When tracing migration patterns, follow bacteria
By Ruth SoRelle, M.P.H.
As prehistoric peoples moved across the globe, populating the various land masses they encountered, they carried their "bugs" or bacteria with them.
Those tell-tale organisms tell the story of humanity and how it moved.
Pacific migrations
Following the line, a scientific consortium led by two scientists from Baylor College of Medicine and the Michael E. DeBakey Veterans Affairs Medical Center in Houston described the two differing prehistoric migrations that populated the areas of the Pacific. The tell-tales were two different strains of a nasty bacteria called Helicobacter pylori. The consortium published their findings in the journal Science.
"It shows that you could follow the migration of the people in the Pacific by looking at the Helicobacter bacteria strains they carried," said David Y. Graham, M.D., professor of medicine – gastroenterology at BCM, who with Yoshio Yamaoka, M.D., Ph.D., an associate professor of medicine – gastroenterology at BCM, pursued the story. "It’s a human infection. It is transmitted person-to-person and usually acquired in childhood, often passed from mother to child. Therefore, you can take almost anyone in the world and look in his or her stomach that’s infected and tell some of that person’s history."
Old bacterium with long history
Helicobacter pylori is an old bacterium now recognized as a major cause of peptic ulcer and gastric cancer worldwide. The study in Science is the latest in a series that began when Yamaoka was working some of the genes of H. pylori. When a report came out that suggested that some South American natives carried "western" strains of H. pylori and suggested that the bacteria was brought to the Western Hemisphere by Columbus, Graham and Yamaoka sought to determine if that was true.
It appears it was not. Using samples from Native Americans in the Amazon jungles of Colombia, they showed that these people carried "Asian" strains of the bacteria. The bacteria had not come from Europe but from Asia, indicating that the people had come from there as well.
Migration theory
This study seeks to determine how this finding fits into the notion of how people migrated across the globe. In this study, they used samples from an aboriginal population in Taiwan obtained with the aid of a postdoctoral student. Through a collaborator at the University of Western Australia, they had access to samples from the aboriginal population there.
Two specific strains of Helicobacter pylori called hpSahul and hspMaori also represented two different migrations, they found.
Tens of thousands of years apart
The strain hpSahul split from the Asian populations of the bacteria 31,000 to 37,000 years ago. The hpSahul found in New Guinea and Australia have changed sufficiently to show that the organisms have been isolated for 23,000 to 32,000 years, which goes along with the notion that people migrated to New Guinea and Australia more than 30,000 years ago.
The strain hspMaori was dispersed into Melanesia and Polynesia about 5,000 years ago.
Two migratory waves
The researchers wrote, "Our results lend support for two distinct waves of migration into the Pacific. First, early migration to New Guinea and Australia accompanied by hpSahul and second, a much later dispersal of hspMaori from Taiwan through the Pacific by the Malayo-Polynesian-speaking Lapita culture."
In the future, Graham expects researchers to look at why different populations have different diseases associated with H. pylori. One population may be more likely to develop peptic ulcer and another gastric cancer. While environment is believed to play a role, the different strains of bacteria might also have an effect.
Virulence factors
"Now we can clone the whole bacteria," he said. "We might find that specific virulence factors might predispose to a certain outcome."
He said he would hope that countries with high rates of gastric or stomach cancer might look at the possibility of treating people with H. pylori infection to reduce cancer rates. However, he pointed out, that in countries with poor sanitation, people might be treated only to be reinfected. Vaccines and better sewage treatment would provide important answers as well.
Others who took part in the study include Yoshan Moodley, Bodo Linz, Steffie Bernhöft and Mark Achtman of the Max-Planck-Institut für Infektionsbiologie in Berlin, Helen M. Windsor and Barry J. Marshall of the University of Western Australia in Perth, Sebastien Breurec of the Institut Pasteur in Dakar, Sénégal and New Caledonia, Jeng-Yih Wu of Kaohsiung Medical University in Taiwan, Ayas Maady of the Republic Hospital No. 1 in Kyzyl City, Republic of Tuva, Russia, Jean-Michel Thiberge of the Institut Pasteur in Paris, France, Suparat Phuanukoonnon and Peter Siba of Institute of Medical Research, Papua, New Guinea, and Gangolf Jobb of Fritz-Kortner-Bogen in Munich, Germany. Achtman is also with the University College Cork in Cork Ireland.
Funding for this study came from the ERA-NET PathoGenoMics (project HELDIVNET), the Science Foundation of Ireland, the National Institutes of Health (NIH) and the Institut Pasteur and the Institut de Veille Sanitaire.
