[1] Univ Calif Davis, Sch Med, Sch Vet Med, Populat Hlth & Reprod, Davis, CA 95616 USA
[2] Cornell Univ, Coll Vet Med, Dept Biomed Sci, Sect Anat Pathol, Ithaca, NY 14853 USA
[3] Univ Calif Davis, Sch Vet Med, Pathol Microbiol & Immunol, Davis, CA 95616 USA
[4] Cornell Univ, Coll Vet Med, Dept Clin Sci, Ithaca, NY 14853 USA
[5] Univ Minnesota, Coll Vet Med, Dept Vet Populat Med, St Paul, MN 55108 USA