Dear Rose, Lori may be correct, but you may be, too. First, PA can be an autoimmune disease, therefore its cause is not always known. Also, I know at least my form of the disease includes the inability to store B12 in the liver, so my symptoms can reappear quickly and may have developed quickly. And, most interesting when speculating about the rat, researchers believe that some cases of PA may come from a bacterium - Helicobacter pylori. I don't know if rats can carry it, but one study found it in dolphins and commented "To our knowledge this represents the first isolation and characterization of a novel Helicobacter sp. from a marine mammal and emphasizes the wide host distribution and pathogenic potential of this increasingly important genus."