1. Federation of Danish Pig Producers and Slaughterhouses; Axeltorv 3 DK-1609 Copenhagen V Denmark
2. Danish Veterinary Laboratory; Bülowsvej 27 DK-1790 Copenhagen V Denmark
3. Department of Microbiology; Royal Veterinary and Agricultural University; Bülowsvej 13 DK-1870 Frederiksberg C Denmark
4. Ministry of Agriculture; Veterinary Services; Vestjyske Slagterier DK-8961 Allingåbro Denmark
5. Federation of Danish Pig Producers and Slaughterhouses; DK-8620 Kjellerup Denmark
6. Division of Ethology and Health; Royal Veterinary and Agricultural University; Bülowsvej 13 DK-1870