Heather Davies1, P-J M Noble1, Gina Pinchbeck1, David R Killick1, Gillian Diesel2. 1. University of Liverpool, Institute of Infection, Ecology and Veterinary Science, Leahurst Campus, Chester High Road, Neston, Cheshire CH64 7TE. 2. VMD, Woodham Lane, New Haw, Addlestone, Surrey KT15 3LS.