1. School of Natural Sciences, Linnaeus University, SE-391 82 Kalmar, Sweden
2. National Veterinary Institute, Technical University of Denmark, Lindholm, DK-4771, Kalvehave, Denmark
3. Department of Virology, Slovak Medical University, Limbova 12, 83303 Bratislava, Slovak Republic
4. Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, 500 University Drive, Hershey, Pennsylvania 17033