Here are some articles to read about Mareks if you have time later:
https://extension.psu.edu/mareks-disease-in-chickens
https://www.backyardchickens.com/articles/the-great-big-giant-mareks-disease-faq.66077/
Here is another good link with pictures. Click on the clinical signs for pictures, and then on gross lesions for more:
https://partnersah.vet.cornell.edu/avian-atlas/#/disease/Marek's_Disease
https://extension.psu.edu/mareks-disease-in-chickens
https://www.backyardchickens.com/articles/the-great-big-giant-mareks-disease-faq.66077/
Here is another good link with pictures. Click on the clinical signs for pictures, and then on gross lesions for more:
https://partnersah.vet.cornell.edu/avian-atlas/#/disease/Marek's_Disease