1. Department of Public Health; Section of Environmental Health; University of Copenhagen; Copenhagen 1014 Denmark
2. Medical Research Council - Centre for Virus Research; Institute of Infection; Inflammation and Immunity; College of Medical, Veterinary and Life Sciences, University of Glasgow; Glasgow G61 1QH United Kingdom
3. School of Life Sciences; Nanosafety Research Group; Heriot Watt University; Edinburgh EH14 4AS United Kingdom