In effect a "binary illness", requiring two or more agents to work off each tother, triggering a persistant illness state either by their own actions and/or triggering auto-immune perpetuation.
this has been talked about for a long time as a possibility with ME/CFS, but how this actually comes about is perhaps becoming something we can soon grasp .
Alas, we still have too many morons in the medical arena (and others) who see the world in most basic, infantile reductionist simplicty:
ie 1 disease = can only have 1 cause, and one causative agent can have only 1 effect in their view.
which flies in the face of reality (which is full of complex interactions, even symbiosis, and synergies).