1. Department of Clinical Sciences, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden
2. Animal and Human Health Program, International Livestock Research Institute, Nairobi 00100, Kenya
3. Department of Microbiology, National Veterinary Institute, 751 89 Uppsala, Sweden
4. Department of Chemistry, Environment and Feed Hygiene, National Veterinary Institute, 751 89 Uppsala, Sweden
5. Department of Disease Control and Epidemiology, National Veterinary Institute, 751 89 Uppsala, Sweden