Oetzi the Iceman, the 5,300-year-old mummy discovered in a melting glacier in the Italian Alps 25 years ago, was infected with the pathogen that gives people gastritis and stomach ulcers, new genetic analysis reveals.

An international team of researchers working with paleopathologist Albert Zink and microbiologist Frank Maixner from the European Academy (EURAC) in Bozen/Bolzano, found evidence of Helicobacter pylori in Oetzi's stomach contents.

"We were able to decode the complete genome of a 5,300-year-old Helicobacter pylori," Albert Zink told Discovery News.

Photos: DNA Analysis Reveals Oetzi Had a Stomach Bug

The finding not only suggests the Iceman may have been feeling ill on the day he was murdered, but provides an unexpected glimpse into the history of Europeans.

Found today in about half the world's human population, this Gram-negative bacterium is commonly transmitted person-to-person by saliva, fecal contamination of food or water and poor hygiene. The pathogen has resided with human hosts for so long that it has become a marker of human dispersal around the world.

Genetic analysis of the different strains that have evolved as humans migrated around the world, can now be used to map the history of human geography.

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Oetzi's stomach bacterium is the oldest known pathogen ever sequenced.

The research, detailed in the journal Science, began in 2010 when the stomach of the Iceman was detected through CT scans after 20 years of research.

The scientists completely defrosted the mummy and took samples of the stomach.

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"Evidence for the presence of the bacterium Helicobacter pylori is found in the stomach tissue of patients today, so we thought it was extremely unlikely we would find anything because Oetzi's stomach mucosa is no longer there," Zink said.

The research team, which included scientists from the Universities of Kiel, Vienna and Venda in South Africa as well as the Max Planck Institute for the Science of Human History in Jena, solved the problem by extracting the entire DNA of the stomach contents.

"After this was successfully done, we were able to tease out the individual Helicobacter sequences and reconstruct its complete genome," Frank Maixner said.

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It emerged Oetzi was infected with a single, potentially virulent strain of H. pylori, to which the Iceman's immune system had reacted.

"We found marker proteins which we see today in patients infected with Helicobacter," Zink said. "Whether Oetzi had developed a gastritis cannot be said with any degree of certainty since the stomach mucosa has not survived. But there is a clear possibility he had stomach issues."

It wasn't, however, a life-threatening condition.

The strain of pathogen that the Iceman harbored revealed a surprising ancestry.EURAC/Marion Lafogler

"He was in quite good shape when he died at 40-50 years old, a ripe age for that time. We think he could have lived another 10-20 years if he had not been killed by the arrow in his back," Zink said.

Today, fewer than 10 percent of carriers develop disease that manifest as gastritis or stomach ulcers, mostly in old age.

But there was more. The strain the Iceman harbored revealed a surprising ancestry.

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"We assumed we would find the same strain of Helicobacter in Oetzi as is found in Europeans today. It turned out to be a strain that is mainly observed in Central and South Asia," Thomas Rattei from the University of Vienna, explained.

The European population of H. pylori is known to be a hybrid between Asian and African bacteria, but there have been different hypotheses about when and where the hybridization took place.

Up till now, it had been assumed that Neolithic humans were already carrying the hybrid European strain by the time they stopped their nomadic life and took up agriculture.

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Research on Oetzi, however, demonstrates that this was not the case.

The Iceman's H. pylori is "a nearly pure representative of the bacterial population of Asian origin that existed in Europe before hybridization," the researchers wrote.

"This puts things into wonderful perspective for us with just one genome. We can say the waves of migrations that brought the African strain into Europe had not occurred, or had not occurred in earnest, by the time the Iceman was alive," Yoshan Moodley, at the University of Venda, South Africa, said.

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Further studies will be needed to draw a more precise historic map of human geography.

"One thing we want to do is to extend our investigation to other mummies and get more H. pylori genomes," Zink said.