1. Center for Wildlife Ecology, Illinois Natural History Survey, 607 E. Peabody Dr., Champaign Illinois 61820, USA
2. Department of Veterinary Pathobiology, College of Veterinary Medicine, University of Illinois, 2001 S. Lincoln Ave, Urbana, Illinois 61801, USA
3. Present Address: Central Research Division, Pfizer, Inc., Eastern Point Rd., Bldg. 274, Groton, Connecticut 06340, USA