The also observed a similar increase in the brains of mice infected with HSV-1. The researchers say that their finding may eventually translate into a vaccine that may help prevent the brain disorder. They, however, admitted that a breakthrough was a long-time off.
In another experiment, the researchers stained brain slices taken from dead Alzheimer's patients and found DNA from HSV-1 attached to the plaques. Previous studies had shown that HSV-1 is found in the brains of up to 70 per cent of Alzheimer's patients, and 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.
The researchers found that the vast majority of Alzheimer's patients they examined carried the gene - and suspect that it works to make HSV-1 more active. Although scientists have yet to establish a direct link between the virus and the disease, the Manchester team believe that the findings offer hope for the future.
"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," the BBC quoted lead researcher Dr Ruth Itzhaki as saying.
"We need to carry out much more work into this, but the problem is people are quite sceptical of a viral link," the researcher added. 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."
He, however, added: "More research is needed before we can establish how relevant it may be to the treatment of people with Alzheimer's disease."