Tom E Fletcher1, Timothy J G Brooks2, Nicholas J Beeching3. 1. Liverpool School of Tropical Medicine, Liverpool L3 5QA, UK. 2. Rare and Imported Pathogens Laboratory, Public Health England, Porton Down, Salisbury, UK. 3. Liverpool School of Tropical Medicine, Liverpool L3 5QA, UK nicholas.beeching@rlbuht.nhs.uk.