Abstract
The human population history in Southeast Asia was shaped by numerous migrations and population expansions. Their reconstruction based on archaeological, linguistic or human genetic data is often hampered by the limited number of informative polymorphisms in classical human genetic markers, such as the hypervariable regions of the mitochondrial DNA. Here, we analyse housekeeping gene sequences of the human stomach bacterium Helicobacter pylori from various countries in Southeast Asia and we provide evidence that H. pylori accompanied at least three ancient human migrations into this area: i) a migration from India introducing hpEurope bacteria into Thailand, Cambodia and Malaysia; ii) a migration of the ancestors of Austro-Asiatic speaking people into Vietnam and Cambodia carrying hspEAsia bacteria; and iii) a migration of the ancestors of the Thai people from Southern China into Thailand carrying H. pylori of population hpAsia2. Moreover, the H. pylori sequences reflect iv) the migrations of Chinese to Thailand and Malaysia within the last 200 years spreading hspEasia strains, and v) migrations of Indians to Malaysia within the last 200 years distributing both hpAsia2 and hpEurope bacteria. The distribution of the bacterial populations seems to strongly influence the incidence of gastric cancer as countries with predominantly hspEAsia isolates exhibit a high incidence of gastric cancer while the incidence is low in countries with a high proportion of hpAsia2 or hpEurope strains. In the future, the host range expansion of hpEurope strains among Asian populations, combined with human motility, may have a significant impact on gastric cancer incidence in Asia.
Highlights
The fragmented distribution of speakers of the five major language families in Southeast Asia is the result of extensive human migrations
H. pylori from Khmer in Cambodia H. pylori isolates were cultured from gastric biopsies obtained from 66 Khmer volunteers during gastroduodenal endoscopy at the Calmette Hospital (n = 37) and at a private medical center (n = 29) in Phnom Penh, Cambodia, in 2004 and 2007
Bayesian clustering algorithms implemented in STRUCTURE [18] assigned 34 (52%) new bacterial haplotypes to the H. pylori population hpEurope and 32 (48%) new haplotypes to hpEastAsia, subpopulation hspEAsia (Table 1), with no significant difference between 2004 and 2007
Summary
The fragmented distribution of speakers of the five major language families in Southeast Asia is the result of extensive human migrations. The H. pylori sequences reflect iv) the migrations of Chinese to Thailand and Malaysia within the last 200 years spreading hspEasia strains, and v) migrations of Indians to Malaysia within the last 200 years distributing both hpAsia2 and hpEurope bacteria.
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