1. Division of Parasitic Diseases, Centers for Disease Control and Prevention, Chamblee, Georgia 30341-3724;
2. Center for Health Studies, Universidad del Valle de Guatemala, and Medical Entomology Research and Training Unit/Guatemala, U.S. Centers for Disease Control and Prevention, Guatemala City, Guatemala;
3. Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, Connecticut 06510;