[1] Univ Liege, Fac Med Vet, Dept Infect & Parasit Dis B43B, B-4000 Liege, Belgium
[2] Univ Cambridge, Addenbrookes Hosp, Dept Med, Cambridge CB2 2QQ, England
[3] INIA, Ctr Invest Sanidad Anim, Madrid, Spain
[4] CSIC, Ctr Nacl Biotecnol, E-28049 Madrid, Spain