Institute of Infectious Diseases and Molecular Medicine, University of Cape Town Cape Town 7000, South Africa. darren@science.uct.ac.za|Institute of Infectious Diseases and Molecular Medicine, University of Cape Town Cape Town 7000, South Africa. darren@science.uct.ac.za|Institute of Infectious Diseases and Molecular Medicine, University of Cape Town Cape Town 7000, South Africa. darren@science.uct.ac.za