Department of Infectious Diseases, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Vasco de Quiroga 15, Belisario Domínguez Sección XVI, 14080 Tlalpan, Mexico City, Mexico. Laboratory of Clinical Immunology and Microbiology, National Institute of Allergy and Infectious Diseases, 10 Center Drive, Building 10CRC 3-3264, Bethesda, MD 20892, USA. Electronic address: jennifer.cuellarrodriguez@nih.gov.