WASHINGTON - Diarrhoea claims nearly two million people annually, the bulk of them being from poor countries in Africa and Asia.

The disease accounts for 18 percent of all deaths among children - and yet is almost always preventable with proper treatment.

Now, new research from MIT indicates that underlying, low-level undiagnosed infection may greatly add to the severity of a significant number of these cases. This realisation could lead to changes in health-care strategies to address the problem.

The findings by David Schauer, MIT professor of biological engineering and comparative medicine, show that these undiagnosed gastro-intestinal infections increase the severity of and delay recovery from acute diarrhoea.

The analysis provides a model that could allow public health officials to evaluate new preventive strategies or therapeutic treatments.

The work grew out of the increasing recognition of the relationship between persistent, chronic infections many people carry and the outcomes of later disease infection.

Schauer and his team said as far as they know this is the first time, for any kind of disease, that an underlying ’subclinical’ infection has been shown to make a later bacterial infection more severe.

And in the case of diarrhoea, this may play a significant role, since about 50 percent of the world population carries a chronic infection with Helicobacter pylori, which causes stomach-lining inflammation but usually no clinical symptoms, and which is closely related to the initial infectious agent used in the mouse experiments.

‘It seemed likely that persistent enteric infection with bacterial agents would also elicit immune responses that could have similar effects. However, this had not been previously studied,’ Schauer said. ‘We wanted to provide proof of principle, and begin to define the mechanism for such an interaction.’

Schauer and his team used lab mice infected first with a strain of bacteria that causes a chronic condition but produces no symptoms, and then with a second infectious agent that causes acute diarrhoea.

They found that even though the underlying chronic infection did not cause disease on its own, it did make the acute infection much worse than in a control group that was only exposed to the second agent, said a MIT release.

The study was published in Infection and Immunity.