The herpes simplex type 1 virus (HSV-1), which causes cold sores, may make the body more vulnerable to Alzheimer’s if a specific variant of a particular gene is also present. The gene variant is known as ApoE-4 and has been linked to Alzheimer’s for many years. Some scientists, in fact, believe that ApoE-4 is not only a contributing factor to dementia but may actually be a causative factor.