1. Division of Comparative Medicine (Box 8061), Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110, ,
2. College of Veterinary Medicine, Magruder Hall 105, Oregon State University, Corvallis, OR 97331‐4802, ,
3. Department of Veterinary Biosciences, College of Veterinary Medicine, University of Illinois, 2001 S. Lincoln Ave., Urbana, IL 61801, USA