[1] Albert Einstein Coll Med, Dept Microbiol & Immunol, Bronx, NY 10461 USA
[2] Univ Calif San Francisco, Dept Med, San Francisco, CA 94143 USA
[3] Univ London London Sch Hyg & Trop Med, Dept Infect & Trop Dis, London WC1E 7HT, England
[4] Swiss Trop Inst, Dept Med Parasitol & Infect Biol, CH-4002 Basel, Switzerland
[5] Med Malaria Venture, CH-1215 Geneva 15, Switzerland