The infection connection: Helicobacter pylori is more than just the cause of gastric ulcers—it offers an unprecedented opportunity to study changes in human microecology and the nature of chronic disease

When Barry Marshall drank a broth of Helicobacter pylori in the mid-1980s, he hoped to prove that the bacteria cause gastric ulcers, a common complaint worldwide. Sure enough, Marshall, then at the Royal Perth Hospital in Western Australia, soon developed gastritis, the precursor to stomach ulcers and gastric cancer. In addition to earning him the 2005 Nobel Prize in Physiology or Medicine with his colleague Robin Warren, this unorthodox—and now infamous—experiment proved that a bacteria caused a chronic disease that had previously been attributed to genetic and lifestyle factors. During the same period, researchers have proposed bacterial and viral triggers for many other chronic diseases, such as cancers and coronary heart disease. But Marshall and Warren's discovery has far wider implications than curing a single disease. "Human microecology is changing, and these changes have manifestations in terms of disease," said Martin Blaser, Chair of the Department of Medicine at New York University (NY, USA). To understand the impact of these changes, researchers need to take a closer look at host–pathogen interactions—both good and bad.

"What's interesting about Helicobacter is that everybody is focusing on its pathogenic role and not enough on its role as an indigenous organism," Blaser said. He thinks that the microbes that live inside humans are not there accidentally—over the course of human history, they have adapted to humans and have made trade-offs to become obligate parasites. As a result, their evolution is inextricably linked to human evolution, as well as to human disease. "Our microbes are a part of human physiology… as much a part… as our liver, or our kidneys, or our heart," Blaser commented. "They are a metabolic compartment or a series of metabolic compartments in the human body and how they behave and… their characteristics are relevant to health and disease."

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