Asia is the cradle of almost every cholera epidemic, genome studies show

Source: Science Magazine

In perhaps the most famous example of shoe-leather epidemiology, U.K. physician John Snow mapped cholera cases in London in 1854 to pinpoint a water pump on Broad Street as the likely source of a deadly outbreak. Removing the pump handle helped stop its spread. Now, scientists have done similar detective work on a global scale, using 21st-century techniques. By sequencing and comparing hundreds of bacterial genomes, they have shown that all of the explosive epidemics of cholera in Africa and the Americas in the past half-century arose after the arrival of new strains that had evolved in Asia.

The work, published in two Science papers this week, could put to rest an old debate about the role of environmental factors in cholera's global burden. It could also have a big impact on the battle against the disease, because it allows public health officials to concentrate their efforts on the imported strains that are likely to be the most dangerous. And it suggests there is no local reservoir for major outbreaks in Africa or the Americas, which means "elimination of cholera in these places is completely achievable," says Dominique Legros, a cholera expert at the World Health Organization (WHO) in Geneva, Switzerland. "This is music to my ears."

Cholera is caused by the bacterium Vibrio cholerae, which spreads through water contaminated with feces. Over the centuries, dangerous strains of the bacterium appear to have spread from Asia to the rest of the world in several waves. The latest, called the seventh pandemic, began in 1961 and is ongoing, causing an estimated 3 million cases each year.