1 Department of Food Hygiene and Environmental Health, Faculty of Veterinary Medicine, University of Helsinki, P.O.Box 66, 00014, Helsinki, Finland. maria.fredriksson-ahomaa@helsinki.fi.
2 Virology Unit, Finnish Food Authority, Helsinki, Finland.
3 Veterinary Bacteriology and Pathology Unit, Finnish Food Authority, Helsinki, Finland.
4 Department of Food Hygiene and Environmental Health, Faculty of Veterinary Medicine, University of Helsinki, P.O.Box 66, 00014, Helsinki, Finland.