[1] ARS, Natl Anim Dis Ctr, USDA, Ames, IA 50010 USA
[2] Washington State Univ, Coll Vet Med, Dept Vet Microbiol & Pathol, Pullman, WA 99164 USA
[3] Univ Minnesota, Dept Vet Populat Med, St Paul, MN 55108 USA
[4] Univ Minnesota, Dept Vet Biomed Sci, St Paul, MN 55108 USA
[5] Michigan State Univ, Dept Anim Sci, E Lansing, MI 48824 USA
[6] BT55&GE Co, Anim Biosci Ctr, TEAGASC, Grange, Meath, Ireland
[7] Inst Anim Hlth, Livestock Dis Programme, Compton RG20 7NN, England
[8] Univ Texas Med Branch, Dept Microbiol & Immunol, Galveston, TX 77555 USA