1. Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA.
2. Prestage Department of Poultry Science, North Carolina State University, Raleigh, North Carolina, USA.
3. Department of Veterinary and Biomedical Sciences, South Dakota State University, Brooking, South Dakota, USA.
4. Bacterial Diseases Branch, Center for Infectious Diseases Research, Walter Reed Army Institute of Research, Silver Spring, Maryland, USA.