[1] CORNELL UNIV, NEW YORK STATE COLL VET MED, DEPT MICROBIOL, ITHACA, NY 14853 USA
[2] CORNELL UNIV, NEW YORK STATE COLL VET MED, DEPT PREVENT MED, ITHACA, NY 14853 USA
[3] CORNELL UNIV, NEW YORK STATE COLL VET MED, NEW YORK STATE DIAGNOST LAB, ITHACA, NY 14853 USA