1. Department
of Veterinary Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, One Shields Avenue, Davis, California 95616, United States
2. Faculty
of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel St, London WC1E 7HT, U.K.
3. Rollins
School of Public Health, Emory University, Atlanta, Georgia 30322, United States
4. Department
of Civil and Environmental Engineering, University of California, Davis, One Shield Avenue, Davis, California 95616, United States