A bacteria associated with travellers' diarrhoea and children in underdeveloped areas of the world causes more severe disease in people with blood type A but not blood type O or B, finds a study.

Enterotoxigenic E. coli are responsible for millions of cases of diarrhoea and hundreds of thousands of deaths every year, mainly of young children. The bacteria release a protein that latches onto intestinal cells in people with blood type A, but not blood type O or B. A vaccine targeting that protein could potentially protect people with type A blood against the deadliest effects of enterotoxigenic Escherichia coli infection.

"We think this protein is responsible for this blood-group difference in disease severity," said James Fleckenstein, Associate Professor at the Washington University in St. Louis. "A vaccine targeting this protein would potentially protect the individuals at highest risk for severe disease." For the study, published in The Journal of Clinical Investigation, the team gave healthy volunteers a dose of an E. coli strain originally isolated from a person in Bangladesh with severe, cholera-like diarrhoea.

They observed the volunteers for five days and obtained data and blood samples from over 100 people and found that people with blood type A got sick sooner and more seriously than those of other blood types. More than eight of 10 (81 per cent) blood group A people developed diarrhoea that required treatment, as compared with about half of people with blood group B or O.

The researchers also found that the bacteria produce a specific protein that sticks to A-type sugars - but not B or O-type sugars - on intestinal cells. Since the protein also sticks to E. coli, it effectively fastens the bacteria to the intestinal wall, making it easy for them to deliver diarrhoea-causing toxins to intestinal cells. The effect of blood group in people infected with this strain of E. coli was striking and significant, but it doesn't mean people should change their behaviour based on blood type, the researchers said.