1. Latvian Institute of Organic Synthesis, Aizkraukles 21, Riga LV-1006, Latvia
2. Biomedical Research and Study Centre, Ratsupites 1, Riga LV-1067, Latvia
3. Division
of Parasitology, MRC National Institute for Medical Research, The Ridgeway, Mill, Hill, London NW7 1AA, U.K.