1. Molecular Virology Group, Department of Medical Microbiology and Genitourinary Medicine, University of Liverpool, Liverpool, United Kingdom1;
2. Department of Human Retrovirology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands2;
3. Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland3; and
4. Paul-Ehrlich-Institut, Langen, Germany4