Last year, a group of researchers at the University of New Mexico proposed that the control of infectious diseases is crucial to a country’s development in a way that had not been appreciated before. Places that harbour a lot of parasites and pathogens not only suffer the debilitating effects of disease on their workforces, but also have their human capital eroded, child by child, from birth. They noted that the brains of newly born children require 87% of those children’s metabolic energy. In five-year-olds the figure is still 44% and even in adults the brain—a mere 2% of the body’s weight—consumes about a quarter of the body’s energy. Any competition for this energy is likely to damage the brain’s development, and parasites and pathogens compete for it in several ways. Some feed on the host’s tissue directly, or hijack its molecular machinery to reproduce. Some, particularly those that live in the gut, stop their host absorbing food. And all provoke the host’s immune system into activity, which diverts resources from other things…[] There is, moreover, direct evidence that infections and parasites affect cognition. Intestinal worms have been shown to do so on many occasions. Malaria, too, is bad for the brain. A study of children in Kenya who survived the cerebral version of the disease suggests that an eighth of them suffer long-term cognitive damage. In the view of Mr Eppig and his colleagues, however, it is the various bugs that cause diarrhoea which are the biggest threat. Diarrhoea strikes children hard. It accounts for a sixth of infant deaths, and even in those it does not kill it prevents the absorption of food at a time when the brain is growing and developing rapidly.
