1. Division of Virology, Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, Tennessee.
2. Emerging Infections Program, U.S. Naval Medical Research Center Detachment, Lima, Peru.
3. Department of Epidemiology, University of Iowa, Iowa City, Iowa.
4. Department of Veterinary and Biomedical Sciences, University of Minnesota, St. Paul, Minnesota.
5. Department of Environmental and Global Health, University of Florida, Gainesville, Florida.