1. Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK
2. National Public Health Service for Wales Aberystwyth, Bronglais Hospital, Aberystwyth, Ceredigion SY23 1ER, UK
3. Institute of Rural Sciences, University of Wales, Aberystwyth, Ceredigion SY23 3AL, UK
4. Department of Molecular Parasitology, Bernhard Nocht Institute for Tropical Medicine, D-20359 Hamburg, Germany
5. Medical College, University of Hué, Hué, Vietnam