1. Department of Molecular Microbiology and Immunology. Johns Hopkins University, Baltimore, MD (BAE, GEG); Division of Viral and Rickettsial Diseases, Centers for Disease Control and Prevention, U.S. Department of Health and Human Services, Atlanta, GA (JNM, JEC); Communicable Disease Unit, Womack Army Medical Center, Fort Bragg, NC (KTM); Instituto Nacional de Enfermedades Virales Humanas, Pergamino, Argentina (MCM, DAE)