Stomach Ulcer Bacteria Migrated with Humans 60,000 Years Ago

In 1985 Australian microbiologist Barry Marshall gobbled a Petri dish full of Helicobacter pylori to prove to the world that the bacteria, rather than stress and spicy foods, were the primary cause of stomach ulcers. Two decades later his recklessness was honoured with the Nobel Prize in Physiology or Medicine, which he shared with his colleague J. Robin Warren. In light of a new study, published in Nature, it is odd that it took so long to finger H. pylori as the source of bouts of abdominal pain, nausea and hemorrhagic vomiting. According to the new work, the pathogen has infected humans for over 60,000 years and its genetic transformation over that time is remarkably similar to that of man—making it a reasonable model for human migration and diversification.

"Like a trail of crumbs, the DNA of our Helicobacter pylori can show where we were born and where our ancestors travelled from over the past 60,000 years," says Marshall, a senior principal research fellow at the University of Western Australia.

According to a 2002 study (published in the New England Journal of Medicine), H. pylori infects 50 percent of the global population. The helical bacterium is the only known microorganism that can survive in the highly acidic mucus lining of the stomach and duodenum, and it is now thought to be the cause of most stomach ulcers and gastritis, an irritation or inflammation of the stomach lining. It is also a risk factor for stomach cancer.

The current study was conducted by an international group of scientists led by University of Cambridge in England and the Max Planck Institute for Biological Infections in Germany. Human populations were broken down by geographic area, moving out of East Africa, believed to be the cradle of human civilization, and into Western Europe, eastern Asia and southern Africa. Researchers were able to estimate that the pathogen emerged from East Africa—not China and southern Africa as previously surmised—between 54,500 and 61,500 years ago. A previous study on human settlement, by Balloux et al. estimated human emergence from the same locale to have occurred 51,500 to 61,500 years ago.

In addition, the research team focused on the microcosm of Europe. They showed that the pathogen was also a viable local model by noting that its pattern of population change on the continent suggested mixing from different geographic sources. This finding is backed by the literature on human migration, which argues that farmers in the Neolithic period moved into Europe from northern Africa and central Asia.

Marshall says molecular epidemiology—"looking at statistical relationships between bacteria from different races"—marks an improvement over studying human migration via ancient human DNA, which degrades if it is more than a few thousand years old. "At present, this is all rather new and the 'clock' has not been calibrated very exactly," he says, "but it is an exciting and fruitful area of new research."

Adapted from materials provided by Scientific American