From Finland comes more evidence that a common group of viral infections may play a role in the development of at least some cases of type 1 diabetes.
The viruses are known as enteroviruses. These viruses cause a number of infections – from the common cold to conditions as serious as polio, according to the US Centres for Disease Control and Prevention.
The study found that children who had signs indicating they might be developing type 1 diabetes had significantly more enterovirus infections occurring at least a year earlier.
Type 1 diabetes is an autoimmune disease. That means the body's immune system mistakenly destroys healthy insulin-producing cells called islet cells. The cells that attack the body's healthy cells are called autoantibodies, and there are specific autoantibodies for type 1 diabetes, called islet autoantibodies. These autoantibodies appear before the symptoms of type 1 diabetes begin.
In type 1 diabetes, enough islet cells are destroyed that the body no longer produces enough of the hormone insulin for survival. Multiple daily injections or a continuously working insulin pump is necessary to replace that lost insulin.
About five percent of people with diabetes have type 1.
"Our results suggest that enteroviruses may induce an autoimmune process against insulin-producing cells in the pancreas," said study lead author Hanna Honkanen. She's a researcher at the University of Tampere in Finland.
"This autoimmune process seems to start several months after the infection, suggesting that slowly operating mechanisms are involved," she added.
Genetically susceptible individuals
The researchers stressed that this study wasn't designed to find a cause-and-effect relationship.
"However, the accumulating evidence clearly suggests that an association exists between these two diseases," said the study's senior author, Dr Heikki Hyoty. He's a professor of virology at the University of Tampere.
"It is likely that enterovirus infection alone cannot cause diabetes, but it may do so in some genetically susceptible individuals," he said.
The researchers suspect that at least half of type 1 diabetes cases might be linked to enteroviruses.
The study included 129 "case" children who tested positive for multiple islet autoantibodies, and 282 similar children without the autoantibodies to serve as a control group. Researchers tested more than 1,673 stool samples from the case children, and more than 3,100 from the control group.
They found infections in 108 case children and 169 in the control group.
Vaccines might help
The study team also noted that the excess of infections in the case children occurred more than 12 months before the first positive autoantibody was seen.
"It is logical that such a lag period exists since it takes time before the virus could activate immune mechanisms that could lead to the autoimmune process," said Honkanen.
There's no known way to prevent enteroviruses – except for polio and enterovirus 71, for which there are vaccines, the study authors said. But, this study, along with past evidence, suggest that vaccines for other enteroviruses might help reduce the incidence of type 1 diabetes.
"However, the development of such a vaccine for human use is a long process," Hyoty explained.
Jessica Dunne is director of discovery research at JDRF (formerly the Juvenile Diabetes Research Foundation).
She said it's "exciting to see what this study adds to what's long been thought to contribute to type 1 diabetes in at least a subset of people."
But, she agreed with the study authors that enteroviruses are probably not the only environmental factor in the development of type 1 diabetes. "Type 1 diabetes is a clinical diagnosis, and it's likely that people get there from multiple pathways. It may not always be enteroviral infections," she said.
Dunne said a vaccine would need to be given "somewhere between birth and 12 months", because of the lag time seen between infection and the development of autoantibodies.
She and the study authors said that parents shouldn't be overly concerned if their child gets sick with an enterovirus. Most youngsters who get the infections don't go on to get type 1 diabetes.
"Enteroviruses are very common and cause everything from colds to hand-foot-and-mouth disease. There's no way to prevent your kids from getting enteroviruses," Dunne said.
"All children will have several enterovirus infections. Thus, it is clear that additional factors [such as genetic factors] are needed for the development of diabetes," said Honkanen.
The study authors said more research is needed to confirm their findings, and to better understand the complex cause of type 1 diabetes.
The study was published in the journal Diabetologia.