1. Animal Parasitic Diseases Laboratory, Animal and Natural Resources Institute, Agricultural Research Service, United States Department of Agriculture, Beltsville, Maryland 20705
2. Institute of Epidemiology, Friedrich-Loeffler-Institut—Federal Research Institute for Animal Health, Seestrasse 55, D-16868 Wusterhausen, Germany
3. SALUVET, Animal Health Department, Faculty of Veterinary Sciences, Complutense University of Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain