Institute of Tropical Medicine, Eberhard Karls University Tübingen, Wilhelmstraße 27, D-72074 Tübingen, Germany; Centre de Recherches Médicales de Lambaréné, B.P. 242, Lambaréné, Gabon; German Center for Infection Research, partner site Tübingen, Wilhelmstraße 27, D-72074 Tübingen, Germany. Electronic address: