1. National Cancer Institute, Division of Cancer Epidemiology and Genetics, Bethesda, MD 20892-7244
2. Beijing Institute for Cancer Research, Beijing, China, 100034
3. U.S. Department of Agriculture, Animal and Plant Health Inspection Service, National Veterinary Services Laboratories, Ames, IA 50010
4. North Dakota State University, Department of Veterinary and Microbiological Sciences, Fargo, ND 58105
5. U.S. Department of Agriculture, Agricultural Research Service, Russell Research Center, Athens, GA 30604-5677