Centre for Geographic Medicine Research Coast, Kenya Medical Research Institute, Wellcome Trust Research Programme, PO Box 230-8010, Kilifi, Kenya. dmagai@kemri-wellcome.org. Department of Clinical Neuro- and Developmental Psychology, Vrije Universiteit, Van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands. dmagai@kemri-wellcome.org. Centre for Geographic Medicine Research Coast, Kenya Medical Research Institute, Wellcome Trust Research Programme, PO Box 230-8010, Kilifi, Kenya. Afya Research Africa, Nairobi, 00202, Kenya. Department of Public Health, Pwani University, P.O. Box 195-80108, Kilifi, Kenya. Institute for Human Development, Aga Khan University, P.O. Box 30270-00100, Nairobi, Kenya. Department of Psychiatry, University of Oxford, Oxford, OX3 7JX, UK. Faculty of Life Sciences and Medicine, King's College London, Strand, London, WC2R2LS, England, UK. Department of Clinical Neuro- and Developmental Psychology, Vrije Universiteit, Van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands.