I have an approximately 20 week old Brahma cross hen who is sneezing, wobbly, and listless. I have her separated from the rest of the birds, and have been giving her duramycin (Duravet 10) in her water for the past 3 days and Poly-Vi-Sol vitamins. She is eating pretty well, poops look normal, but she's not really getting better. I got her 2 months ago from a breeder who said she was vacinated for Mareks, but he only told me that when I asked if he vacinated. I got 10 hens from him all at the same time, the rest seem fine. The weather was cool here, but it's been 70 for the past week. I've posted a photo, as I think her eyes look odd - which is one of the signs of Mareks, but seems that chicken's eyes do look a bit odd when they aren't feeling well. Since there have been so many posts on Marek's recently I am concerned. I am new to chickens, and fortunately have not had any serious illnesses (yet). Any ideas would be welcomed. Thanks.