This Ancient Stomach Bug Was Also a Feature
The bacteria known as H. pylori are depicted by the CDC as a terrifying and fast-spreading germ. A 1998 fact sheet says that infection causes ulcers and stomach cancer, and that it afflicts two-thirds of humans worldwide.
But more recent science shows that H. pylori is disappearing from the human population, and this may not be good news. Our relationship with H. pylori turns out to be long and complex -- quite long, according to scientists who announced this week that they’ve found H. pylori DNA in the stomach of the so-called Ice Man, a 5,300-year-old naturally mummified body that was pulled from an Alpine glacier in 1991. That makes H. pylori the oldest human pathogen to have its DNA sequenced.
The finding, published in Science, adds to growing evidence that this bug is not the agent of a rising epidemic but a longstanding component of the so-called human microbiome -- the zoo of microbes that have found a home in and on our bodies. The health effects of infection are mixed. Carriers are at more risk for some diseases and less risk for others. In evolution, relationships like these are not necessarily just good or just bad. Living things get stuck with each other and adapt with imperfect truces and compromises.
One scientist who was not surprised by the Ice Man’s very posthumous diagnosis was NYU biologist Martin Blaser. For years, he’s argued that the impending extinction of H. pylori is a massive experiment with unpredictable and irreversible consequences.
By analyzing the DNA of the bug in modern people from around the world, scientists have inferred that H. pylori has been with us for more than 100,000 years. As one of the authors of the Ice Man study, Yoshan Moodley, said of H. pylori in a press conference, “The worldwide population structure is a mirror image of the population structure in humans.” That is, there’s a Chinese strain, a European strain and Australian Aboriginal strain -- and all trace back to a common origin in Africa, just as human DNA does.
The notion that H. pylori is disappearing is also inferred from studies of modern people. In places such as the Amazon rainforest, where there’s little modern medicine, everyone has it. Among Americans, prevalence is 70 percent among those born in the early 20th century and 6 percent for those born in the 21st. Blaser attributes the decline to the use of antibiotics for various childhood infections.
The health impact, says Blaser, is a mixed bag. Infection really is a risk factor for ulcers and stomach cancer, but it appears to protect carriers from esophageal reflux, esophageal cancer and asthma. There are hints, he said, that it might protect children against the kind of diarrhea that has historically been a major factor in infant mortality.
None of these problems were likely high on the list of the Ice Man’s worries. A series of examinations showed he was about 45 years old, had bad knees, a bad back, a parasite called whipworm, an arrowhead in his left shoulder and signs of blows to the head. Despite the discovery of H. pylori in his gut, the scientific consensus holds that it was the arrow and the beating that did him in.
Since his stomach lining has decomposed in the 5,300-some-odd years that he’s been dead, the scientists can’t tell if his H. pylori led to ulcers.
What Blaser finds particularly fascinating about H. pylori is that while the human stomach can function without it, it functions differently. Multitudes of types of bacteria live in human intestines, but upstream in the stomach, it’s H. pylori that dominates, if it’s present at all. There, it influences the immune system and the secretion of appetite-controlling hormones ghrelin and leptin. Some scientists have suggested a connection between loss of this bacteria and the obesity epidemic. Blaser says there isn’t any direct evidence for this, but that there might be a more general connection between obesity and the 20th century change in our microbiota brought on by antibiotic use.
It seems surprising that we could inadvertently wipe out a hitchhiker so persistent as to stick with us all those millennia. Wouldn’t people get re-infected after courses of antibiotics were finished? Not necessarily, said Blaser. Many of our microbes come to us at birth, from our mothers, or colonize us soon afterward. C-sections are also a factor that may interrupt transmission. Studies show C-section babies pick up very different microbial communities.
Blaser isn’t suggesting that anyone suffering ulcers should forego the antibiotic treatments that can lead to dramatic cures, any more than someone with acute appendicitis should forgo surgery. Nor will it perhaps be possible to stop H. pylori from going extinct. But nature abhors a vacuum, he said, and the human stomach could become colonized by some other bacteria -- perhaps something less benign.
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