1. From the Department of Histology and Embryology, and the Department of Physiology and Immunology, Faculty of Medicine, University of Rijeka, 51000 Rijeka, Croatia; and the Max von Pettenkofer-Institut für Hygiene und Medizinische Mikrobiologie, Lehrstuhl Virologie, Ludwig-Maximilians-Universität, München, D-80336 München, Germany