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Tuesday, 5 November, 2002, 02:40 GMT
Cancer bug carried for millennia
Stomach ulcer
Stomach ulcers have been blamed on H. pylori
A bacterium blamed for causing stomach ulcers and gastric cancer has been carried by humans for at least 11,000 years, scientists have calculated.

Researchers only discovered that the bug, Helicobacter pylori, lives in the human stomach 20 years ago.

But a new study analysing the distribution of certain genes in the bacterium shows that humans have actually been harbouring the bug for thousands of years.

Previous studies suggested that H. pylori was first introduced to the Americas by European travellers several hundred years ago.

But the genetic analysis by researchers at the New York University School of Medicine suggests that the bug was actually introduced to the New World thousands of years earlier by migrants from East Asia.

Tell-tale genes

The researchers focused on variations of three genes.

These variations are frequently found in people from East Asia, but never in Europeans.

Genetic tests were carried out on samples of H. pylori taken from the Amerindian people who live in the isolated Amazonian communities of Venezuela.

It was found that the bacteria had the tell-tale genetic stamp of East Asia.

This strongly suggests that the bug was introduced to the Amerindian community by migrants from the East - who travelled to the New World at least 11,000 years ago.

Thus, the researchers were able to conclude that H. pylori must have existed in humans since at least that time.

Researcher Dr Martin Blaser said it was possible that H. pylori had been present in humans for thousands of years because it has beneficial, as well as potentially harmful, effects.

These include protection from diarrhoeal diseases, and from acid reflux in the food pipe.

Common problem

H. pylori is a spiral-shaped bacterium that lives in the mucous layer lining the stomach where it can exist for decades.

It is estimated that more that half the world's population carries the bug, although it causes no ill-effects in many.

It is thought to cause ulcers by burrowing into and weakening the stomach lining.

Its link to cancer - and even to heart disease - is not clear, but is thought to be a result of the toxin that the bug injects into the cells in the stomach lining, starting a chain reaction which helps it feed.

Patients with ulcers who test positive for H. pylori may be given a combination of powerful drugs to eradicate the bacteria as part of their treatment.

The research is published in the journal Proceedings of the National Academy of Sciences.

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