A preventable tragedy

ONE of the mysteries of epidemiology is why Asia does not suffer from yellow fever. The disease is endemic in Africa, the continent where it evolved. It is widespread in South America, having been carried there by European slave ships. It was once found in both North America and southern Europe, but it was eradicated by the application of considerable effort and money—and both places shared the good fortune of lacking monkeys, which act as reservoirs for the yellow-fever virus. Yet, although much of Asia is plagued by , the mosquito that spreads yellow fever, it remains blessedly free of infections.