The Iceman's Stomach Bug

Fig.1. Reconstruction of Ötzi
(Credit: Thilo Parg/Wikimedia Commons, License: CC BY-SA 3.0)

In 1991, two hikers stumbled upon a mummy high in the Ötztal Alps, right on the border between Austria and Italy. This mummy - nicknamed Ötzi, or the Iceman - is Europe’s oldest natural human mummy and is arguably one of the most studied cadavers in science. From his eye color (brown) to his dental health (poor), Ötzi reveals an amazing amount about how Europeans looked and lived 5,300 years ago. An international group of scientists released a study last week in the journal Science that added yet another detail to the treasure trove of research on the corpse, which may inform our understanding of ancient human migration into Europe.

The Iceman’s Stomach Ache

Lead author Frank Maixner, a researcher at the Institute for Mummies and the Iceman in Italy, and his colleagues examined the stomach contents of the ice mummy with an in-depth genetic analysis. They looked for the gut bacterium Helicobacter pylori, which is present in more than half of the world’s human population and has been linked to gastric ulcers and chronic gastritis. Beyond giving its host a stomach ache, researchers believe that ancient strains of H. pylori accompanied modern humans out of Africa and have evolved and diversified along with their bipedal hosts ever since. The strong association this pathogen has with humans means that scientists can study the evolution and geography of H. pylori strains to track human migration through time.

Genetic studies of H. pylori suggest at least six ancestral branches make up the microbe’s family tree, including two strains dubbed AE1 and AE2 that mixed to form the modern European strain. AE1 evolved in central Asia and gave rise to a common modern strain in south Asia, whereas AE2 hails from northeast Africa. Maixner and his colleagues cross-referenced the Iceman’s H. pylori with modern strains and found that the ancient stomach bug was much closer genetically to AE1. This suggests that the major migrations to Europe from northeast Africans probably took place after Ötzi died.

Ötzi’s H. pylori strain is consistent with archaeological and genetic evidence that points towards a changing European population around 5,000 years ago. The Iceman died about 300 years before the major waves of migration into the continent, which introduced new strains of H. pylori and formed modern types of the pathogen. 

Fig.2. Electron micrograph of H. pylori with multiple flagella
(Credit: Yutaka Tsutsumi)

Human Movement in One Person

The phylogeographical differentiation, which clearly connects specific strains H. pylori to the geography of human hosts, means that this pathogen serves as an excellent marker for migration. Other pathogens with a long history of association with humans, such as Mycobacterium tuberculosis and the herpes simplex virus type 1 (HSV-1), also offer proxies for human movement through time. Such studies require a thorough understanding of molecular change of pathogens and the ability to compare ancient strains to modern genomes. Indeed, Ötzi’s H. pylori sequence joins a body of research on sequences and genetic information in databases for scientists to use in future studies.

The Iceman, however, seems to have an outsized impact on science for just one specimen. Maixner et al. certainly extrapolated details of an individual to understand a larger population. In the case of modern emerging infectious diseases, researchers sometimes work from a scant amount of information to draw conclusions about an outbreak. But the study of Ötzi has become almost personal in the quest to uncover all of his secrets.

Researchers know that he had brown eyes, was lactose intolerant, and probably lived in a farming community closely related to modern Sardinians. The life of this early European was certainly difficult, as he suffered from whipworm infestation, possible chronic illness, rib fractures, and suspected frostbite. Even with this information, researchers are still curious to learn more about Ötzi, from his stomach pathogens to how he died. Beyond adding another detail to our understanding of migration, Ötzi remains a veritable time capsule for how early Europeans lived and died.


References
Greshko, M. (2016, January 07). Iceman’s gut holds clues to humans’ spread into Europe. National Geographic. Retrieved from: http://news.nationalgeographic.com/2015/12/150107-otzi-iceman-stomach-microbes-science/

Kolb, A. W., Ané, C., & C. R. Brandt. (2013, October 16). Using HSV-1 genome phylogenetics to track past human migrations. PLOS One, vol. 8 (10): e76267. doi: 10.1371/journal.pone.0076267

Maixner, F., et al. (2016, January 08). The 5300-year-old Helicobacter pylori genome of the Iceman. Science, vol. 351 (6269): 162-165. doi: 10.1126/science.aad2545

Yamaoka, Y. (2009, September). Helicobacter pylori typing as a tool for tracking human migration. Clin Microbiol Infect., vol. 15 (9): 829-834. doi: 10.11/j.1469-0691.2009.02967