1. Department of Biology, Center for Infectious Disease Dynamics, Huck Institutes of the Life Sciences, Pennsylvania State University , University Park, PA 16802, USA
2. Department of Biochemistry and Molecular Biology, Center for Infectious Disease Dynamics, Huck Institutes of the Life Sciences, Pennsylvania State University , University Park, PA 16802, USA
3. Viral Oncogenesis Group, The Pirbright Institute , Woking GU24 0NF, UK
4. United States Department of Agriculture, Agricultural Research Service, US National Poultry Research Center, Southeast Poultry Research Laboratory , Athens, GA 30605, USA
5. United States Department of Agriculture, Agricultural Research Service, US National Poultry Research Center, Avian Disease and Oncology Laboratory , East Lansing, MI 48823, USA