1 Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Dyrlægevej 100, DK-1870 Frederiksberg C, Copenhagen, Denmark. Electronic address: eph@sund.ku.dk.
2 Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Dyrlægevej 100, DK-1870 Frederiksberg C, Copenhagen, Denmark.
3 Population Health and Immunity Division, The Walter and Eliza Hall Institute, Parkville, Victoria 3010, Australia; Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Parkville, Victoria 3010, Australia.