1. Center for Infectious Disease Research and Vaccinology, Department of Veterinary Science, South Dakota State University, Brookings, South Dakota 57007
2. Department of Diagnostic Medicine and Pathobiology, 1800 Denison Ave., Kansas State University, Manhattan, Kansas 66506
3. Boehringer Ingelheim Vetmedica, Inc., Ames, Iowa 50011
4. Animal Parasitic Diseases Laboratory, ANRI, ARS, USDA, Beltsville, Maryland 20705