[1] Univ Guelph, Ontario Vet Coll, Ctr Publ Hlth & Zoonoses, Guelph, ON N1G 2W1, Canada
[2] Univ Guelph, Ontario Vet Coll, Dept Populat Med, Guelph, ON N1G 2W1, Canada
[3] Iowa State Univ, Vet Med Res Inst, Ames, IA 50011 USA
[4] Univ Calif Davis, Sch Vet Med, Dept Med & Epidemiol, Davis, CA 95616 USA
[5] Iowa State Univ, Dept Anim Sci, Meat Lab 215F, Ames, IA 50011 USA
[6] ARS, USDA, Beltsville, MD 20870 USA
[7] Univ Prince Edward Isl, Atlantic Vet Coll, Dept Hlth Management, Charlottetown, PE C1A 4P3, Canada
[8] Amer Vet Med Assoc, Schaumburg, IL 60173 USA
[9] Colorado State Univ, Coll Vet Med & Biomed Sci, Dept Clin Sci, Ft Collins, CO 80523 USA