[1] Univ Cambridge, Cambridge Infect Dis Consortium, Dept Vet Med, Cambridge CB3 0ES, England
[2] Zool Soc London, Inst Zool, London NW1 4RY, England
[3] CSIRO Livestock Ind, Australian Anim Hlth Lab, Geelong, Vic 3219, Australia
[4] Queensland Hlth, Coopers Plains, Qld 4108, Australia