Enormous growth over 22 years has brought challenges, both from within and from outside; we examine the tech behemoth’s prospects. Wealth has always exploded wherever humans interacted more—and so have epidemics. We look back on the historical links between economic success and hygiene. And Dubai tries to lure tourists for its sweltering summer season. For full access to print, digital and audio editions of The Economist, subscribe here www.economist.com/intelligenceoffer