In Samuel Elliot Morison's excellent book "Christopher Columbus; Mariner" he mentions a manuscript found in the Spanish Archives by a scribe of Queen Isabella's court where Columbus cites speaking to Portuguese fishermen that have been "drying cleaning fish on the shores of a distant large island in the Western Ocean Sea for generations." He goes on to say that the Portuguese have established a small colony as a base for fish factory operations on this land.
The Vatican documents that you may be referring to might be letters from Bishop Erc (a Catholic saint) of Ireland to the Pope Vigilius that reports that St. Brendan had traveled to "Terra Repromissionis" (or Paradise) which he called a "most beautiful land with luxuriant vegetation". He went on to provide a murky description of the location of Terra Repromissionis that might have been anywhere. Its the opinion of a friend of mine (a naval officer with more than 30 years of experience) that St Brendan hit New England and returned to Ireland by way of the Canary Islands. Bishop Erc provides one other tantalizing fact: St Brendan left Ireland with 150 "monks" and returned with only 18. Further Brendan returned from his voyage with a "fruit" that sounded suspiciously like potatoes, a native North American vegetable.
The disease and wheel argument are two excellent points. Taking the second one first a disk object was found in 1946 when a suburb tract was being developed on Long Island. Carbon tests run in 1975 dated the wheel like object to 700 AD. It was rejected at the time (and regrettably tossed into a land fill) since "everyone knew" that American Indians didn't have wheels. There is a similar incident tied to a wheel along the St. Lawrence River.
As for disease I have a book somewhere here in the disaster area I call my office about this same point (sorry I couldn't easily find it). Its an old book I found about 40 years ago. As I remember the author asked the same question and it was hypothesized by a physician that an extended period of marginal isolation (about 20 years) would have probably turned over most (80%? maybe) of the power of contagions. If you are intersted I have other references. I got caught up with this subject a number of years ago and still have both notes and reference material floating around. Drop me an e-mail if you are interested.
Very interesting. Thank you very much! Somewhere I read about a letter, I think found in German archives, that referenced the Catholic priests. IIRC, it was found in the late 19th century. I didn't know that St. Brendan was supposed to have left with so many fellow monks. I thought that isolated Irish monks traveled westward to live quietly by themselves. Morison's book also mentions the rotted hull of a book Columbus found on one of the islands. Another writer suggested that sounded like the Arab boats, forget their name. A teacher I had said that pictures had been found out west of Africans--obviously princes by the way they were dressed. Forget details. Actually, America wasn't all that far to the west in the northern ocean, so all this makes sense.
I would love to read what your book has to say about disease. I'd never heard it addressed before. If your office is like mine, I realize that you may never find it, but if you do, I'd love to know the name of it. Again, many thanks.