1. Department of infection Biology; University of Liverpool; Leahurst Campus, Neston South Wirral CH64 7TE UK
2. Merial S.A.S., 29 Avenue Tony Garnier Lyon cedex 07 69348 France
3. MSD Animal Health; Walton Manor Milton Keynes MK7 7AJ UK
4. Poultry Health Centre; Dalton Thirsk North Yorkshire YO7 3JA UK