I was thinking about the Lipkin study looking for pathogens and I was wondering why it's so hard to find pathogens in the first place? Why is it so hard? Is it because viruses actually dont spend much time in the blood but rather inside tissue cells instead? I know some viruses like herpes can hide in cells in a latent state. My understanding is that they embed their dna into the host cell and wait inactive, and while they are waiting the cell is undergoing normal cell division and creates copies of the herpes virus in the process. Then one day something turns the herpes virus on and it takes over the host cell, and replicates like any other virus. For an illness like ME/CFS where no one has found the cause yet, does that suggest a pathogen like herpes which hides away in a latent state like this? Is it hard to look at the dna of a cell and spot DNA that doesn't belong and may be the cause?