1. Virginia-Maryland Regional College of Veterinary Medicine, University of Maryland, College Park, Maryland, USA
2. Division of Basic Science, Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA
3. Division of Surgical Sciences, Duke University, Durham, North Carolina, USA
4. Program of Comparative Medicine, Departments of Pathology, Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, Maryland, USA