What percentage of Alzheimer’s cases, characterized by abnormal proteins forming amyloid plaques and tau tangles throughout the brain, are caused by chronic virus infection within the brain?

We can tell you that virtually all of Alzheimer's can be categorized as a viral disorder. Keep in mind, that it is, many times, a catchall diagnosis as it is tricky to make with great accuracy, and for many years now has only been confirmed at autopsy through microscopic examination of brain tissue to document the characteristic alterations. There are people with cognitive impairment falsely diagnosed with Alzheimer's, but really have some other issue. So that is a confounding factor in trying to impose truth on a flawed world having many uncertainties and gaps in knowledge.