Lets say you are feeling a little off. Maybe a cold, maybe a bad diet, maybe lack of exercise, maybe you are just constantly told to behave yourself and feel no room to be yourself. Who is to say? No tests can measure the cause.
So the doctor prescribes some prophylactic antibiotics. You take them like the good patient that you are and you get a bad case of diarrhea. The doctor tests the diarrhea and declares that your problem is...oh lets say...nosema...
Given what I know about bacteria and the delicate balance of life inside of our bodies as well as most other life forms on this planet, I am venturing to guess that nosema is no CAUSE of anything..