1. A. S. P. Jansen, X. V. Nguyen, V. Karpitskiy, A. D. Loewy, Department of Anatomy and Neurobiology, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110, USA.
2. T. C. Mettenleiter, Federal Research Centre for Virus Diseases of Animals, Friedrich-Loeffler Institutes, Institute of Molecular and Cellular Virology, D-17498 Insel Riems, Germany.