1. Department of Avian and Aquatic Animal Medicine, New York State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA
2. Present address: Experimental Pathology Laboratories, Inc., P.O. Box 474, Herndon, Virginia 22070, USA
3. Department of Natural Resources, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca, New York 14853, USA