1. Institute of Poultry Diseases, Free Berlin University, Koenigsweg 63-14163 Berlin, Germany
2. Animal Health Research Institute, P.O. Box 246-Dokki, Giza-12618, Egypt
3. O.I.E. and National Reference Laboratories for Avian Influenza and Newcastle Disease, Friedrich-Loeffler Institute, Suedufer 10, Isle of Riems, 17493 Greifswald, Germany