The only way you will even have an educated guess as to where it came from, is to follow the path of these birds. Where you got them, private or commercial hatchery? Know anyone else who obatianed their birds from these people? See if you can find out and ask how their stock is doing. It could be one of the cases where it did come from the enviroment. There are so many ways it can be introduced to your birds. I would start with looking at the hatchery and seeing if you can find anything online pro or con about them. I am sorry this has happened to you and if you are planning on moving....there are two thoughts to this. You can take your remaining birds, knowing[?] you have Marek's in the flock and practise biosecurity until you wish you'd never heard that word or you can cull. Either way, to be honest, there is no guarantee you will not see this happen with new birds. Something you have to know now, since Marek's has been brought up, you need to act as if you, yourself have Marek's and take precautions to not spread this to anyone elses birds. You can carry the virus on your clothing, shoes, hair, etc., etc.. If you have a bird who has been diagnosed by a local Vet with Marek's I would be contacting the people at the link I will give you. You can have a blood sample drawn and sent off to these people and know for sure if you do in fact have Marek's there. I highly recommend this. http://tvmdl.tamu.edu/tests_service...sease-(PCR)&unit_id=1187&unit_effdt=02-JUN-10 I would also tell you to read this and every other thread or information you can find on this disease.