1. Viral Epidemiology Section, AIDS Vaccine Program, SAIC Frederick, NCI-Frederick, MD 21701, USA
2. National Centre for Tropical Medicine, University of Guayaquil, Guayaquil, Ecuador
3. Department of Medicine, Division of Infectious Diseases, Michigan State University, East Lansing, MI, USA
4. Laboratory for Stem Cell Research, Department of Health Science and Technology, Aalborg University, Denmark
5. Viral Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD, USA