As a researcher, you discover a new disease afflicting human populations. Your research shows that, 1) the disease is caused by a toxin released somewhere in the intestine, 2) that drugs obstructing cell division as well as drugs obstructing gene expression in general seem to prevent the progression of the illness, but fail to bring patients back to normal health, 3) that the intestine and surrounding region do not contain any foreign or 'non-native' flora, and 4) antibiotics initially help restore health, but symptoms resume soon after patients finish taking them. Based on all these findings, what is the most likely explanation about the ultimate cause of the disease?
-The disease is caused by a prion
-The disease is bacterial
-The disease is caused by a viroid
-The disease is viral
-None of the above