1. Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney DiseasesNational Institutes of Health 9000 Rockville Bethesda MD 20892-0815 USA
2. Institute of ChemistrySlovak Academy of Sciences 84238 Bratislava Slovak Republic
3. Institute of Epidemiology, Faculty of MedicineComenius University Špitálska 24 81372 Bratislava Slovak Republic
4. Infectious Diseases DivisionInternational Centre for, Diarrhoeal Disease Research, Bangladesh (icddr,b) Dhaka Bangladesh
5. Division of Infectious DiseasesMassachusetts General Hospital Boston MA 02114 USA
6. Harvard Medical School Boston MA 02115 USA
7. Department of Immunology and Infectious DiseasesHarvard T.H. Chan School of Public Health Boston MA 02115 USA