We have a flock of 7 Rhode Island reds. We purchased 2 silkies at a local supply store sale. They are young -- not yet laying. We quarantined them for a month and then allowed them to free range with our reds. The silkies have seemed healthy. Yesterday, I found one of them paralyzed. There was no sign of trauma. We quarantined her. She would not eat or drink. She passed away today after only 1 day of sickness. Could this be Mareks? Should we be concerned about the rest of the flock?