1. Departments of Pathology, New York State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA
2. Microbiology, Immunology and Parasitology, New York State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA
3. Florida Game and Freshwater Fish Commission, 4005 South Main Street, Gainesville, Florida 32601, USA