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Stomach bugs are never pleasant, but for some they could trigger something nastier than diarrhoea and vomiting: diabetes.

People with diabetes can no longer regulate their blood sugar levels effectively via the hormone insulin, which is produced by beta cells in the pancreas. Type 1 diabetes, which usually starts in childhood, is an autoimmune disease in which the immune system attacks the body’s own beta cells. But what sets it off?

For type 1 diabetes, suspicion has long fallen on a group of viruses called Coxsackie B enteroviruses (CBV), partly because outbreaks have sometimes been followed by a surge in diabetes cases. As well as this, newly diagnosed diabetics are more likely to have antibodies to the virus.

Proof that CBV is the culprit has been hard to establish, though, as no one has been able to study a human pancreas as it develops diabetes. That’s because it may take many months or years after the initial CBV infection before a person develops symptoms of diabetes and even then, researchers cannot start taking pancreas biopsies from children just to satisfy their curiosity.

This year, however, British researchers turned up the strongest evidence yet for the theory. Using tissue samples taken from the pancreases of children who had died from type 1 diabetes shortly after diagnosis, they found that more than 60 per cent had a CBV protein in their beta cells. In contrast, the virus was virtually absent in a control group who had died from other causes ().

Some researchers suspect that CBV triggers the autoimmune attack because part of one of its proteins resembles an enzyme found in beta cells, called glutamic acid decarboxylase, so antibodies against the virus may cross-react to GAD. However, Noel Morgan, a pharmacologist at the Peninsula Medical School in Plymouth, who was part of the UK team, thinks it’s more likely that CBV infection alters the beta cells in such a way that the body sees them as foreign.

More surprisingly, the same group showed that CBV might cause type 2 diabetes. This form usually occurs in older people, and is caused by their body becoming less responsive to insulin, often initially because they are overweight; their beta cells respond by pumping out more insulin and eventually wear out. In the same paper the group showed that the pancreases of 40 per cent of people with type 2 diabetes contained the CBV protein, compared with 13 per cent of controls.

The team do not say type 2 diabetes involves autoimmunity. Instead, they speculate that the virus impairs the beta cells’ ability to secrete insulin, which tips a worn-out pancreas over the edge into diabetes.

What does this mean for the future? A vaccine against CBV is a possibility, one which Swiss-based drug company Novartis is investigating. It could be given to children with a genetic susceptibility to type 1 diabetes, such as those with a family history of the disease.

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Read more: Six diseases you never knew you could catch