Thank you for the question. Tbh, I don't think the theory is that strong. Several studies have attempted to detect HSV-1 genetic material/protein in the brain of AD patients at autopsy, and not all of them were positive. After all, being seropositive (blood test) for HSV-1 doesn't mean the virus invaded the brain.

In this sense, HSV-1 isn't a pre-requisite to developing AD. This is unlike the case for multiple sclerosis, for example, where it's nearly impossible to develop it without a prior EBV (another type of herpesvirus) infection.

Therefore, HSV-1 plays a contributory role at best, perhaps in the majority of cases, and helps explain, at least partly, why AD begins in the hippocampus.