1. Ifakara Health Institute, Bagamoyo, P.O. Box 74, Pwani, Tanzania.
2. University of Notre Dame, Department of Biological Sciences, South Bend, IN 46556, USA.
3. Epidemiology and Public Health Department, Swiss Institute of Tropical and Public Health, Soccinstrase 57, 4002 Basel, Switzerland.
4. University of Basel, Petersplatz 1, 4003 Basel, Switzerland.