During their research, scientists spotted the DNA of the herpes simplex virus type 1 (HSV1) in protein plaques in the brains of Alzheimer's victims.
Professor Ruth Itzhaki, who led the research, said: "We suggest that HSV1 enters the brain in the elderly as their immune systems decline."
The virus could be in a dormant state, and could be triggered by stress and infections causing brain cells to die and disintegrate, according to Prof Itzhaki.
Drugs employed to treat cold sores, may also help in the treatment of Alzheimer's, scientists said. Alzheimer's disease is known to affect about 20 million people globally.
Detailed research is required to understand this link and its implications in the treatment of Alzheimer's disease.
The findings are published in the Journal of Pathology.