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Saturday, 13 May, 2000, 00:20 GMT 01:20 UK
How ulcer bug travelled the world
Inca city
Did the Incas get infected by the Spanish?
Scientists have uncovered more about the world history of that scourge of middle-aged executives, the stomach ulcer.

It suggests that some of the earliest explorers of the New World may have given natives an unwelcome present - the bug which causes ulcers.

And more evidence suggests that the bacteria may originally have come from livestock to humans.

Helicobacter pylori, the bug concerned, is thought to be a contributory factor in the majority of stomach ulcers.

Before H. pylori was discovered, these were blamed entirely on poor diet, excessive drinking and stress - which is why middle-aged men working in high pressure jobs seemed more than usually prone.

All these factors may make it worse once it happens - but the bacteria plays a key role, popping up in samples taken from the vast majority of gastric ulcers.

It has also been linked with gastric cancer cases, heart disease and even strokes.

World bacteria

The scientists in this study decided to analyse the DNA of H. pylori samples taken from around the world.

Bacteria from Britain, China, Guatemala, India, Japan, Peru, South Africa, Spain, Sweden and the US were all extracted and examined.

The team looked at "vestigial genes" in the bugs - those which appear to have no actual purpose.

They found key differences - and, more importantly, unexpected similarities.

While, as predicted, strains from most different geographical areas showed pronounced differences, African strains were very similar to those from South American - and Spain.

Unsurprisingly, one English strain had a characteristic matched by a strain taken from West Virginia.

But none of the Asian characteristics showed up in the US bugs, despite the native population's arrival from across the Bering Straits thousands of years before.

Professor Douglas Berg, an expert in molecular microbiology and genetics from the Washington University School of Medicine in St Louis, has his theory on who gave what to whom.

'Given to the Incas'

"My favourite interpretation of the finding is that the Spanish brought H. pylori to Peru when they conquered the Incan empire nearly 500 years ago, and that the bacterium was not present in the ancestors who crossed the Bering Strait from Asia more than 10,000 years ago."

H. pylori is thought to be carried by more than half the world's population, although it causes no ill-effects in many.

"People haven't paid any attention to the possibility that human H.pylori infection might have become widespread only in more recent history," said Professor Berg.

The genetic clues uncovered by the research also suggest that an animal host was the first to pass the bug to humans - with each different area having a different animal source.

"For example, the ancestors of European strains of H. pylori might have come from mice or sheep, whereas the ancestors of various Asian strains might have come from cats, pigs, or Mongolian gerbils.

"All of these animals can be infected with certain H. pylori strains recovered from human patients."

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.

Scientists know that hardy H. pylori has been around for a while - a separate project found traces of the bug in samples taken from 1,800-year-old Egyptian mummies.

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20 Jan 99 | Medical notes
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