We started with 6 chickens, purchased at a Swap last October. They were all about 14-16 weeks old. Within 1 day, a speckled cochin died of an apparent respiratory illness that included coughing, sneezing, and total body paralysis. All seemed well until a few weeks ago, when 2 of our hens (1 dominique and 1 black cochin) began standing on one leg, and eventually giving up use of one leg entirely. On Monday morning, we moved the black cochin to our garage under a heat lamp, with easy access to food and water, because she wasn't able to stand at all. The dominique wouldn't stand up on Tuesday morning, then we found her dead in the run on Tuesday night. Today, the black cochin is still alive, but unable to use her right leg at all. Her leg does not have any visible wounds, scales, or redness. If I touch her leg, she doesn't indicate any pain, or try to pull it away. She sits in the crate, pecking at food and water, alert, but barely moving. She hasn't laid an egg in over a week. Other than her leg, she appears healthy. The 3 hens (1 dominique, 1 lavender bantam cochin, 1 NH red) that remain in the coop are healthy and laying regularly. From everything I can find online, the signs point to Marek's disease. We don't know if any of the hens were vaccinated. If you have any other ideas, please let me know. My questions are: 1. Do we need to kill our entire flock? 2. What is the best method for disinfecting the coop? 3. Will we need to disinfect the run? 4. How long must we wait to bring new chicks in? This is our first year with chickens. Thank you for your help.