Viruses, bacteria and other pathogens are implicated in a number of human diseases including Alzheimer's disease, epilepsy, muliple sclerosis and Parkinson's disease, ADHD, autism, bipolar disorder, depression and schizophrenia, arthritis, irritable bowel syndrome, obesity, cancers and many others.Their involvement is listed on this page with outclicks to Pubmed:
http://www.polygenicpathways.co.uk/microbiome.htm