1. Department of Veterinary Pathology, Microbiology, and Immunology, University of Calfornia, Davis, California 95616
2. Department of Zoology, Arizona State University, Tempe, Arizona 85287
3. Biotechnology Center, Utah State University, Logan, Utah 84322
4. Veterinary Genetics Laboratory, University of Calfornia, Davis, Calfornia 95616
5. Environmental, Population, and Organismic Biology, University of Colorado, Boulder, Colorado 80309