[1] UCL, Div Infect & Immun, Dept Infect, Cruciform Bldg,90 Gower St, London WC1E 6BT, England
[2] Univ Messina, Dept Vet Sci, Polo Univ Annunziata, I-98168 Messina, Italy
[3] UCL, Canc Inst, Dept Canc Biol, 72 Huntley St, London WC1E 6BT, England
[4] UCL, MRC Lab Mol Cell Biol, Gower St, London WC1E 6BT, England
[5] Univ Cambridge, Dept Vet Med, Transmissible Canc Grp, Madingley Rd, Cambridge CB3 0ES, England