1. Centre for Virology, Burnet Institute, Melbourne, Victoria, Australia and Department of Infectious Diseases, Aarhus University Hospital, Skejby, Brendstrupgaardvej 100, 8200 Aarhus N, Denmark.
2. Centre for Virology, Burnet Institute, Melbourne, Victoria, Australia
3. Centre for Virology, Burnet Institute, Melbourne, Victoria, Australia and Department of Medicine, Monash University, Melbourne, Victoria, Australia
4. Centre for Virology, Burnet Institute, Melbourne, Victoria, Australia and Department of Medicine, Monash University, Melbourne, Victoria, Australia and Department of Microbiology & Immunology, University of Melbourne, Melbourne, Victoria, Australia