1. Virus
and Prion Diseases of Livestock Research Unit, National Animal Disease
Center, USDA, Agricultural Research Service, Ames, Iowa
50010
2. Department of Veterinary
Diagnostic and Production Animal Medicine, College of Veterinary
Medicine, Iowa State University, Ames, Iowa
50011
3. Division of Virology, St.
Jude Children's Research Hospital, Memphis, Tennessee
38105
4. Department of Microbiology,
Mount Sinai School of Medicine, New York, New York
10029