The gnawing pain of a stomach ulcer affects about a tenth of Americans at some point in their lives. The culprit, researchers now know, is not stress but a corkscrew-shaped bacterium called Helicobacter pylori. When the bug infects the stomach lining, it provokes a persistent immune response that can lead to ulcers and stomach cancer. One thing that isn’t clear, though, is how the infection is transmitted. Researchers at MIT have recently raised the disturbing possibility that H. pylori may spread through water supplies--at least in one region of Colombia where infection is almost universal.
H. pylori is rife everywhere; one person in two harbors the bug, which probably makes it the world’s most common infection. In 1982, Australian gastroenterologist Barry Marshall was the first to suggest that H. pylori caused stomach disorders. To prove his point, Marshall drank a bug-filled solution and made himself sick to his stomach. At first his claim was considered outlandish--no one thought bacteria could survive in stomach acid--but gradually the medical community has come to accept it. Just last year the National Institutes of Health recommended antibiotics for the treatment of stomach ulcers.
But the question remains of how the infection spreads. H. pylori was long suspected to have an exclusive preference for humans; the assumption was that it was transmitted from person to person, either through oral contact or through contact with infected feces. As techniques for detecting the organism improved, however, researchers began finding it in animals--for instance, in research cats. No studies have been done yet to see whether people may be infected by their pets.
Meanwhile, two epidemiological studies in South America turned up the worrying possibility that the infection might be spread by sewage- contaminated water. Those studies prompted veterinarian David Schauer of MIT and his colleagues to look for H. pylori in the water supply of Nariño, a region in Colombia where 93.5 percent of the population is infected with the bacterium. Nariño also has the world’s highest rate of stomach cancer-- roughly 100 cases per 100,000 people per year, more than 12 times the U.S. rate.
Schauer’s colleagues in Colombia gathered water samples from a variety of sources in Nariño and shipped them to Schauer on ice. Using the polymerase chain reaction technique, Schauer succeeded in isolating a DNA segment from the water that only H. pylori possesses. It is the first demonstration of H. pylori in a water supply, he says. Finding the bug in water, though, doesn’t prove that people in Nariño are becoming infected that way; to be certain, Schauer must still show that the bacteria in the water are alive and that they belong to the same strains that have been found in patients.
He would also like to test a water supply in the United States, which hasn’t been done yet. There are reasons to doubt that the infection is waterborne in this country. Municipal water here, unlike in Nariño, is typically treated for bacteria. Moreover, whereas in Colombia and other developing countries it is common for children to become infected with H. pylori before the age of ten, in the United States people tend to become infected later. That’s not what you’d expect if the bug were transmitted by drinking water.
But in truth no one knows how H. pylori is spread--nor why infection can produce such different outcomes. The vast majority of infected people show no symptoms. Among those who do, the damage takes one of two forms: ulcers or stomach cancer, which is the second most common cancer in the world. One does not lead to the other, says Schauer. They are two different pathways, and you can go one way or the other. We don’t really know why yet.
In the face of all this ignorance, it is still good news that a bacterium, and not the stress of modern life, should be responsible for so many stomach problems. Antibiotics are already proving far more effective against ulcers than traditional ulcer drugs ever were, and at less than a hundredth the cost. And several research groups are developing vaccines that have already worked in mice. Someday soon it may be possible to vaccinate children against both ulcers and stomach cancer--whereas it will never be possible to vaccinate them against stress.
