Well, my experience with Mareks is that it is spread by the infected dander of the infected bird. The only experience I ever had was once when a man brought some 8 month old Cochin Cockerels over to be butchered. Well, I did not take them into my chicken buildings but did store them in rabbit hutches for two days while butchering them. They all had been vaccinated for mareks when babies. As I felt the dander flying off the birds got into my pens as some of my old birds soon afterwards got the paralysis of the wings, legs and neck. But as each one became infected and signs became evident I killed them. Also it was at time in August when Iowa weather is very hot. That added to the stress of Mareks. I had no need to try and save them as to my thinking there is no cure but death for mareks infected birds. Most birds of this type become paralized and lay on their side and cannot eat or drink without you putting them up to the water or feed. So not much need to infect the rest of the birds. This type of Mareks is a neutral type, loss of body weight, anemia, labored resporation and diarrhea are all common symtoms. Many birds that are pre laying age will come down with it. Mareks is a virus belonging to the Herpes virus group. The virus is concentrated on the feather folicles and shed in dander, being sloughed from skin and feather cells. The virus has a long survival time in dander and can be found in chicken houses that have been isolated for long periods of time. Young birds are the most suseptible as the virus has a short period of incubation time. Mareks also has a visceral type,with lesions seen in the gonads, liver, spleen, kidney,and heart, lungs and muscles. Most birds dying rapidly with massive tumors inside the body. Then there is the Leukosis type Mareks disease, usually called gray eye. Which mortality is not as fast, but the blinding of the eye and gray iris in the eye. Then the emaciation diarrhea and death will follow. The skin leukosis is in the feather folicles and causes skin lesions, this being the most infectious as it is in the dander and feathers. Most all hatcheries today vaccinate day old chicks for mareks and will only sell chicks non vaccinated if you order plenty ahead of time.It is a subcutaneous injection in a sterile environment. 90% effective vaccine.My reference material is from a Texas A&M Vet book on diseases. Also you can catch information at the web site of Mississippi University at http://www.msstate.edu/dept/poultry/disviral.html Also my web site at http://www.gkpet.com has articles one of which is Mareks. If one does get this disease I would suggest burning the bodies as the feather dander would then be destroyed. Also may I suggest that you feed your birds electrolytes and vitamins and good mash with fresh oyster shell and grit either boughten or can obtain river sand, most birds do not succumb to this disease. Feeding greens such as swiss chard, kale, turnip greens, mustard greens, chick weed, lambs quarters, and the like. Now regular head lettuce is a waste of time and energy as it is mostly water and no food value to the birds. Makes such a mess in the bird pen or house. I always raked up the greens if they were old and tossed them out, so as not to have spoiled feed for the birds. The vitamins and minerals from the greens is great for the birds. Also another item that can be fed to the birds is soaked whole oats with buttermilk and yoguart Take a gallon of whole dry oats and in a stainless steel or crock container put the oats and use a 1/2 gallon of buttermilk and a quart of yoguart, any flavor, and soak over night and then stir and feed the birds in a clean trough. When they have eaten them wash the trough and dry for another days usage. This gives the birds a good source of stomach lactobicilus and stablizes the birds to not take on sickness so easily. As you know clean water daily is very important to your birds health. Sanitize the waterers every week with a solution of 1 cup clorox in a 5 gallon bucket of water, let the wateres sit submerged in the water for at least three hours and then scrub with a bottle brush in clean water. As to the mareks situation I would take one of the birds perferably a live sick bird to a diagnostic laboratory and see what they say. If you have a agricultural lab around this is great. Call a Vet and ask where in your area there is one. Also if you start to vaccinate you will have to continue to vaccinate all hatches of birds.