1 Department of Basic Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, Mississippi, USA.
2 Viral Diseases Branch, Walter Reed Army Institute of Research, Silver Spring, Maryland, USA.
3 Department of Pathobiology and Population Medicine, College of Veterinary Medicine, Mississippi State University, Mississippi State, Mississippi, USA.
4 Department of Clinical Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, Mississippi, USA.
5 Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, Tennessee, USA.