1. School of Veterinary Medicine, Hebrew University, Rehovot 76100,1 and
2. Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario N1G 2W1 Canada2; and
3. Division of Parasitology, Kimron Veterinary Institute, Beit-Dagan 500250,3 Israel;
4. College of Veterinary Medicine, Auburn University, Alabama 368494