Pedro F C Vasconcelos1, Alan D T Barrett2. 1. Department of Arbovirology and Hemorrhagic Fevers, Evandro Chagas Institute, Ministry of Health, Ananindeua, Brazil; Department of Pathology, Pará State University, Belém, Brazil. Electronic address: pedrovasconcelos@iec.gov.br. 2. Department of Pathology and Sealy Institute for Vaccine Sciences at University of Texas Medical Branch, Galveston, TX, USA.