1. Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, TX 77555, USA.
2. Institute for Human Infection and Immunity, University of Texas Medical Branch, Galveston, TX 77555, USA.
3. Department of Pathology, University of Texas Medical Branch, Galveston, TX 77555-0609, USA.
4. World Reference Center for Emerging Viruses and Arboviruses, University of Texas Medical Branch, Galveston, TX 77555, USA.