1 Stroke Research Centre, UCL Queen Square Institute of Neurology, London WC1B 5EH, UK; Institute of Infection, Veterinary, and Ecological Sciences, University of Liverpool, Liverpool, UK. Electronic address: l.benjamin@ucl.ac.uk.
2 University of Malawi, College of Medicine, Blantyre, Malawi.
3 Stroke Research Centre, UCL Queen Square Institute of Neurology, London WC1B 5EH, UK.
4 Institute of Infection, Veterinary, and Ecological Sciences, University of Liverpool, Liverpool, UK.