As far as security details go, mine is pretty unflappable. They are seldom fazed by unruly crowds or post-conflict hotspots. But travelling in East Africa one day last year, I stepped into a swarm of mosquitoes. From the expressions on their faces, I realised that close protection was no match for this unarmed threat the size of a speck. Malaria is a relentless killer. In the time it takes to read this article, six more children will die of the disease. Each year, as many as half a billion people catch malaria. More than a million die.