop tumors. Some may become blind. You need to calm down and educate yourself. One thing you could do is find out about having a necropsy done on your sick bird--call the state vet and ask questions about if they can put her down, and if not, how you can ship the body to them or drive it to them. They need to test for Mareks, and that may take several weeks to get a final report back. It may not be Mareks at all, but just avitamin deficiency. Here is the state vet info: http://www.michigan.gov/mdard/0,4610,7-125-48096---,00.html