Most likely. I don't have any solid " proof" But I've had plenty birds die with seemingly no cause ( just depressed, lame, not eating etc ) And only a few ever get better. What I find interesting is that so far, all the birds that I have lost have been EEs, or ameraucanas. No other birds have gotten ill. The last bird to die, dies with a fever, so that wasn't mareks, what it was. I don't know...salt & pepper - do you think you have mareks too?