1. United States Department of Agriculture, Agricultural Research Service, Beltsville Agricultural Research Service, Animal Parasitic Disease Laboratory, Building 1001, BARC-East, Beltsville, Maryland 20705-2350.
2. Department of Health and Human Services, Food and Drug Administration, Center for Food Safety and Nutrition, Office of Applied Research and Safety Assessment, Division of Virulence Assessment, Laurel, Maryland 20708.
3. United States Department of Agriculture, Agricultural Research Service, Beltsville Agricultural Research Center, Electron and Confocal Microscopy Unit, Building 12, Beltsville, Maryland 20705-2350.
4. Departamento de Anatomía Patológica, Hospital Universitario Fundación Jiménez Díaz, Universidad Autónoma de Madrid, Spain.