1. Dstl Porton Down, Salisbury, Wiltshire SP4 0JQ, UK 2Department of Biological Sciences, Imperial College, London SW7 2AZ, UK 3M-SCAN Mass Spectrometry Research and Training Centre, Silwood Park, Ascot SL5 7PZ, UK 4Department of Infectious and Tropical Disease, London School of Hygiene and Tropical Medicine, Keppel St., London WC1E 7HT, UK