I am writing a novel and am trying to come up with a theoretically sound way for mankind be overrun with sometime of viral, bacterial, fungal, etc. evolution which our bodies would be completely incapable of battling without a Homo Sapiens evolution as well. This condition, attack on our species, needs to specifically attack the brain and be able to cause a variety of conditions such as Alzheimer’s, Cerebral Palsy, Multiple Sclerosis, Parkinson’s, Huntington’s, Pick’s disease, ALS, Dementia, etc. Any creative and knowledgeable input would be greatly appreciated. Thank you.