1. H. Rüssmann, Y. Fu, J. E. Galán, Department of Molecular Genetics and Microbiology, School of Medicine, State University of New York at Stony Brook, Stony Brook, NY 11794–5222, USA. H. Shams, F. Poblete, R. O. Donis, Department of Veterinary and Biomedical Sciences, University of Nebraska-Lincoln, Lincoln, NE 68583–0905, USA.