Cholera is still very much a modern disease, infecting millions and causing the deaths of close to 100,000 people around the globe each year. Caused by a bacteria, it now seems that nearly all of the explosive epidemics seen within the last 50 years have originated from one region: Asia.
This astonishing and potentially groundbreaking discovery has been reported in two papers published this week in Science, one of which focused on the cholera epidemics that have struck the Americas, and another that looked at those which have burned through Africa. From sequencing and then comparing the genomes of over a thousand samples of the disease, it seems the road leads all the way back to the Far East.
This is a fascinating finding for a number of reasons. Since the 1800s there have been seven cholera pandemics, with the current pandemic having started in the 1960s. It is caused by a single lineage of the bacterium Vibrio cholerae known as 7PET. This pandemic has led to various epidemics, with particularly large ones occurring in South America and Africa.
The first epidemic from this most recent spread in Africa sprung up in the 1970s, while in South America there were two; one started in Peru in 1991, while another was identified in Haiti in 2010. There has been a long-running, and often vitriolic debate over where these epidemics originated, with some arguing that in certain regions of Africa, the V. cholerae is endemic, surviving in reservoirs in the environment for years before rearing its head and starting a new epidemic.
But this research shows that this theory is unlikely to be completely accurate. While it is true that some strains of cholera are indeed endemic, the studies found that those which cause the massive epidemics that spread quickly and kill thousands are all members of the 7PET lineage, and so all originated in Asia.
“Our results show that multiple new versions of 7PET bacteria have entered Africa since the 1970s,” explained François-Xavier Weill, who led the African research. “Once introduced, cholera outbreaks follow similar paths when spreading across that continent. The results give us a sense of where we can target specific regions of Africa for improved surveillance and control.”
But not only that, it means that when a cholera outbreak occurs, researchers can first test to see if it is 7PET, and if it is, measures can be stepped up to contain the potential new epidemic. It also means that the complete eradication of cholera in places like Africa is absolutely achievable, which is no doubt going to be welcome news to the World Health Organization, which plans on cutting cholera deaths by 90 percent by 2030.