1. Department of Pathobiological Sciences, University of Wisconsin, School of Veterinary Medicine, 2115 Observatory Drive, Madison, WI 53706, USA.
2. Department of Pathology and Laboratory Medicine, University of Wisconsin, School of Medicine and Public Health, 1685 Highland Avenue, Madison, WI 53705, USA.
3. Department of Zoology, Oregon State University, Corvallis, OR 97331, USA.