[1] Washington State Univ, Coll Vet Med, Field Dis Invest Unit, Pullman, WA 99164 USA
[2] Washington State Univ, Coll Sci, Dept Microbiol, Pullman, WA 99164 USA
[3] Washington State Univ, Coll Vet Med, Dept Vet Microbiol & Pathol, Pullman, WA 99164 USA