Genetic analysis of the mummified remains of Otzi the Iceman, the Copper Age man who was discovered in a glacier in 1991, has shown that his stomach contained a bacterium found in half of all humans today.
The researchers believe that the findings may shed new light on human migration.
The theory that humans were already infected with this stomach bacterium called Helicobacter pylori -- which is transmitted only through initimate contacts -- at the very beginning of their history could well be true, the study said.
"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 that we would find anything because Otzi's stomach mucosa is no longer there," explained one of the researchers Albert Zink from European Research Academy in Bolzano, Italy.
"We were able to solve the problem once we hit upon the idea of extracting the entire DNA of the stomach contents," Frank Maixner, who is also from European Research Academy in Bolzano, added.
"After this was successfully done, we were able to tease out the individual Helicobacter sequences and reconstruct a 5,300 year old Helicobacter pylori genome," Maixner said.
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The scientists found a potentially virulent strain of bacteria, to which Otzi's immune system had already reacted.
"We had assumed that we would find the same strain of Helicobacter in Otzi as is found in Europeans today," Zink noted.
"It turned out to be a strain that is mainly observed in Central and South Asia today," Zink said.
The study was published in the Science magazine.