The inflammatory bowel disorder Crohn's disease may be caused by a bacterial infection responsible for a similar disease in cattle, sheep and goats, researchers said today.

A team of American scientists investigated the presence of the Mycobacterium avium paratuberculosis (MAP) bacteria in the blood of 28 individuals with Crohn's disease, nine with another form of inflammatory bowel disease (IBD) called ulcerative colitis, and 15 without IBD.

Live bacteria was found in the blood of half the Crohn's patients, and 22% of those with ulcerative colitis. None were obtained from people who did not have inflammatory bowel disease.

Crohn's disease affects 100,000 people in the UK and can cause a variety of symptoms, ranging from a lack of appetite to chronic diarrhoea and abdominal pain.

Dr Saleh Naser, from the University of Central Florida, who led the study published in the Lancet medical journal, said: "Detection of viable MAP in the blood of Crohn's disease patients suggests that MAP infection in this IBD may be systemic. A multi-centre, larger-scale investigation is urgently needed."

He said the two patients with ulcerative colitis who had MAP may represent misdiagnosis.

In an accompanying commentary, Warwick Selby, from the University of Sydney, Australia, said: "Whatever one's view, MAP cannot continue to be ignored in Crohn's disease.

"Funding bodies, laboratory and clinical researchers must clarify with some urgency, once and for all, whether this organism is important in Crohn's disease or is merely a curious bystander. This is not just for the patients but also in the interest of public health."