1. Department of Clinical Veterinary Science; University of Bristol; Langford House Bristol BS40 5DU
2. Poultry Health Centre; Alfreds Way, Wincanton Business Park Wincanton Somerset BA9 9RU
3. Institute of Parasitology; Department for Infectious Diseases; Hannover School of Veterinary Medicine; Buenteweg 17 D-30559 Hannover Germany