I'm so sorry about this. (I just got back on line after the stomach flu or I would have responded.) I'm very interested in the vet's necropsy (I do necropsies on my own birds. Took a workshop and am otherwise self-taught.) I'm surprised a city vet knew how to do a necropsy on a chicken. Did he/she send her out to a lab? How did they determine it was Marek's? I don't think that the vent issues were related to the Marek's. I've had chickens that have gotten sick and suddenly died after severe cold/rain/damp. I've learned my lesson and am very careful to keep things dry and provide dust baths in kitty litter tubs (you can see them on my livestreaming cam at www.HenCam.com) Anyway, I'm surprised by the Marek's diagnosis, and would be interested to hear more.