1. Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, New Bolton Center, Kennett Square, PA 19348
2. Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, New Bolton Center, Kennett Square, PA 19348
3. Department of Toxicology, Diagnostic Laboratory, Cornell University, Ithaca, NY 14850
4. Department of Microbiology and Immunology, Center for Neurovirology, Thomas Jefferson University, Philadelphia, PA 19107