[1] Food & Agr Org United Nations, Anim Prod & Hlth Div, I-00153 Rome, Italy
[2] Colorado State Univ, Anim Populat Hlth Inst, Coll Vet Med & Biomed Sci, Campus Stop 1644, Ft Collins, CO 80523 USA
[3] Royal Vet Coll, Vet Epidemiol Econ & Publ Hlth, Hatfield AL9 7TA, England
[4] Food & Agr Org United Nations, European Commiss Control FMD, I-00153 Rome, Italy
[5] Wageningen Biovet Res, POB 65, NL-8200 AB Lelystad, Netherlands