The cold sore virus has been linked to Alzheimer's disease

In lab tests, Manchester University found brains infected with the herpes simplex virus, HSV-1, saw a rise in a protein linked to Alzheimer's.

Scientists believe the discovery could pave the way for a vaccine that may help prevent the brain disorder, New Scientist magazine reported.

But such a breakthrough was a long-time off, experts said.

We need to carry out much more work into this, but the problem is people are quite sceptical of a viral link

Dr Ruth Itzhaki, of Manchester University

The researchers infected cultures of human brain cells with the virus and found a "dramatic" increase in levels of the beta amyloid protein - the building blocks of deposits, or plaques, which form in the brains of people with Alzheimer's.

A similar increase was seen in the brains of mice infected with HSV-1.

In a separate experiment, the team stained brain slices taken from dead Alzheimer's patients and found DNA from HSV-1 attached to the plaques.

Gene interaction

Previous research has established that HSV-1 is found in the brains of up to 70% of people with Alzheimer's.

And a team from the University of Rochester Medical Center in New York found that it was more likely to cause a problem in people who carry a mutant version of a specific gene called ApoE4, which is involved in the breakdown of fats by the body.

They found the vast majority of Alzheimer's patients they examined carried the gene - and suspect that it works to make HSV-1 more active.

Scientists have still to establish a direct link between the virus and the disease, but the Manchester team believe the findings offer hope for the future.

Lead researcher Dr Ruth Itzhaki said: "Alzheimer's is a multi-factorial disease, there are many different causes.

"But our work implies that for some a mixture of the gene variant and the virus could be contributing to it.

"In the future - although it is a long way off - people could even be immunised against the virus which could help protect people against Alzheimer's."

"We need to carry out much more work into this, but the problem is people are quite sceptical of a viral link."

Professor Clive Ballard, director of research at the Alzheimer's Society, said: "A link between the virus and Alzheimer's disease was first suggested ten years ago."

But he added: "More research is needed before we can establish how relevant it may be to the treatment of people with Alzheimer's disease."