1. UMR BIPAR/AFSSA/INRA/ENVA/UVPM, 94703 Maisons-Alfort, France
2. AFSSA/LERPAZ Unité d'épidémiologie, 94703 Maisons-Alfort, France
3. Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA 95616, USA
4. Institut fur Medizinische Mikrobiologie, Virologie und Hygiene, Universitat Rostock, Rostock, Germany