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INFECTIOUS disease is taking an unexpected toll by sapping people’s brainpower in the world’s poorest countries. So say Christopher Eppig and colleagues at the University of New Mexico, Albuquerque, who found that a country’s disease burden is strongly linked to the average IQ of its population.

Building and maintaining the brain requires 87 per cent of all the body’s energy in newborns and 44 per cent in 5-year-old children. Fighting infection also takes enormous amounts of energy, so children may struggle to do both at the same time.

Eppig reasoned that an increased risk of catching an infectious disease during …