1. a Vveterinary Medical Research , Institute of the Hungarian Academy of Sciences , P. 0. Box 18, Budapest, 1581, Hungary
2. b Federal Research Centre for VirusDisease of Animals , Institute of Diagnostic Virology, Friedrich-Loeffler-Institutes , Insel-Riems, 0-17 498, Germany
3. c Institute für Geflügelkrankheiten , Justus-Liebig-Universität , Frankfurter Strasse 91, Giessen, D-35392, Germany