I have mostly two year old chickens. Most were hatched her except the first 4 chicks 2 1/2 years ago. And a silkie pullet who was added 8 months ago and quarantined 30 days. None of the originals were vaccinated. One silkie roo got coccidiosis 3 months after adding the one new silkie, probably no connection The same silkie roo, 2 years old, hatched by me, not vaccinated. A month ago he was put down after contracting Marek's ( the nerve one), or Equine Encephalitis (EEE). Question, should I not add any adult chickens even if quarantined? If the roo contracted Marek's, where did he get it from, why now, even 8 months after the pullet was introduced whose status was unknown and he's 2 years old? How does one know if they're adding a carrier of anything that doesn't show up during quarantine? Is it a risk people take?