1. Department of Medicine and Epidemiology, School of Veterinary Medicine, One Shields Avenue, University of California Davis , Davis, CA 95616 , USA
2. Department of Public Health Sciences, School of Medicine, Medical Sciences 1C, One Shields Avenue, University of California Davis , Davis, CA 95616 , USA
3. Department of Pathology, Microbiology, and Immunology, School of Veterinary Medicine, One Shields Avenue, University of California Davis , Davis, CA 95616 , USA
4. California Department of Public Health, Vector-Borne Disease Section , 1616 Capitol Avenue, MS 7307, P.O. Box 997377, Sacramento, CA 95899 , USA