[1] Leibniz Inst Expt Virol, Heinrich Pette Inst, Hamburg, Germany
[2] Univ Oxford, Sir William Dunn Sch Pathol, Oxford OX1 3RE, England
[3] Univ Marburg, Inst Virol, D-3550 Marburg, Germany
[4] Univ Tubingen Hosp, Inst Pathol, Tubingen, Germany
[5] Max Delbruck Ctr Mol Med, Berlin, Germany
[6] Inst Hyg & Environm, Hamburg, Germany
[7] Med Univ Lubeck, Inst Biol, D-23538 Lubeck, Germany