SCIENCE FILE : After 100,000 Years, a Bug Is on the Run : Linked to everything from peptic ulcers to cancer, the Helicobacter pylori bacterium has long made the inhospitable human stomach home for its own evolution. But with antibiotics and improved sanitation, its days may be numbered.
From dark ocean trenches to frozen summits to scorching hot springs, the world is full of nasty places to live. But few habitats are more hostile than the human stomach. It oozes acid that can dissolve iron. It is awash in digestive enzymes that can tear meat to bits.
Yet there is a microbe that makes this awful place home, the now-infamous bacterium Helicobacter pylori. And since researchers in Australia discovered it about 20 years ago, they and others have shown that it is a leading cause of peptic ulcers, an ailment previously tied to the stresses of modern life.
Those findings not only challenged the received wisdom about this highly symbolic affliction, they also opened the way to treating--and often curing--the disease with antibiotics.
Still, the bug’s unusual lifestyle raises major scientific questions, not least of which is when H. pylori first set up housekeeping in the belly of humanity.
Though common sense might suggest that the invasion was recent, a team of scientists in Italy and California now say there is genetic evidence that the newly discovered bug has been infecting people for more than 100,000 years--and perhaps even pre-humans long before that.
In a study published in the spring in the journal Science, the researchers compared data on the genetic makeup of four strains of the bacterium from people in Europe, China, Japan and New Zealand. The slight differences found in the DNA of these widely dispersed strains were consistent with patterns of human migrations that began 100,000 years ago.
While the bacterium has apparently evolved in step with the earliest human beings originating in Africa, analysis of DNA from an H. pylori strain in Europe shows that the bug is not exactly the same as one isolated in China. And that difference, according to the researchers, coincides with the notion that early human beings settled in China 20,000 years before they reached Europe.
That view has implications for understanding the microbe’s complex role in the several diseases linked to infection, including ulcers, stomach inflammation and stomach cancer. For one thing, the notion that the bug is at least as old as the earliest human beings raises the once unthinkable possibility that Neanderthals had peptic ulcers. That would dramatically undercut the ailment’s reputation as a hallmark of modern times, one of the so-called “diseases of civilization.”
“I think H. pylori was living with man for a long time and was capable of causing disease, though perhaps early people did not live long enough to show manifestations of disease,” said the study’s lead author, Dr. Antonello Covacci, a medical geneticist at the Siena, Italy, laboratory of the U.S. biotech firm Chiron.
Covacci and other researchers speculate that H. pylori infection was universal in prehistoric times. In fact, they trace the genetically distinct strains of the bacterium to a common ancestor that predated humanity by millions of years. It went on to infect the first human community, spreading from there and evolving over the millenniums as people carried it across continents.
Dr. Martin Blaser, director of infectious diseases at the Vanderbilt University School of Medicine, agrees that H. pylori stomach infection was universal, but argues that it was basically harmless throughout most of human history, much as E. coli bacteria accommodated themselves to the human colon. In that view, he says, the 20th century, with its declining infection rates, is the exception to the great span of human history.
The appearance of peptic ulcers in the Western world in the last century, Blaser says, was not caused by an epidemic of H. pylori infection, as some researchers have argued. Rather, something else, perhaps dietary changes or a delay in acquiring the infection until later in life, must have suddenly made it more pathological.
Researchers believe that H. pylori has been gradually disappearing this century in developed countries with improved sanitation and, recently, widespread use of antibiotics. Access to cleaner water is thought to reduce transmission of the bacterium, which is passed along primarily in childhood by oral contact with infected fecal matter.
On the Way Out
Roughly 30% of Americans are infected today, and that level is projected to drop. Julie Parsonnet, an epidemiologist at Stanford University and a co-author of the Science paper, says she and her co-workers calculate that, with an added push from vaccines now in the works, H. pylori infections will practically vanish from the U.S. in the next century.
“Given today’s trends, the organism looks as though it will disappear,” she said. “We’ve lived with it 100,000 years, and for that to happen in such a short time would be quite remarkable.”
Perhaps the surest signs of H. pylori’s ancient origins, researchers say, are the elaborate tools it evolved to survive the harsh environment of the human stomach. Among other things, it has enzymes that convert urea, a chemical breakdown product found in the stomach, into carbon dioxide and bicarbonate, which help neutralize the stomach’s acid. And its very shape--the helical corkscrew that gives the bug its name--helps it burrow through the thick mucus lining the stomach.
These adaptations would have taken a long time to develop in the course of evolutionary trial and error, Covacci suggested. That’s another reason it is hard to conceive of ulcers and other H. pylori diseases as strictly modern maladies. “You need a pathological organism that is very special,” he said. “And that doesn’t happen in a few days.”
(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)
In the Belly of Humanity
Helicobacter pylori--a bacterium that can survive in the human stomach--is now thought to be at least as old as the earliest human beings, raising the possibility that Neanderthals had peptic ulcers. Scientists in Italy and California say there is indirect genetic evidence that the newly discovered bug has been infecting people for at least 100,000 years.
*
Harsh living conditions
A spiral-shaped bacterium that lives in the stomach and duodenum (the section of intestine just below the stomach), H. pylori has a unique way of adapting in the harsh environment of the stomach.
The inside of the stomach is bathed in about half a gallon of gastric juice every day. Gastric juice is composed of digestive enzymes and concentrated hydrochloric acid, which can readily tear apart the toughest food or microorganism.
The stomach is protected from its own gastric juice by a thick layer of mucus that covers the stomach lining. H. pylori takes advantage of this protection by living in the mucus lining.
*
Tracking migration patterns
Researchers compared data on the genetic makeup of four strains of the bacterium from people in Europe, China, Japan and New Zealand. The slight differences found in the DNA of these widely dispersed strains were consistent with patterns of human migrations that began 100,000 years ago.
*
H. pylori organisms thrive amid cells of the stomach’s mucus lining in a computer simulation, above. A microscopic view of an infection, left. Arrow points to a single bacterium.
