1. a Central Institute for Disease Control (CIDC-Lelystad) , 8203 AA , P.O. Box 2004 , Lelystad
2. b Department of Pathology, Faculty of Veterinary Medicine , University of Utrecht , 3508 TD , P.O. Box 80158 , Utrecht
3. c Department of Poultry Disease, Faculty of Veterinary Medicine , Al-Fateh University , P.O. Box 13662 , Tripoli
4. d Institute for Animal Science and Health (ID-Lelystad) , 8200 AB , P.O. Box 65 , Lelystad