Eighteen years ago, scientists began to suspect that the bacterium Helicobacter pylori is a frequent cause of peptic-ulcer disease. The microbe resides in the stomachs of roughly half the world’s people and has been considered an ancient stowaway, already present in our prehistoric ancestors.
A study of H. pylori from 11 countries, however, suggests that the bacterium could be a relatively recent hitchhiker in people. The microbe perhaps jumped from animals only 10,000 years ago, roughly when animal domestication took hold.
Blood samples taken from 526 people with stomach problems on five continents turned up three major strains of H. pylori. Type I predominates in southern Europe, the Americas, and Africa. Type II turns up most often in the Far East. Type III prevails in India. The study appears in the June Journal of Bacteriology.
Of 68 Peruvians and 27 Guatemalans participating in the study, nearly all had the Type I H. pylori strain. A few had Type III and none had Type II, even though many had Native American lineage and likely descend from Far Eastern peoples.
This indicates that conquistadors first brought H. pylori to South America in the 1500s, says study coauthor Douglas E. Berg, a microbiologist at Washington University Medical School in St. Louis.
New data from native peoples in Alaska, also apparently of Asian descent, show little evidence of the Far Eastern strain. Instead, the Alaskans have Type I, which probably came from Russian occupation of Alaska in the 1800s, Berg says.
He acknowledges that the Type I strain of H. pylori could have knocked out an existing strain of the bacterium already in South America. Evidence from his team’s studies of several H. pylori genes suggests otherwise, however. H. pylori strains swap their genes freely, says Berg. Yet the South American Type I H. pylori resembles, remarkably closely, the current European strain.
This indicates that H. pylori found a home in previously uninfected South Americans about 500 years ago, say the researchers. With frequent gene swapping, it’s unlikely that one entire strain outcompeted another and stayed intact, they assert.
Instead, travelers probably distributed the microbe around the globe, says Berg. These traceable movements suggest a recent—in evolutionary terms—H. pylori transfer to people from animals, he says. Dogs, sheep, cats, gerbils, and pigs can all harbor H. pylori.
Tuberculosis, measles, and chicken pox all came from animals, notes Berg.