While watching Karl Morten's presentation at the 2020 CMRC conference he says, at this point This is the paper he refers to. https://www.cell.com/current-biology/fulltext/S0960-9822(17)31663-9 If I understand right Karl wonders if perhaps the toxins released by bacteria might play a role in ME (and other conditions).
Moreover, animals are known to be a host within a symbiosis of several bacteria and maybe even fungi (?), and here as well a common behaviour may be present and could be out of a healthy balance. For the fungus candida albicans a toxin has been identified (candidalysin) which provokes an immune response, but normally the fungus is reluctant to build it (and staying in a non-hyphal form). This is as far as I remember. I find this quite interesting. The failure even might be partly on the side of the host, allowing the symbiotic organisms to behave like so.