[1] Washington State Univ, Coll Vet Med, Sch Mol Biosci, Pullman, WA 99164 USA
[2] Washington State Univ, Coll Vet Med, Paul G Allen Sch Global Anim Hlth, Pullman, WA 99164 USA
[3] Columbia Univ, Mailman Sch Publ Hlth, Ctr Infect & Immun, New York, NY 10027 USA