1. *Parasite Biology and Epidemiology Laboratory, Livestock and Poultry Sciences Institute, Agricultural Research Science, U.S. Department of Agriculture, Beltsville, MD 20705–2305, U.S.A.
2. †Metzger Animal Hospital, 1044 Benner Pike, State College, PA 16801, U.S.A.
3. ‡Animal Diagnostic Laboratory, The Pennsylvania State University, University Park, PA 16802–1110, U.S.A.
4. §Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL 36849, U.S.A.
5. |Pathology Division, U.S. Army Medical Research Institute of Infectious Diseases, Ft. Detrick, MD 2170–5011, U.S.A.