1. Division of Infectious Diseases, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School , Boston, Massachusetts, USA
2. Pathogen Molecular Genetics Section, Laboratory of Bacteriology, National Institute of Allergy and Infectious Diseases , Bethesda, Maryland, USA
3. Department of Veterinary Medicine, Virginia-Maryland Regional College of Veterinary Medicine,University of Maryland , Bethesda, Maryland, USA