"The rate of detection of MAP in individuals with Crohn's disease is highly significant and implicates this pathogen in disease causation," they said in the Journal of Clinical Microbiology.

"The problems caused by the MAP bug are a public health tragedy," said Hermon-Taylor, who has sent a copy of the paper to Britain's Chief Medical Officer Liam Donaldson.

Crohn's disease causes inflammation of the intestine and symptoms include diarrhea, pain, weight loss and tiredness. About 100,000 people in Britain alone are affected, with about 5,000 new cases reported every year.

The study was backed by the medical charity Action Research, which said previous findings showed MAP is present in two percent of retail pasteurized milk cartons.

"The discovery that the MAP bug is present in the vast majority of Crohn's sufferers means it is almost certainly causing the intestinal inflammation," it said in a statement.

"Action Research does not recommend that anyone stops drinking milk. However, for those individuals with Crohn's disease or their close relatives who may feel particularly at risk, it may be sensible to start drinking UHT milk.

"As UHT involves higher pasteurization temperatures, it is probable that MAP is destroyed," it said.

It called for Crohn's to be made a reportable disease, for more stringent milk pasteurization, for tests for MAP in dairy herds, and procedures for reducing MAP infection on farms.

Hermon-Taylor said an unexpected finding of the research showed that patients suffering from irritable bowel syndrome may also be infected with MAP.

"In animals, MAP inflames the nerves of the gut," he said. "Recent work from Sweden shows that people with IBS also have inflamed gut nerves. There is a real chance that the MAP bug may be inflaming people's gut nerves and causing IBS."

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