Are there any ways to prevent Alzheimer's disease?

No no, viruses don't think. In fact, officially, they aren't regarded as living at all. They are regarded as mere particles that are just injected into the body and, by chance, they bind to the surface of the target cells and are taken inside the cell.

The surface of every cell has proteins jutting out of it called 'receptor' proteins. The viruses are genetically-engineered to target these proteins and to bind with them. That's how they recognise their target cell.

Kevin