1. Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, 1060 William Moore Drive, Raleigh, North Carolina 27607, USA;
2. Department of Biological Sciences, Virginia Tech, 4036 Derring Hall, Blacksburg, Virginia 24061, USA;
3. Department of Pathobiology and Veterinary Science and Center of Excellence for Vaccine Research, University of Connecticut, 61 N Eagleville Road, Storrs, Connecticut 06269, USA;
4. Cornell University, Laboratory of Ornithology, 159 Sapsucker Woods Road, Ithaca, New York 14850, USA;