1. Animal Biosciences and Biotechnology Laboratory, Beltsville Agricultural Research Center (BARC), Agricultural Research Service (ARS), U.S. Department of Agriculture (USDA), Beltsville, MD 20705
2. Environment Microbial and Food Safety Laboratory, BARC, ARS, USDA, Beltsville, MD 20705
3. Biostatistics Center, Duke Human Vaccine Institute, Durham, NC 27708