[1] Ifakara Hlth Inst, Dar Es Salaam, Tanzania
[2] Minist Hlth & Social Welf, Dar Es Salaam, Tanzania
[3] Inst Trop Med, B-2000 Antwerp, Belgium
[4] Royal Trop Inst, NL-1105 AZ Amsterdam, Netherlands
[5] London Sch Hyg & Trop Med, London WC1, England