1. Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030
2. Centro de Microbiología y Biología Celular, Instituto Venezolano de Investigaciones Científicas, Caracas 1020-A, Venezuela
3. Clinical Microbiology and Public Health Laboratory, Addenbrooke's Hospital, Cambridge CB2 2QW, United Kingdom