> Evidence is scarce and the article is talking about brains with active illnesses. They compared them to control brains, which also had microbes. > It could

> Evidence is scarce and the article is talking about brains with active illnesses. They compared them to control brains, which also had microbes. > It could be that there isn't any microbiome normally but if the safety mechanisms fail and bacteria colonize the brain, that would cause the illnesses described. That would describe a scenario where the blood-brain barrier isn't 100% effective, no? If it's not 100% effective (which we know to be true), it is also seems unlikely that 100% of the things that cross the blood-brain barrier cause something that we currently consider a disease. Heck, in healthy individuals, latent taxoplasmosis' effects are often so minimial I don't think we'd call it a disease (otherwise 30%+ of the world has the disease).