Behind The Headlines: Could an infection cause diabetes?

Clusters of diabetes cases have suggested an infectious cause for the disease, writes Rachel Liddle.

WHAT IS THE STORY?

Common infections might trigger type-1 diabetes in children and young adults, according to media reports.

The press cited a 25-year study carried out in Yorkshire which looked for clusters of diabetes cases in certain locations at different times.

Among 10- to 19-year-olds in the clusters, more cases of diabetes were reported than expected. This trend was evident in girls with 7-14 per cent more cases than expected in those aged 10-19 years in the clusters.

Such a 'space-time clustering' pattern is typical of conditions triggered by infections, the papers said.

WHAT IS THE RESEARCH?

In the UK, type-1 diabetes is increasing annually by 3-4 per cent. The cause of this rise is unknown, but environmental factors, including infectious agents, have been suspected.

Researchers analysed data from two sets of children and young people diagnosed with type-1 diabetes. One set included 3,019 children aged up to 14 years who were diagnosed with diabetes between 1978 and 2002, and the other 989 patients aged 15-29 years diagnosed between 1991 and 2002.

The addresses of the participants at the time of diagnosis were referenced to the nearest 0.1km and used to look for space-time interactions with type-1 diabetes.

The researchers found that diabetes tended to occur in clusters, with excess numbers of cases appearing within small geographical locations over limited time periods.

Space-time clustering normally happens when a disease has a transient local cause, such as an infectious outbreak. It was found in those aged 10-14 years and 15-19 years. But it was only statistically significant if the clusters contained at least one girl.

WHAT DO THE RESEARCHERS SAY?

Lead researcher Dr Richard McNally, from the child health department at the University of Newcastle, said that these results fit in with the hygiene hypothesis which proposes that low exposure to infection in early childhood could lead to a higher risk of autoimmune disorders, including type-1 diabetes.

An infection late in childhood could then trigger the development of type-1 diabetes, Dr McNally said.

'In certain circumstances where there's a genetic predisposition, infection may act as a trigger, but that doesn't rule out other environmental influences,' he said. He added that the actual risk of developing type-1 diabetes because of infection was still unknown, and any particular pathogens responsible were yet to be identified.

Research to see if the same clustering trends exist in other countries was needed to confirm these findings, he added.

WHAT IS THE EXPERT OPINION?

Dr Angela Wilson, director of research at Diabetes UK, agreed that the hygiene hypothesis could account for recent increases in diabetes incidence.

'The rate of increase of type-1 diabetes is quicker than can be explained by genetics, and it is thought that the environment might be causing it,' she said.

'It could be a relative lack of infections that used to be commonplace in childhood that could be responsible for this increase of 3-4 per cent.'

But she added: 'This study documents a statistical phenomenon, but we are no closer to finding out what's going on.'

While previous research has indicated that exposure to the coxsackie virus might be associated with development of type-1 diabetes in children, Dr Wilson said other viruses might actually provide protection against the condition.

Diabetes UK research due to be published in Research Matters, found that in diabetes-prone mice, infection with a strain of salmonella prevented the condition from developing.

She said: 'It looks like two opposing roles for the viruses, but it may be that different viruses are doing different things.'

However, Professor Edwin Gale, professor of diabetic medicine at the University of Bristol, said he doubted that infection was a cause of diabetes.

He said people had been studying whether or not environmental agents cause diabetes for the past 30 years, but had not produced any strong evidence.

'Type-1 diabetes is a slow-burning condition,' he said. 'These things aren't causing it, they're modulating it.'

In people on the precipice of developing type-1 diabetes, infection may push them over the insulin threshold, just as the stress of a major injury or emotional upset might, he explained.

He added: 'It's more plausible that our general susceptibility to these conditions has increased because we have a decreased number of immune contacts.'

WHAT THE PAPERS SAID
"Infections may cause diabetes in the young" - The Times
"Common infections 'may trigger diabetes'" - Daily Mail
"Infections 'may cause diabetes'" - BBC

INFORMING PATIENTS

- Researchers found that type-1 diabetes cases tended to appear in clusters.

- This was only evident for 10- to 19-year-olds.

- This could indicate that infection is the underlying cause of diabetes.

- It is still uncertain what causes type-1 diabetes.

- The evidence that infection causes diabetes is weak.

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